Area Forecast Discussion
Issued by NWS Sterling, VA

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056 FXUS61 KLWX 120222 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 922 PM EST Wed Jan 11 2017 .SYNOPSIS... A cold front moves southward across the region Friday. The front will stall to the south and a few waves of low pressure will ride eastward along the front over the weekend into early next week. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... As of 920 PM, main batch of steady light showers associated with weak mid-level vorticity lobe and WAA in the low/mid levels continues to push northeast across the NE corner of the forecast area. Amounts have been rather underwhelming across much of the region...with a paltry ~0.06" at our office in Sterling...with the steady rain having just ended. A little more in other places...though generally less than a quarter inch. Steady rain clears the remainder of the area by 11 PM. Though, will be holding onto slight chance overnight PoPs from I-66 northward, mainly for a few residual showers...as advertised by hi-res guidance. Lows tonight holding steady from their current values...with M40s across much of the area. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/... Have not made many substantive changes to the Thursday forecast. The day will be spent in the warm sector of the low pressure system which by that time will be moving up the St. Lawrence Valley. A few showers may brush by the Highlands, but otherwise it should be dry. High temperature forecasts are warmer than previous cycles, which already were soaring. Have raised high temperature forecasts based on better performing guidance packages and the current temperature observations. The associated cold front will push south through the area late Thursday night or Friday morning. Will lean on the earlier side, to support cold advection and dropping temps Thursday night. (No temperature guidance supports extremely warm low temps.) The precipitation coverage in doubt too, and am keeping much of the area dry through frontal passage. Believe that high pressure will be seeping south on Friday. That will support the drainage of low level cold air. Meanwhile, the mid-level flow gradient is tightly packed, with the upper jet just north of the area. That would support waves of precipitation, especially Friday night1. How much precip would fall is still to be determined, and precip type is highly questionable. Just about the only thing that (perhaps) could be ruled out is pure rain or pure snow; ie: it would be a mixed bag of some kind. That makes forecasting any specifics problematic at best. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... Strong Arctic high builds over New England Saturday as precipitation moves over the area. Low-level cold air wedged beneath warm air advection aloft favors a wintry mix of freezing rain...sleet and snow. Precipitation likely transitions to rain for southeastern areas but remains freezing rain for the northwestern half or so of the CWA by late Saturday or Saturday evening. There is uncertainty in exactly when and where precipitation changes from snow to sleet to freezing rain and eventually plain rain, but as is typical in these setups, expect the northwestern corner of the CWA to hold on to cold air for quite a while (possibly through Sunday night). This could lead to a prolonged period of freezing precipitation with multiple rounds of steady light precipitation and drizzle in between. A more substantial warming trend should ensue early next week, with conditions expected to be plenty warm enough for plain rain as a larger area of low pressure moves toward the region during the middle part of next week. && .AVIATION /02Z THURSDAY THROUGH MONDAY/... Rain is beginning to move out of the area. MVFR still possible at a few sites (e.g., BWI/MTN) until rain pushes eastward over the next hour or so. Should see improvement to VFR soon after showers depart. Think that the ground now warm enough to preclude fog development in the wake of the rain. There would be concerns if skies clear though. Dont believe that will happen, but the potential still there. Of greater certainty is the low level wind shear potential, as a 50 kt low level jet slides north along the I-95 corridor tonight. That phrasing in TAFs. Thursday should be VFR, with the cold front to the northwest of the terminals. Low clouds may redevelop Thursday night. Cold front will slip south early Friday, but should have little impact other than the wind shift. The next disturbance could bring wintry precipitation late Friday night, but confidence in particulars is low. Sub-VFR likely over the weekend in freezing/frozen precipitation. May transition to -RA from CHO to DCA by Sun AM. Very light NELY flow during this time. && .MARINE... Low level jet increases tonight. A Small Craft Advisory begins at 1 AM and goes through Thursday night. While mixing will be poor tomorrow night, the magnitude of wind close to the waters surface can`t be ignored. A cold front will move through early Friday. It`s a little uncertain if the northerly surge behind the front will be strong enough to warrant an SCA. A wedge of high pressure should keep winds light over the waters over the weekend. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 1 AM Thursday to 3 AM EST Friday for ANZ530>534-536>541-543. Small Craft Advisory from 1 AM to 6 PM EST Thursday for ANZ542. Small Craft Advisory from 8 AM to 6 PM EST Thursday for ANZ535. && $$ SYNOPSIS...MSE/HTS NEAR TERM...MSE/HTS SHORT TERM...HTS LONG TERM...DFH AVIATION...MSE/HTS/DFH MARINE...MSE/HTS/DFH

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