Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 210959 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 459 AM EST Wed Feb 21 2018 .SYNOPSIS... A strong ridge of high pressure will remain off the southeast coast providing much above normal temperatures through the remainder of the week. Chances for rain increase late Wednesday into Thursday with a cold front, followed by a better chance of showers with another front by later in the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 430 AM EST Wednesday... High pressure along the southeast Atlantic coast will provide for another unseasonably warm day across the Mid-Atlantic courtesy of southerly winds transporting warm moist air northward from the Gulf of Mexico and northern Caribbean. Dewpoints have risen into the lower 60s across the Carolinas, and this air is flowing north around the periphery of the high. Actual baroclinic zone resides west of our region from East Texas up through the MS Valley and into the Great Lakes. This will be the boundary for repetitive rains the next few days while we bask in the warmth from the subtropical connection. The only fly in the ointment as we bridge into Thursday will be for a backdoor surge of somewhat cooler air to intrude from the northeast, impacting Lynchburg and into NoVA. For the near term, even Lynchburg and NoVA will partake in the near record breaking warmth. Fog this morning is not nearly as extensive as yesterday morning, in part due to cloud cover. The rising boundary layer dewpoints and deepening moisture is allowing for more cloud cover thus limiting the radiational effects. As we transition into the afternoon, surface heating will combine with this moisture to provide for more cumulus, some of which will develop into showers along and west of the Blue Ridge. Have maintained an isolated threat for thunder across far western VA west of I-77 and from the VA Highlands west into WV, where lifted indices drop below zero for a few hours this afternoon and CAPE values approach 500 j/kg. Tonight will be another mild night, dewpoints above 50 deg F and cloud cover helping to maintain boundary layer warmth. && .SHORT TERM /THURSDAY THROUGH SATURDAY/... As of 400 AM EST Wednesday... Large-scale mid-level features remain essentially unchanged in this period, governed by an anomalous 594-dm ridge centered just west of Bermuda and mean downstream troughing across the Intermountain West/Desert Southwest. A quasi-stationary front, likely focusing repetitive rain events across the Ohio, Tennessee and Mississippi Valleys will make slow eastward progress. A colder high pressure area north of New England will force northerly flow and cooler temperatures into the northern mid-Atlantic region early in the period, forcing a backdoor front southward/southwestward against the Blue Ridge/northern Piedmont areas Thursday. 00z NWP guidance continues to show large variability in the southward push of this boundary. This results in a great deal of uncertainty and potential for large temperature busts Thursday and possibly Friday, especially from the Blue Ridge foothills eastward. The quasi-stationary front then gains more eastward momentum very late in the period as powerful shortwave energy ejects across the Plains. Overall, period will continue to be ruled by well above normal temps with generally limited but non-zero chances for rain. Those rain chances increase as we move into the latter part of Saturday. At least modest diabatic warming should take place through the morning on Thursday, but the NAM and GFS each show northeast flow and vestiges of the backdoor front into the northern/central Piedmont late Thursday. The NAM is somewhat further south than the GFS is. Areas of light rain falling on the cold side of the boundary will likely reinforce the air on the cold side, while at least modest diabatic heating will bolster the southwestern milder side of the frontal zone. Expect some push southward at least as far as route 460 east of the Ridge Thursday, but its progress may be halted some until diabatic cooling can occur Thursday night. One only needs to look at the MAV and MET guidance highs temps for Danville to get a better sense of the uncertainty in high temps here - with a 21 degree difference in forecast highs (MAV shows mid 70s while MET is mid 50s). Sided closer to the milder MAV under the idea the boundary may slow as it pushes south. Overall temps should run into the 60s, but utilized raw guidance to show an early high in the VA Piedmont before hovering then falling. Best chance at rain Thursday is in northern sections either more closely tied to the stationary front to our west or from the backdoor boundary, with a minimum toward evening. May see a fair amount of drizzle, mist or fog in the cooler eastern sections Thursday night but will leave for later shifts to further diagnose. Lows should run in the 50s, except mid/upper 40s from Bath County southeast to Appomattox/Buckingham. Still likely to have mild southwest flow west of the Ridge on Friday, while also still dealing with remnants of the backdoor front at least early in the day. This latter feature either washes out in southerly flow and/or lifts northeast during the day with temperatures recovering as it lifts out. With uncertainty with when this happens, sided toward cooler side of guidance - an earlier surge would result in even warmer temps than shown. Kept temps in the 60s, mildest along and southwest of the New River. Into Saturday, quasi-stationary front well to our west begins to pick up more steam. This should result in an increase in clouds and a west to east increase in PoPs to Chance levels in the far west, and slight chance in the Piedmont/foothills. Still looks like the best chance of rain is later into Saturday night. A bit more cloud cover will keep temperatures in the 60s. && .LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/... As of 300 PM EST Tuesday... A low pressure system will organize over the lower Mississippi River Valley on Saturday and track eastward toward the Mid Atlantic by Sunday. Model solutions continue to slow the timing of this frontal passage for our area, which appears to be during Sunday afternoon based on the GFS. Chances of rain were lowered a little on Saturday but increased a fair amount for Sunday. It is worth noting that the ECMWF solution is a little slower with the cold front than the GFS as it displays a Sunday evening frontal passage. Therefore, some questions remain on how much the moisture could linger into Sunday night and Monday morning, especially in northwest North Carolina. Eventually, high pressure should build overhead toward Monday afternoon. The upper level pattern turns more zonal by Tuesday, which looks dry with plentiful sunshine at this point. Temperatures still will reside well above normal throughout this period although it should turn a little cooler by early next week. && .AVIATION /10Z WEDNESDAY THROUGH SUNDAY/... As of 1230 am EST Wednesday... Expecting widespread low clouds and especially dense fog east and south of the Blue Ridge overnight/early this morning with potentially localized dense fog further northwest to included KBCB/KLWB toward daybreak. Little change expected in the overall weather pattern with main features strong subtropical ridge off southeast U.S. coast, and very active baroclinic zone across the Midwest/Ohio Valley. Expect widespread dense fog with IFR- LIFR cigs/vsbys across the Piedmont, Southside VA, and the North Carolina Foothills. The only place that should remain VFR throughout the period is KBLF although some VFR cigs likely to affect that area late tonight into Wednesday ahead of the next cold front. Low clouds will again be slow to exit eastern sections on Wednesday given southwest flow and deeper moisture. Also a band of pre-frontal moisture likely to affect the far western sections by midday although appears any showers should hold off until after the valid TAF period so not including mention at this time. Ceilings should improve to MVFR or better by mid- morning/early afternoon, but return to MVFR or worse in fog development again after 00Z Thu. Extended Aviation Discussion... May again see widespread sub-VFR develop again Wednesday night as the front approaches but stalls allowing better pooling of moisture under weak south/southeast flow. Lingering MVFR or worse conditions in showers likely Thursday with the cold front spilling south into the area. This front lifts back north Friday with continued threat of showers and potential low clouds. This front will linger nearby into Saturday with a continued threat of showers, but cigs/vsbys should a little better south of the front. && .CLIMATE... As of 330 AM EST Wednesday... Today will again feature well-above normal temperatures that may approach or eclipse daily record highs and daily record high minimum temperatures. It`s also possible that all-time warmest February minimum temperatures could be approached or broken in this period. Following are daily records, as well as the all-time warmest minimum temperatures recorded in the month of February, for our five climate sites with long-established periods of record: Wednesday 2/21/2018 Site MaxT Year HiMin Year BLF 65 1996 54 1997 DAN 75 2011 55 1953 LYH 75 1930 50 1981 ROA 73 1930 48 1997 RNK 71 1986 49 1953 Warmest HiMin - February: Site HiMin Date BLF 57 Feb 5 2008 DAN 60 Feb 18 2008 LYH 59 Feb 20 1939 ROA 57 Feb 12 1932 RNK 52 Feb 16 1990 && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH NEAR TERM...PM SHORT TERM...AL LONG TERM...PW AVIATION...RAB CLIMATE...AL is the U.S. government's official web portal to all federal, state and local government web resources and services.