Area Forecast Discussion
Issued by NWS Sterling, VA

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541 FXUS61 KLWX 201344 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 944 AM EDT Mon Mar 20 2017 .SYNOPSIS... High pressure will cross the region today. Low pressure will cross the region tonight. A cold front will cross the area Tuesday night. High pressure will return Wednesday through Thursday night. A warm front will cross the region Friday. Low pressure may affect the area Sunday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... High pressure resides over the upper Ohio Valley this morning. Any early morning clouds have eroded, leaving behind mostly sunny or sunny skies. The trend has been for the remainder of the day to be dry as the center of the high slips toward the southeastern states, although showers may approach the Highlands late. Clouds will increase some during the afternoon as well...a combo of mid level warm advection and upper level remnants of midwest convection. High temperatures will be near normal, ranging from 50 in northeast MD to the lower 60s in central VA. && .SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY NIGHT/... Convective complex in Illinois is expected to hold together in some fashion across the Ohio Valley and move into the Appalachians this evening. By this point, precipitation will be driven by a shortwave trough and low level jet, with nearly zero instability remaining. SREF MUCAPE and hi-res lightning threat suggest if there was a stray rumble, it would be in the far southwest CWA. This cluster of showers will move across the area overnight. Have bumped POPs up, but have held off on 100s for now due to some timing and placement differences amongst guidance. Less than a quarter inch of rain is expected. Low clouds/fog may develop as the rain exits, as the surface low reflection passes south of the area and mixing will be poor. Tuesday will be mostly cloudy as a broad baroclinic zone settles southward. However, it should be dry and mild with temperatures pushing above normal, from the upper 50s north to near 70 south. GFS/NAM/ECMWF have taken a decided shift south with the area of low pressure Tuesday night, keeping most of the area dry. However, GEFS still shows a large spread of QPF, and have thus only stepped POPs down 10-20% from previous forecast at this time. With this southward shift, there is less of a chance colder air arriving from the north will overlap moisture. Reinforcing cold front will be pushing through the area around daybreak Wednesday, resulting in gradually clearing skies. However, cold advection will result in breezy conditions and temperatures dipping back below normal. Highs will be in the 40s, up to the lower 50s in central VA. While high pressure will be building in Wednesday night, it won`t be directly overhead, so there will be some variance in decoupling. However, colder spots are likely to dip into the teens with 20s elsewhere. && .LONG TERM /THURSDAY THROUGH SUNDAY/... Guidance is in relatively good agreement regarding the progression of systems through the long term. Canadian high pressure will cross the region on Thursday, with unseasonably cool temperatures remaining in place. Skies should be fairly sunny with relatively light winds. A warm front will then approach from the southwest on Friday as high pressure heads east off the coast. There may be some overrunning rain with the front, mainly in western MD and WV, as it crosses the area, but right now most of the region appears to stay dry. As the front pushes through, winds will become southerly to southwesterly and should increase with some gusts up to 20-25 mph possible. Temperatures will depend on the progression of the front, with above normal temps possible wherever the front passes before evening - most likely southern parts of the CWA. Saturday now looks drier than it did yesterday, as the ridge aloft holds on longer than previously projected. This should allow temps to spike into the 70s across much of the region for the first time since March 9th. A closed low then approaches from the west at the same time as a cold front drops down from the north on Sunday, with cooler and wetter weather possible to end the weekend. && .AVIATION /14Z MONDAY THROUGH FRIDAY/... VFR conditions today with high pressure and light northwesterly winds. Disturbance will cross the area tonight with a 3-6 hour window for showers. The showers will be fairly light, but it does appear that as they exit, low clouds and possibly fog will develop and last through mid morning. IFR will be possible, but will keep at MVFR in TAFs now until certainty is higher. The remainder of Tuesday should be VFR, although mid-level clouds likely persist. Trend has been for low pressure to be farther south Tuesday night, reducing precipitation chances. Cold front pushes south early Wednesday morning, with gusty NW winds to 25 kt possible through the rest of the day. VFR conditions will dominate Thursday and Friday, though a few showers and reduced cigs are possible Friday as a warm front crosses the area. Winds will become southerly and may gust 15-20 knots behind the warm front. && .MARINE... Winds are diminishing, but still have some gusts in the mid teens. The pressure gradient should relax by noon. Winds will be light this afternoon as high pressure builds. A disturbance will bring showers tonight, but no wind issues are expected. NW winds are expected Tuesday as a front pushes south of the area, but am forecasting sub-SCA at this time. Stronger winds will come with a reinforcing cold front late Tuesday night and the last through at least Wednesday evening. Northerly gusts of 20-30 kt will be possible during this time. Winds should be sub-SCA on Thursday as high pressure crosses the area. A warm front will lift north across the area on Friday, with 20 knot gusts possible as winds become southerly. A small craft advisory may be necessary. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...RCM NEAR TERM...ADS/HTS SHORT TERM...ADS LONG TERM...RCM AVIATION...ADS/RCM MARINE...ADS/HTS/RCM

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