Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 180539 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 139 AM EDT Sun Mar 18 2018 .SYNOPSIS... A low pressure system will arrive from the northwest tonight. This system will move southward toward South Carolina and Georgia by Sunday morning. Another complex storm system works in from the west next week with wintry precipitation possible. && .NEAR TERM /THROUGH TODAY/... As of 800 PM EDT Saturday... Isolated showers and thunderstorms continue to drift eastward from Kentucky and Tennessee into southeast West Virginia and far southwest Virginia. SPC maintains a hail and wind threat due to steep lapse rates aloft and decent effective bulk 0-6 km shear. The severe thunderstorm watch remains in effect until midnight tonight. Pea size hail has been reported in a few locations, but the storms have not yet been impressive. The convection is racing the clock to sunset as instability should sharply cut off afterward. Little if any thunder may reach the southern Virginia and North Carolina Piedmont after midnight as the showers head toward the southeast along the warm front. Minor adjustments to POPs and temperatures for this update. Thickening stratus overnight and a decent thermal gradient makes this forecast for lows a little tricky. Low clouds appear most likely over the New and Roanoke river valleys toward Sunday morning. Deep moisture fades from drying aloft early Sunday as upper support exits and shortwave ridging starts to take shape. This in conjunction with weak high pressure under light north/northwest flow should allow for clearing from north to south by afternoon with comfortable highs in the 50s to lower 60s similar to the latest ECMWF MOS. && .SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/... As of 300 PM EDT Saturday... The transition of the upper pattern from an eastern ridge to a broad ridge is now looking to be a rather complex evolution as the ridge flattens and several spokes of southern stream short wave energy gradually carve out a successively deeper trof. Expectation is for generally wet weather through midweek. The first part of Sunday night looks to be dry, but a developing wedge will combine with low pressure emerging along the coast to bring southeasterly flow and robust isentropic lift over the region, which leads to increasing rain chances overnight. The situation remains relatively unchanged for Monday with increasing dynamic support and increasing coverage of rain as a wave moves through the Mississippi valley and approaches the Appalachians from the west. The wave will move through the region Monday night with a good dose of widespread precipitation. There also looks to be potential for convective development upstream outside of the wedge that would slide into the region and greatly enhance precipitation, though any specific details are murky at this point. Also of note is the steady cooling of the airmass from north to south which allows for a gradual transition/mix of ptype far north Monday night but any slushy accumulations look minimal through early Tuesday. After perhaps a brief respite early on Tuesday, the next wave will approach late in the day and renew precipitation across the region with good forcing over the wedge and potential convection developing/moving in from outside of the wedge. Complex situation continues to unfold Tuesday night as additional short wave energy fuels coastal low redevelopment with good isentropic, large scale synoptic ascent, and mesoscale deformation over the region as the cooling wedge deepens. Very early in the game but accumulating wet snow looks to be a possibility across a good part of the region by daybreak Wednesday. With the developing upper trof expect temperatures to be trending downward to well below normal through midweek. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 300 PM EDT Saturday... Additional short wave energy continues to fuel the train of coastal low formation through Wednesday which will keep a good chance of some wet snow across the region. Diurnal effects in late March may limit any accumulations to along/west of the Blue Ridge but far too early for specifics. As the closed upper low moves across the region synoptic forcing lingers along with the decreasing possibility for wet snow through early Thursday. Northwest flow will also be on the increase and will support upslope snow showers at the higher elevations west of the Blue Ridge into Thursday night. The upper trof axis finally pushes to our east and allows for a break of fair weather on Friday before a warm front starts to push precipitation back in our direction from the west late Friday night. Temperatures will start the period well below normal, then moderate a bit but remain on the cool side through the end of the week. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/... As of 0135 AM EDT Sunday... Widely scattered showers and a few stray storms ahead of an upper level disturbance will continue to move southeast and are expected to exit the WFO RNK forecast area by 10Z (6 AM EDT). Kept a few hours of SHRA for all TAF sites early this morning. LIFR ceilings at KBLF, KLWB and KBCB are expected to improve during the morning hours as light northeast/east sfc winds ushers in drier air. By 16Z, all TAF sites should be VFR, but confidence on the timing of this improvement is low. Higher confidence for VFR conditions for this afternoon and this evening. Extended Aviation Discussion... Moisture returning in advance of the next storm system for early next week could bring a return to MVFR/IFR ceilings for the mountains TAF sites late tonight/early Monday morning. This system should push eastward from the Plains on Monday. The warm front associated with this system could bring IFR/MVFR conditions due to ceilings and showers for Monday night into Tuesday. As the low pressure system heads offshore on Tuesday night, precipitation wrapping along the western periphery of this system could bring a period of snow showers, MVFR/IFR conditions, and gusty north to northwest winds on Wednesday. Drier air should finally bring conditions back to VFR by Thursday as high pressure builds from the northwest. && .EQUIPMENT... As of 940 AM EDT Friday... The Mount Jefferson NWR remains off the air and will likely be sometime next week before it is operational again. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH/PW NEAR TERM...JH/PW SHORT TERM...MBS LONG TERM...MBS AVIATION...PH/PW EQUIPMENT...JH is the U.S. government's official web portal to all federal, state and local government web resources and services.