Area Forecast Discussion
Issued by NWS Blacksburg, VA

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163 FXUS61 KRNK 251137 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 737 AM EDT Thu Aug 25 2016 .SYNOPSIS... High pressure over the region shifts slowly east today into tonight. The upper ridge will remain overhead through the end of the week. && .NEAR TERM /THROUGH TONIGHT/... As of 300 AM EDT Thursday... High to mid clouds from the Ohio Valley convection will continue to spread eastward across the region this morning. The combination of low level moisture and light winds has resulted in patches of low clouds and fog this morning. These low clouds and fog will lift by mid to late morning. The center of the upper high slides across the Appalachians and Tennessee Valley this afternoon into tonight. Building heights aloft will keep most showers and thunderstorms limited. The day one convective outlook places our area in general thunderstorms with slight risk of severe to our northwest in the Ohio Valley and Great Lakes Region. A weak shortwave rotating through the region could generate a few morning showers in the northwest mountains, then isolated to scattered showers and thunderstorms may develop this afternoon across the higher terrain. High temperatures this afternoon will range from the upper 70s in the mountains to the lower 90s in the Piedmont. Heat index values are expected to remain below heat advisory criteria this afternoon. Any convection will diminish quickly this evening with loss of heating, leaving clear to partly cloudy skies tonight. With light winds, patchy of low clouds and fog will develop tonight into Friday morning especially in the valleys. Low temperatures tonight will vary from the lower 60s in the west to around 70 degrees in the east. && .SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/... As of 430 AM EDT Thursday... The main story through the period will continue to be a strong subtropical ridge that will drift from the Midsouth into our region by the weekend. The weak front that will move into the area today will drift slowly south into the Carolinas and basically wash out by the weekend. Heat, moisture, and instability are certainly sufficient for diurnally driven showers and thunderstorms, but upper-level forcing/dynamics are nil under the strong upper ridge. Most models indicating a scattering of convection/qpf across the region focused near the dissipating frontal boundary or more notably across the northwest NC mountains. Thus, have focused slight chance to low chance pops in these areas. Over the weekend, the front will continue to dissipate to our south/southwest as a new similar front moves into the region by Sunday. Have continued advertising diurnal slight chance to low chance pops mainly western mountains areas through the period. With weak dynamics and very little forcing, the severe threat is little to none with manily pulse thunderstorms. Duration should be limited, so heavy rain should also not be a problem. Temperatures will average well above normal through the period. Expect a fairly good jump in maximum temperatures between today and Friday as 850mb temps surge into the +20C to potentially as high as +24C (per GFS) range Friday. This will yield maximum temperatures in the lower to mid 90s across the Piedmont and well into the 80s elsewhere. These readings are a good 10 degrees above normal. Minimum temperatures will also be on the increase through the period as dewpoints/RH values continue to increase toward 70F. Look for lows to average a good 10 degrees above normal as well into the weekend with 60s mountains to lower 70s Piedmont. && .LONG TERM /MONDAY THROUGH WEDNESDAY/... As of 450 AM EDT Thursday... The upper-level ridge will begin to weaken as we progress into the mid part of next week but will also be the key to steering a tropical system that is forecast by most models to track into south Florida early in the week. Although the track is now relatively similar among the models, there are vast differences in the intensity. While the GFS shows a weak tropical low drifting slowly north to northeast across FL into southeast GA and eventually the Carolinas through the week, the ECMWF develops a tropical storm/hurricane, which it similarly moves northeast, albeit much quicker than the weaker GFS system. Meanwhile, as the upper high weakens and shifts south of our area, another weak front is progged to drift into the region by midweek. Much of the time, our region will likely remained sandwiched in between the frontal precipitation to our north/west and the tropical system to our south. However during the later part of the week, the tropical system could begin to impact at least the southeastern parts of our CWA and with the pattern in place, there is always at least some concern of a predecessor rain event. At any rate, considerably uncertainty remains and such considerations still remain just beyond this forecast period. Therefore, will continue the trend established in the short term period of slight chance to low chance diurnally driven pops and well above normal temperatures moderating only slightly closer to normal by the end of the period as cloud cover and moisture increase, the upper high weakens, and 850mb temps drop back a few degrees. && .AVIATION /12Z THURSDAY THROUGH MONDAY/... As of 730 AM EDT Thursday... VFR conditions will prevail through most of the TAF valid period as high pressure both surface and aloft moves slowly east across the region. The main exception to VFR conditions will be patchy dense fog and localized IFR-LIFR vsbys/cigs through 13/14Z this morning at the usual spots, namely KLWB and KBCB and again after 07Z Fri morning. Otherwise, extensive mid/high clouds will spread across the region again today in association with a weak cold front that will drift from northwest to southeast across the area. The associated cloud bases are expected to 035 to 050, namely VFR. An isolated -shra cannot be completely ruled out as activity is drifting southeast along the front from WV. However, forcing/dynamics are very weak under the upper high. The front will drift south of the area by Fri morning leaving the region with just scattered mid cloud/high clouds and again the potential for patchy fog late tonight. Winds are expected to veer more to the west today at speeds of 4-7kts, becoming calm most areas after 04Z. Medium to high confidence in cigs through the TAF valid period. Medium to high confidence in vsbys through the TAF valid period. Medium to high confidence in wind speed/direction through the TAF valid period. Extended aviation discussion... Storms will again be isolated and mainly confined to the mountains on Friday as upper ridging strengthens, while a weak surface front stalls to the south. Brief MVFR conditions could occur where any convection does develop but appears mainly VFR given spotty nature to any showers. The front washes out during the weekend, but another weak front will drift into the area Sunday. Isolated to scattered diurnal showers and thunderstorms still possible each day. Coverage will be limited in area and duration. Monday high pressure bubbles in but still a very humid airmass to keep isolated mountain storms around in the afternoon, but mainly VFR. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...KK NEAR TERM...KK SHORT TERM...RAB LONG TERM...PM/RAB AVIATION...JH/KK/RAB

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