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Area Forecast Discussion
Issued by NWS Blacksburg, VA
Issued by NWS Blacksburg, VA
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335 FXUS61 KRNK 161404 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1004 AM EDT Fri Aug 16 2024 .SYNOPSIS... High pressure slides off the coast this afternoon while a cold front approaches the Appalachians this evening. This front will be slow moving and will not exit our area until Sunday. && .NEAR TERM /THROUGH TONIGHT/... As of 1000 AM EDT Friday... No changes for the morning update. Key Message: Increasing chances for showers and storms this afternoon into tonight, mainly across the mountains. Some of the storms could bring torrential downpours. On the weather map, we have high pressure situated from the mid-Atlantic into the Carolinas. A warm front stretches from the Midwest into KY, with a cold front from Wisconsin to the southern Plains. Warm frontal showers are advancing across the Ohio Valley and will become more numerous across our western CWA this afternoon. The forecast today is a blend of models as they all seem to be in good agreement in bringing in showers/few storms to the mountains as shortwave energy shifts across the upper TN Valley. Upper flow become difluent to aid in lift and will be in the warm sector with increasing pwats and humidity. This should lead to any heavier storms to bring torrential downpours, so cannot rule out some localized flooding in the mountains, with less coverage into the Piedmont. As for severe storms, majority of models are keeping higher instability along/west of the Appalachians, so although a strong storm or two may occur, thing severe threat is low. Also cloud cover may inhibit instability this afternoon. Upper low will shift toward the Great Lakes tonight and our area remains in a difluent upper pattern, so appears showers/few storms will linger into tonight with best coverage still over the mountains. With more clouds today, but with southerly flow, highs will run close to normal with mid 80s east to mid 70s to lower 80s west. Increasing dewpoints, with showers and clouds will bring low on the muggy side about 5-10 degrees above normal tonight, with mid 60s to around 70 for most. Forecast confidence is above average, except average on clouds and pops. && .SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/... As of 130 AM EDT Friday... Key Points: 1. Good coverage of showers/storms Saturday and Sunday, especially areas west of the Blue Ridge. 2. Less coverage on Monday, still best coverage west of the Blue Ridge. 3. Locally heavy rain possible Friday through Saturday night. 4. Above normal temperatures on Saturday with values trending downward through Monday. A look at the 15 Aug 12Z NCEP Ensemble Mean 500 mb Geopotential heights shows a shortwave trough that moves from the western Great Lakes into the Lower Ohio Valley Saturday into Sunday. Sunday into Monday the trough amplifies as its trough axis becomes centered over the region. By late Monday night, the trough axis is slightly east of the region. At the surface, on Saturday morning, low pressure is expected to be over Michigan with an associated cold front trailing southwest into the mid-Mississippi Valley. By Sunday morning, the low is expected to be over Lake Erie with the cold front extending south into the eastern Kentucky and Tennessee. By Monday morning, the low is expected to be over central Pennsylvania with its cold front extending south to central or eastern Virginia/North Carolina. By late Monday night, the low is expected to be over New England with front just off the coast of the mid-Atlantic region of the US. Concurrently, high pressure will be centered over the Upper Mississippi Valley by late Monday night. Output from the 15 Aug 12Z Ensemble Situational Awareness Table shows 850mb temperatures across the region averaging +18C to +20C on Saturday, +15C to +17C on Sunday, and +13C to +15C on Monday. The low end of range of temperatures on Monday correspond to the 2.5 to 10 percentile of the 30-year climatology. Precipitable Water values on Saturday are expected to range from 1.50 to 1.75 inches, 1.25 to 1.50 inches on Sunday and Monday. The above weather scenario continues to offer a Saturday with increasing chances of showers and storms from west to east as the day progresses. Coverage wanes only slightly Saturday night with the best coverage remaining over western sections. On Sunday, a cold front crosses the region. The timing of the front across the region does not look to coincide with peak heating of the day. However, its presence will still act as a focus for shower/storm development. Additional coverage is expected during peak heating of the day in association with the approach and arrival of the parent upper trough. Coverage will be best across western sections. By Monday, the axis of the upper trough is expected to be over, or just east of the region. This will place the region within a northwest flow regime. Precipitation chances will be greatest over Southeast West Virginia, south into the Northern Mountains of North Carolina where the effects of upslope northwest flow will be the greatest paired with heating of the day. Daytime coverage should wane through the evening hours of Monday. Temperatures will be highest on Saturday and trend lower through the period. Confidence in the above weather scenario is moderate to high. && .LONG TERM /TUESDAY THROUGH THURSDAY/... As of 130 AM EDT Friday... Key Points: 1. Little to no precipitation. 2. Below normal temperatures. A look at the 15 Aug 12Z NCEP Ensemble Mean 500 mb Geopotential heights shows a trough just to our east Tuesday morning. Through Thursday, this feature is expected to decrease in amplification as is it retrogrades to back over the Lower Ohio Valley. At the surface, on Tuesday morning low pressure is expected to be over New England with front just off the coast of the mid-Atlantic region of the US while high pressure will be centered over the Upper Mississippi Valley. As we progress into Thursday, the front near the coast loses its depiction within the ensemble mean. However, high pressure shifts east and is centered over the central Appalachians by Thursday morning. Output from the 15 Aug 12z Ensemble Situational Awareness Table shows 850mb temperatures are expected to range from +12C to +14C on Tuesday. For many locations, especially northern parts of the region, the low end of this range corresponds to the 2.5 to 10 percentile of the 30-year climatology. For Wednesday, values are only slightly milder in the +13C to +15C range. On Thursday, values of +14C to +16C are forecast. Precipitable Water values are expected to range from 0.75 to 1.00 inch on Tuesday. The low end of this range across far Southwest Virginia and Northwest North Carolina will fall into the 2.5 to 10 percentile of the 30-year climatology. Values slowly increase through Thursday when values are expected to average 1.00 to 1.25 inches across the area. The above weather scenario offers primarily dry conditions through the period with below normal temperatures. Confidence in the above weather situation is moderate to high. && .AVIATION /14Z FRIDAY THROUGH TUESDAY/... As of 635 AM EDT Thursday... Overall forecast through the afternoon will be VFR but showers/storms could bring sub-VFR to the mountains. Less coverage in the Piedmont so keeping storms out of tafs for now at LYH/DAN. Ceilings are likely drop Friday night at all sites to MVFR east to IFR or lower in the mountains. Confidence is slightly above average except on storms impact/timing on individual airports. .EXTENDED AVIATION OUTLOOK... Slow moving front will keep scattered-numerous showers/storms around into the weekend with sub-VFR at times. Upper trough advances overhead by Monday so despite front being east, showers/few storms will likely occur in the heating of the day so anticipate some sub-VFR condition, but generally Sat-Mon outside of storms will be VFR and any late night fog. Confidence higher for dry and VFR Tuesday as high pressure builds in. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...WP NEAR TERM...PM/WP SHORT TERM...DS LONG TERM...DS AVIATION...WP