Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 301650 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1250 PM EDT Fri Sep 30 2016 .SYNOPSIS... A strong upper level area of low pressure will remain just west of the mountains today before slowly lifting to the north later tonight into Saturday. This system will combine with a residual stationary front across the region to produce periods of showers and thunderstorms into late tonight. The low will move northeast, away from the region, resulting in drier weather this weekend. && .NEAR TERM /THROUGH TONIGHT/...
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As of Noon Friday... Showers and thunderstorms continue to develop along the leading edge of a large nearly stationary cutoff low in the upper levels of the atmosphere. These showers/storms are initiating in a very soupy near 70 dewpoint airmass over southside va and the piedmont of NC and then quickly moving north with the mean wind...the activity congealing into a broad area of moderate to heavy rain as it passes over the VA Blue Ridge and into the Highlands of VA. Concerns this afternoon will be for torrential downpours and potential for flooding. Greatest rainfall the last 24 hours has occurred from Bedford north and west into the Highlands of VA where 3 to as much as 7 inches has been observed. Per radar trends an additional 1 to 3 inches of rain is certainly possible across this same area this afternoon. Per reports of streams already at near bank full in some locations a burst of very heavy rain would produce flash flooding. As such, a flash flood watch has been issued from Bedford north into the southern Shenandoah Valley and including the Highlands of VA from Covington north. Additional weather threats this afternoon will include potential for thunderstorms with large hail. CAPE of 1500-2000 j/KG over the NC piedmont will fuel healthy thunderstorm updrafts, and with 500h temps of m12 deg C and potential to suspend the cores aloft by supercell conducive wind profiles, looking at another afternoon with long lived hail producing thunderstorms. Certainly can`t rule out an isolated tornado...with the main threat for sort of outcome favoring the NC piedmont and into southern VA along the VA/NC border east of Martinsville/Eden. Highest rain threat this afternoon will be along and east of the highway 220 corridor with likely to categorical pops. A dry air intrusion aloft will limit coverage farther west with parts of the forecast area seeing little or no rain this afternoon. Areas from the western New River Valley down into the Mountains of North Carolina and northwest NC piedmont may actually see quite a bit of sun. By tonight, the upper low should begin to lift north allowing drier air aloft to gradually win out from southwest to northeast. This should result in decreasing shower coverage with time. With more clearing anticipated in the west, it should allow temps to fall into the 40s in spots with overall low/mid 50s elsewhere, except low 60s far east.
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&& .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 305 AM EDT Friday... Drying trend will continue over the weekend as the upper low finally lifts farther north and weak high pressure slides in from the west. May still have an isolated shower around early Saturday over the north, otherwise cutting pops with more sunshine on tap by the afternoon. Another spoke of energy looks to rotate around the upper low Saturday night with this feature reaching the western mountains later Sunday. Moisture quite limited with the weak associated front but cant totally rule out an isolated shower western slopes late Sunday into Sunday night. Otherwise expecting mainly clear skies Saturday night and mainly sunny Sunday before clouds invade the west late. High temps to remain mild under west/southwest flow aloft with mostly 70s both Saturday and Sunday and lows mostly 50s Saturday night given good radiational cooling conditions. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 330 PM EDT Thursday... The upper low will give way to ridging in the eastern US through the early part of next week. This stall the approaching front and allow a large area of high pressure to settle over New England and wedge down the east side of the Appalachians. The big variable lies with the potential track of TS Matthew as it is expected to turn north and move up the Atlantic coast. The exact track of Matthew will determine how much, if any, precipitation it can push into the region from the east and how much overrunning precipitation will develop as it interacts with the wedge. Right now, the most likely scenario is for some light overrunning precipitation to develop by Tuesday and increase a bit into Wednesday especially in the east, with any significant effects form Matthew remaining to our east. && .AVIATION /16Z FRIDAY THROUGH TUESDAY/... As of 711 AM EDT Friday... Variable but overall sub-VFR conditions will prevail this morning with cigs fluctuating between MVFR and low end IFR at times. Best coverage of showers/storms resulting in vsby restrictions look to occur along the KBCB-KROA corridor this morning with weaker bands elsewhere espcly around KLWB. Thus will include either a vicinity or tempo mention with perhaps a brief prevailing group of lower cigs/vsbys at these locations. Uncertainty continues with the degree of added convective coverage today with the upper low starting to retrograde while the occluded boundary to the west shifts east and starts to cutoff deeper moisture late. Models continue to focus showers and storms across the northwest corridor through midday, then along and north of a KLWB- KDAN line. Should see any IFR conditions slowly improve to MVFR/VFR by midday/early afternoon though think places like KROA/KLYH/KLWB will keep MVFR to the end of this taf period. Will include more showers and storms given decent probability during the afternoon in most locations with tapering of showers by the evening as the main corridor of deeper lift slides north. Extended aviation discussion... A deep upper low will finally shift farther to the north by Saturday and away from the region on Sunday. This should allow for a gradual improvement in cigs after early sub-VFR Saturday with widespread VFR Sunday as weak high pressure builds in. Looks like overall VFR to then prevail into early next week outside of some upslope low clouds Monday and perhaps along the Blue Ridge Tuesday as another weak wedge develops under high pressure to the north. && .HYDROLOGY...
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As of 1230 PM EDT Friday... Focus this afternoon will be on the potential repetitive showers and thunderstorms along and east of the highway 220 corridor with amounts of 1 to 3 inches. Parts of the forecast area has already received 3 to 7 inches, and this additional rainfall will only aggravate the situation. Given the now saturated soil conditions from the highlands of VA to along the VA Blue Ridge northeast of Roanoke it will be easier for flooding or flash flooding to develop while still appears most mainstem rivers will stay below flood levels for now.
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&& .RNK WATCHES/WARNINGS/ADVISORIES...
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VA...Flash Flood Watch until 6 PM EDT this evening for VAZ019-020- 023-024-034-035. NC...None. WV...None.
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&& $$ SYNOPSIS...AMS/JH NEAR TERM...JH/PM SHORT TERM...JH LONG TERM...MBS AVIATION...AMS/JH/WP HYDROLOGY...JH/PM

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