Area Forecast Discussion
Issued by NWS Blacksburg, VA

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824 FXUS61 KRNK 270551 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 151 AM EDT Tue Jun 27 2017 .SYNOPSIS... Weak high pressure over the region tonight will give way to a fast moving upper level disturbance that should cross the area from the northwest on Tuesday. Other than some isolated to scattered showers and storms in association with this feature on Tuesday, high pressure will provide for dry and cool weather for much of this week. The chance for more abundant showers and storms, as well as increasing temperatures, return Friday into the weekend. && .NEAR TERM /THROUGH TODAY/...
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As of 147 AM EDT Tuesday...No significant changes needed with this update. Did opt to increase sky cover slightly per 3.9 micron infrared imagery showing stream of mid-level cloudiness ahead of mid-level disturbance over the Great Lakes region, with leftover altocu layer generally near/north of the Roanoke Valley. Other than that minor change, forecast generally holding for this evening. Previous discussion... Return of moisture slowly occurring across the region this evening as seen via the latest blended TPW and PWATS off soundings just south of the area. This in advance of a fast moving upper disturbance across the Midwest this evening per latest water vapor loop. Some of this moisture from spreading out of afternoon cumulus remains stuck under the inversion aloft this evening with even a few sprinkles showing up across the far western I-81 corridor. Although not expecting too much eastward progression of any light showers, will include a shower or sprinkle mention for an hour or two to start late this evening. Otherwise main inbound axis of deeper moisture likely to fade upon arrival into the drier air aloft after loss of heating late tonight as evidenced by latest drier solutions. However likely best to keep some low end pops going late tonight as the NCAR Cam ensemble shows some light showers far west late and perhaps jumping the Blue Ridge early in the morning. Otherwise beefing up clouds over the west and central overnight with partly cloudy to clear elsewhere. Also bumped up lows a little given slightly higher dewpoints southeast, and earlier arrival of strato-cu over parts of the mountains, but still mainly 50s overall by daybreak. Previous discussion as of 230 PM EDT Monday... Daytime cumulus clouds should give way to mostly clear to clear skies this evening. However, the approach of an upper level disturbance will start to bring a return of cloud cover to the area after midnight tonight, and conditions will remain mostly cloudy to cloudy through the day on Tuesday. Isolated showers may reach the far western sections of the area by late tonight, but chances will increase during the day Tuesday. The best potential for showers and storms will extend from roughly Lewisburg, WV to Bluefield, WV to Marion, VA to Boone, NC. East of this region, precipitation in the form of isolated showers will be more likely, east to roughly a Lynchburg, VA to Reidsville, NC line during the afternoon. Temperatures will continue to be on the cool side for this time of year. Lows tonight will range from the upper 40s to the lower 50s across the mountains and the mid to upper 50s across the Piedmont. High temperatures on Tuesday will range from around 70 to the lower 70s across the mountains to the mid to upper 70s across the Piedmont.
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&& .SHORT TERM /TONIGHT THROUGH THURSDAY/... As of 240 PM EDT Monday... At 00z Wednesday (8 pm EDT Tuesday)...the axis of an upper level trof will be exiting our forecast area and any lingering mountain showers will have ended. With a large area of high pressure settling over the region...morning lows Wednesday will be well below normal and went a few degrees below guidance. The COOP MOS guidance is forecasting lows in the upper 30s at Burkes Garden. High pressure continues to influence our weather on Wednesday. With limited mixing...leaned toward the cooler guidance for highs which should range form the lower 70s in the mountains of NW NC to the lower 80s in the NC/VA Piedmonts. The transition to higher humidity levels and warmer temperatures begins Wednesday night into Thursday as higher low level theta-e air lifts north into the region as a deepening west/southwest flow arrives. Most the area will remain dry on Thursday, but a few showers cannot be ruled out in the southern Blue Ridge of NW NC and far southwest VA on the nose of a low level theta-e ridge, increasing PWATs and differiental mountain heating. With downsloping winds, pushed high temps Thursday up a degree or two from the previous forecast. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... As of 200 PM EDT Monday... A return to weather conditions more typical for summer are expected during the long term period, as the long range models show good agreement transitioning from an upper level zonal flow early in the period to an upper trof forming somewhere around the Great Lakes and extending south into the eastern U.S. by late in the weekend into Monday. This will result in increasing temperatures and humidity, as well as an increase in storm chances. An upper level disturbance moving out of the western Gulf of Mexico into eastern VA on Friday/Friday night will help lead a surge in higher PWAT air our area. This higher moisture combined with a series of upper level disturbances...with the usual differences in timing shown in the long range models...will help generate scattered showers and storms each day during the long term period, especially during the peak heating in the afternoon and early evening hours. With increasing CAPES, but low shear through the period,a few pulse severe storms and locally heavy rain are possible. Warmest temperatures are expected Sunday and Monday as 850mb forecast temps approach +20C. This may generate heat index values in the low to mid 90s in the east. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/...
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As of 147 AM EDT Tuesday... VFR through the TAF period. Expect a greater coverage in SCT to OVC VFR mid-level cloudiness from west to east through 12z with moisture on the increase ahead of a mid-level disturbance now making its way across the eastern Great Lakes. Given how dry today was across the region, prospect for radiation fog at the TAFs is very low - the best chance may be at Danville where slightly higher surface moisture exists, though confidence is too low to mention in the TAF at this point. Should see winds light westerly to calm. For Tuesday, aforementioned mid-level disturbance moves east- southeast across the airspace. Expect mid-level clouds persisting until mid-afternoon with a few cumulus developing underneath these. Some showers or sprinkles possible through the first half of the day, but well-mixed boundary layer progged by most model guidance suggests that visibilities in showers likely > 6 SM. Winds west 4-8 kts with gusts to 17kts. Expect clearing to occur by late afternoon and into the evening hours with high pressure ridge building into the region. Though winds should also gradually abate, there still should be enough of a northwesterly wind between 00-06z to limit any fog development to after 06z Wednesday. Extended Aviation Discussion... Expect VFR conditions with a limited potential for IFR to LIFR overnight radiation fog after 06z Wednesday. Confidence in development currently low but a better chance of occurrence if wetting rain affects any of the airports Tuesday. VFR conditions then anticipated until Friday, with potential for overnight IFR to LIFR radiation fog Wednesday and Thursday evenings. Friday into Saturday, the potential for sub-VFR conditions increase as showers and storms become more numerous. Saturday appears to feature a greater coverage of showers and storms associated with a cold frontal passage. Likewise, an increase in the boundary layer moisture will also lend itself to better chances of late night/early morning patchy fog.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...DS/JH NEAR TERM...AL/JH SHORT TERM...PH LONG TERM...PH AVIATION...AL/DS

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