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Saturday: Simmering but Serene

Jason Samenow @ 8:44 AM

This weekend's forecast, compared to last weekend's, is a walk in the park. No deluge to worry about, just some characteristic DC summertime heat....

Forecast Confidence: Very High
Mostly sunny and hot. As Camden mentioned yesterday, we'll have full sunshine and just a touch of humidity as high pressure sits over the Mid-Atlantic. The high temperature will be near 90. It's a great pool or beach day...just be sure to wear sunscreen--the UV Index will be 9--which is very high. Overnight, expect fair skies and a low near 70 (65-70 in the suburbs).

Outdoor enthusiasts may find this Washington Post article interesting: One's Place in Food Chain Molds Post-Storm Prospects. Excerpt:
About 172 billion gallons of rainwater fell on the District and Montgomery and Fairfax counties this week, in time for one of summer's biggest recreational weekends. Is that bad?

If you are a large fish, mosquito, tree, tomato plant or angler, no. If you are a very small fish, an oyster, crab, kayaker or Little Leaguer, it's a problem.

Forecast Confidence: High
Sizzling, Sultry. As high pressure moves offshore, and southwesterly flow kicks in, the mercury will climb upwards and so will humidity levels. Expect a high in the low to mid 90s, and maximum heat indices of 93-97. An isolated storm could pop up in the evening (25% chance).

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Humidity Hiatus; To Return in July

A. Camden Walker @ 1:02 AM

Forecast: We'll Simmer, not Scorch

Sunshine today will be accompanied by low humidity. Considering we're entering our climatologically highest daily maximum temperatures, I think it's a bargain not having a sweaty suit drenched when arriving at my desk. From our 60s this morning, we'll slowly climb into the mid-80s by 4pm. Enjoy today's very decent summer weather, but warmth minus mugginess can't last! It's DC and July approaches...No clouds, no rain, high pressure reigns!

Above graphic courtesy of

simply cloudy, but radiational cooling may vary with locationTonight will be at least partially cloudy, but lows will slip below 70--even downtown. Some suburbs may see 60°. The humidity will begin to creep in by dawn...

Saturday & Sunday: July Says Hello

humidity returns, and with storms?Saturday's mugginess compounds the possibility of 90 degrees an unpleasant reality check. Storm chances are very low, despite your craving refreshment from the heat. With few clouds in the sky, UV will be high-- so wear the sunscreen.

Sunday continues the trend and the oven really begins to bake. 72° or 73° for a morning low (urban areas) launches our trek to 95 degrees under mainly sunny skies. It will feel like July. Humidity will be high (if you didn't already sense my dread) and T-storms have a decent 25-30% of popping in an isolated manner through the Metro Area. Seek shaaaaade and water.

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Good Ol' Summertime

Steve Scolnik @ 4:10 PM

A Severe Thunderstorm Watch is in effect for the area until 11pm.

OK, you know the drill by now. It's summer, it's warm and humid (although a little less so than yesterday), there's an extra source of moisture from the high ground water content, and there are a couple of triggering mechanisms in the form of two weak frontal boundaries in the region and some upper-level instability rolling through this evening.

Accordingly, the NWS has issued a severe thunderstorm watch for the area until 11pm. The Flash Flood Warning for the Lake Needwood Dam in MoCo also continues. By 4pm, radar showed only isolated activity, some of which was locally intense, ranging over the map in location from upper MoCo (weakening as it moved eastward) to nearing Culpeper, to north of Charlottesville, and to west of Ocean City. The forecast for tonight through the weekend and beyond are below the fold.

Climate Corner: Comedy Central Coverage

Last night's Daily Show on Comedy Central devoted half the program to an interview with ex-next President Al Gore on the subject of his climate-change documentary "An Inconvenient Truth". The show will be repeated this evening at 8pm and most likely during their holiday break next week.

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10-Day Outlook: Back to Normal...Phew!

Josh Larson @ 11:00 PM

Today's Weather

Forecast Confidence: HighToday's forecast calls for abundant sunshine much of the day, with warm afternoon highs near 87; scattered late-afternoon and early evening thunderstorms -- some of which may be strong -- cannot be ruled out, though many places should remain dry. Humidity levels will be noticeably lowered compared to recent days, however. Expect mostly clear skies overnight, with lows in the mid 60s.

The rest of the forecast, through the weekend and beyond, continues below after the Pattern Overview.

Pattern Overview

I am elated to report that in the it does not appear that any fronts will stall over the region over the next 10-days. Second, I'm quite relieved that we will not have to discuss "drought conditions" again for at least the next 8 weeks. In fact, it doesn't appear that there'll be much of any significant weather-related excitement for our area over the foreseeable future (other than rising flood-waters in the immediate short term); this is also quite okay with me after the past few days' "excitement."

What we will have is a return to refreshingly benign, quite typical summer weather for late June into early July. After a trough lifts out of the Northeast over the next 48 hours, surface high pressure will build into the area this weekend, and it looks like we'll be left with relatively zonal flow aloft (no strong ridges or troughs over the region) for much of next week.

The result will be temperatures about as normal as you can possibly get -- and mostly in the mid to upper 80s for highs and the mid 60s to near 70 for lows -- with a chance of what we meteorologists like to call "airmass" (or pop-up) thunderstorms each day. The next cold front will probably hold off until mid next week, and thereafter we can probably expect slightly cooler temperatures.

Pictured above: the GFS' representation of relatively zonal/flat flow over much of the continental US by the start of next week; this will produce very typical weather for this time of year.

The next 5 days (June 29 - July 3)

Forecast highs/lows: 87/68 (normal = 87/69)
Forecast precip: Below normal...phew!

Forecast Confidence: Medium-HighAfter today's warm temperatures and chance for afternoon thunderstorms, we'll see slightly calmer weather on Friday, with abundant sunshine, slightly cooler highs near 84, and little, if any, chance for precipitation. Mostly clear and pleasant overnight, with lows in the mid 60s. Saturday and Sunday will feature nearly the same forecast: mostly sunny skies, bearable humidity levels and afternoon highs in the upper 80s (perhaps approaching 90 on Sunday) with overnight lows in the upper 60s to near 70. Monday will feature partly sunny conditions, a chance for afternoon thunderstorms, and highs in the mid to upper 80s.

The following 5 days (July 4-8)

Forecast highs/lows: 85/67 (normal = 88/69)
Forecast precip: Near normal

Forecast Confidence: Medium-HighDuring the following five days, it appears that the zonal flow aloft may be replaced with a trough in the Northeast by week's end; a cold front delivering this change to likely slightly cooler weather will probably push through on Wednesday. But for all-important July 4, the outlook is for partly to mostly sunny skies with scattered afternoon thunderstorms and highs in the mid to upper 80s, with overnight lows near 70. We'll call for a good chance of showers and thunderstorms on Wednesday, with highs near 85 and lows near 70. For Thursday through Sunday, high pressure will probably build back in, while weak northwest flow aloft will allow for dry conditions and pleasant high temperatures in the low to mid 80s, with overnight lows in the mid 60s.

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And Now For Something Completely Different . . .

Steve Scolnik @ 4:05 PM

Right Now

Garden-variety (as opposed to the industrial grade of recent days) thunderstorms with some areas of heavy rain are affecting parts of the area this evening.

With the threat of storms, a Flash Flood Warning remains in effect for Montgomery County where seepage at a Rockville dam is a concern.

Tonight and Tomorrow

Tonight, it will be warm and humid with scattered thunderstorms and lows near 71° in the city, mid to upper 60s in the cooler 'burbs. Tomorrow will be mostly sunny and a little less humid with seasonable highs in the upper 80s and a slight chance of afternoon or evening thunderstorms.

For the outlook into the weekend, see Dan's post below.

Deficit Demolished

Water-weary Washingtonians woke Wednesday with wonder: Sunshine! Blue Sky! After days of near-Biblical deluges, the rain finally stopped. At National, the rain ended at 3:48 am this morning, to be followed by a few minutes of drizzle. The excess precipitation since Friday was more than enough to wipe out the accumulated deficit for the year. In fact, what had been a deficit over 30% quickly reversed to an even larger surplus of 32% through yesterday. chart from NWS data, photo © Kevin Ambrose

Metaphorical Meteorological Meanings

Tom Toles finds a symbolic interpretation of the recent storms in today's WaPo editorial cartoon. (Note to online WaPo: That omnipresent Sprint/Nextel Flash ad is a CPU HOG! It gets your window closed immediately on the PM Update computer every time. Talk about negative advertising!)

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Record Rains Subside After Overnight Final Punch

Dan Stillman @ 1:40 AM

Mother Nature delivered one last blow to some parts of the area in the form of soaking overnight showers. Today, finally, brings a return to more typical summer weather, which does include chances of showers and thunderstorms through the weekend, but not as widespread or as frequent as in recent days.

Despite the improving conditions, the waterlogged Washington area is facing a host of problems, including the continued threat of flooding, possible dam failure, street closures, water-damaged homes, government closings and unhappy tourists. And, DC Mayor Anthony Williams has declared a State of Emergency.

Pictured: Rock Creek fills its banks in the Cleveland Park neighborhood of Northwest DC, by photographer Ian Livingston.

Today's Weather

A lingering morning shower north and east of town is possible. Otherwise, the clouds that have persisted for so many days will finally give way to clearing skies and afternoon highs in the mid-to-upper 80s. Forecast Confidence: Medium-HighShowers and thunderstorms are possible during the evening and overnight hours (30% chance) as tonight's low drops to the upper 60s to around 70.

Tomorrow and Beyond

Forecast Confidence: Medium-HighTomorrow, partly sunny skies early will turn partly cloudy with scattered showers and thunderstorms possible during the afternoon and evening (20% chance). High temps should reach the mid 80s as the humidity finally begins to

Forecast Confidence: HighFriday, weak high pressure builds in. The result will be mostly sunny skies, drier air, and only a slight chance of an isolated late afternoon or evening shower or thunderstorm. Highs in the mid 80s.

Forecast Confidence: Medium-HighThe Weekend: High pressure slides off the coast and moister air starts to flow in off the Atlantic behind it. At the same time a front will be approaching from the north, though it may not make it here until late Sunday. A preliminary forecast is for partly sunny skies and a 20 percent chance of afternoon or evening showers and storms. Temperature-wise, highs should be in the mid-to-upper 80s on Saturday, while Sunday will feature an increase in humidity and highs near 90.

Rising Rivers

Flash flood watches and warnings for the area expire this morning, but in their place is a coastal flood warning in effect until 12pm today. Believe it or not, the coastal flood threat is not a direct result of the rain, but rather a byproduct of prolonged southeast winds (associated with the storm event) pushing water up the Chesapeake Bay and Potomac River. The National Weather Service says "minor to moderate" flooding is possible.

While winds will shift today to a southwesterly direction, the flooding threat isn't quite over. All the rain that has fallen to our west is draining downhill and into the Potomac and Rappahannock rivers. Flood stage could be reached or slightly surpassed at various locations along these rivers between now and Thursday. The National Weather Service has the details.

Reports and Records

  • NWS has the latest reports for total storm rainfall here. Reagan National finishes with 13.47 inches, Dulles with 11.23".

  • According to this thread on Eastern US Weather Forums, the four-day total of 12.11 inches at Reagan National (as of 8am yesterday) beats the old four-day record at National of 8.72 inches on August 12-15, 1955.

  • Yesterday's 1.47 inches of rain at Dulles broke the old daily record of 1.26 inches set in 1968.

  • More records to come as last night's rainfall totals get calculated into the mix.

Rain Drenches D.C. Hole

Weather junkies know it as the "DC hole" -- the bare spot on radar that seems to form over Washington during some precipitation events. True or not, the perception is that DC never seems to be in the bullseye of rain or snow.

This time, however, the District and its close-in suburbs were in the thick of the action. The Doppler radar-estimated rainfall map at right, which shows estimated rainfall totals from 4:18pm Thursday through 12:44am this morning, shows that DC and vicinity was in the thick of the action. Legend is not included as the radar estimates are uniformly underdone.

Image courtesy National Weather Service.

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Moderate to Monsoon: State of Emergency

Steve Scolnik @ 8:00 PM

Flash Flood Watch is in effect for the entire DC area until Wednesday morning

State of Emergency declared in Washington, DC

9pm update: Heaviest rain is west of the beltway where the highest rainfall totals are likely tonight. Generally 1-3" should fall across the area (with isolated higher amounts--especially west) with rainfall tapering off late tonight. Rain may be enhanced as tropical low moves northward for a time between about 10pm and 3am. Washington Post: More Rain Heading to Washington.

6:45 Update:Flash Flood Warnings have now been issued for most of the immediate DC metro area.

5:30 Update: The low pressure area in the Atlantic moved inland near Morehead City NC before it could develop. However, it is spreading heavy rains and gusty winds across the Outer Banks as it moves northward.

To follow the current storm progress in the Washington area, periodically refresh the radar image from
For storm related links and a timeline through tomorrow, scroll down to Matt's earlier post below.

With the lower half of the atmosphere almost completely saturated, storms can break out just about anywhere in the region the rest of this afternoon and evening, and storms now in central Virginia will continue moving north or west of north toward the DC area. Although some downpours may be brief, they can also be quite heavy.

After 2.56" of rain fell at National Airport in the 24 hours ending this morning, by early this afternoon, only 0.02" fell, but a heavy shower has raised that by 0.21" in only 14 minutes in the past hour. In an almost complete reversal of the usual thunderstorm path in this area, that storm moved from Prince George's County across the District from Southeast to Northwest, and is now pushing into Montgomery County, where rain is ranging from moderate to monsoon outside the window of Afternoon Blog Central. The main focus of activity so far today, however, is somewhat to the west of the immediate metro area. The most widespread heavy storms extend from near Hagerstown to south of Charlottesville.

Another issue of concern is a weak low pressure area about 35 miles off the lower North Carolina coast. The National Hurricane Center reported this afternoon that a reconnaissance flight found some gale force winds in the eastern portion of the area, but there was no closed circulation; therefore, it is not a tropical cyclone, at least yet. It does have the potential to develop into a tropical storm, however. Depending on the exact track of this disturbance as it moves northward, it could inject even more moisture into the DC region, or it could remain closer to the coast. In any case, the models are predicting several more inches of rain through the next day or so.

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Forecast Still on Track, Circulation Off Carolinas Could Develop

Matt Ross @ 12:00 PM

The DC Metro Area is Still Under the Gun

The entire metro area is still on board for flooding rains this afternoon and evening. Continue to refer to this morning's post for important links and storm timeline.

Additionally, there is a possibility that an area of circulation currently off the South Carolina Coast could develop into a tropical depression and perhaps storm.

So, what is the impact for us?

The area of circulation was already expected to be a player in the current system, and is unlikely to develop quickly enough to have an impact on our area that differs from the one already forecast. Look for updates from the National Hurricane Center.

Here is the upshot:

Expect scattered storms to become more numerous this afternoon and evening. The line of rain to our west will start to pivot east and link up with the plume of moisture coming from the Carolinas. Areas of rain will become more consolidated as the moisture moves to the northeast. Flash Flooding, Road Closures, Strong to Severe Thunderstorms, and Training are likely. The consolidated area of rain will give way to scattered light showers during the overnight hours.

Stay Tuned for Updates this afternoon and evening.

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Historic June 2006 Flood: Day Three

Matt Ross @ 11:45 PM

After historic flooding during the past 48 hours, the DC area braces itself for the possibility of more flooding rain. This post begins with important links followed by the forecast and climate information.

Important Links and Resources

Timeline and Forecast

Today we will likely experience a continuation of the periodic torrential rain that has plagued the area for two days.

Here is an approximate timeline of what to expect:

6am to Noon
: Overcast with occasional light to moderate showers, with temps in the mid 70s.

Noon to 6pm
: Showers and Thunderstorms increasing in coverage and intensity, especially in Loudoun, Fairfax, and Prince William County, but affecting the entire metro area. Temps in the mid and upper 70s.

6pm to Midnight
: Occasional heavy downpours will continue west of town and increase in coverage over the entire metro area as the heaviest axis of rain pivots to the north and east.

During the afternoon and evening hours, flash flooding, road closures, and torrential downpours are likely. Rainfall totals of an additional 2-4" are probable with higher localized amounts through Wednesday morning.

Midnight to 6am: Heavy rain will eventually taper to lighter showers as we head toward dawn.

On Wednesday, it will warm up into the mid and upper 80s -- starting to break from this pattern, although occasional showers and thunderstorms (especially during the afternoon and evening) are likely through the end of the week.

Updates will be posted throughout the day as needed.

Image Above Right: The latest model data show a continuing plume of tropical moisture over our area for the next 36+ hours, with 2-4" rainfall potential.

Torrential rain in Reston yesterday afternoon, courtesy of Photographer, Kevin Ambrose. Another deluge of several inches of rain is likely this afternoon and evening, especially west of town.

Climate Information and Event Facts

As of about 10:30 last night, DCA had recorded 13.45" of rainfall for the month. What does this mean?
  • It is the wettest June of all time in over 100 years of records, easily surpassing the 11.53" that fell in June of 1972 mostly as a result of Agnes.
  • DCA recorded its second greatest 24 hour rainfall total yesterday with 7.09" ending at 8am Monday morning.
  • June 2006 is now the 4th wettest month of all time. The number 2 spot is less than 1" away and has a very good chance of being reached. We are 4" from reaching the #1 wettest month ever in DC (September 1934, 17.45"). I think we have about a 50-50 chance of attaining this record.
  • We are approaching a rain surplus of 5" for calendar year 2006. Any concerns over drought conditions are mostly irrelevant for the greater DC area.
Stay tuned for updates on these numbers over the next several days.

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Flood Threat Continues

Steve Scolnik @ 12:25 PM

FLASH FLOOD WATCHES AND WARNINGS are in effect for the entire DC metro area. See details in the Current Watches and Warnings box above. Headed out for the commute home? Listen live to WTOP for the latest road conditions.

6:30pm Update: Light to moderate rain now falling in much of the metro area will become heavier at times in many places over the next couple of hours as stronger storms move in from the south.

For the outlook through tomorrow, and a recap of events since yesterday night, scroll down to Jason's post below.

5:00pm Update: The Flash Flood Warning has been extended for DC and the immediate area except for Prince George's County until 11pm. An area of moderate to heavy rain extends from Springfield northward along much of the VA Beltway and is moving into western Montgomery County.

3:30pm Update: Storm activity is now located almost completely outside the Beltway. The heaviest showers are in southern Montgomery and western Fairfax Counties. Another area of moderate to heavy rain is in southwestern Prince George's County. Dulles has recorded 1.43" of new rain since 8am today. A band of storms extends southward just west of I-95 in Virginia to south of Richmond.

1:30pm Update: Right now, the local areas most affected by showers are in a narrow band from near Bowie southwestward across the eastern portion of DC through Alexandria and along I-95. Don't be fooled if you're seeing sunshine and some blue sky, as we are here in west-central Montgomery County. The air is extremely juicy; dewpoints in the area are in the low to mid 70s, and Stafford is reporting a super-tropical 81°. The sun just adds fuel to the mix, and bands of showers and storms extend (with some breaks) from north of Baltimore southward well into southern Virginia. These storms are moving a little east of north and will impact various parts of the DC region intermittently through the afternoon and evening, some with heavy downpours.

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Flash Flood 2006: Special Coverage

Jason Samenow @ 8:25 AM

Flood watches remain in effect. Click on your county in the list above to view the latest information.



Widespread flash flooding occurred Sunday night in DC as well as surrounding suburbs. Particularly hard hit were areas of Montgomery County which received upwards of 6". Numerous reports of stranded vehicles, road closures and water rescues were documented. Conditions remain favorable for more episodes of flooding rain through Tuesday, and rainfall totals will likely break records in some areas.


Forecast Confidence: Medium-HighPeriods of heavy rain, with some breaks A stalled front to our west coupled with an area of slow moving low pressure to the south is promoting uninhibited moist, southerly flow. Accordingly, the potential remains for flooding rain, with another 2-4" possible by Tuesday morning.

As was the case yesterday, due to the somewhat random nature in which these storms develop, some areas may receive less than this while some may receive more. And some areas may well experience significant periods of time with no rain and even some sunshine. High temperatures should be near 80, with lots of humidity. Rain coverage/intensity is likely to be greatest during the late afternoon and evening.

Overnight, the potential for heavy rain remains for much of the area. Pinpointing who gets exactly what is difficult, but everyone should be aware of the possibility of dangerous, flash flooding.

Pictured: The NAM computer model predicts 3-5" (red color) of rain through Wednesday morning for much of the area. Some areas are likely to experience locally heavier amounts.


Forecast Confidence: MediumFlood potential continues. Another wave of tropical moisture is likely to move northward through the area, potentially dropping 2-4" more rain, with locally higher amounts. Some areas may experience 5-day rainfall totals of over one foot. High temperatures Tuesday will likely be between 75-80. Sometime late Tuesday night, the potential for flooding rain may diminish, as high pressure begins to build in from the west.

Sunday night: Flood Recap

  • Through 2am Monday morning, Reagan National had received 6.83" in 24 hours, 6.30" in 5 hours from 9pm to 2am, and 1.5" in one hour between 1am and 2am.
  • New daily rainfall record at Dulles Airport of 5.94"
  • Selected 24-hour rainfall totals (as of late Sunday night): DC Zoo, 3.91"; Bethesda, 4.71"; Chevy Chase: 5.58"; Arlington, 4.36"; Reston, 6.3"; Falls Church, 3.9"
  • Floods Trap 30 In Chevy Chase Recreation Center
  • Major road closings in DC, including Pennsylvania Avenue
  • Numerous water rescues in eastern and western Montgomery County
  • All major roads closed in Fairfax City
Pictured: Doppler rainfall estimates in DC area between 9pm and midnight last night. Darkest red shade is 4", dark green shade is 1".

(Note: the usual 7-day forecast has been pre-empted for coverage of this flood event).

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Sunday Soaking

Jason Samenow @ 9:53 AM

A Flood Watch is in Effect through this evening.


Intermittent showers this afternoon, heavier rain tonight. Steady rain this morning will give way to just spotty shower activity this afternoon. The best chance of heavy rain and thunderstorms will be overnight tonight. Rainfall potential through tomorrow morning is around 2", with locally higher/lower amounts possible depending on the track of showers/t'storms. It will be cloudy and humid this afternoon, with highs near 80.

Conditions for the early part of the coming week look wet. Forecast details for the week ahead will appear tomorrow.

Booz Allen Classic Outlook: Course conditions will be wet, but a window of opportunity to finish the tournament could occur this afternoon. Otherwise, play may need to be extended until tomorrow.

Weather Conference: July 7 to 9

The registration deadline for the conference is July 2. The conference, to be held near BWI, will include a wonderful set of presentations from well-known meteorologists such Paul Kocin, Tony Pann (WUSA and WeatherTalkRadio--airring today at 3:05pm), Justin Berk (ABC Baltimore and co-host of WeatherTalkRadio with Pann), and Louis Uccellini. Last year's conference was outstanding and I would recommend that any weather buff attend this year's edition which should be bigger and better.

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