Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 160822 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 422 AM EDT Fri Mar 16 2018 .SYNOPSIS... High pressure will cover our area today from the northwest, with a warm front working into the area from the southwest tonight. A low pressure will move along this front Saturday into Saturday night, with the front sinking south into the South Carolina and Georgia by Sunday morning. Another storm system works in from the west early next week. && .NEAR TERM /THROUGH TONIGHT/... As of 320 AM EDT Friday... Jet at 8h around 50kts early this morning still causing gusts over 45 mph in portions of the NC mountains/Grayson Highlands. Models showing this jet later this morning, but with some cold advection and latest RAP showing 50-60kt jet lingering, will go with a wind advisory for the NC mountains/Grayson til 9am. The jet lifts northeast late this morning. The overall low level flow turns more north later this morning as high pressure builds in from the Great Lakes and Ohio Valley. Stronger wind gusts over 35 mph not out of the question along I-77 in Fancy Gap, as the winds shift more north, which squeezes thru the gap. Otherwise, looking at some variance in temperatures due to mixing versus where winds have calmed. As of 3am, temperatures ranged from as warm as the mid to upper 50s in the NC foothills, to as cool as the upper 20s to lower 30s over portions of SE WV into the Alleghanys, but there are some readings in the mountains in the 40s, and some readings in the piedmont in the 30s. This will of course lead to a complicated temperature forecast, but overall, going with warmer temps today compared to previous forecast, despite the flow turning north to northeast at the surface. Expect some mid to upper 60s along and south of Highway 421 in Wilkes/Yadkin County, with upper 50s to lower 60s across the rest of the NC piedmont into southside VA, then dropping to the upper 40s to lower 50s from the Mountain Empire of SW VA and the NC High Country northeast into the New, Roanoke and Shenandoah Valley, with lower to mid 40s in the Alleghanys and most of Southeast WV. Again some areas could see warmer temps, but enough cold advection on north winds should tamper it northwest of Roanoke. Expect the standing wave Altocu associated with the westerly low level jet to dissipate this morning, with mostly sunny skies expected. Will start seeing mid and high clouds increase from the southwest/west later this afternoon, with warm advection aloft ahead of a warm front. Tonight, clouds should continue to increase and lower, but drier air in the east appears to delay/erode clouds per 00z NAM/CMC depiction. Models have trended a little slower with arrival of precipitation until after midnight, and possibly not until dawn over the west. This will still complicate ptype, but appears as clouds move in, temps should start to warm, so some of the mountains may see their lows reached late this evening or around midnight, then rise with the clouds, then cool again once precip arrives. The best lift looks to stay west of the Appalachians into the Ohio Valley with the main upper low tracking through Iowa/Illinois. Enough low level convergence and isentropic lift over warm front with a sheared vort will allow for some rain to make it as far east as Lewisburg WV south to Boone NC by dawn. With temps around freezing, some freezing rain was thrown in given the warm nose aloft. However, climatologically should not see any issues this late in the season with ice on roads, and with precip being light only a hundredth or two of an inch of ice may cling to metal objects or tree branches, if that. Lows tonight will range from the mid to upper 20s in the Greenbrier Valley to southern Shenandoah Valley, but warm to around freezing by dawn, with most areas having lows in the 30s, but with temps warming late. && .SHORT TERM /SATURDAY THROUGH MONDAY/... As of 400 AM EDT Friday... A couple of storm systems will be present in the short-term period, mainly on Saturday and the beginnings of the following one on Monday. Forecast confidence in this period, mainly temperatures and especially into Monday in regard to PoPs/Wx, is on the low side. Saturday looks to be the most active of the three days, as initial warm front associated with weak surface low over the Ohio Valley spreads east-northeast. Precipitation should be ongoing from the overnight period, gradually spreading east into the morning hrs. As temperatures project to be near or just below freezing into the early Saturday morning hours in the Alleghany Highlands/Greenbrier area, some light freezing rain remains possible. It`s questionable if any accretion may develop on roads but could see some light ice accretion on trees or elevated surfaces before temps rise above freezing by mid-morning. 850 mb baroclinic zone is quite sharp and with warm frontal precip falling along it, could see the northern tier of counties (along I-64 to Lynchburg) struggle to climb much out of the 40s to near 50. As rain clears south of this area, and with 850 mb temperatures in the +5 to +7C range, it`s possible that temps may soar into the upper 50s/low 60s especially south of route 460, conditional on sufficient clearing. By afternoon, there may be enough instability from a line along/southwest of a Bluefield to Reidsville line to support a conditional risk of thunder as primary surface low and potent vort max progress southeast. SPC`s Day-2 convective outlook has introduced a 5% severe/Marginal Risk area in this area, owing to potent vort max which shifts into the WV coalfields and into the central NC Piedmont by Saturday around 03z. GFS also shows a plume of rather steep mid-level lapse rates of around 6.5 C/km, though total instability is limited by low dewpoints and somewhat cool temperatures. Progged CAPE values are only around 500 J/kg or less. The NAM and some of its finer-res WRF members also show some multicell development in simulated reflectivity in the area outlooked by SPC. Severe threat may be overstating things and would think any thunderstorm coverage is isolated to at best widely scattered. If storms develop, small sub- severe hail would be the main convective threat given the lapse rates aloft if better instability can result, mainly between 20-02z. Areas north of Bluefield to Reidsville are too stable to support anything more than showers. As passing surface low progresses southward, cold thermal advection associated with building wedge then settles in after midnight, with N-S clearing and PoPs trending lower into early Sunday morning. Lows mainly in the 30s. Sunday`s the pick of the weekend with mostly sunny skies, though 850 mb temperatures around 0 to +2C will keep highs in the 50s. Warm advection pattern then begins Sunday night. Though would expect an increase in cloud cover, but it appears any precip should hold off until Monday. Lows again in the 30s. Next warm front associated with a powerful mid/upper low over the central Plains then begins to spread rain showers into Monday, though the best timing in guidance is quite hazy. NAM/SREF mean and the ECMWF bring some forecast precip into southwestern counties early Monday, spreading northeastward with time. On the other hand the GFS develops a convective complex in central GA which restricts moisture return northward and keeps the area largely dry until Monday night. Will side toward the SREF/NAM/ECMWF consensus in showing Chance-ish PoPs Monday. So still a good deal of detail to be ironed out in the Monday period. Highs should reach into the 50s again on Monday, though with less clouds cooled temps down closer to the low-mid 50s. && .LONG TERM /MONDAY NIGHT THROUGH THURSDAY/... As of 400 AM EDT Friday... Active period in store as brief zonal flow to start evolves back to large scale upper troffiness by the end of the week. This initially set in motion by a stacked system coming out of the southwest states that looks to cross the region on Tuesday. Warm advection type overrunning along a warm front ahead of this feature likely to bring widespread rainfall into the area by Monday night before tapering on Tuesday. Main track of the surface low still a bit in question in just how far north it will go before perhaps redeveloping offshore, but appears mostly rain on the front end at this point given deep cold air farther north. Storm system like previous systems will deepen offshore the Mid-Atlantic Tuesday night into Wednesday with a wrap around type belt of deeper moisture lingering inland along the leading edge of the developing upper trough to the west. However this remains uncertain given dry slotting between the two, although appears enough moisture/lift to warrant continued pops again later Tuesday night into Wednesday, with a gradual shift toward another round of at least decent upslope snow showers by Wednesday west. Moisture should finally wane heading into Thursday with snow showers fading under dry but cold high pressure. Temps to remain below normal through the period and moreso behind the system for midweek when will drop well below 0C at 85h under strong northwest flow cold advection. && .AVIATION /08Z FRIDAY THROUGH TUESDAY/... As of 115 AM EDT Friday... VFR conditions will continue through this period, with some standing wave AC near BLF this morning. Gusty west winds should persist through the night along the higher ridges, but winds at the airport terminals should subside to under 15 kt. Will see increasing high clouds late in the period over the mountains. Confidence is high on all parameters. Extended Aviation Discussion... Conditions are expected to remain VFR through Friday night, with next threat of precipitation and associated MVFR ceilings and visibility Saturday into Sunday. A more organized low pressure system will track into the area from the central and southern Plains for Sunday night and Monday. This is expected to bring sub-VFR ceilings and visibilities and widespread rain. MVFR conditions are expected Monday night into Tuesday. && .FIRE WEATHER... As of 330 AM EDT Friday... The winds today will not be as strong as Thursday, but with a northwest to north flow, downsloping will keep dewpoints low, and will see another dry afternoon as RH values dip to 15 to 25 percent along/east of the Blue Ridge, with 30 to 35 percent in the west. 10 hour fuels running about 8 to 10 in the Alleghanys/Southern Shenandoah Valley to 6 to 8 in the piedmont. May have to issue an fire danger statement if winds do not subside before the humidity drops below 35 percent. && .EQUIPMENT... As of 1005 PM EDT Wednesday... The Mount Jefferson NWR remains off the air. Our goal is to have it up and working by Friday evening. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Wind Advisory until 10 AM EDT this morning for VAZ015. NC...Wind Advisory until 10 AM EDT this morning for NCZ001-018. WV...None. && $$ SYNOPSIS...KK/WP NEAR TERM... SHORT TERM...AL LONG TERM...AL/JH AVIATION...PW/WP FIRE WEATHER...WP EQUIPMENT...AMS is the U.S. government's official web portal to all federal, state and local government web resources and services.