Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 231737 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 137 PM EDT Thu May 23 2019 .SYNOPSIS... Low pressure over the Great Lakes will pull a warm front north through the Ohio Valley and Mid Atlantic region this morning, then bring a cold front into Virginia and the Carolinas tonight and Friday. Another low taking a similar track across the northern United States will repeat the pattern Saturday through Monday. && .NEAR TERM /THROUGH TONIGHT/... As of 1213 PM EDT Thursday...After reviewing the 12z guidance and assessing mesoscale environment, sent a quick update to the forecast to add enhanced wording for gusty thunderstorm winds through 00z from a line from Bluefield- Blacksburg-Roanoke- Lynchburg north/west. Ongoing convective line continues to move across central WV - and across our area, the air mass has destabilized rather substantially with CAPEs for a surface-based parcel between 2500-3000 J/kg per SPC`s mesoanalysis. This has led to cumulus in the western third of the CWA, a few of which started to deepen a bit further. It seems highly probable that ongoing storms will move into this favorable juicy/unstable air mass and strengthen. 12z convective-allowing guidance suite has now come around to the idea of bringing this initial line of storms into southeast WV between 1-3 PM, then into the Alleghany Highlands/southern Shenandoah to the I-81/Route 460 areas between 3 and 7 PM. It`s this area that a few storms may produce sporadic instances of severe weather, capable of gusty to localized damaging winds especially as downdraft CAPEs continue to amplify (currently just under 1000 J/kg). Hail may be possible but it would take a really robust updraft to do so given the high freezing levels. Otherwise, no other changes made attm. Previous discussion from 315 AM... Upper low over Minnesota early this morning moves east across southeast Canada today and will be off the Maine coast by Friday morning. This in turn shifts the upper ridge west which results in northwest flow over the Mid Atlantic region tonight. Bufkit forecast soundings from the HiResNMM and ARW, along with the NamNest showed the stratus diminishing after sunrise with enough heating by noon to overcome any cap/warm air aloft. Models bring two main bands of showers and thunderstorms across the Mid Atlantic region. One from Pennsylvania into central Virginia this afternoon and the next over West Virginia tonight. Enough shear that strong storms may develop but better forcing and dynamics are confined to the north. Inverted-V sounding suggest the potential for evaporative cooling and enhanced downdrafts with any of the stronger storms. Downdraft CAPES from the SPC SREF are forecast to be in the 500 to 1000J/KG range this afternoon and evening. At the surface the parent high moves farther offshore this morning but a piece of the ridge remains over the Carolinas which will produce west to southwest winds over the area and continue advect in higher dew points. Southwest Virginia, northwest North Carolina and southeast West Virginia will stay in the warm sector for the rest of the day. A cold front will approach from the north tonight and may be as far south as Hot Springs by Friday morning. Due to the clouds this morning, and especially north of the warm front will be staying on the cooler side of guidance for maximum temperatures today. Warmer air mass and surface dew points well into the 60s tonight will keep lows mild. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 310 AM EDT Thursday... A broad upper level ridge, centered over the Gulf States, will cover the eastern half of the United States on Friday. With the area being on the northeast corner of this ridge, our wind flow will be out of the northwest. Any storms developing/tracking over the mountains will drift into the foothills through the day. However, deep northwest flow will have storms decaying very quickly moving east of the Blue Ridge. Friday`s 85h temperatures averaging around +19C which translates to surfaces temperatures across the mountains in the 80s. Out east, warm temperatures aloft and downsloping flow will produce temperatures in the lower 90s. With the lose of heating Friday night, a weak cold front is expected to slide across the region. Behind the front, winds become northeasterly through the morning. If low clouds and northeasterly winds can hang on into the afternoon, temperatures will be a little cooler Saturday compared to Friday. However, weak wedges in late May tend to not stick around for long. Temperatures should warm back into the 80s across the mountains to the mid to upper 80s east of the Blue Ridge. A Theta-E ridge is expected to replace the wedge Saturday afternoon and evening, allowing dew points to creep into the low to mid 60s. With increasing moisture, scattered diurnal showers and thunderstorms are possible across the mountains Saturday afternoon and maybe an isolated thunderstorm over the foothills in the evening. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 229 PM EDT Wednesday... Waxing and waning of the eastern upper ridge will allow energy sliding along surface fronts to periodically affect the Appalachians and central mid Atlantic region through the first part of next week, while keeping us locked in to temperatures well above normal. Outside of scattered diurnal convection, there may be a chance for enhanced thunderstorm activity with an upstream MCS developing late Sunday/Sunday night. Thereafter, uncertainties in handling of the upper ridge into next week make for low confidence in identifying any specific potential periods of concern for severe weather. Will have to monitor this closely over the next several days to see exactly what degree of severe threat materializes. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... As of 113 PM EDT Thursday... Lingering low stratus has finally started to thin out away from Southside into the NC Piedmont; but the main concern for the remainder of the afternoon is for scattered strong/severe thunderstorms. Threat appears greatest for most TAFs except Danville, and have included SHRA VCTS in association with a likely line of storms progressing eastward from central WV now through 00z. Storms may be capable of lightning, gusty winds capable of localized turbulence, and brief IFR visby from heavy rainfall. Storms should weaken as instability wanes after sunset, though a few additional showers capable of brief restrictions toward Lewisburg late this evening. Kept TAFs at mainly VFR, but will be quick to issue TEMPOs for any convective threat this afternoon/tonight. Winds outside of thunderstorms mainly southwest 6-10 kts. Should see mainly VFR conditions through 18z Friday. May see isolated thunderstorms build up southwest of I-77 into the mountains of northwest NC very late in the 18z TAF period, but not likely to affect any TAFs. Winds west to northwest 6-9 kts. Forecast confidence is moderate on thunderstorm potential, and moderate to high on aviation categories outside of thunder. EXTENDED AVIATION DISCUSSION... VFR conditions are expected across the region Friday thru Sunday. Exception is with evening/overnight fog but confidence low on development attm. SCT MVFR showers and thunderstorms are possible Monday in the west. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AMS NEAR TERM...AL/AMS SHORT TERM...RCS LONG TERM...MBS AVIATION...AL

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