Area Forecast Discussion
Issued by NWS Blacksburg, VA
Issued by NWS Blacksburg, VA
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369 FXUS61 KRNK 231907 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 307 PM EDT Mon Sep 23 2024 .SYNOPSIS... High pressure is situated across the Mid-Atlantic today, wedged against the eastern face of the Appalachians. A slow-moving cold front will meander along the Ohio River Valley over the next several days, triggering rounds of showers and thunderstorm activity that will persist through much of the workweek. PTC 9 lifting northward from the Gulf of Mexico toward the end of the work week may bring more widespread rainfall to the region. && .NEAR TERM /THROUGH TONIGHT/... As of 300 PM EDT Monday... Key Messages: 1) Rounds of widely scattered showers and thunderstorms mainly impacting the mountains during the afternoon and into the evening are expected today. 2) Additional rounds of showers and thunderstorms are expected again on Tuesday, with another marginal risk for excessive rainfall forecast across a majority of the forecast area. A marginal risk for severe thunderstorms is also forecast across western portions of the forecast area for Tuesday. 3) Cloudy conditions again tonight are expected with patchy fog and periods of drizzle. A mid-level shortwave vorticity perturbation is expected to push across the region late Tuesday afternoon and evening. This coupled with a stalling cold front west of the Appalachian mountains, and an upper level trough digging into the mid- Mississippi valley will provide sufficient upper level support/forcing for ascent for widespread shower and thunderstorm developing Tuesday afternoon. A surface wedge situated across the coastal plain will lead to southeasterly flow across the VA/NC border during the afternoon and evening hours on Tuesday. Current CAM guidance suggests that a warm front will remain situated along or just north of the VA/NC border tomorrow, which may provide a focus for severe weather, and training thunderstorms. The biggest caveat will be the placement of this boundary Tuesday afternoon, and the amount of clearing south and west of this boundary to allow for destabilization. WPC currently has an areawide marginal risk for excessive rainfall on Tuesday as widespread rainfall totals of 1-2 inches are forecast. SPC similarly has a marginal risk for severe thunderstorms for much of the western portion of the area where destabilization is expected to be greatest. Overall, expect highs in the upper 70s where clearing occurs across SW Virginia and the VA/NC border, and low 70s to upper 60s where low clouds hang around across interior Piedmont locations. Confidence in the near term is moderate. && Short Term .../TUESDAY NIGHT THROUGH THURSDAY NIGHT/ As of 215 PM EDT Monday... Key Messages: 1: Daily showers and storms 2: Potential for outer bands of PTC9 to bring further rain Thursday A glacially slow cold front attendant to a low in the southern Great Lakes will continue its march to the east in our direction. The southerly flow will fetch plenty of Gulf moisture to interact with a stationary front over the Mid-Atlantic, leading to showers and storms for most of the day through Wednesday evening. Wednesday there is a marginal risk of severe storms west of the Blue Ridge, where orographic effects could enhance the freely available moisture and moderate instability into stronger convection. Main threat would be damaging thunderstorm winds. Localized flooding may also be a concern, as PWATs will be in the 1.5-1.75" range for most of the CWA, and storms in this environment have been observed to be extremely efficient rain producers. This problem could be exacerbated by freshly fallen leaves as we are getting into the fall season, which could be piled up from the aforementioned thunderstorm winds. This can clog drains and sewer openings, preventing runoff in streets and sidewalks. By Thursday evening, we may be close enough to feel the impacts of Potential Tropical Cyclone 9`s outer rain bands. PTC 9 is progged to be quite a wide storm, so even though the center of the storm (according to the current NHC track) will be near the panhandle of Florida, the outer rain bands (and tropical moisture to interact with the pre-frontal environment) could impact our NC counties as early as Thursday evening. Temperatures will be around normal, with little diurnal sway due to high dewpoints and widespread thick cloud cover. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 200 PM EDT Monday... Key Messages: 1) Confidence is increasing that Potential Tropical Cyclone Nine will affect the area Friday into the weekend, though exact impacts remain uncertain. 2) Rainy, cloudy, and breezy conditions will persist and keep below average high temperatures in place through the weekend. High pressure over New England and the Great Lakes region will begin to back out of the area on Friday, as PTC9 moves northward towards our area. This high pressure, along with a cutoff upper-level low over the Great Plains will steer PTC9 towards the northwest. Where this turn occurs is still uncertain and will determine the magnitude of impacts seen across the RNK CWA. Most model ensembles continue to indicate the center of the low somewhere in the southern Appalachian Mountains on Friday, but the past few model runs have not been consistent with the track post-landfall, varying east to west. Should the current forecast track continue with the storm moving into far western North Carolina, heavy rainfall will be expected across the CWA on Friday into Saturday as models are consistently showing a band of rain spreading over the area. Regardless of the exact track of the system, moisture is expected to increase with showers possible each day through the period. PoPs have been raised to reflect recent model runs and taking into account that a tight gradient between the low pressure system to the south and the high pressure system to the north will allow strong easterly upslope flow to further enhance rainfall across the area. This setup will continue into Saturday, though PTC9 will weaken as dry air begins to overtake the system. The aforementioned high pressure over New England will wedge back in on Saturday, keeping cloudy and cool conditions in place, but decreasing rain chances. Showers remain possible Sunday into Monday, though Monday is trending drier. Highs throughout the period will generally be in the 60s and low 70s, with breezy conditions persisting. Low temperatures will remain mild, around 60 degrees this weekend before lowering into the 50s next week. && .AVIATION /19Z MONDAY THROUGH SATURDAY/... As of 130 PM EDT Monday... MVFR to IFR CIGs are still present across much of the Piedmont this afternoon. Some drier air aloft is trying to sneak into the region from the west, and is aiding in VFR conditions at BLF, BCB, and LWB; however, it is unlikely to reach LYH and DAN. ROA may lift to VFR conditions briefly this evening before quickly dropping back into MVFR to eventually LIFR CIGs during the overnight hours. All sites are expected to drop to LIFR CIGs during the overnight hours before some breaking/lifting in the clouds across the VA/NC border lifts north throughout the afternoon on Tuesday. EXTENDED AVIATION OUTLOOK... MVFR/IFR stratus and fog are expected to occur in rounds through at least the middle of the week, and increasingly likely to persist through the end of the workweek. Rounds of showers and thunderstorms will also continue to pass across the lower Mid- Atlantic. Low pressure lifting northward from the Gulf of Mexico toward the end of the week may bring more widespread rainfall and sub- VFR conditions to the region. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...NF NEAR TERM...EB SHORT TERM...VFJ LONG TERM...JCB AVIATION...EB/NF