168 FXUS61 KRNK 122331 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 731 PM EDT Thu Jul 12 2018 .SYNOPSIS... High pressure will build across the region from the north overnight and remain in place through much of the upcoming weekend. This should allow for drier weather under seasonable temperatures the next few days. Increasing heat and humidity should return along with better chances of showers and storms ahead of the next cold front for early next week. && .NEAR TERM /THROUGH FRIDAY/... As of 731 PM EDT Thursday...No major change needed to going forecast. Still looking at isolated to widely scattered showers with perhaps a rumble of thunder in the mountains of NW NC, with individual cells drifting southward. These showers/embedded thunderstorms forming due to east flow on northern end of 850 mb stalled frontal zone over central NC, aided by a weak 500 mb vort max pivoting out of east-central KY. Most recent 18z NAM and past couple HRRR cycles suggest a continuation of at least showers from Grayson County VA into the mountains of NW, NC even after sunset and in spite of cloudy/rain- cooled air as easterly flow continues. Later tonight and into the overnight, majority of guidance advects axis of of 925-850 mb RH westward against the Blue Ridge on the northern extent of the stalled front. This should lead to an increase in cloud cover especially near and within a few miles either side of the Blue Ridge/mountains of NW NC. It's less certain how far north/east the extent of clouds will be, which could be low-based. May see intervals of mist at times in the western mountains but likelihood of at least partly to mostly cloudy skies limits how low visbys may get in any fog/mist. Temps look to be on track with lows in the 60s, though will tend into the lower 60s further north and west into the Alleghany Highlands/Greenbrier Valley. Previous discussion follows... Convection remains limited across the region this afternoon with the latest SPC mesoscale analysis showing only weak instability across far southern and eastern sections. This in locations where higher dewpoints and subsequent low level moisture persist near the stalled 850 mb front aloft. Latest CAM model solutions including the HRRR still show isolated showers mainly NC ridges late afternoon/early evening with much of this after sunset once mixing relaxes. Also seeing a weak shortwave remnant within the upper trough pushing through the far southwest overnight. This may tend to keep some convection going until midnight if not longer per latest Nam so keeping in low pops mainly NC mountains overnight. Also guidance indicates a bit stronger boundary layer easterly trajectory developing behind the exiting wave late, possibly resulting in more low clouds near the Blue Ridge by daybreak so boosted clouds some late given consensus. Otherwise clear north to partly/mostly cloudy south as current cumulus fields likely transition to trapped strato-cu in spots with loss of heating. Lows mostly low/mid 60s with a few 50s northwest/valleys. Better push of drier air will occur on Friday with any residual deeper moisture over the southwest sliding to the south Friday morning as the earlier shortwave exits. Guidance then suggests a pretty dry column by afternoon as the surface high to the north continues to build in. However still perhaps enough low level moisture along with weak upslope southeast flow to pop isolated showers across the NC ridges, but chances less than today given lack of instability and soundings showing very limited moisture beneath the inversion around TNB. Otherwise expect any low clouds/fog to quickly mix out Friday morning with sunshine increasing under rather deep easterly flow during the afternoon. High temperatures appear similar to Thursday despite more sunshine with highs mainly low/mid 80s per only slight warming aloft. && .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/... As of 325 PM EDT Thursday... Ridge of high pressure initially extending from Halifax to the mid- Atlantic coast will maintain near normal temperatures along with dry conditions for most of the Blacksburg forecast area through Saturday night. Exception will continue to be from the NW NC mountains north toward the Grayson Highlands of SW VA, where combination of upsloping easterly flow on the periphery of the high pressure system and a slightly moister and marginally unstable airmass will persist supporting the development of mid-afternoon into evening isolated showers or thunderstorms. Situation expected to change slightly Sunday into Sunday night as surface ridge drifts offshore allowing lower tropospheric flow to veer into more of a south to southwesterly component. Weak warm moist advection on backside of departing surface ridge and approach of subtle weak short wave trofs embedded in nearly zonal flow aloft will support an expansion of the threat for widely scattered to scattered showers/thunderstorms to most of the forecast area, especially in the afternoon and evening - maximized across the western flanks of the Appalachians. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 325 PM EDT Thursday... Longer range models continue to reflect a series of weak, but randomly spaced and difficult to time short waves embedded in westerly flow aloft - each of which will support redevelopment of diurnally-driven widely scattered to scattered showers/storms - with the threat again maximized across the mountains due to upsloping flow across the western flanks of the Appalachians coupled with better differential heating due to local topographical influences. The highest threat for precipitation during the long-term period now looks to be in the Tuesday into Tuesday night timeframe. The ECMWF has now come more in line with what was the more progressive GFS in maintaining the integrity of a cool front pushing southeast into/through the Blacksburg forecast area during this period. A higher degree of confidence now exists for this more aggressive scenario; however, as is typical for this time of year for weakening fronts pushing this far south, boundary expected to slow/stall just south of the area before washing out or beginning a drift back northward toward the mid-Atlantic region on Thursday. Uncertainty of frontal position warrants maintaining at least a low threat of precipitation on Wednesday into Wednesday night, although it may very well end up being a dry period if front indeed remains progressive. Regardless, by Thursday, especially by later in the day across southern portions of the forecast area, threat should again be on the increase as lower level winds begin to veer into the south in advance of an even stronger cool front that is expected to arrive on Friday or Saturday. && .AVIATION /23Z THURSDAY THROUGH TUESDAY/... As of 731 PM EDT Thursday... VFR conditions should prevail through the rest of the afternoon until late this evening. Isolated to scattered showers with embedded thunder still possible through 01z along the mountains of NW NC, with isolated showers in this general area through the rest of the overnight. After around 05z, should see a period of restricted conditions develop as low clouds begin to develop across at least the southern Blue Ridge into Floyd/Montgomery Counties. 15z SREF probabilities of MVFR ceilings are quite high (around 70-90% within a few miles of the Blue Ridge). Have currently shown MVFR ceilings in this area (mainly affecting Blacksburg and later Bluefield TAFs), though some level of uncertainty on northern extent of this MVFR deck from Roanoke north. May see some mist in the western mountains but coverage limited to the river valleys and visbys no worse than IFR. Winds tonight from the east between 3-6 kts. Should be able to scatter out any MVFR low clouds by around mid- morning Friday revealing SCT Cu/SCu and VFR conditions. Winds mainly east 3-5 kts except southeast at Bluefield on the western end of the wedge. Extended Aviation... High pressure will dominate with VFR conditions into Saturday before moisture increases ahead of the next upstream cold front for early next week. This may allow for isolated convection Sunday, including localized restrictions to ceilings and visibilities, to become more widespread especially mountains by Monday afternoon and across the region on Tuesday. However confidence is too low to pinpoint where the showers and thunderstorms may occur. && .EQUIPMENT... As of 1205 PM EDT Thursday... The NOAA weather radio transmitter in Hinton, West Virginia, WXM72 on a frequency of 162.425 MHz, is back on the air. We thank our listeners for their patience during this extended outage. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH NEAR TERM...AL/JH SHORT TERM...WERT LONG TERM...WERT AVIATION...AL/JH EQUIPMENT...JH