Saturday, February 18, 2006
Winds of change: Light snow possible today
Jason Samenow @ 12:42 PM
12:30pm update: Light snow is mainly focused to our south and southeast with just some flurries around town. Expect any intermittent flurry activity to taper off by 2pm, followed by gradual clearing and COLD temperatures.
After highs in the 60s for the past two days, high temperatures today will be a good 25 degrees colder AND there's snow in the forecast. Bundle up -- but you don't need to rush to the grocery store :)
A STRONG cold front moved through yesterday, bringing gusty winds to the region (see photo to the right). Behind said front, cold air has been trickling in, and highs today will only be 35-40. A weak wave passing well to our south is likely to have a large enough shield of precipitation that at least part of the area will see snow.
Snow notes:
Expect very cold conditions overnight with lows in the upper teens downtown and in the mid teens in the colder suburbs. Tonight may be the coldest night of the season. Sunday will be mostly sunny but COLD, with highs just 30-35.
Pictured: The winds blows in Greenbelt, Md. yesterday. By CapitalWeather.com photographer Kevin Ambrose.
This outstanding photo was submitted by BrownPau and is entitled: "Washington Monument Tree Panorama". Photos of last weekend's snow continue to trickle in via Flickr -- check them out. I will post visitor photos on weekends that are particularly good/creative. Keep them coming.
After highs in the 60s for the past two days, high temperatures today will be a good 25 degrees colder AND there's snow in the forecast. Bundle up -- but you don't need to rush to the grocery store :)
Forecast Details
A STRONG cold front moved through yesterday, bringing gusty winds to the region (see photo to the right). Behind said front, cold air has been trickling in, and highs today will only be 35-40. A weak wave passing well to our south is likely to have a large enough shield of precipitation that at least part of the area will see snow.Snow notes:
- Snow is most likely to fall between 8am and 2pm.
- The southern suburbs are the most likely areas to see snow.
- Intensity should be mostly light although brief periods of moderate snow are possible, particularly south of DC.
- There is a 40% probability that enough snow will fall to whiten the ground in the immediate metro area, but only a 20% probability of 1" or more of accumulation. This leaves about 40% chance of seeing just a couple flurries or zip, zilch, nada.
- Watch the radar tomorrow morning. This is going to be more or less a nowcasting event. I'll post updates if conditions warrant and I encourage you to post comments with reports from where you live.
- The warm ground and daytime timing of the event will minimize the impact of any snow that falls.
Expect very cold conditions overnight with lows in the upper teens downtown and in the mid teens in the colder suburbs. Tonight may be the coldest night of the season. Sunday will be mostly sunny but COLD, with highs just 30-35.
Pictured: The winds blows in Greenbelt, Md. yesterday. By CapitalWeather.com photographer Kevin Ambrose.
Visitor Feature Photo
This outstanding photo was submitted by BrownPau and is entitled: "Washington Monument Tree Panorama". Photos of last weekend's snow continue to trickle in via Flickr -- check them out. I will post visitor photos on weekends that are particularly good/creative. Keep them coming.
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Friday, February 17, 2006
Winter Springs Back
Steve Scolnik @ 4:50 PM
The Washington official temperature peaked out today above 60° for the third time this month (at 10am!). Temperatures are dropping behind a strong cold front, but they are still well above the long term average, in the low 50s at mid afternoon. The core of an Arctic high pressure area was centered in the northern Rockies today, and the cold air reached all the way to the Pacific Northwest, where Seattle was just barely over freezing at noon local time. As the air mass works its way eastward, we will see below-average temperatures in this area over the weekend, but the cold air will be moderated somewhat by the time it reaches us. The ground it will be traveling over is sparsely snow-covered, and the Great Lakes are not frozen.
CapitalWeather.com chart from NWS data, photo © Kevin Ambrose
Tonight and Tomorrow
For tonight, lows will be in the low 30s in the city to the upper 20s in the 'burbs with diminishing winds and increasing clouds. Clouds in the morning tomorrow will decrease in the afternoon with highs only in the upper 30s. There is a 20% chance of some light snow or flurries tomorrow as a weak disturbance moves eastward to the south of the area. (Note: Forecast confidence is especially low today, since I have been unable to access the latest model output, evidently because of a network problem at NCEP.)
Icy U
Researchers at the University of Kansas and NASA have jointly published a study of the Greenland ice sheet in this week's issue of the journal Science. Using remote sensing via microwave, they were able to determine that glacier melting has accelerated in the last decade to about 220 cubic km per year, more than double the earlier estimate. (By comparison, the entire city of Los Angeles uses about 1 cubic km of water per year.) This means that previous projections of sea level rise from climate change have been too low.The WaPo featured a story, "Glacier Melt Could Signal Faster Rise in Ocean Levels" on this subject on page A1 today. Other media coverage includes:
- Scientific American: "Greenland's Glaciers: Melting and On The Move"
- USA Today: "Greenland glacier runoff doubles over past decade"
- U.K. Telegraph: "Greenland warming speeds rise in sea level"
- London Times: "Coastal cities could disappear as glaciers melt faster than predicted"
- N.Y. Times: "More Greenland Ice Flowing Into Sea, in Sign of Warming"
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The Week-end Welcomes Waning Warmth
A. Camden Walker @ 2:02 AM
1pm update: The cold front has passed through the area. Look for slowly dropping temperatures and gradually clearing skies. Winds will continue to be gusty out of the northwest!
Experience two days within one day, today. Dress deliberately so that you aren't caught off-guard by cold wind ushering in Winter by sunset.
Our DC temperature will reach 60 by noon but under generally cloudy morning skies. We may see more sunshine this afternoon once a potent cold front blows through. Winds will shift from the southwest to northwest--this dryer, blustery air will make afternoon 50s feel cooler than that. After sunset, expect gusty winds to diminish a little but temperatures only to be in the 40s.
Kevin Ambrose captures bright sun, warm temperatures, and melting snow in Reston.
Snow Lover's Crystal Ball 
Next Chance of Accumulating Snow: Monday, Feb. 20
Probability: 20%
Potential Impact:
Commentary: I will keep the hopes alive for Monday, despite this snow event's potential being on life-support.
Two distinct, relative-to-average "settings" dictate whether said pressure fields formulate a "positive" oscillation setting for the North Atlantic, or instead a "negative" setting. Does each translate into distinct, DC weather? You can focus your attention on two, staple features that essentially run this show.
[1]"L" = Semi-permanent low pressure center between Greenland and Iceland ("Icelandic vortex")
[2]"H" = Semi-permanent high pressure off of the coast of Africa named the "Azores" high (for the island chain it often sits over)
When the NAO is in a "Positive" phase, both the Azores high and Icelandic (vortex) low are amplified. SEE IMAGE AT LEFT. Pressures over Iceland are very low, as storm energy swirls around a fast-moving Jet Stream. Warmth can be experienced in the Mediterranean as, simultaneously, the Azores high pressure system builds in strength.
Mild, moist conditions are usually experienced in DC and the Eastern Seaboard as the center of the Azores high moves a little further westward, building into and often connecting with our familiar "Bermuda high". However, despite giving you this DC weather correlation for Positive NAO, I should note that much more distinct "behavior modification" comes during Negative NAO. Almost always during wintertime Negative NAO phases, Washington DC's temperatures remain below-average--but I get ahead of myself.
When the NAO is in a "Negative" phase: weak, weak, weak, is the key word. SEE BOTTOM, RIGHT IMAGE. The Azores high moves eastward, hugging the African coast near its namesake islands. Ridging is suppressed--and thus warm air--to more southern, tropical regions.
The pressures over Iceland are relatively higher-than-average, since the Icelandic low vortex isn't asserting control. Slight Jet Stream ridging is possible, but more plausible are slower Jet Stream speeds through the area--since we all know the Jet Stream feeds on gradients in temperature and pressure--undermining the strength and number of storm systems.
More often than not, DC experiences below-average precipitation under this regime. However, most of our Arctic Air outbreaks also correlate to a "Negative" NAO phase. If the Icelandic low breaks down somewhat, there is a greater opportunity for a trough to develop in the Jet Stream just to the west of Greenland--over the eastern portions of the North American continent.
If this times properly (NAO playing an indirect role) cold air plunging southward during a Negative NAO can produce moderate snowstorms for DC when said Arctic Air comes in contact with warm Gulf, Atlantic waters.
Forecast: "Beltway Rollercoaster"
Experience two days within one day, today. Dress deliberately so that you aren't caught off-guard by cold wind ushering in Winter by sunset. Our DC temperature will reach 60 by noon but under generally cloudy morning skies. We may see more sunshine this afternoon once a potent cold front blows through. Winds will shift from the southwest to northwest--this dryer, blustery air will make afternoon 50s feel cooler than that. After sunset, expect gusty winds to diminish a little but temperatures only to be in the 40s.
Next Chance of Accumulating Snow: Monday, Feb. 20 Probability: 20%
Potential Impact:
Commentary: I will keep the hopes alive for Monday, despite this snow event's potential being on life-support.
FRIDAY FEATURE
The North Atlantic Oscillation (NAO): Whacky Warmth for DC when "positive"
Two distinct, relative-to-average "settings" dictate whether said pressure fields formulate a "positive" oscillation setting for the North Atlantic, or instead a "negative" setting. Does each translate into distinct, DC weather? You can focus your attention on two, staple features that essentially run this show.
[1]"L" = Semi-permanent low pressure center between Greenland and Iceland ("Icelandic vortex")
[2]"H" = Semi-permanent high pressure off of the coast of Africa named the "Azores" high (for the island chain it often sits over)
When the NAO is in a "Positive" phase, both the Azores high and Icelandic (vortex) low are amplified. SEE IMAGE AT LEFT. Pressures over Iceland are very low, as storm energy swirls around a fast-moving Jet Stream. Warmth can be experienced in the Mediterranean as, simultaneously, the Azores high pressure system builds in strength.
Mild, moist conditions are usually experienced in DC and the Eastern Seaboard as the center of the Azores high moves a little further westward, building into and often connecting with our familiar "Bermuda high". However, despite giving you this DC weather correlation for Positive NAO, I should note that much more distinct "behavior modification" comes during Negative NAO. Almost always during wintertime Negative NAO phases, Washington DC's temperatures remain below-average--but I get ahead of myself.
When the NAO is in a "Negative" phase: weak, weak, weak, is the key word. SEE BOTTOM, RIGHT IMAGE. The Azores high moves eastward, hugging the African coast near its namesake islands. Ridging is suppressed--and thus warm air--to more southern, tropical regions.
The pressures over Iceland are relatively higher-than-average, since the Icelandic low vortex isn't asserting control. Slight Jet Stream ridging is possible, but more plausible are slower Jet Stream speeds through the area--since we all know the Jet Stream feeds on gradients in temperature and pressure--undermining the strength and number of storm systems.
More often than not, DC experiences below-average precipitation under this regime. However, most of our Arctic Air outbreaks also correlate to a "Negative" NAO phase. If the Icelandic low breaks down somewhat, there is a greater opportunity for a trough to develop in the Jet Stream just to the west of Greenland--over the eastern portions of the North American continent.
If this times properly (NAO playing an indirect role) cold air plunging southward during a Negative NAO can produce moderate snowstorms for DC when said Arctic Air comes in contact with warm Gulf, Atlantic waters.
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Thursday, February 16, 2006
10-Day Outlook: Rollercoaster Weather!
Josh Larson @ 12:00 PM
Today's Forecast
We'll serve up abnormally warm temperatures for the second day in a row today. Expect the proverbial mercury to reach 60-65 -- a departure of 15+ degrees from our normal high -- under abundant sunshine. Partly cloudy tonight with mild temperatures in the mid to upper 40s in most spots.
Pattern Overview
Befitting the often volatile weather we frequently experience in Washington, DC in late winter, after a week of below normal temperatures and a major snowfall, we're now seeing "blowtorch warmth" as the atmosphere adjusts itself to more southwesterly flow aloft over the eastern US. The 50s (and even 60s) we'll see today and tomorrow, however, will vanish in a hurry as a very strong cold front comes barreling through Friday afternoon. By Saturday, the weather map will feature some semblance of a broad trough stationed over the entire northern third of the nation with frigid low-level cold air pressing down from the north to our neck of the woods -- see 850mb chart above. Thereafter, we have the potential for up to two (light) precipitation events from the period Saturday through next Wednesday. Models suggest that during this period low-level cold air to our north may clash with weak waves of low pressure to our south, which may bring a few flakes to parts of the area. (See Snow Lover's Crystal Ball below.)
As such, after the next two days' warmth, we're going to get very cold in a hurry, with high temperatures ranging from the upper 20s to mid 30s Saturday through Monday -- some 15 degrees below normal -- with frigid overnight lows in the teens, or colder, areawide. Thereafter, the cold will moderate somewhat, but it appears that we'll hold onto below normal temperatures through at least the end of the work week.
In addition, new evidence -- especially from of the magnitude and extent of cold air over Canada, as well as the forecast behavior of the NAO -- suggests that below normal temperatures (and chances for more snow) may continue through the end of month and perhaps even into early March.
The next 5 days (Feb 16-20)
Forecast highs/lows: 45/29 (normal = 47/30)
Forecast precip: near normal
Friday will feature partly sunny skies to start the day, with temperatures quickly climbing to near 60 in most locations once again. The afternoon, however, will feature very gusty winds 20-50mph with a line of sprinkles or isolated showers as temperatures drop some 15-20 degrees in a matter of hours in the cold front's wake. By sunset, temperatures will be in the mid 30s; a continued blustery evening will give way to overnight lows in the mid 20s. Saturday will feature dramatically different weather, with partly sunny skies, blustery conditions, and a stray snow shower (especially south of town); very cold highs will only reach the mid 30s (though windchills will remain in the 20s), with frigid overnight lows expected near 10 across the cooler suburbs to the upper teens downtown. Sunday will be one of the coldest days of the entire winter, under partly sunny skies. Highs will range from the upper 20s to lower 30s! Bitter cold once again Sunday night, with lows ranging from 10-20 degrees in most spots. Monday will feature partly to mostly cloudy skies with a slight chance for some light snow; highs will top out in the mid to upper 30s, with overnight lows in the upper 20s.
The next 5 days (Feb 21-25)
Forecast highs/lows: 44/28 (normal = 49/31)
Forecast precip: near normal
The forecast for the following five days is a little less certain, due mostly to the projected low amplitude atmospheric pattern; as a result, individual waves of weak low pressure will be difficult to track and time. Case in point: a slight chance of some lingering flurries on Tuesday as a little weak energy may linger around the area; warmer highs, though, near 40, with overnight lows in the mid 20s. Wednesday and Thursday appear to be dry and seasonably cool, with highs from 40-45 and overnight lows from 25-30. Some models indicate that a stronger area of low pressure may try to form during the Friday through Saturday period, perhaps bringing a chance for rain or snow for our area. Expect temperatures to remain near 40-45 for highs with overnight lows near 30.Next Chance of Accumulating Snow: Monday, February 20
Probability: 25%
Potential Impact:
Commentary: Some models hint at the potential for an overrunning-type precipitation event as a weak wave of low pressure interacts with low-level cold air late Sunday into Monday. Thus, we have a chance for light precipitation in the form of snow, sleet, or freezing rain on Monday. This does not appear to be a major event at this point.
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Wednesday, February 15, 2006
Waning Winter Wednesday
Steve Scolnik @ 5:00 PM
The spring catalogues coming through the mail slot have been accompanied by spring-like temperatures in the Washington DC area this afternoon. At 10¾ hours of daylight, our sunshine 5 weeks before the equinox is as strong as it was the week before Halloween. South-facing roofs and some sections of grass are now bare in this outside-the-Beltway neighborhood. Temperatures around the metro area are in the upper 50s with some 60s in the southern fringes of the region.A low pressure area moving northeastward from Oklahoma toward the Great Lakes on this afternoon's weather map will keep us in the warm temperatures for a couple more days until the colder air behind it brings some of the chilliest (no, not "silliest", Spell-Check!) readings of the season for the weekend. After that, some type of storm activity is likely to develop along the front to the south, but nothing major is showing up yet. We'll be keeping an eye on it as usual in the days ahead. (Even though the PM Update will be taking a "non-snow" day tomorrow, we'll still be watching while we catch up on some other projects.)
Surface weather map at 1pm today from HPC/NWS/NOAA
Tonight and Tomorrow
For tonight, lows will be near 40 in the city to the mid 30s in the 'burbs under scattered to broken clouds. Tomorrow's highs will be near 60 with some scattered clouds.Budget Blues
Yesterday's WaPo Federal Diary reports that budget cuts are prompting the National Weather Service to offer early retirement to about 1000 employees. Based on past experience, only 50 are likely to volunteer, but naturally such a program impacts the areas with the most experience. The St. Petersburg Times points out that 13 out of 42, or 30%, of the staff members at the National Hurricane Center are eligible. This has prompted Florida Senator Bill Nelson to say,
"That's the most ridiculous budgetary policy decision I've ever heard, when you're dealing with a matter of life and death, of inbound hurricanes."
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An Eye for Snow
Jason Samenow @ 1:13 AM
High temperatures in the 50s for the next three days are going to put a big dent in the snow cover. Thankfully for snow fans, a number of CapitalWeather.com visitors captured beautiful images of weekend's snowfall and contributed them via Flickr. So while the snow itself will soon be history, images of the storm, in all their glory, remain. Today's edition showcases photos from our visitors, who we thank for their submissions.You may still submit shots if you like, or as always, you can check out snowfall results from this weekend.
Pictured: The visible satellite image of the weekend storm shows an eye-like feature off the Delmarva peninsula Sunday morning. Submitted by CapitalWeather.com visitor "vvakeuplookup"
Photos from CapitalWeather.com visitors
Photos top left to right by "mattdemarco","Miss Chatter" and "tinabgibby". Location of left and center image unknown, right image taken in Fairfax. Bottom images of statues on Capitol Hill taken by Nick Sundt.
Photos by Kevin Ambrose
Here are a couple images from CapitalWeather.com photographer Kevin Ambrose, taken in Reston and Oakton, respectively during the last couple of days:
Next Chance of Accumulating Snow: Saturday, February 18 and early during week of Monday, Feb 20
Probability: 15% and 25%
Potential Impact:
Commentary: After a strong Arctic front passes through Friday night significantly dropping temperatures, a wave of low pressure may develop along the front to our south. Any snow that develops is likely to stay south of us, but it bears watching. Early next week, a number of waves may develop in the south, but it is unclear whether any of them will head northeastward towards our area or stay suppressed and go out to sea.
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Tuesday, February 14, 2006
Snow, You're My Favorite Work of Art
Matt Ross @ 1:00 AM
Forecast
After a very chilly start this morning, temperatures will rebound nicely this afternoon. It will be sunny with seasonable highs in the mid 40s. Any melting that doesn't occur today will likely occur over the rest of the week as a brief warm-up sends our temps into the 50s during the Wednesday through Friday period. A cold front will usher in below normal temps again for the weekend. Unlike the cold fronts of January, this one has the potential for some very cold air to come in behind it. Pictured Above Right: Snow in Oakton, Va Does a Number on a Hoop, Courtesy of Kevin Ambrose
Impact Versus Actual Amounts
There has been a lot of post storm chatter about how the impact of this past weekend's snowstorm did not match the impressive totals throughout the East Coast. One measure of the impact of an East Coast Storm is the Northeast Snowfall Impact Scale(NESIS). This scale was devised by Paul Kocin(The Weather Channel) and Louis Uccellini(National Weather Service) to measure the significance an East Coast snowstorm based on its overall impact. The somewhat complicated formula factors in amount of snow that fell, surface area it fell over, and population directly affected. It is my understanding that this weekend's event(Blizzard of 2006) will rank as a Category 3 or Major storm on the NESIS scale. I think this classification of storms is both interesting and important. Yet it doesn't completely capture the impact of the snowfall. Factors like what days it fell, what time it fell, how well it stuck to roads, and how quickly it melted are not figured in. While this past storm was certainly formidable and caused many headaches, we have basically recovered back to normal in less than 48 hrs. Even New York City with its record snowfall has a snow depth less than half of what fell, and clear streets and sidewalks. While not exact, our areas totals for the storm were comparable to those that fell in the surprise storm of January 25th, 2000. Yet that storm in my opinion had a much bigger impact as it fell during the week and with much colder temperatures both prior to and after the storm. Additionally, it fell on some preexisting snowcover. Absent this morning downtown, in 2000 there were large snowbanks all over the city for a good week after the storm as temperatures stayed very cold. The Blizzard of 2006 will most be remembered for its overperformance, beautiful, heavy wet snow, and incredible snowfall rates and banding. Unlike the Blizzard of 1996, Back to Back storms of 1987, etc, the disruption to our lives, and post storm impact are largely absent just a couple of days later. Perhaps that is the way it should be sometimes.
Seasonal Snowfall Amounts
This latest storm brings DC's totals to 13.6" or just a couple inches shy of our seasonal average over the last 30 years. It also surpasses the last 2 winters to become our second snowiest season of the 2000's, well behind the monster winter of 2002-03(40.4"). If we are able to surpass 16" for the season, it will be only the 3rd time in the last 17 winters. The Blizzard of 2006 also added substantially to the totals of most other Northeastern cities. Boston is now just 5" shy of its seasonal norm with 37.4" of snow, and New York is now more than 10" ahead of its seasonal norm with 38.6", just short of what would be a record 4 consecutive 40"+ seasons. However, for other locations, especially those that mostly missed the Blizzard of 2006, seasonal averages are still a long way off. Albany, NY only has 26.2", well short of its 63" average, and Raleigh, NC has yet to see its 1st measurable snow this year. For snowlovers, even if it doesn't snow again this winter, we have approached our seasonal average(about 15.5") and hit our seasonal median(about 12.5") for 3 consecutive seasons. While we haven't received the good fortune of New York City, we really can't complain given the worst case scenario at the start of every winter. That we go virtually snowless, like 1997-98 and 2001-02.
Next Chance of Accumulating Snow: Saturday, February 18th through Monday, February 20th
Probability: 15%
Potential Impact:
Commentary: A strong Arctic front with a lot of cold air behind it will affect our region on Friday. A system may ride along the front and bring us some snow on Saturday. Right now it does not look like a big impact event. Thereafter, the pattern will be ripe for storminess and cold air will be locked in for at least several days. Stay tuned, as after the tranquility and warmth of the next few days, we should have plenty to discuss heading into the weekend and next week.
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Monday, February 13, 2006
Calling Inspector Morse
Steve Scolnik @ 5:20 PM
There hasn't been much of a thaw today except in the sunnier spots. Temperatures are maxing out mainly in the high 30s, but melting will be accelerating into this week. The model statistical outputs are all suggesting at least an approach to the 60 degree level by midweek.
For tonight, lows under partly cloudy skies will range from the upper 20s in the city to low 20s in the 'burbs. The warmup begins tomorrow with highs around 47 and partly cloudy skies.
The development of the storm which brought our snow over the weekend and record-breaking amounts to New York City and central New England will certainly provide a lot of material for future investigations. Detailed data on snowfall rates are hard to obtain, because snowfall measurement is very subjective and therefore not easily automated. I took a stab at analyzing the intensity of the storm over time with the chart on the right. It's based on the "hourlies" (METAR data, or aviation reports), from Washington National for the 36-hr period from early Saturday morning through early Sunday afternoon.
Time is shown on the horizontal scale. Bear in mind that distance along the axis is not directly proportional to time, because the observations are not evenly distributed in time. They are made every hour on the hour, and then whenever a change in conditions requires an update. Although Microsoft® Excel is the Swiss Army Knife® of data analysis, it is notoriously inept at handling unevenly distributed data points.
The vertical scale represents the type and intensity of precipitation. Positive values are snow reports, and negative values are rain reports. A magnitude of 1 is "light", 2 is "moderate", and 3 is "heavy". You can see that most of the morning had intermittent light rain, then light snow mixing in the afternoon. This became all snow by late afternoon, occasionally moderate through the evening. The real fun began after midnight, when there were 8 reports of heavy snow. By 9am, the steady snow was over, and there was a snow flurry in early afternoon (and possibly 1 or 2 more after the cutoff time in the chart).
I think an important factor in the higher snow depths which were recorded was not just the usual temperature-dependent frozen-to-liquid ratio, but also the very high rate of fall, which prevented the kind of settling which would happen over a longer period. Depths have visibly decreased a lot today, but I would suggest that this is more an effect of settling, rather than melting, given the temperatures we've had.
Chart © CapitalWeather.com, photo © Kevin Ambrose
Tonight and Tomorrow
For tonight, lows under partly cloudy skies will range from the upper 20s in the city to low 20s in the 'burbs. The warmup begins tomorrow with highs around 47 and partly cloudy skies.
Snow Intensity and Depth
The development of the storm which brought our snow over the weekend and record-breaking amounts to New York City and central New England will certainly provide a lot of material for future investigations. Detailed data on snowfall rates are hard to obtain, because snowfall measurement is very subjective and therefore not easily automated. I took a stab at analyzing the intensity of the storm over time with the chart on the right. It's based on the "hourlies" (METAR data, or aviation reports), from Washington National for the 36-hr period from early Saturday morning through early Sunday afternoon. Time is shown on the horizontal scale. Bear in mind that distance along the axis is not directly proportional to time, because the observations are not evenly distributed in time. They are made every hour on the hour, and then whenever a change in conditions requires an update. Although Microsoft® Excel is the Swiss Army Knife® of data analysis, it is notoriously inept at handling unevenly distributed data points.
The vertical scale represents the type and intensity of precipitation. Positive values are snow reports, and negative values are rain reports. A magnitude of 1 is "light", 2 is "moderate", and 3 is "heavy". You can see that most of the morning had intermittent light rain, then light snow mixing in the afternoon. This became all snow by late afternoon, occasionally moderate through the evening. The real fun began after midnight, when there were 8 reports of heavy snow. By 9am, the steady snow was over, and there was a snow flurry in early afternoon (and possibly 1 or 2 more after the cutoff time in the chart).
I think an important factor in the higher snow depths which were recorded was not just the usual temperature-dependent frozen-to-liquid ratio, but also the very high rate of fall, which prevented the kind of settling which would happen over a longer period. Depths have visibly decreased a lot today, but I would suggest that this is more an effect of settling, rather than melting, given the temperatures we've had.
Chart © CapitalWeather.com, photo © Kevin Ambrose
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Assessing the Past, Predicting the Future...
Jason Samenow @ 12:00 AM
After a snowy weekend, it's back to work and back to school (for some, not others). Be careful when you head out this morning, as icy spots are likely given low temperatures in the low 20s downtown and in the teens in the suburbs. We'll see a good deal of sunshine this afternoon with temperatures reaching the upper 30s. These conditions will allow for plenty of melting.
After every significant winter storm, CapitalWeather.com evaluates its performance. What follows is an objective as possible self-evaluation:
Were we succesful in identifying the storm threat well in advance? We first identified the potential for a coastal snowstorm last Sunday in our "Snow Lover's Crystal Ball". We mentioned it every day subsequently, initially (Mon-Wed) as a low probability event (20-25%), but by Thursday indicated it was a high probability event (66%). We might have trended up probabilities more gradually, but were successful in recognizing/communicating the potential for a storm almost a week ahead of time. Grade: A-
Were we consistent in our forecasts? Our forecast accumulation forecast of 4-7" was made Thursday night (or Friday morning) before any other media outlet. As guidance came in suggesting the storm would be more significant, we bumped up forecasted totals to 5-8" on Friday evening, and to 6-9" Saturday morning. While conditions warranted our gradual upward adjustments to the accumulation forecast ahead of the storm, unlike almost every other media outlet, we did not alter our forecast during the storm. In general, we told an internally consistent story and stuck with it. Grade: A-
How accurate was our forecast for the storm's evolution/impact? We correctly stated that most of the accumulating snow and the storm's greatest impact would occur overnight Saturday. However, we did not forecast the rain that fell Saturday morning into the mid afternoon hours instead forecasting light (non-accumulating) snow. In practice, there isn't much difference between light rain and light snow that doesn't stick, but we made a mistake by assuming surface temperatures would be cold enough to support snow during this phase of the storm (which resulted from the lack of a cold high to the north). Grade: B+
How accurate was our forecast for the storm's intensity/accumulation amounts? Our forecast of 6-9" in the metro area was a bit low, as totals ranged from 6-16". Our greatest underestimates occurred in the north and west suburbs. Nonetheless, we did indicate that we wouldn't be surprised if there were some double digit totals if convective snows developed (as they did) and correctly stated the heaviest totals would probably occur to the northeast of DC (Howard County received the heaviest snows). Grade: B+ (Related article: Some Get a Dusting, Others Still Digging Out)
Overall Grade: A-/B+
How did other media outlets do?
Given the length of this post, the week ahead preview this week will be abbreviated. We will experience a significant warming trend through midweek, with dry conditions and temperatures reaching the 40s Tuesday and 50s Wednesday and Thursday. A strong cold front will bring the threat of rain showers Friday, before much colder air (highs in the 30s) returns for the weekend. There are some early indications a storm with the potential to bring wintry precipitation to the area may develop late in the weekend or early next week. For more, keep reading....
Snow Lover's Crystal Ball
Next Chance of Accumulating Snow: Sun-Mon, Feb. 19-20
Probability: 20%
Potential Impact:
Commentary: Another area of low pressure could develop in the deep south by the weekend. The questions are: Will it really develop? How strong will it be? And will a huge area of Canadian high pressure suppress it to the south and east or will it head toward us like the last storm? Only time will tell.
Snow Post Mortem: Grading Our Performance, Assessing Others'
After every significant winter storm, CapitalWeather.com evaluates its performance. What follows is an objective as possible self-evaluation:Were we succesful in identifying the storm threat well in advance? We first identified the potential for a coastal snowstorm last Sunday in our "Snow Lover's Crystal Ball". We mentioned it every day subsequently, initially (Mon-Wed) as a low probability event (20-25%), but by Thursday indicated it was a high probability event (66%). We might have trended up probabilities more gradually, but were successful in recognizing/communicating the potential for a storm almost a week ahead of time. Grade: A-
Were we consistent in our forecasts? Our forecast accumulation forecast of 4-7" was made Thursday night (or Friday morning) before any other media outlet. As guidance came in suggesting the storm would be more significant, we bumped up forecasted totals to 5-8" on Friday evening, and to 6-9" Saturday morning. While conditions warranted our gradual upward adjustments to the accumulation forecast ahead of the storm, unlike almost every other media outlet, we did not alter our forecast during the storm. In general, we told an internally consistent story and stuck with it. Grade: A-
How accurate was our forecast for the storm's evolution/impact? We correctly stated that most of the accumulating snow and the storm's greatest impact would occur overnight Saturday. However, we did not forecast the rain that fell Saturday morning into the mid afternoon hours instead forecasting light (non-accumulating) snow. In practice, there isn't much difference between light rain and light snow that doesn't stick, but we made a mistake by assuming surface temperatures would be cold enough to support snow during this phase of the storm (which resulted from the lack of a cold high to the north). Grade: B+
How accurate was our forecast for the storm's intensity/accumulation amounts? Our forecast of 6-9" in the metro area was a bit low, as totals ranged from 6-16". Our greatest underestimates occurred in the north and west suburbs. Nonetheless, we did indicate that we wouldn't be surprised if there were some double digit totals if convective snows developed (as they did) and correctly stated the heaviest totals would probably occur to the northeast of DC (Howard County received the heaviest snows). Grade: B+ (Related article: Some Get a Dusting, Others Still Digging Out)
Overall Grade: A-/B+
How did other media outlets do?
- Channel 9 led the way in consistency with forecasts all in the ballpark of 5-8". Grade: A-/B+
- Channel 7 was also pretty consistent with forecasts of 6-10" until they unfortunately decreased them to 4-8" Saturday night at 11pm. Grade: B+
- The National Weather Service had the best final call of 6-12", but wavered quite a bit with an initial forecast of 4-8" followed by a sharp increase to 8-14" before settling on 6-12". Grade B+
- Fox 5 was consistently too low -- with forecasts of 3-5" (Friday) and 4-6" (Saturday). I do give Sue Palka props for correctly and effectively communicating the fact the storm was just getting going at 10pm Saturday night. Grade: B
- The John Kerry award for flip flopping goes to Channel 4. Channel 4 first called for 5-9" (Friday and Saturday morning), then decreased totals substantially to 3-6" (Saturday at 6pm) before (prudently) upgrading them to 5-8" just hours later (Sunday at 12am). Grade: B-
- Related article: Fickle Storm a Test of TV Divination
Other Storm Notes
- Be sure to check out the map of snowfall totals across the area generated by reports from dozens of CapitalWeather.com visitors. Thanks to all of you who submitted totals. The map is cool!
- CapitalWeather.com photographer Kevin Ambrose has a nice gallery of storm photos.
- During the storm we received 1,166 comments from CapitalWeather.com visitors (this does not include the hundreds of comments received before and after the storm). The comments were interesting, insightful and polite (I did not have to edit or delete any), and we hope we were able to answer questions that came in. We were pleased to have several local TV meteorologists stop by and offer perspectives and answer questions. Thanks to all of you took part in the action.
- I'm sure everyone knows that this storm had a huge impact in the Northeast, with all-time record snowfall accumulations in Central Park, NY and Hartford, Connecticut. See this NY Times article: Wind and Snow Strike 14 States; Record Accumulation in N.Y.
The Week Ahead
Given the length of this post, the week ahead preview this week will be abbreviated. We will experience a significant warming trend through midweek, with dry conditions and temperatures reaching the 40s Tuesday and 50s Wednesday and Thursday. A strong cold front will bring the threat of rain showers Friday, before much colder air (highs in the 30s) returns for the weekend. There are some early indications a storm with the potential to bring wintry precipitation to the area may develop late in the weekend or early next week. For more, keep reading....
Next Chance of Accumulating Snow: Sun-Mon, Feb. 19-20
Probability: 20%
Potential Impact:
Commentary: Another area of low pressure could develop in the deep south by the weekend. The questions are: Will it really develop? How strong will it be? And will a huge area of Canadian high pressure suppress it to the south and east or will it head toward us like the last storm? Only time will tell.
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Sunday, February 12, 2006
Storm Starts Slow, Finishes Strong
Dan Stillman @ 4:45 PM
Yesterday was a day of nonaccumulating snow, skeptical naysayers and waffling predictions from some forecast outlets (we won't name names -- in this post, at least). But as darkness fell, the action was just getting started. Those who went to bed thinking the first winter storm of 2006 had underperformed woke up this morning to the biggest snowfall since the Blizzard of 2003.Storm totals in and around the District were generally in the 12-inch range, though 15 to 20 inches was common going northeast toward Baltimore. For compiled storm totals, check out:
- CapitalWeather.com's reporting map
- National Weather Service Public Information
Pictured: A wintry White House, photographed today by CapitalWeather.com's Ian Livingston.
Schoolcast
Despite having all day today to clean up, it's likely there will be many delayed openings tomorrow, as well as a number of closings. CaptialWeather's official Schoolcast for tomorrow is two apples, which corresponds to a 50-50 chance of no school and a good chance of a delay, although several school systems have already thrown in the towel. WTOP has the latest on closings and delays.
Forecast
Partly cloudy tonight with a low in the low 20s. Tomorrow will be partly sunny, breezy and cold with highs 35-39. Jason will have the day-by-day forecast for the week ahead in tomorrow's post.
Nervous Nellies Strike Again
As the storm got off to a slow start yesterday and into the early evening, the Nervous Nellies were out in full force once again on our comment boards. They feared the storm was going to depart without leaving behind a significant accumulation of the white stuff, many prematurely proclaiming the storm a bust.
Ye of little faith. The storm not only lived up to expectations, but in many areas exceeded them by the time it exited this morning. Jason will have a full postmortem on CapitalWeather's forecast as well as those from other outlets in tomorrow's post.
As for the Nervous Nellies -- we still love you, and to be honest it wouldn't be the same without ya.
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Overnight Pummeling: Storm Update #4
Jason Samenow @ 7:46 AM
Very heavy bands of snow set up over the area overnight, resulting in impressive accumulations across the area. Anywhere between 6" and 17" fell throughout the region, with light snow still falling in many places.
Reagan National officially had received 8" as of around 7:00am and most areas in Montgomery and Fairfax Counties had received over 10", with amounts as high as 17" in some locations. In northwest DC, I measured about 11", after receiving heavy snow accompanied by instances of vivid lighting and some thunder overninght.
Light snow and flurries will gradually taper off from southwest to northeast this morning...shutting down everywhere by around noon. Less than 1" of additional accumulation is expected. It will be windy and cold, with subfreezing temperatures this morning and a high in the low 30s this afternoon.
Dan will post a storm recap sometime this afternoon. You may also want to tune into WeatherTalkRadio on WCBM-AM 680 (Baltimore) today, at 3:00pm, as meteorologists Tony Pann and Justin Berk plan a lively show recapping the storm.
Reagan National officially had received 8" as of around 7:00am and most areas in Montgomery and Fairfax Counties had received over 10", with amounts as high as 17" in some locations. In northwest DC, I measured about 11", after receiving heavy snow accompanied by instances of vivid lighting and some thunder overninght.
Report and Map Snow Totals Where You Live Here.
Share Your Storm Photos with CapitalWeather Here.
Forecast
Light snow and flurries will gradually taper off from southwest to northeast this morning...shutting down everywhere by around noon. Less than 1" of additional accumulation is expected. It will be windy and cold, with subfreezing temperatures this morning and a high in the low 30s this afternoon.
Storm Recap
Dan will post a storm recap sometime this afternoon. You may also want to tune into WeatherTalkRadio on WCBM-AM 680 (Baltimore) today, at 3:00pm, as meteorologists Tony Pann and Justin Berk plan a lively show recapping the storm.
Media/Resources
- National Radar
- WUSA Local Radar
- Closings/cancellations from WTOP
- Map of Live Temperatures around Region
- Washington Post Article: Got Milk? And Bread and Shovels?
- Washington Post Article: Major Snow Storm Pounds Washington Area
- Local community perspectives: Backfence.com
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Bands of snow overnight: Storm update #3
Jason Samenow @ 12:00 AM
The next update will be around 8am.
Bands of snow will continue overnight, some heavy and with thunder. The forecast remains for total accumulations to be in the range of 6-9" by morning, but more likely towards the lower end of that range (or a bit less) in downtown DC and near the Potomac River on the south side of town.
Where will the heaviest snow fall? North and west of town and northeast of town.
What was up with the rain? Is that going to affect how much snow we get? I attribute the rain to the lack of a strong high to the north that would've helped funnel cold air southward at low levels. So even though it was sufficiently cold aloft for snow, it was too warm at the surface. This fact was overlooked by all forecasters. However, as we weren't expecting most of the accumulation until night time and the amount of rain was light, I only imagine it would eat into about 5-10% of the accumulation potential.
When will travel be most difficult? In the next 4-8 hours.
When will conditions improve? Most snow should taper off by mid morning Sunday. However, it will remain breezy and cold and it may take until Sunday night and Monday for neighborhood roads to be plowed.
What are other forecasters saying? Here is a summary of forecasts which have been updated:
Report and Map Snow Totals Where You Live Here.
Bands of snow will continue overnight, some heavy and with thunder. The forecast remains for total accumulations to be in the range of 6-9" by morning, but more likely towards the lower end of that range (or a bit less) in downtown DC and near the Potomac River on the south side of town.
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Travelcast: Schoolcast (Mon.): | |
Frequently asked Questions (updated as of 4:30pm)
Where will the heaviest snow fall? North and west of town and northeast of town.
What was up with the rain? Is that going to affect how much snow we get? I attribute the rain to the lack of a strong high to the north that would've helped funnel cold air southward at low levels. So even though it was sufficiently cold aloft for snow, it was too warm at the surface. This fact was overlooked by all forecasters. However, as we weren't expecting most of the accumulation until night time and the amount of rain was light, I only imagine it would eat into about 5-10% of the accumulation potential.
When will travel be most difficult? In the next 4-8 hours.
When will conditions improve? Most snow should taper off by mid morning Sunday. However, it will remain breezy and cold and it may take until Sunday night and Monday for neighborhood roads to be plowed.
What are other forecasters saying? Here is a summary of forecasts which have been updated:
- The National Weather Service is forecasting 6-12" total
- Channel 4 (Chuck Bell) is calling for 5-8" in the metro area, more N & W and less S & E
- Channel 5 is forecasting 4-6"
- Channel 7 is calling for 4-8"
- Tony Pann and Topper Shutt (Channel 9) are forecasting 5-8"
- Paul Kocin, Winter Weather Expert at The Weather Channel says 4-8" for DC
Media/Resources
- National Radar
- WUSA Local Radar
- Closings/cancellations from WTOP
- Map of Live Temperatures around Region
- Washington Post Article: Got Milk? And Bread and Shovels?
- Local community perspectives: Backfence.com
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