Area Forecast Discussion
Issued by NWS Blacksburg, VA

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122 FXUS61 KRNK 151124 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 724 AM EDT Thu Mar 15 2018 .SYNOPSIS... Strong westerly winds will occur today between high pressure over the Gulf Coast and low pressure over the northeast U.S. A weak frontal boundary will situate itself over the area tonight, then shift south Friday. Another weak area of low pressure will pass south of the area along this front early in the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 320 AM EDT Thursday... Upper trough that has been bringing us colder temperatures shifts east today, but at the same time a sharp gradient develops between low pressure across the northeast and high pressure over the Gulf Coast. At 8h a 45-55kt jet moves across the area this morning weakening somewhat by the afternoon. Not our typical cold advection wind events, but associated with warm advection despite a surface trough moving across. Will see sustained winds of 15 to 25 mph, with gusts as high as 45 to 50 mph in the mountains/along and either side of the Blue Ridge, hence the wind advisory. No changes needed for this. Will be warmer today with more sunshine as temps climb to normal levels for mid March. Look for highs ranging from the upper 40s to lower 50s in the mountains, to mid 50s to lower 60s from the Roanoke valley east to the piedmonts of NC/VA. Tonight, weak baroclinic setup across our area, may bring a few sprinkles/flurries to our far southwest VA counties, but suspect dry air will win out and keep most dry, with some increase in cloudiness late. Gradient relaxes overnight with lows north of the frontal zone expected to be in the mid 20s to lower 30s, which is mainly north of the VA/NC border, with mid to upper 30s, along/south of the VA/NC border. && .SHORT TERM /FRIDAY THROUGH SUNDAY/... As of 335 AM EDT Thursday... Friday appears uneventful with surface ridging in place and mid- level subsident/confluent flow aloft. This is a bit of a change as model forecasts from earlier runs were indicating some limited northward return of warm-frontal precipitation. It appears at this point as though subsidence in place will win out. Should overall be a rather pleasant day with temps mid/upper 40s west of the Blue Ridge to mid/upper 50s for the Piedmont. Temps probably closer to the upper 30s/low 40s in the snow-covered Greenbrier mtns. Pattern then turns a little more active as deamplifying 500 mb shortwave disturbance over the Plains pushes aforementioned warm front across the Blacksburg forecast area overnight Friday into Saturday. Today`s 00z NWP suite suggests that 850 mb temperatures will rise overnight, to the point where values run around +3 to +6C by Saturday morning. Where this is potentially problematic from a sensible weather perspective is in the Alleghany Highlands, southern Shenandoah Valley and into the central VA Piedmont where surface temperatures are likely to radiate for a good part of the overnight, preceding the warm frontal precip shield. I`ve shown temperatures in these areas in the upper 20s when precip starts mainly in the pre- dawn hours. Using the top-down methodology, that supports a p-type of freezing rain in these areas, with a cold rain forecast further south/west. This is confirmed by model forecast soundings off the GFS and NAM which show a very shallow near-32F layer at Lewisburg and Hot Springs. How cold surface temps can radiate to will crucially dictate precip type, so I`ve also indicated light rain in these areas where there`s still some level of uncertainty. Forcing with the front is meager so any QPF will be light at best, and as such have only shown Chance-level PoPs. Did run the freezing rain accumulation tool (FRAT) which outputs a couple hundreths of ice accretion. Would envision any icing to be a road impact mostly, but I will say it is pretty uncommon to get ice accumulating on roads this late in winter. With confidence on p-type being only medium to low, will phrase in HWO as low-probability; wouldn`t discount some possible limited travel impact, however. Cloudy and wet Saturday in store with 850 mb temps rising to +4 to +8C. While the warm front doesn`t appear likely to produce much QPF, what 00z/15th NWP guidance indicates could yield a little more QPF is Saturday afternoon and night as primary mid-level vort max/weak surface low dives southeastward from the southern WV coalfields into central NC. PoPs were increased to the high-Chance/lower Likely range for Saturday afternoon into the first part of Saturday night. The overnight hours should feature diminishing rain chances and enhanced east/northeast flow as CAD/wedge front shifts southward into the Carolinas. Kept temps cooler on the highs and milder on the lows, with highs in the upper 40s to the 50s, and lows in the 30s to low 40s. Broad high pressure builds in Sunday with cold advection on northeast/east flow (850 mb temps within a few degrees of 0C on either side). Kept sky conditions mostly sunny/partly cloudy, though worth noting the GFS is much more robust with cloud cover along the Blue Ridge than is the ECMWF. Should be a dry day though. Though I did lower highs somewhat on Sunday by a couple degrees using MOS, it`s still possible forecast highs in the 50s to around 60 are too warm if more clouds are expected. && .LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/... As of 200 PM EDT Wednesday... Mid level flat west-northwest flow will continue Sunday night before more upper amplification takes place allowing for re- development of the persistent eastern trough regime by the middle of next week. Likely to see weak perturbations work along the baroclinic zone north of a warm front to the south Sunday night into Monday resulting in perhaps some spotty light showers, but looks too isolated to include at this point given overdone nature of models. This before better upper phasing begins to take shape with a system heading out of the Rockies Monday and across the region later Monday night into Tuesday as a more robust/complex low pressure system. Latest guidance has trended farther north with this feature resulting in more of a rain threat until the associated front passes later Tuesday. Behind this front should see another round of at least upslope driven snow showers by Tuesday afternoon into the overnight with drying elsewhere. Chilly high pressure to follow within the upper troughiness to result in dry but cool weather on Wednesday. Thus after low chance pops early on, will keep high high pops later Monday into early Tuesday across the region followed by mountain snow showers into Tuesday night. Temps still below normal but warmer Monday and colder with 40s west to low 50s east by midweek. && .AVIATION /12Z THURSDAY THROUGH MONDAY/... As of 721 AM EDT Thursday... Expect VFR conditions through the period, with some ceilings in the 4-6kft range near LWB. However, the main aviation issue will be low level wind shear this morning as strong low level jet pushes overhead, but should be short-lived as once the sun gets higher in the sky, winds will pick up at the surface, so gusty winds are expected through the the day at most sites, in particular ROA/BCB, where some gusts over 40 kts may occur. Confidence is high on all parameters. Extended Aviation Discussion... Conditions are expected to remain VFR through Friday, 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. && .FIRE WEATHER... As of 330 AM EDT Thursday... Fuels continue to dry out especially east of the mountains, and with stronger west winds today and lower humidity an uptick in fire danger is expected. After coordination with surrounding offices, have posted an Enhanced Fire Danger SPS for all counties east of the Blue Ridge. If not for the snow we had, we could well be looking at ideal red flag conditions, but 10 hr fuels are still running around 10, but some dropped below 10 east of the mountains Wed afternoon/evening. Winds diminish and RH increases by 6-7pm today. && .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 8 PM EDT this evening for VAZ009-012>020- 022>024. NC...Wind Advisory until 8 PM EDT this evening for NCZ001-002-018. WV...None. && $$ SYNOPSIS...WP NEAR TERM...WP SHORT TERM...AL LONG TERM...JH AVIATION...AMS/RCS/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.