Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 241853 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 253 PM EDT Tue Apr 24 2018 .SYNOPSIS...Low pressure over South Carolina will slowly move up the mid-Atlantic coast tonight before passing by to our east Wednesday. A cold front will pass through Wednesday evening and high pressure will return for Thursday. Low pressure may impact the area overnight Thursday into Friday before a cold front passes through Saturday. High pressure will return by the end of the weekend. && .NEAR TERM /THROUGH TONIGHT/... Rain has been very slow to move into northern VA today, but it`s finally moving in. Strengthening onshore flow rest of today into this evening will lead to a period of rain tonight ending by midnight in the south but lingering into the early morning hours in northeast MD. Model QPF has trended lower this cycle with amounts likely to remain below an inch in most places except in the south and on the eastern slopes of the Blue Ridge mountains where amounts greater than an inch have been reported in Highland county and approaching an inch in Augusta county. Mid-level dry slot will start working into southern areas by 09Z as low pressure moves over southern MD. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... Steady rain will end by 12Z everywhere as onshore flow weakens and low pressure passes just to the east. Not much in the way of forcing available to generate precip, but can`t completely ruled out a few showers as weak instability develops with passage of upper level trof axis. Otherwise, most cloudy skies with some breaks in the clouds possible over the VA piedmont in the afternoon. Very weak high pressure builds Wed night and Thu. A second area of low pressure will move across the area Thu night with increasing chances of showers. && .LONG TERM /FRIDAY THROUGH TUESDAY/... On Friday, a upper level 500mb trough will be situated over the Midwestern US. A 500mb shortwave will move through the system and be over our region on Friday. The associated sfc low pressure system will shift into the region from the southwest. The exact location of this sfc low is still uncertain as the 12Z GFS keeps the low further north and west in northern Maryland and PA. The 00z Euro has the low approaching and moving east north east just to our south. The difference between solutions is that the GFS tries to keep the majority of the precipitation to the north and west of our forecast area while the Euro tries to take the low further southward. The 12Z Euro run may bring the low further north like the GFS increasing the the chances for higher precip amounts. As of now, this seems like a fairly weak frontal passage that will bring light precipitation. The front associated with this sfc low will likely move out of our forecast area by early Saturday morning. Temperatures will rise Friday up into 60s with some areas reaching the 70s due to warm air advection from the south to southwest. A isolated thunderstorm wouldn`t be out of the question on Friday. Behind the weak frontal passage, a strong high pressure will build into the area from the Upper Midwest and the Great Lakes region. The high will remain over the region through early next week leading to clear skies and temperatures close to average for this time of the year with temperatures in the upper 60s to low 70s. && .AVIATION /19Z TUESDAY THROUGH SUNDAY/... Developing MVFR/IFR conditions tonight in rain if they haven`t already as low pres over SC lifts ne and onshore continues to strengthen. Winds will remain gusty through 00Z-03Z, then start to diminish after 06Z. Gradual improvement in cigs expected Wed, but still plenty of clouds. Clouds will increase on Friday as a low pressures system moves in from our south. Brief lowering of cloud bases and visibility will be possible if showers and isolated thunderstorms move through the region. Sub-VFR conditions will be possible on Friday. Clearing skies along with light winds are expected over the weekend leading to VFR conditions. && .MARINE... SCA conditions expected through 03Z-06Z tonight, then winds diminishing rapidly as sfc low moves overhead. Light winds expected on Wed, then strengthening somewhat Wed night behind departing low. Marginal SCA conditions possible, but confidence low attm for any SCA. A low pressure approaching from out south on Friday will lead to a southerly flow and increasing clouds. The southerly flow will likely warrant the need for small craft advisory on Friday as winds flow up the chesapeake bay. Over the weekend, a strong high pressure will be present leading to clear skies and lighter winds. SCA unlikely Saturday and Sunday as of now. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 4 AM EDT Wednesday for ANZ530>534- 537>543. Small Craft Advisory until 10 PM EDT this evening for ANZ535- 536. && $$ SYNOPSIS...LFR NEAR TERM...LFR SHORT TERM...LFR LONG TERM...JMG AVIATION...LFR/JMG MARINE...LFR/JMG

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