Tuesday, February 21, 2006
Spring Delayed For At Least A Week or Two
Matt Ross @ 1:00 AM
Forecast
Today will be mostly sunny and seasonable. High temperatures will reach the mid to upper 40s, and it will feel reasonably comfortable outside this afternoon in the late February sun. Clouds will approach on Wednesday as a system passes to our south and provides a chance for some light snow/rain during the day, particularly in our southern and eastern suburbs(see Snow Lover's Crystal Ball for more). Some very cold air looks to arrive in the Saturday/Sunday period.
Cheetah's enjoy near 70 degree temperatures last Thursday at the National Zoo, Courtesy of CapitalWeather.com contributor Ian Livingston
Cold February Day
No, it wasn't just you. Sunday was in fact by almost any measure very cold. With a low temp of 14 degrees and a high of 30 degrees, Sunday was our 2nd coldest day in the last ten February's. So through today, that is the 2nd coldest out of 275 February days dating back to February 1st, 1997. Not too shabby. Nobody will be surprised by the coldest February day during this span. That would be February 16, 2003 or right in the middle of the President's Day Snowstorm. With a low of 15, a high of 25, and 13.3" of snow for the day(storm total was 16.7"), that day is a bit more memorable. It should be mentioned that February 1996 which occurred just a year prior to the referenced time period featured 3 consecutive days(February 2-4, 1996) colder than the 2 mentioned above. The next arctic blast coming in toward the end of this weekend looks very potent. I may just have to update these stats next week.
Geese during a cold sunset yesterday in Fairfax, Courtesy of CapitalWeather.com Photographer Kevin Ambrose
Sun Angle
The sun angle or declination is the measure of the angle between the sun's rays and the equator. This angle is highest during the summer solstice in late June and lowest during the winter solstice in late December. However our climatology here in DC does not necessarily correlate with the angle of the sun. Our warmest time of the year is in late July about a month after the summer solstice and our coldest average period is in late January, about a month after our winter solstice. Currently the angle of the sun and the length of the days is equal to that of late October, even though our average high temp is almost 20 degrees colder. Atmospheric patterns trump the sun angle and during this time of year allow colder air masses to penetrate our area much more easily. However, the sun angle is still a factor. Even though surface temperatures in the shade may not reflect it, the sun will feel stronger on the days it is out. One of the biggest effects is on the accumulation of snow.
Some may have witnessed in last weekend's storm that the snow accumulated first in areas that aren't exposed to as much sun during the day. This occurrence will be a factor in any snow events from now until Spring. There are several factors that will allow snow to accumulate more easily thus offsetting the sun angle, especially during the day and on paved surfaces. Cold temperatures for an extended period of time before the onset of snow, heavy intensity of snowfall, cold surface temperatures during the storm, and snow after dark. For snowlovers, we ideally want a nighttime snowfall. If we cannot get that, it helps to have moderate to heavy snow, and temps in the mid to upper 20s in a preexisting cold air mass. Of course, beggars can't be choosers. I will gladly take anything, including slushy accumulation on grassy surfaces.
Next Chance of Accumulating Snow: Wednesday, February 22nd
Probability: 20%
Potential Impact:
Commentary: A system will pass to south and east on Wednesday, but may just come far enough north to clip our area. Right now this looks like a very low impact event. It will occur mostly during the day with surface temperatures above freezing, and upper level temperatures may be warm enough for precipitation to fall as rain. Stay tuned for any late developments.
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