Area Forecast Discussion
Issued by NWS Blacksburg, VA

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685 FXUS61 KRNK 272328 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 728 PM EDT Tue Jun 27 2017 .SYNOPSIS... Cool and dry high pressure will be in control of our weather pattern through at least Thursday. Our weather will turn a bit wetter and milder Friday into, and through the weekend with the approach and arrival of a cold front. Our weather pattern may stay active into early next week as the frontal boundary stalls over or near the region. && .NEAR TERM /THROUGH WEDNESDAY/... As of 200 PM EDT Tuesday... The axis of an upper level shortwave trough is currently entering the area. A jet streak on the east side of this feature is currently bringing some mid to high level clouds across the area, all while diurnal cumulus blossom. So far, none or few of these cumulus have continued to develop into the congestus stage. Our current forecast for isolated showers across the mountains is probably leaning on the more optimistic side of formation. However, none are currently forecast, nor will they be forecast for, the start of the new TONIGHT period of the forecast. Overnight, we expect skies to trend mostly clear to clear from west to east. First the cumulus will dissipate around sunset, and then the mid to high level clouds will exit with the translation of the upper trough to the East Coast. Temperatures tonight will be on the cool side thanks to good net radiational cooling, light or calm surface winds, and boundary layer dew points already in the 40s across much of the area. Two of our climate sites are expected to experience a low temperature close to record levels, Bluefield, WV and Lynchburg, VA. Others are expected to have lows about five to seven degrees above the record. Please see the CLIMATE section of this discussion for details. Low temperatures tonight will range from the mid to upper 40s across the mountains with some sheltered and elevated areas closer to the lower 40s. Across the Piedmont, lows around 50 to the lower 50s will be more common. For Wednesday, high pressure will control our weather pattern with cooler and drier conditions in place across the region. Any cloud cover should be limited to a few cumulus across the mountains with sunny skies likely across the Piedmont. High temperatures will range from the mid to upper 70s across the mountains, with higher and sheltered area a little cooler in the lower 70s. Across the Piedmont expect highs around 80 to the lower 80s. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/... As of 240 PM EDT Monday... The medium range models are in good agreement that an upper level ridge builds over our area during this period, bringing a return to warmer and more humid conditions. With a large sfc ridge axis over the region Thursday morning and light winds along with most clear skies, went a couple of degree below guidance Thursday morning. On Thursday, the surface high continues to migrate east resulting in a light southerly flow by late in the day. While there is some modest recovery in PWAT values, forecast values are still expected to be 75-100% of normal. With forecast raobs keeping a low level dry profile, a large portion of our region will remain dry. However, some low level moisture return into NW NC by late in the afternoon could spark isolated to widely scattered showers/storms. Temperatures Thursday will be warmer, and with a downsloping flow kept highs a couple of degree above guidance. The more impressive surge of moisture arrives Thursday night and Friday, which may contribute to some low clouds and patchy fog Thursday night, along with warmer temperatures. The models have been consistent with the idea of a weak disturbance coming out of the western Gulf of Mexico and undercutting the upper ridge, moving toward our region on Friday. This weakness combined with increased instability should generate widely scattered to scattered storms Friday with high temps near average for late June. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... As of 200 PM EDT Tuesday... During this period of the forecast, our region will be between a large upper ridge off the southeast U.S. coast and an upper trof that pushes east from the upper midwest Saturday, into eastern Canada into New England by Tuesday. This will result is series of upper level disturbances moving over area and keeping a daily chance of afternoon and evening showers and storms. The long range models all show differences in timing and strength of these systems, but the GFS appears to show slightly more run to run consistency, especially later in the long term period. The best chance for showers and storms during the long term period will be Saturday as a surge of higher PWAT air that the GEFS indicates in about 2 standard deviations above normal move into areas east of the Blue Ridge. The GFS and ECMWF indicate an upper level wave entering the west late on Saturday. By Sunday, there is modest agreement that a sfc boundary (likely not the true cold front) moves into our area bringing slightly drier air. Therefore kept lowest POPS on this day of the period. Monday and Tuesday a low level south flow is re-established pushing up dew points/PWAT values/instability (especially Monday). All the long range models and ensembles hint that at least one upper level wave moves through sometime during this time which may result in slightly more organized convection Monday. With 850mb temps climbing to 1-2 standard deviations above normal late in the period (Monday-Tuesday), went a degree or two above guidance during this time. These temps combined with higher humidity levels will likely push heat index values at least into the mid 90s in the east for the first half of the week including the 4th of July. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
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As of 725 PM EDT Tuesday... Cu field will dissipate with loss of heating this evening and expect VFR all sites this TAF period as high pressure settles over the area. Expect very good radiational cooling tonight, but given low dew points and dry antecedent conditions expect fog to be confined to river valleys with no fog/stratus affecting airfields. Good flying conditions will continue into tomorrow with light winds and just a few fair weather Cu and cirrus around. Extended Aviation Discussion... VFR conditions expected through at least early Friday. Small chance of patchy late night/early morning mountain or river valley fog. Friday afternoon through Sunday, especially Saturday, showers and storms return to the forecast as well as an increase in low level moisture in general. Anticipate better chances of sub-VFR ceiling and visibilities. Most of these during the day will be temporary, associated with conditions immediately under any of the stronger showers and storms. Overnight, chances of MVFR/IFR late night/early morning fog will be greater.
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&& .CLIMATE... As of 220 PM EDT Tuesday... Record Low Temperatures for June 28th Blacksburg, VA...40 in 1970 Bluefield, WV....48 in 1987 Danville, VA.....48 in 1987 Lynchburg, VA....51 in 1987 Roanoke, VA......48 in 1927 && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...DS NEAR TERM...DS SHORT TERM...PH LONG TERM...PH AVIATION...MBS/DS CLIMATE...DS is the U.S. government's official web portal to all federal, state and local government web resources and services.