Area Forecast Discussion
Issued by NWS Sterling, VA

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849 FXUS61 KLWX 201430 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 930 AM EST Mon Feb 20 2017 .SYNOPSIS... High pressure will build from the west today. Cooler air will seep south tonight into Tuesday. A weak disturbance will cross the area Tuesday night into Wednesday. High pressure will be located off the southeast coast of the United States for the second half of the week. && .NEAR TERM /THROUGH TONIGHT/... Upper-level ridge will build overhead today while high pressure builds over eastern Canada into New England. A north to northeast flow will develop overhead ahead of the building high. The northerly component to the surface wind will allow for cooler conditions compared to recent days...but max temps will still be well above climo. High clouds rotating around the periphery of the upper-level ridge will filter sunshine at times. Flow turns northeast ahead of the ridge axis tonight, which will allow marine air to move inland and overspread the area. Meanwhile, flow aloft will be southwest, making for an overrunning setup. Have increased clouds, first in the mountains (where the low-level flow will be upslope) but eventually areawide. Am focusing more on clouds than fog. Further, these clouds don`t look partularly low. In spite of the cloudcover, advection will bring temperatures down into the 30s. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... A 500 mb full-latitude shortwave axis will approach the area Tuesday into Wednesday. However, it appears as though the northern and southern streams will split-- the northern vortmax breaks down the ridge in the northeastern United States while the southern vort gets left behind along the Gulf Coast. The impact to the Mid Atlantic a bit muddled. Certainly, this will be a cloudy period, and can`t rule out scattered showers beginning Tuesday night. However, am having difficulty believing it will be as wet as current guidance runs suggesting...or for as long. Did increase clouds/PoPs on Wednesday, but am still holding onto the thought that there will be clearing in the wake of the vortmax Wednesday afternoon. Tuesday will be the coolest artifact of clouds and onshore flow. However, once the ridge axis pushes east of the area, there is sufficient warmth ready to return. && .LONG TERM /THURSDAY THROUGH SUNDAY/... Shortwave-ridge builds over the area Thu and Fri. It will be very warm especially Thu with highs in the 70s. Some locations may reach mid to upper 70s. Deep low pressure moving across the Great Lks Fri night and Sat will push a cdfnt through the area Sat morning with showers and t-storms likely some of which could be strong to severe and pose a risk of damaging winds given fast 0-6km mean flow of 45-50kt and weak instability. Cooler wx returns for early next week. && .AVIATION /14Z MONDAY THROUGH FRIDAY/... VFR for the valid TAF period. As onshore flow commences tonight, low clouds will increase...first in the mountains but eventually everywhere. The greatest probability is that conditions remain VFR. There is a lower chance that ceilings dip below 3000 ft. Ceiling lift but remain broken Tuesday. Then a disturbance adds a shower chance Tuesday night into Wednesday morning. If there is an opportunity for flight restrictions, this would be the time frame that it would happen. No significant wx expected on Thu. Strong cdfnt fcst to cross the area Sat morning with t-storms possible. && .MARINE... High pressure will build over the waters through tomorrow, resulting in relatively light winds-- 10 kt or less. Winds will become north today, northeast then east tonight, and eventually south by Tuesday or Tuesday night. A passing disturbance may provide a shower chance Tuesday night into Wednesday. Strong cold front will move through the waters Sat morning with showers and t-storms likely, some of which could be severe and produce strong damaging winds. Gale force winds are also likely post-frontal. && .CLIMATE... Record high minimums were set yesterday at IAD and BWI. See RERs for more details. More record high mins are likely later this week especially on Fri with possible record highs on Thursday. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...HTS NEAR TERM...BJL/HTS SHORT TERM...HTS LONG TERM...LFR AVIATION...BJL/LFR/HTS MARINE...BJL/LFR/HTS CLIMATE...LFR is the U.S. government's official web portal to all federal, state and local government web resources and services.