Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 111343 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 943 AM EDT Wed Oct 11 2017 .SYNOPSIS... A frontal zone will remain nearly stationary across the Mid-Atlantic through this evening. An area of low pressure will track along the front tonight and push it to our south and east late tonight into Thursday. High pressure will build north and east of the area later Friday through Saturday before moving offshore Sunday. A stronger cold front will pass through the area early next week. && .NEAR TERM /THROUGH TONIGHT/...
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A nearly stationary boundary remains over the Potomac Highlands into central Virginia today. The boundary separates cooler marine air to the north and east vs. warm and humid air to the south and west. The boundary will remain nearly stationary over the area today...but shortwave energy will pass by to our north this afternoon. This will cause the low-level boundary between 925-850mb to move north and east as a warm front. Thus...warm and moist air will be overrunning the surface cooler air in place and the added lift from the low-level boundary will cause showers throughout the day along with plenty of clouds. Will continue to the slight chance for thunder across the Potomac Highlands into central Virginia and southern Maryland...closer and to the south of the surface boundary. PWATS over 2 inches in spots will cause rain to be moderate to locally heavy at times. As of now...any flood threat is low due to recent dry conditions preceding the rainfall. Max temps will range from the 60s across northern Maryland...to the lower and middle 70s near Washington and Baltimore...to the upper 70s and lower 80s across portions of central Virginia. More shortwave energy will pass by to the north tonight while the surface boundary remains nearly stationary overhead. More showers are expected across the area along with possible thunderstorms to the south and west of the boundary across central Virginia into the Potomac Highlands and southern Maryland. The shortwave energy will move off to the east overnight and the surface boundary will drop south and west as a cold front. The onshore flow will cause low clouds along with areas of rain and drizzle/fog overnight.
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&& .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
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The pattern through the end of the week (Thursday and Friday) will be similar, marked by east/northeasterly flow around building high pressure over New England. Model guidance exhibiting a pattern of cold air damming, with light precipitation lingering along the Mid Atlantic. Forecast will be for ample clouds, chance of rain, areas of drizzle, and patchy fog. The mountains will be preferred for precipitation due to upslope, but chances reside just about everywhere. Temperatures will be substantially cooler, likely struggling to reach 70 degrees during the day, and staying near the dewpoints (in the 50s) at night.
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&& .LONG TERM /SATURDAY THROUGH TUESDAY/... A strong mid-upper level ridge will remain anchored to the south on Saturday with a return to above normal temperatures on Sat after a couple of cool days Thu and Fri. The ridge will be pushed to the east Sunday as a shortwave-trough and associated cdfnt move across the Great Lks region Sun night. There could be a few showers Sun night with the frontal passage but the westerly sfc wind trajectories ahead of the front and lack of instability at night suggest any rainfall will be very light at best. The trof axis will move across the area Mon night with a taste of fall weather middle of next week as sfc high pressure builds in from the northern Rockies. && .AVIATION /13Z WEDNESDAY THROUGH SUNDAY/...
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A stationary boundary will remain to the south and west of all the terminals except KCHO through this evening. An easterly flow to the north and east of the boundary will cause low clouds along with occasional showers. MVFR to IFR conditions are most likely. Timing of IFR conditions still remain uncertain as of now. For KCHO...low clouds this morning may break this afternoon behind the stationary boundary. However...a few showers and even a thunderstorm are likely into this evening and this will cause restrictions at times. The boundary will drop south and west as a cold front late tonight. An onshore flow behind the boundary will cause more low clouds and some fog along with areas of rain and drizzle. MVFR-IFR likely to linger for a majority of the time through the remainder of the week with a real taste of fall weather for the middle of next week. Cdfnt will be crossing the area late Sun night and early Mon with only a few showers but no flying restrictions anticipated at this time.
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&& .MARINE...
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An onshore flow will persist across the waters through this evening. A Small Craft Advisory is in effect for the middle portion of the Bay and lower Tidal Potomac into this afternoon. There may be a break in the winds later this afternoon and evening...but onshore winds should be increasing this later tonight. A Small Craft Advisory in effect for the Bay and lower tidal Potomac after midnight, and have extended it through Thursday. It likely will need to be extended further. Small craft advzy conditions likely Sun into Tue with a small chance of gale conditions Mon night due to cold air advection over warm water.
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&& .TIDES/COASTAL FLOODING...
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Tidal anomalies have already begun to increase due to the onshore flow. The onshore flow will continue through late this week and this will cause water levels to increase. Minor tidal flooding is possible with the high tide cycle this evening across St George Island. Chances for minor flooding will increase across all locations Thursday through Friday.
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&& .EQUIPMENT...
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The NWS 88D Sterling radar (KLWX) will be down during the day from 7 AM through 5 PM today through Saturday this week. This is for nationally scheduled maintenance on the radome. Our surrounding 88D radars as well as FAA terminal radars will continue to scan our skies during this downtime.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from midnight tonight to 6 PM EDT Thursday for ANZ530>534-537-539>541-543. Small Craft Advisory until 3 PM EDT this afternoon for ANZ533- 534-537-541>543.
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&& $$ SYNOPSIS...LFR NEAR TERM...BJL/HTS SHORT TERM...HTS LONG TERM...LFR AVIATION...BJL/LFR/HTS MARINE...BJL/LFR/HTS TIDES/COASTAL FLOODING...BJL/HTS EQUIPMENT...BJL

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