Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 250749 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 349 AM EDT Tue Jul 25 2017 .SYNOPSIS... A weak cold front will stretch the NC west into Tennessee today then gets pushed further south tonight by high pressure building in from the northeast. Another cold front approaches from the northwest Thursday into Friday exiting to our southeast by Saturday morning. && .NEAR TERM /THROUGH TONIGHT/... As of 320 AM EDT Tuesday... Have a little fog/low clouds banked up across southern WV into the Mountain Empire where an inverted sfc trough lingers. Expect these clouds/fog to erode after 8-10am. High pressure will bring drier airmass/dewpoints to much of the region today, with models showing deeper moisture shunted south of our forecast area. Still enough of a gradient plus some return flow and inverted trough along the southern Appalachians to maybe generate isolated storms across the NC High Country possibly moving into the NC foothills this afternoon. Otherwise enough subsidence for overall mostly sunny skies with highs low/mid 80s mountains to upper 80s to around 90 east of the Blue Ridge. Any convection weakens and shifts out of our ares this evening with skies staying generally clear. High pressure will be over New England late Tuesday night so some return flow may still generate lower stratus/fog along the southern Appalachians, but overall confidence is low and another day of drying should limit this. Lows running close to normal with upper 50s to lower 60s mountains, to mid to upper 60s east of the Blue Ridge, but including Roanoke- Lexington. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 330 AM EDT Tuesday... High pressure over New York Wednesday morning will slide east in the Atlantic ocean Wednesday night into Thursday. Some weak orographic lift may combine with solar heating to create isolated to scattered diurnal showers and thunderstorms mainly along the southern Blue Ridge. High temperatures Wednesday will range from the the mid 70s in the mountains to the mid 80s in the piedmont. Any convection will taper off quickly Wednesday evening with loss of solar heating. Under partly cloudy skies, low temperatures Wednesday night will vary from around 60 degrees in the west to near 70 degrees in the east. Low pressure with a trailing cold front will move east across the Ohio Valley Thursday into Thursday night. The timing looks a little faster than yesterday. Thus, increased pops on Thursday and bring likely into the western mountains Thursday night. High temperatures on Thursday will climb to around 80 degrees in the mountains to about 90 degrees in the Piedmont. SPC has placed most of the forecast area in a slight risk for severe weather Thursday afternoon into Thursday evening. The main threat is for fast moving bands with damaging winds. Also, any thunderstorm could produce locally heavy rains. With clouds and rain, low temperatures Thursday night will generally be in the mid 60s in the mountains to the lower 70s in the Piedmont. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 1245 PM EDT Monday... Upper pattern amplifies starting on Friday with the upper ridge over the western United States slightly retrograding and a trof digging in the east. An upper low may eventually close off somewhere over the Tennessee Valley or Mid Atlantic region by Sunday or Monday. This closed low solution was not supported by a majority of the extended guidance. Probability of showers and thunderstorms will increase on Friday and Saturday with some vorticity advection and lowering heights. Air mass ahead of the trough stays in the +16 to +20 range for temperatures at 850MB and will be a little cooler on Sunday and Monday. && .AVIATION /08Z TUESDAY THROUGH SATURDAY/... As of 105 AM EDT Tuesday... Concerns this morning mainly focus around fog development and possible low cloud development along the Alleghany front. Will discuss the later first as that possibility seems limited due to decreasing upslope W-NW flow becoming near calm or light and variable, possibly even light northeast. Will include for now as it remains a possibility per model soundings. Fog development at LWB and BCB especially seems a better possibility due to recent rainfall, hence moist ground in the area, clearing skies, and near calm winds. Have continued earlier thinking on this and continued potential for IFR-LIFR FG at BCB and LWB in the 08Z- 12Z time frame. Will hold off on fog elsewhere, although MVFR BR conditions at LYH and DAN do not seem out of the question, just not enough confidence to include at this time. Winds will be light WSW-WNW 4-6kts this evening, becoming calm overnight at most sites. Winds will be light and variable Tuesday, but good potential for light northeast winds east of the Blue Ridge. Medium confidence in ceilings through 13Z, then high confidence in VFR ceilings. Medium to high confidence in visibilities through 13Z, then high confidence in VFR visibilities. Medium to high confidence in wind speed and direction through the TAF valid period. Aviation Extended Discussion... A frontal boundary will remain stalled to our south through Wed, with high pressure wedging southward on Wed from the northeast U.S. Overall VFR, but with flow turning more east, this could bring some MVFR/IFR ceilings, which should quickly dissipate by Thursday. Any convection also likely to remain isolated and south of the TAF sites again later Wednesday. Next best threat for showers and storms arrives late Thursday as a new front approaches from the north with more widespread activity in the area Friday as the front drifts slowly southeast through the region. Saturday looks drier with northwest flow, but could see lingering low end VFR/high end MVFR ceilings in SE WV. && .EQUIPMENT... As of 345 AM EDT Tuesday... The temperature sensor on the observing equipment at Lynchburg has failed, therefore no temperature data will be available until technicians can replace the defective part later this week. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH/WP NEAR TERM...WP SHORT TERM...KK LONG TERM...AMS AVIATION...JH/RAB/WP EQUIPMENT...WP

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