Area Forecast Discussion
Issued by NWS Charleston, WV
Issued by NWS Charleston, WV
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358 FXUS61 KRLX 261457 AFDRLX AREA FORECAST DISCUSSION National Weather Service Charleston WV 1057 AM EDT Thu Sep 26 2024 .SYNOPSIS... Daily chances for showers and thunderstorms continue this week in response to a stationary disturbance over the Ohio Valley and a tropical system sailing up from the Gulf coast. && .NEAR TERM /THROUGH TONIGHT/... As of 1051 AM Thursday... Sent a quick update to expand Flash Flood Watch now to include from Pocahontas, south through the eastern zone of Webster, Nicholas and Fayette, including all Raleigh and Wyoming counties until Friday evening. In addition, extended former Flash flood watch for McDowell, Buchanan and Dickenson until Friday evening. As of 245 AM Thursday... Cloudy skies with rain showers and periods of steady rain will be the theme for today. Thunderstorm probability is very low, therefore elected to leave mention of them out of the forecast. Cannot rule an isolated one out, but for the most part this period will endure stable stratiform rain. The rain could be heavy at times, especially across southern WV and southwest VA. Parts of these areas are under a flood watch still and we may need to expand the watch further north when day shift reevaluates. According to just the EURO we would likely expand as the plume of higher QPF does not change path too much and goes through Friday. Although other guidance seems to be on a slightly drier solution which justifies the reason to hold off for now. The pressure gradient will start to tighten later on in the evening in response to Hurricane Helene coming up from the south. This feature will raise winds to near advisory criteria along the peaks and ridges of southeastern WV and southwestern VA. Depending on the track, southerly flow looks to be the best solution which will create downsloping to enhance wind speeds across those mountains. Forcast soundings indicate 50KT+ at 2000FT elevation so a watch or an advisory may be needed. However, most guidance (other than the NAMDNG) is not indicating or showing any signal for high wind, therefore elected to pass this on to the next shift so they can evaluate with newer guidance. The time frame we are looking at is Friday at around 9Z to Saturday at 03Z. It looks like most of the QPF will fall along the southern half of our CWA and this is where the most rainfall has gathered in the past several days to where some locations have seen several inches of rainfall. Flooding will be the main threat today if these areas are inundated with more heavy rainfall or exceed certain rain rates which could lead to flooding issues from low lying areas, flood prone areas or even smaller creeks coming out of their banks. With all the cloud coverage expected and rain cooled air, temperatures were tweaked toward slightly lower than guidance with much of the area not expected to surpass the 75 degree mark, with slightly cooler temperatures in the mountains. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 430 AM Thursday... Key Points * The remnants of Hurricane Helene, coupled with a stationary system over the Ohio Valley, will promote periods of heavy rain on Friday and into this weekend. * An additional half an inch to an inch of rainfall is possible through Saturday. * A tightened pressure gradient inflicted by this system may yield strong wind gusts along the higher terrain Friday morning into the early afternoon. After Hurricane Helene makes landfall Thursday evening, the system will march northward through the Mississippi Valley and congeal with the stationary upper level low positioned just west of the forecast area. This transformation will continue to usher in a plethora of moisture up into Central Appalachia and maintaining active weather for Friday and into the start of the weekend. A resultant tightening pressure gradient from this stacked disturbance will impose strengthening winds in the low to mid levels, especially along the mountain range. One of the many challenging pieces with this forecast will be whether this strong winds aloft can be pulled down to the surface. Forecast soundings depict a predominantly moist profile, which could keep these stronger winds capped above, but could also be dragged to the surface with showers and potentially strong thunderstorms. The motion of Helene as the storm lifts over land will also dictate wind uncertainty as it takes a sharp western turn and becomes absorbed with a baroclinic system over the Tennessee Valley. Forecast offices to the south have already hoisted a High Wind Watch for their mountain range on Friday, but with some uncertainty still prevalent with gust potential, will hold off on jumping on headlines with this issuance. In regards to rainfall, the best opportunity for higher QPF amounts will occur Friday morning into the afternoon as Helene takes the aforementioned western trajectory across the southern Appalachians into the the middle Ohio Valley. An additional inch of rain could be achieved during this time through the Tug Fork river basin and up into the Ohio River Valley. Localized flooding is still feasible, but the higher flash flooding threat remains progged to be south of the forecast area down into the Tennessee Valley and Carolinas. At the start of the weekend, the tail end of precipitation associated with a nearby frontal boundary will detach from the Ohio Valley upper level low. The forecast area enters into a rain shadow period, where lessening POPs overtake the area as the low deepens southward and pivots showers further away to the west, and the eastern flank of moisture pushes offshore. However, this should be short-lived on Saturday as rejuvenated moisture wraps around the stacked upper level low and the system slowly drifts back to the east. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 430 AM Thursday... The second half of the weekend features the strong upper level disturbance becoming an open wave and slowly shifting into the Central Appalachians. Rain bands circulating the center of the system will become less impressive as the long term period marches on, but still could produce chance to likely (50-75%) POPs. This trend will hold through the first half of the work week as the open 500mb wave and the remnants of the surface low continues to pivot over the Mid-Atlantic region. The last batch of rain departs the forecast area late Wednesday night into Thursday, with the forecast becoming dry under establishing high pressure. Temperatures will be around seasonable for this time of year throughout the period, with afternoon highs ranging in the 60s along the higher terrain and mid to upper 70s across the lowlands. && .AVIATION /15Z THURSDAY THROUGH MONDAY/... As of 630 AM Thursday... For the most part, this period will generally accompany MVFR CIGs with some minimal VIS restrictions and temporary low stratus under heavier rain. Periods of fog will affect some of the sites with VIS restrictions and low stratus until 13Z-14Z (CRW/EKN). Thereafter, stratocu with rain showers will be the theme for the day with very low probability for thunderstorms, therefore elected to leave out mention in the TAFs. Winds will be fairly light and easterly except for down by BKW where winds will start to climb tonight in response to the Hurricane Helena coming up from the south. LLWS will certainly become a concern for Friday as intense upper level winds associated with Helena will cause llws if surface flow is weak. Currently, no sites will be affected if the forecast winds stay similar, but note that HTS/BKW will likely have some Friday morning if winds are less than anticipated. FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 12Z FRIDAY... FORECAST CONFIDENCE: Medium to high. ALTERNATE SCENARIOS: Timing and extent of low CIGs will vary somewhat from the forecast. EXPERIMENTAL TABLE OF FLIGHT CATEGORY OBJECTIVELY SHOWS CONSISTENCY OF WFO FORECAST TO AVAILABLE MODEL INFORMATION: H = HIGH: TAF CONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL. M = MEDIUM: TAF HAS VARYING LEVEL OF CONSISTENCY WITH MODELS. L = LOW: TAF INCONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL. UTC 1HRLY 15 16 17 18 19 20 21 22 23 00 01 02 EDT 1HRLY 11 12 13 14 15 16 17 18 19 20 21 22 CRW CONSISTENCY L H H M M M M H H H H H HTS CONSISTENCY H H H H H H M M M M H H BKW CONSISTENCY H H H M M M H H H H H H EKN CONSISTENCY L L L H H H H H H H H H PKB CONSISTENCY H H H H H H H H H H H H CKB CONSISTENCY L L L H H H H H H H H H AFTER 12Z FRIDAY... Brief, but repetitive periods of IFR conditions possible in showers and storms throughout the week and into the weekend. && .RLX WATCHES/WARNINGS/ADVISORIES... WV...Flood Watch through Friday evening for WVZ033. Flood Watch through Friday evening for WVZ034-515-516-518-520- 522>524. OH...None. KY...None. VA...Flood Watch through Friday evening for VAZ003-004. && $$ SYNOPSIS...MEK/JZ NEAR TERM...ARJ/JZ SHORT TERM...MEK LONG TERM...MEK AVIATION...JZ