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10-Day Outlook: Winter Hangs On...

Josh Larson @ 2:00 PM

Today's Forecast

Expect a cloudy, damp start to the day today with a stray shower in spots through early afternoon. As the day wears on, expect partly to mostly sunny conditions to develop with drying conditions. Highs should top out near 50 in most spots.

Tonight will feature partly cloudy conditions, with widely scattered snow showers possible overnight. Expect lows to range from the upper 20s to the mid 30s downtown.

School bus stop in Herndon, VA on Wednesday amid the snow. By photographer Kevin Ambrose.

Pattern Overview

I said in last week's outlook that, "evidence -- especially from 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 snow) may continue through the end of the month and perhaps even into early March. "

Sure enough, after the next two to three days of temperatures at near-normal levels, we can expect below normal temperatures (including a period of much below normal temperatures) to persist through the remainder of the month and into the start of March.

The reason? Over the next week, we will witness a textbook negative-NAO pattern developing. In the CPC SuperEnsemble Height Anomaly Map, note (1) the extremely strong positive height anomalies over Greenland, which we call "blocking"; (2) the strong negative height anomalies over the Northeast -- which will lock cold air in over our region. (See image above, courtesy CPC.)

As a result, expect temperatures over the next 10 days to average 8-12 degrees below normal, with a four day period from Sunday, Feb 26 through Wednesday, March 1 to average nearly 15-20 degrees below normal. As for precipitation, though no models hint at any major storm systems developing during the next 7-10 days, the NAO- pattern might be conducive to snowfall for our region if storms do develop.

The next 5 days (Feb 23-27)

Forecast highs/lows: 41/25 (normal = 50/32)
Forecast precip: below normal

Another pleasant day can be expected on Friday: we'll see mostly sunny skies with highs in the upper 40s and overnights lows in the mid to upper 20s. Saturday will be a day of change as an Arctic cold front barrels through during the afternoon. Expect partly sunny skies and high temperatures near 50 during the afternoon, but it will become blustery and colder by evening, with temperatures dropping rapidly. Scattered snow showers cannot be ruled out Saturday night, though little or no accumulation is expected at this time; overnight lows will be in the lower 20s in most locations.

Sunday will feature times of clouds and sun with blustery northwest winds 15-30mph and gusty. Highs will only be in the lower 30s, with wind chills in the teens and 20s. Frigid Sunday night with lows from the mid teens to near 20 downtown. A reinforcing shot of cold air will blow through the area on Monday, which may make it the coldest day of the winter: expect partly sunny skies, blustery conditions, and scattered snow showers. Highs will only be in the mid to upper 20s, with overnight lows from 5-15 depending on location.

Note: Like last week, I am going some 5-10 degrees colder than model guidance values for this weekend's weather. The models are particularly vulnerable to underestimating the amount, and magnitude, of cold air present behind Arctic cold fronts. (Last weekend's temperatures are a great example of this model flaw as well as why I went below guidance for last week's forecast and will continue to do so for this week's forecast.)

The following 5 days (Feb 28 - Mar 4)

Forecast highs/lows: 41/26 (normal = 51/33)
Forecast precip: near normal

It seems likely that much colder than normal conditions will hang on for Tuesday and Wednesday of next week. I expect high temperatures both days in the mid to upper 30s, with overnight lows from the teens to the mid 20s. As the NAO- pattern likely breaks down (and returns to neutral or even positive phase), it appears that temperatures will begin to moderate by the second half of the week: Expect highs to range from the low 40s on Thursday to the upper 40s by Saturday, with overnight lows in the 20s. A storm system may develop over the Eastern US during this period, but rain appears to be the favored precipitation type at this point.

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