Area Forecast Discussion
Issued by NWS Sterling, VA

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163 FXUS61 KLWX 091958 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 258 PM EST Fri Dec 9 2016 .SYNOPSIS...
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High pressure over the Upper Midwest builds east through Saturday before moving off the Mid-Atlantic coast Sunday morning. A cold front crosses the area Monday followed by a reinforcing cold front Wednesday. Cold high pressure builds back into the area for the latter half of next week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Afternoon surface analysis shows 1040+ mb high pressure continuing to build east of the continental divide. Blustery conditions will continue for the remainder of the afternoon. Web cams show upslope snow continuing to fall along the Allegheny Front, but with minimal accumulations. This activity will begin to wane overnight as the inversion height falls. The center of the high will move toward the lower Ohio Valley tonight. There should be enough of a gradient to keep a breeze, especially northern parts of the area. Locations which can decouple (and the higher elevations) will likely fall into the teens, with 20s elsewhere. Wind chills will be in the teens area- wide...even colder in the higher elevations.
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&& .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
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The center of the high will build overhead Saturday into Saturday night. There will still be a bit of a breeze on Saturday before calming Saturday night. Temperatures will remain below normal, with highs again struggling to rise through the 30s and lows in the teens and 20s. The amount of cloud cover will be critical for how far temperatures drop Saturday night. A low pressure system will track from Colorado to Michigan Sunday into Sunday night. There is still model spread on how extensive the warm frontal precipitation is. If any light snow were to fall Sunday, it would be within a county or two of the MD/PA border. The rest of the area will just see increasing clouds with another day of below normal temperatures. The forecast for Sunday night is tricky as moisture begins to advect into the area. The trend for the 12Z models has been to keep the first half of the night dry...at least for the eastern half of the area...as we are in the "warm" sector of the storm system. However, temperatures won`t have to fall very far to reach freezing, which could be accomplished if clouds thin a bit. While there could be a little snow or sleet across far western and northern parts of the area, it appears that by after midnight, a strong low level jet will push temperatures aloft well above freezing. Models also show surface temperatures rising overnight. While this isn`t a classic CAD setup with NE flow, am hesitant to bite on the full magnitude of this warming due to the overnight time frame. Therefore we could run the risk of freezing rain, especially near and west of the Blue Ridge, as precipitation spreads in after midnight. Have introduced this into the grids and HWO.
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&& .LONG TERM /MONDAY THROUGH FRIDAY/...
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For the early part of the week the upper level flow will be zonal. This will take a short wave across the eastern Great Lakes and into northern New England. In the Mid Atlantic warm air will be drawn into the area ahead of a cold front pushing temperatures into the 50s. Both GFS and Euro are pushing pops up to 80%. It does appear that a line of showers will be moving through the region Monday. QPF`s of up to 1/2 inch could occur. Timing of the line is the primary question..with the GFS being slower with the progression. As we are still three days away I`ve kept the entire 12 hour period in likely/cat PoPs...but this will need to be fine tuned in the coming days. High pressure pushes overhead Monday night with cold advection bringing temps back down into the 30s. Tuesday will start out dry with high pressure overhead, however some guidance develops a wave of low pressure to the south which may brush the region later in the day. This could bring light precip to the southern part of the forecast area. A broad upper level trough develops over Quebec during the second half of the week. This will allow a cold front to push through the Mid Atlantic Wednesday. There will be a potential for rain/snow with the front, and snow showers as the colder air moves in Wednesday night. Mid Dec average temperatures are mid 40s highs/mid 20s for lows. Right now it`s looking like Thursday/Friday highs will be more like 30-35 with lows around 20. Upslope snow showers can be expected in the Highlands during the second half of the week. The cold shot looks to be short lived as the upper trough exits offshore for next weekend.
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&& .AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
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VFR conditions are expected through Sunday, with some stratocumulus above FL040 at times. NW wind gusts 20-30 kt will diminish this evening, with lesser gusts of 15-20 kt on Saturday. There is a small chance of light snow near MRB on Sunday. As a low pressure system moves into the Great Lakes, conditions may deteriorate Sunday night, especially after midnight as precipitation arrives. This should be mostly rain, although a little snow, sleet, and freezing rain will be possible at MRB. Rain showers...perhaps heavy at times...can be expected with a cold frontal passage Monday. This will lead to degraded ceilings/ visibility. No problems expected Tuesday.
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&& .MARINE...
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Solid SCA conditions with NW flow continue this afternoon. Winds should decrease some tonight, with the SCA dropping off for the narrower waterways. Even though high pressure will be building closer on Saturday, there seems to still be enough gradient across northern portions of the Bay to warrant another SCA. Lighter winds expected with high pressure Saturday night into early Sunday. Increasing southerly flow ahead of the next storm system may warrant another SCA by late Sunday. SCA level winds expected Monday...dropping off Tuesday.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 6 PM EST Saturday for ANZ531-532- 539-540. Small Craft Advisory until midnight EST tonight for ANZ530-536- 538-542. Small Craft Advisory from 9 AM to 6 PM EST Saturday for ANZ530- 538. Small Craft Advisory until 9 AM EST Saturday for ANZ533-534- 537-541-543. Small Craft Advisory until 9 PM EST this evening for ANZ535.
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&& $$ SYNOPSIS...ADS/WOODY! NEAR TERM...ADS SHORT TERM...ADS LONG TERM...WOODY! AVIATION...ADS/WOODY! MARINE...ADS/WOODY!

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