Area Forecast Discussion
Issued by NWS Blacksburg, VA

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847 FXUS61 KRNK 291118 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 718 AM EDT Thu Jun 29 2017 .SYNOPSIS... High pressure off the coast of VA/NC will allow for increasing humidity and temperatures today into tonight. Showers and storms will be on the increase Friday into the weekend as a cold front approaches from the northwest. && .NEAR TERM /THROUGH TONIGHT/... As of 225 AM EDT Thursday... Quiet wx for the most part today with high pressure over the coast of the Carolinas. High clouds this morning may limit fog to the river valleys. Will see increasing dewpoints, and during the afternoon scattered cumulus will form. Looking at deeper moisture plume over the Gulf Coast in assocation with an upper low/trough near the Louisiana coast. Models are having this plume shift northeast toward our area by tonight. For this afternoon, overall looking dry and model soundings showing shallow layer of moisture in the 850-800 mb layer. Still expect some towering cu, though both nam/gfs showing a decent cap in place even over the NC mountains. High-res models showing isolated coverage along spine of the Blue Ridge and synoptic models are mainly keeping any convection over the NC/TN border mountains to the Smokys. Will keep pops on the low side with isolated wording. Some thunder possible but with strong cap seems limited. Should be somewhat of a lull this evening before the deeper moisture and better upper support shift to the southern Appalachians. Still appears best coverage stays southwest of us over the Smokys into the Gulf Coast states, so pops no higher than 25 percent. Should be mostly sunny today, but sun may be obscured by the high clouds early. Warmer and slightly more humid with dewpoints rising into the upper 50s to lower 60s. Highs to range from the mid 70s in the higher ridges, namely the NC mountains, with lower 80s over the rest of the mountains/valleys along/west of the Blue Ridge. Meanwhile, Roanoke, east to the piedmont temps are going to reach the mid to upper 80s. Tonight, should be mild with lows in the upper 50s/around 60 west, to mid 60s east. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 350 AM EDT Thursday... High pressure off the Mid Atlantic coast will gradually shift east into Saturday night. Southerly surface winds on the backside of the High center will advection warm and moist air into our region. A weak disturbance drifts northeast from out of the northern Gulf Coast states towards and through the Mid-Appalachian Region. This system will likely significantly weaken and shear out by the time it arrives. In any case, the threat for scattered diurnal showers and thunderstorms will increase. The combination of weak forcing combining with increasing lower and mid tropospheric moisture supports the best chances over the mountains, with a lower potential across the Piedmont which will be a bit further removed from the weakening system. Increased pops Friday in the west especially along the western slopes which match up nicely with RLX and GSP. High temperatures Friday will range the lower 70s in the mountains to the mid 80s in the piedmont. Convection slowly tappers off Friday evening into Friday night with the loss of solar heating. Then, patchy fog develop overnight into Saturday morning. Low temperatures Friday night will vary from around 60 degrees in the west to the upper 60s in the east. The upper trough approaches Saturday with richer low level moisture. The combination of instability and orographic lift will create showers and thunderstorms Saturday afternoon into Saturday evening. Held on to the likely pops west of the Blue Ridge mountains. The Day three SPC convective outlook has the marginal risk of Severe thunderstorms to our west across the Ohio Valley with the better instability and lift. High temperatures on Saturday will climb into the mid 70s in the west to the mid 80s in the east. Expect a few showers and isolated thunderstorms to end Saturday evening as the initial weak short wave trof moves away from the forecast area. It will be a mild Saturday night with lows from the lower 60s in the west to around 70 degrees in the east. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 350 AM EDT Thursday... Several weak disturbances and associated weakening fronts are expected to move east through nearly zonal upper flow during the long-term period. First wave expected to move into/through the area on Sunday, which may lay down a weakening cool front that will stall out over/near the area by Sunday - with additional weak disturbances moving east and through the area through mid week. Both the GFS and ECMWF are hinting the Monday behind the first wave may be the drier day. However, exact timing of each wave is still somewhat problematic, but daily proximity of waves combining with a moist airmass and an old frontal boundary warrants a continuation of some widely scattered mainly diurnally-driven shower/thunderstorm threat throughout the long term period. Overall forcing and thermodynamics will remain lackluster through this period, so severe weather threat expected to remain extremely limited. && .AVIATION /11Z THURSDAY THROUGH MONDAY/... As of 710 AM EDT Thursday... Fog never formed at BCB/LWB, and given insolation taking place, and vis sat showing no fog, will not have any this morning in the tafs Cirrus will be around thru the day, mainly thin. Some cumulus to form in the afternoon, in the 5-9kft range, but overall few-sct mainly south of a BLF-BCB line. Few showers possible late south of HLX-TRI line. VFR through tonight, but may see some increase in clouds late toward BCB. With increase in dewpoints still cannot rule out fog at LWB/BCB if they stay clear, so taking them down to IFR overnight. Extended Aviation Discussion... Better threat of storms Friday, as deeper moisture pushes northeast ahead of a frontal boundary and in associated with upper trough/shortwave over the southern Appalachains. With any storms expect localized, brief sub-VFR vsbys/cigs. Friday night, the potential for IFR/MVFR fog will be greater, along with some areas with sub-VFR stratus formation. Saturday should see good coverage of showers and storms with front moving to the eastern Ohio Valley southwest to the mid-MS valley. Sunday looks like less coverage, with even drier conditions expected Monday. Aside from any storms moving over, and any late night/early morning fog/stratus, expect VFR conditions. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...DS/JH/WP NEAR TERM...WP SHORT TERM...KK LONG TERM...KK/WERT AVIATION...DS/MBS/WP

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