Area Forecast Discussion
Issued by NWS Blacksburg, VA

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932 FXUS61 KRNK 251844 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 244 PM EDT Tue Jul 25 2017 .SYNOPSIS... A weak front across northern North Carolina will shift south of the area tonight into Wednesday before dissipating. High pressure north of the region should continue to ridge south across the area through Wednesday night keeping overall dry weather in place. Another cold front approaches from the northwest Thursday into Friday exiting to our southeast by Saturday morning. && .NEAR TERM /THROUGH WEDNESDAY/... As of 215 PM EDT Tuesday... Surface front has drifted farther south this afternoon with dry advection having pushed into northern North Carolina per latest dewpoints. This has basically shifted instability to the south of the CWA with only the far southwest currently holding onto a bit more of a cumulus field. Appears best chance at seeing any isolated showers will be across the North Carolina mountains where a weak inverted trough lingers and expect a little more convergence as winds start to turn more easterly by early evening. However not more than a 20 pop at best with clear skies elsewhere this evening. High pressure to the north shifts east overnight allowing a little deeper easterly trajectory to develop by morning. Some guidance again trying to bring low level moisture back into the Blue Ridge espcly far south where dewpoints should be a little higher. Think too dry elsewhere as models remain too moist, so running with mostly clear to partly cloudy overnight with patchy fog/stratus around. Should be quite comfortable overnight with low dewpoints and better radiational cooling under the high allowing temps to fall well into the 60s most spots, with even some 50s possible in the valleys. Will start to see low level moisture start to slowly rebound on Wednesday as the high to the north shifts farther east resulting in a gradual veering of the flow to a more southerly component later in the afternoon. This seen via model jump in dewpoints and northward shift in progged PWATs from south to north during the day. However instability remains lacking as well as upper forcing with any convection likely due to weak southeasterly flow convergence and orographics. This again mainly over the southwest with ridging holding across the north and east so trimmed pops back to only isolated/low chances mainly southern Blue Ridge. Otherwise expect any low clouds to mix out to more sunshine by afternoon with highs cooler, mostly upper 70s to mid 80s, within a lingering east- southeast flow until late. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/... As of 205 PM EDT Tuesday... Surface high pressure will weaken Wednesday night into Thursday as a cold front approaches from the west. This front is stuck in zone flow and will slowly move from the upper Midwest Wednesday night to the Ohio Valley Thursday. This front will pick up speed, moving over the mountains early Friday morning, then east of the Blue Ridge Friday afternoon as an upper level low tracks across the Great Lakes. Diurnal heating and orographical lift should generate isolated to scattered showers and thunderstorms across the mountains early Thursday afternoon. These storms may slowly drift over the foothills towards evening. As the front approaches the mountains early Friday morning, the chance for wide spread showers will increase. Despite these showers coming in during non-diurnal heating, linger instabilities and a 30-40 knot low level jet could allow some strong storms to pass over the area overnight. The chances for showers and thunderstorms will move east of the Blue Ridge Friday morning, exiting the piedmont by sunset. The best dynamics with this front will remain north over Pennsylvania and Maryland Thursday night then along the New England coast Friday. For the forecast area, the severe weather outlook for Friday is marginal with scattered strong storms to possibly a few severe cells across the foothills and piedmont counties. If the front is slower by 6 or more hours, the severe threat could increase to slight as this would place the frontal passage during peaking heating Friday afternoon. Even if the timing is slower, the best dynamics will remain to the north. Temperatures will be slightly warmer than normal Thursday with low to mid 80s west of the Blue Ridge and upper 80s to lower 90s east. Friday will be a lot cooler across the mountains with morning showers and a frontal passage. High temperatures will range from the mid 70s to near 80F across the mountains. Temperatures will warm to near normal east of the Blue Ridge with afternoon temperatures in the mid 80s. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... As of 240 PM EDT Tuesday... An upper level low will track from the Great Lakes Friday, then south over Virginia Saturday. Heating under this cold pool will bring scattered showers to the region Saturday afternoon. Temperatures will actually be cooler than normal for the first time since late June. Surface high pressure will build over the region starting Sunday. This ridge of high pressure will keep the area cool and dry into early next week. && .AVIATION /19Z TUESDAY THROUGH SUNDAY/... As of 1245 PM EDT Tuesday... Good flying conditions to continue this afternoon with VFR expected under some passing scattered-broken cumulus mainly across southern/eastern sections. Any convection later this afternoon will be isolated and stay confined to locations south and west of the terminals into North Carolina. West to northwest winds at 5 to 12 kts should prevail with ocnl gusts to around 20 kts along the ridges. Low level flow turns more easterly around high pressure to the north overnight providing some potential for moisture to bank up along the mountains late. This could result in a period of sub- VFR cigs if patchy low canopy forms per latest Nam. Otrw leaving out most low cigs given dry air for now and trending VFR overnight outside of any fog/stratus. However the fog threat late tonight again looks minimal, so only including a brief mention at KBCB/KLWB toward daybreak. If enough of an east wind develops, fog forming over the Greenbrier River could push into KLWB resulting in a period of MVFR or worse late. Should stay VFR under high pressure Wednesday though some scattered- broken VFR cigs possible in the mountains. Looks like most isolated convection will again remain mainly south/west of the taf sites later in the afternoon. Therefore leaving out any mention at this point, with any shra/tsra also likely not developing until after the valid taf period. Aviation Extended Discussion... Should start to see a front approaching with better threat of showers/thunderstorms Thursday into Friday. Outside of storms expect VFR conditions, with possible late night fog by Friday morning. Saturday looks drier with northwest flow, but could see lingering low end VFR/high end MVFR ceilings in SE WV along with a few added shra/tsra mainly southern sections Saturday afternoon. Expect widespread VFR to return Sunday under high pressure following the front. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH NEAR TERM...JH SHORT TERM...RCS LONG TERM...RCS AVIATION...JH/RAB/WP is the U.S. government's official web portal to all federal, state and local government web resources and services.