Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 210105 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 905 PM EDT MON JUN 20 2016 .SYNOPSIS...
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A cold front will approach the region from the northwest tonight and cross the region Tuesday into Tuesday night. High pressure will briefly pass to the north on Wednesday. Another low pressure will move west to east just north of the region on Thursday. High pressure will return for the weekend.
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&& .NEAR TERM /THROUGH TUESDAY NIGHT/...
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The weather pattern remains fairly non-descript across the eastern United States. Light southerly flow is in place, but dewpoints are still low (upper 50s to lower 60s). Mesoscale analysis suggests that any CAPE/shear resides in the Potomac Highlands, with a much more favorable air mass west of there. There were a couple of thunderstorms that initiated west of the forecast area just prior to sunset, but these are on the verge of dissipating. Moisture advection will continue through the night, which will allow instability to creep in. It likely will be elevated due to nocturnal cooling. But, a couple of thunderstorms may develop along the nose of the theta-e ridge. More recent mesoscale guidance runs (HRRR/RAP/LWX WRF-ARW4) not as emphatic as eariler offerings, and have trimmed the PoPs back. However, am still maintaining a verbal metion during the late night/early morning hours. Tuesday remains a bit of a question. Guidance has generally slowed the progress of the front down and it appears to wait until late in the day or the early evening before clearing the area. Indices are fairly robust but westerly flow would suggest that the models are overdoing convective coverage. Any storms that do manage to fire could go severe...but think coverage will be below 50 percent. Front clears the area Tuesday evening and a drier and slightly cooler air mass arrives behind it.
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY/... Wednesday will be a day between systems with high pressure nudging south from Canada and another dry air mass. Temperatures won`t drop that much however with readings well into the 80s. Warm front pushes into the area from the southwest on Wednesday night with showers and perhaps some embedded thunder. Some steady rain is possible Wednesday morning as the front pushes through. Most guidance now has the front lifting north of us and bringing a very moist...warm and unstable atmosphere across our area for Thursday afternoon. With good shear and instability and the approaching cold front to our northwest...would think we will have a severe weather episode during the afternoon and evening. With PW`s so high also would expect some heavy rain and if any training or repeat storms occur...flash flooding might be a concern as well. Lows Wednesday night will be high 60s to low 70s with highs Thursday in the high 80s to low 90s. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... A low pressure system will move along the Mason Dixon line Thursday night. Heavy showers and thunderstorms will accompany the low. Temperatures will be seasonable. The low pressure system should move offshore later Thursday night and early Friday. Wrap-around showers or a rumble of thunder could linger right into midday Friday. High pressure will begin to work its way into the region Friday and linger through Sunday morning. Drier and slightly cooler air will evolve through the weekend. High pressure lingers Sunday night before moving offshore Monday. A warm and more humid return flow will evolve, helping to fuel a couple of showers over the western half of our zones Monday. && .AVIATION /01Z TUESDAY THROUGH SATURDAY/...
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No substantive changes to the TAFs at this time. Generally VFR thru TAF period and beyond through Wednesday all terminals. Scattered thunderstorms may result in gusty winds and reduced CIGs and VIS Tuesday. Winds which are light currently may pick up and gust up to 20 knots from the W even outside of storms. Returning to VFR with light winds Tuesday night into Wednesday. Storm system moving in Wednesday night and Thursday may again result in reduced VIS and CIG from rain showers and thunderstorms. Returning to VFR for the weekend.
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&& .MARINE...
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Based on mesoscale guidance runs (HRRR/LWX WRF-ARW4) launched a Small Craft Advisory for the Chesapeake Bay/lower tidal Potomac River for southerly channeling through the late night. It has failed to materialize thus far. However the favored time frame runs from 10pm-midnight through 3 or 4am. Therefore, will let it stand. Winds pick up a bit ahead of incoming cold front on Tuesday. With convection also expected, decided to raise SCA thru most of the day. May need to extend a little later than currently have it. NW flow behind system may result in another SCA day on Wednesday. Additonal issues with more rain and t-storms expected Thursday. Should quiet down for weekend.
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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 4 AM EDT Tuesday for ANZ530>534- 537>541-543. Small Craft Advisory from 9 AM to 6 PM EDT Tuesday for ANZ530>543.
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&& $$ SYNOPSIS...HTS/RCM NEAR TERM...HTS/RCM SHORT TERM...RCM LONG TERM...KLW AVIATION...HTS/RCM/KLW MARINE...HTS/RCM/KLW

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