Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 251856 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 256 PM EDT Thu Apr 25 2019 .SYNOPSIS... A warm front will move north across Virginia today and into Maryland tonight. Low pressure will track across the Ohio Valley and eastern Great Lakes tonight into Friday, pulling a cold front across the area Friday afternoon. High pressure will build in behind this front for the early part of the weekend. Another storm system could approach the region Sunday. && .NEAR TERM /THROUGH TONIGHT/... Frontal boundary is residing in southern Virginia this afternoon and will move northward across the region this evening and tonight. Isolated to scattered showers/sprinkles exist across portions of the area this afternoon, but coverage/intensity has been minimal so far. As the front lifts north later today and this evening, the surface low tracks northeastward through the Ohio Valley, and the upper trough approaches, showers should increase in coverage. Some instability may develop and an isolated thunderstorm or two is also possible, mainly across eastern WV and VA. Lows tonight will range from the mid 50s to low 60s. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... Surface low pressure will move northeastward through the eastern Great Lakes during the day Friday with its attendant surface cold front crossing the region during the afternoon and early evening hours. Some showers and/or elevated isolated thunderstorms may be ongoing early Friday morning, with activity waning during the late morning hours. This will allow for temperatures to rise and some instability to develop. Latest model guidance including 12z NAM and 12z HREF members indicate that between 500 and 1000 J/KG of SBCAPE is likely to develop ahead of the frontal boundary. This combined with strong low to mid level wind field and 40 knots or so of bulk shear will set the stage for strong to locally severe thunderstorms, mainly from the Blue Ridge Mountains eastward, with the highest probability of severe across portions of central VA, eastward to DC, and into southern Maryland where a Slight Risk of severe thunderstorms was introduced. Showers/thunderstorms will likely develop around noon or so across eastern WV and central VA, and move eastward across the region, exiting east of the Chesapeake Bay by 7 PM. The highest threat window for severe thunderstorms will likely exist between 2 PM and 6 PM. Several discrete cells are possible ahead of what may become a more organized developing squall line. The primary threat will be isolated damaging wind gusts, but given low level directional shear and relatively high helicity values, an isolated tornado is also possible, with the highest probabilities in southern MD. Heavy rainfall will also occur with these showers/thunderstorms, and while a widespread flood event is not likely, an isolated incident of flooding is possible if any training thunderstorms occur. Highs on Friday will range from the upper 60s to low 70s. The front will then push eastward Friday night with strong west-northwest flow following behind. Gusty winds are expected with 30-40 mph likely, although mixing may be limited at night. It`s possible a Wind Advisory may be needed, especially across the higher elevations, but uncertainty exists at this time. The wind field begins to weaken Saturday but mixing will increase during the daylight hours, so gusty winds may actually max out Saturday morning. Highs Saturday in the 60s to around 70F. A weak ridge of high pressure moves overhead Saturday evening before shifting eastward and offshore by Sunday morning as a weak area of low pressure approaches. Some showers become possible Saturday night.Lows in the 40s to low 50s. && .LONG TERM /SUNDAY THROUGH THURSDAY/... A cold front will cross the area Sunday afternoon. Moisture and instability will be limited with the best moisture and instability focused to our region`s north. Rainfall amounts will be light. Dry weather is expected Sunday night as strong high pressure builds in from the northwest. Moisture returns Monday night as high pressure shifts east. A developing front over the Ohio Valley will be the focus for showers and thunderstorms. Although disturbances will move along the front, the front will remain nearly stationary with very little shower or thunderstorm activity initially. Expect unsettled weather to redevelop toward the middle and latter part of the week with a chance for thunderstorms. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... Primarily VFR conditions expected through the period. Ceilings will gradually lower and clouds will thicken this evening and tonight. Showers and even a few isolated thunderstorms will develop this evening and tonight. Brief reductions to MVFR are possible, with the highest probabilities of more consistent MVFR ceilings at MTN/MRB. A strong cold front will then cross the terminals Friday. Predominant VFR anticipated, but local IFR possible within showers/storms. In addition, local gusty winds (40-50 kt) possible in stronger storms. Placement of these cells problematic this far out, but the general time frame for strong winds/wind shift will be mid afternoon MRB/CHO and late afternoon at the hubs (IAD/DCA/BWI). Gusty northwest winds will continue behind the front Friday night into Saturday before diminishing Saturday night. Gusty NW winds anticipated once again Sunday afternoon through Sunday evening behind another frontal passage. A few showers are also possible Monday night. Conditions could briefly become MVFR in these showers. && .MARINE... Generally light winds expected on the waters through tonight. Flow which is predominantly northerly this afternoon will become south this evening and tonight as a warm front slowly crosses the waters. By Friday, a sharp cold front will be approaching the waters. While mixing won`t be ideal, there will be a healthy gradient wind in advance of this front. A Small Craft Advisory is in effect beginning at 12 Noon. The environment will also become favorable for development of clustered showers/thunderstorms Friday afternoon capable of producing gusty winds in excess of 34 knots and possibly up to 50 knots, and Special Marine Warnings may become necessary. In the wake of the cold front Friday night into Saturday the gradient remains tight, with 30-35 kt (and depending upon model solution, perhaps up to 40 kt) still available. Momentum transfer will be more optimal. A SCA is in effect, but an upgrade to Gale may be needed. The strong winds will continue into Saturday morning before gradually relaxing during the afternoon hours. Small craft advisory conditions expected Sunday and Sunday night with frequent gusts to around 25 knots. Winds diminish below criteria later Sunday night through Monday night. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from noon Friday to 6 AM EDT Saturday for ANZ530>543. && $$ SYNOPSIS...MM NEAR TERM...MM SHORT TERM...MM LONG TERM...KLW AVIATION...MM/KLW MARINE...MM/KLW is the U.S. government's official web portal to all federal, state and local government web resources and services.