Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 261523 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1123 AM EDT Sun Mar 26 2017 .SYNOPSIS... A series of low pressure systems will bring unsettled weather with a good chance for showers and thunderstorms, mainly west of the Blue Ridge, through Tuesday. Temperatures will remain well above normal with a gradual warming trend bringing high temperatures well into the 70s through the first part of next week. && .NEAR TERM /THROUGH TONIGHT/... As of 1100 AM EDT Sunday... Radar indicated a 30 mile wide band of rain showers propagating east across the western CWA. As of 11AM the leading edge was along the I-77 corridor. Movement was to the east at 20 mph. Rain band was associated with a front aloft, extending N-S from Low pressure moving through the western OH Valley and into the Great Lakes. The actual surface front was over western KY/TN, so this initial rain band has outrun any surface instability and has been weakening with time. Rainfall amounts have been averaging about a quarter of an inch, but think as this band of showers moves east, the overall qpf will diminish with amounts of a tenth of an inch. Timing suggests these showers will reach Highway 220 corridor...Clifton Forge, Roanoke, Martinsville, Reidsville between 2-3PM. Once the initial front aloft passes and the showers come to an end then clouds will thin with instability driven showers increasing across the KY/TN ahead of the actual surface front. These showers and potential for thunderstorms will approach from the TN valley late in the afternoon with primary impact to areas west of I-77 after 5PM. As the main upper level low slides by to our northwest tonight, dynamic support will decrease. The actual surface front is forecast to wash out before crossing the mountains so this will maintain a persistent southerly flow across the forecast area overnight. As such, there will be a continued chance of showers mainly along and west of the Blue Ridge overnight, although nothing severe per waning instability. Temperatures this afternoon will be warm with highs 5 to 10 degrees above normal with lower 70s in the east to upper 50s/middle 60s in the west. Temperatures tonight will also well above normal with lows mainly in the 50s. && .SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/... As of 315 AM EDT Sunday... Both the 00z GFS/ECMWF seem to be in fairly good agreement with the 5h pattern with some minor differences with the surface and precip output. Monday still looks like to be cloudier with some low level convergence working across the mountains, so will still see some showers and isolated thunderstorms developing namely in the mountains. Temperatures despite the cloud cover rise to the mid to upper 60s mountains to lower to mid 70s foothills/piedmont. Surface front and upper shortwave enter the mountains by 12z Tuesday so increasing threat of showers and some thunderstorms late Monday night in the mountains, with coverage increasing along and east of the Blue Ridge after 8am Tuesday. Some forecast differences shaping up Tuesday afternoon, since both 00z models showing a faster drying solution starting to move in from the southwest. Will leave high chance to low likely pops mainly along and north of a Bluefield- Pulaski-Chatham line, but will see less coverage over the NC mountains/foothills/piedmont after 2-4pm. Sfc low somewhat weak, but as the low moves across, the 8h jet of 30- 35kts with some westerly flow along/behind the front should bring some gust to 20-25 mph. High temperatures dependent on sunshine and showers, thinking the piedmont will see potential for some sunshine more than the mountains, with even better chance of more sun arriving in the NC foothills in the afternoon. Warm temperatures overall with highs in the mid to upper 70s east of the Blue Ridge, with upper 60s to around 70 in the mountains. Brief period of residual showers across the Appalachians Tuesday night with drying elsewhere. Frontal boundary will shifts to the coast by 12z Wednesday, but extends west into the Gulf Coast States. Meanwhile, high pressure over Ontario will build southward into the TN valley. This high shifts east Wednesday into Wednesday night, with a battle between drier/cooler air north and more moist air south. Will start to see lower dewpoints work in Wednesday afternoon on a north to northeast wind. Not out of the question to keep some clouds around, especially across the NC mountains/foothills with sprinkles possible. Wednesday night, the flow in the low levels should turn more southeast, and cannot rule out the chance for showers to develop along the southern Blue Ridge and adjacent foothills from Floyd to Boone. High temps Wednesday will mild, though if there is more clouds we could be cooler. For now going with lower to mid 60s mountains, to lower to mid 70s foothills/piedmont. && .LONG TERM /THURSDAY THROUGH SATURDAY/... As of 400 PM EDT Saturday... Mainly dry Thursday outside some showers over the southern Blue Ridge in the morning, with some increasing moisture after 00z Friday in the southwest Virginia area. By Friday, the next, and fairly potent, upper low tracks toward the area. However, there is considerable discrepancy between the GFS and the ECMWF in the configuration and timing of this system into the eastern U.S. The GFS depicts more of an open wave reaching the CWA as early as Thursday night moving east of the area by Friday afternoon. Meanwhile, the ECMWF is much slower, deeper, and further south with a cutoff upper low lifting it slowly north-northeast into the Ohio Valley by late Friday. The difference between the two models can be accounted for in noting the strength and blocking of an upstream ridge across the Atlantic. This upstream ridge is much stronger per ECMWF, which also depicts a notable wedge down the east side of the Appalachians as the closed low lifts north into the Ohio Valley. The ECMWF would result in a much wetter and stormier pattern for the CWA, although it would not arrive until Friday as opposed to Thu night per GFS. For now, have generally broad brushed the area with high chance to likely pops beginning Thu night and continuing into Friday. In addition to the differences noted above, there are also massive differences between the two models regarding instability and the potential for severe, with the ECMWF much more noteworthy in this category. For now, have included a chance for thunder without any further details. It will likely take several runs for the models to resolve their differences on this system. Another system is slated to follow by the end of the weekend or the beginning of the next week, so the active pattern is expected to continue into the next week. Temperatures will be closer to normal Wed-Thu, then begin to trend back to above normal levels Fri-Sat. && .AVIATION /15Z SUNDAY THROUGH THURSDAY/... As of 725 AM EDT Sunday... Should see VFR cigs/vsbys for most taf sites this morning, with some period of MVFR cigs near BCB/BLF. A slow moving stacked low pressure system will move into the Great Lakes region and push a frontal system into the area from the west. This will increase our shower threat, mainly along/west of the Blue Ridge from late morning into this evening. As such will start seeing cigs lowering toward low end VFR into MVFR by early afternoon BLF/LWB/BCB, and into ROA after 00z. For now, not expecting LYH/DAN to drop to MVFR or lower. Overall should see VFR vsbys with lighter showers, though some MVFR is likely in BLF/LWB and BCB at times this afternoon. Cannot rule out some thunder in BLF/LWB but overall threat is too low to have in TAFS. Extended Aviation Discussion... An active weather period with a series of vigorous upper-level low pressure areas tracking from west to east across the U.S. during the week. Monday the area will be between systems, but a moist/unstable air mass will remain in place and widely scattered showers and isolated thunderstorms are possible. Areas of sub-VFR cigs/vsbys are also possible, especially during the morning hours, in low clouds and fog. The next upper-level low will arrive Tuesday with another chance for showers and thunderstorms along with periods of sub-VFR conditions. Wednesday-Thursday may bring a period of improved aviation conditions as a weak cold front temporarily pushes the deeper moisture south of the area. However, by Friday the next in the series of upper-level systems arrives with another chance for showers, thunderstorms, and sub-VFR conditions. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...MBS NEAR TERM...PM SHORT TERM...WP LONG TERM...PM/RAB AVIATION...MBS/WP is the U.S. government's official web portal to all federal, state and local government web resources and services.