Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 052325 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 725 PM EDT Thu Aug 5 2021 .SYNOPSIS... An upper level disturbance will move across the Virginias today providing a chance for showers and isolated thunderstorms, otherwise high pressure will be the dominant feature through Friday resulting in little or no rainfall. Another upper level trough of low pressure will cross the area Saturday, providing another opportunity for scattered showers and storms. && .NEAR TERM /THROUGH FRIDAY/...
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As of 700 PM EDT Thursday... Shortwave axis passing over Virginia this evening. The tail-end of this trough is bringing a few showers to Rockbridge and Amherst Counties this evening. Some thunder may be heard early, then showers fade with lose of heating by 9p. As of 200 PM EDT Thursday... Scattered showers and storms will wane quickly this evening followed by a dry Friday... Upper level shortwave axis is in the process of crossing the forecast area from west to east this afternoon. This has resulted in showers and thunderstorms developing farther east than they were yesterday. The character of the convection will be similar to yesterday in that heavy rainfall is the only real concern. However, things should quiet down faster with the main forcing for ascent associated with the trough shifting east by early evening. Dew points in the 50s and temperatures in the 70s and 80s have made for a pleasant day. Cloud cover will decrease tonight as drier air moves in, and temperatures should drop quickly once it does. Lows should be in the 50s to lower 60s, with the coldest river valleys/ lower depressions dropping into the upper 40s even. Fog will develop in the valleys and perhaps across parts of the WV/VA border where it rains tonight. Ridging builds in briefly tomorrow, however a frontal boundary over the southeastern states will begin to move back north in response to the next approaching short wave trough to our west. This will result in increasing cloud cover later in the afternoon/early evening Friday. During the daytime hours, it will be a few degrees warmer than today under mostly sunny skies.
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&& .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
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As of 230 PM EDT Thursday... Low Pressure Brings Possibility Of Rain Saturday.... An upper level trough starts to approach the region Friday night, increasing cloud cover overnight and trying to get a more saturated airmass in place. Saturday, the trough is accompanied by a weak area of low pressure that will originate out of the southern states from the current stalled front. This low will provide the greatest chance for precipitation Saturday...if it can get close enough to us. Guidance is gradually coming into better agreement on this disturbance passing through NC, bringing the opportunity for some of the heavier rainfall to occur out in Southside. That said, it still won`t be drought busting and there`s still limitations to the forecast as guidance still struggles to really show a good flux in moisture as PWATs struggle to break 1.5 inches. Regardless of small changes in the track at this point, a majority of the forecast area will miss this system`s rain. Instead, others may be able to pick up some precipitation from the trough/front, though this will be confined more so in the west. While overall precipitation coverage is still a tough "absolute" call for Saturday, increased cloud cover is a given at this point, which should hold temperatures below normal. Sunday sees the trough already out of the region and a ridge/high pressure returning. That means temperatures climb back up to near normal for the afternoon. Instability driven by diurnal heating should help provide the isolated opportunity for a shower or thunderstorm in the afternoon.
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&& .LONG TERM /MONDAY THROUGH THURSDAY/... As of 200 PM EDT Thursday Heat builds back in for the long term, storm chances toward the middle of the week... There is reasonable consensus among global models and their ensembles that the dominant feature early next week will be the subtropical ridge. The ridge is anticipated to build in westward and northward from the Atlantic Monday into Tuesday. This will usher in a period of sunny skies and warming temperatures, particularly Monday. The heat will continue to build on Tuesday in the area, but as instability increases the chances for isolated to scattered convection will rise. Any further focus for convection appears unlikely Tuesday, as heights are generally expected to remain around 594 dam with the mid-latitude temperature gradient further to the north. Although differences exist regarding modeled jet placement toward the middle of next week, both the ECMWF and GFS provide a bit more of a focus for convection on Wednesday, especially in the higher elevations. This is likely a product of shortwave troughs passing to the north of the CWA on Wednesday in both models, which would enable a weak frontal boundary to enter the northern and western zones. Temperatures in the Piedmont will remain in the low-to-mid 90s on Wednesday, where chances of precip are lower. The GFS tends toward more of a ridgeline convection scenario on Thursday, while the ECMWF is somewhat more progressive with higher rain chances across the lower elevations of the CWA. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/...
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As of 715 PM EDT Thursday... Mainly VFR conditions expected for nearly all TAF sites through the 24hr period. Showers/storms continue to move east, north of ROA/LYH this evening. Shower activity is expected to wane quickly after sunset with clouds decreasing tonight. Winds through the forecast period are expected to be light and variable... with stronger outflow gusts vcnty of any convection. Expecting patchy fog, some of it dense, and this will again mainly affect LWB. High pressure will keep the area dry Friday. VFR cloud bases will range between 6-8kft Friday. Extended Aviation Discussion... A frontal boundary will remain positioned SW-NE along the east coast of the U.S heading into the start of the weekend. Disturbances moving along the front will maintain periods of cloud cover and the chance for showers, especially towards DAN. Patchy fog is likely each morning from 09-13Z, particularly at LWB.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...SH NEAR TERM...RCS/SH SHORT TERM...RR LONG TERM...RR AVIATION...RCS/SH

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