textproduct: Charleston

WHAT HAS CHANGED

The Flood Watch has been extended for southeast Ohio and northwest West Virginia through Thursday morning to account for additional rounds of heavy rainfall tonight. The Flood Watch has been cancelled for the remainder of the forecast area due to lesser antecedent rainfall and lower convective training potential.

KEY MESSAGES

1. Repeated rounds of moderate to heavy rainfall tonight into Thursday will maintain a flood threat, particularly across southeast Ohio and northwest West Virginia where a Flood Watch remains in effect.

2. Anomalous warmth is expected Friday and Saturday, with afternoon temperatures nearing or exceeding daily records in the upper 70s to lower 80s.

3. A cold front crossing the region Saturday afternoon and evening will bring a threat for strong to severe thunderstorms. Damaging winds and an isolated tornado are possible, provided sufficient instability develops.

DISCUSSION

KEY MESSAGE 1...

As we move into tonight, a nocturnally enhanced low-level jet will develop and overrun the stalled boundary, providing focused ascent for widespread showers and elevated thunderstorms. The primary focus for the heaviest and most persistent precipitation tonight into early Thursday morning will be a southwest to northeast oriented band positioned across southeast Ohio and northwest West Virginia. This region is particularly vulnerable to runoff given significant rainfall over the past 24 hours that has resulted in saturated soils.

Flow aloft is oriented roughly parallel to the surface boundary, establishing a highly favorable kinematic setup for cell training. While deterministic NBM guidance suggests areal average accumulations near 1 inch through Thursday morning, persistent training of convective elements could easily yield localized totals approaching 2 inches. Rainfall rates exceeding 1 inch per hour in the heaviest convective cores will rapidly translate to surface runoff, overwhelming small basins and narrow hollows. Consequently, the Flood Watch has been extended in time for these northern and western counties. Further south and east, lesser antecedent rainfall and lower probabilities for convective training have allowed for the cancellation of the watch.

KEY MESSAGE 2...

Precipitation coverage will wane Thursday afternoon and evening as the frontal boundary finally lifts north as a warm front, placing the forecast area firmly within the warm sector. H500 ridging will amplify across the Southeast US and extend into the Ohio Valley on Friday and Saturday. Southwesterly surface winds of 10 to 15 mph will advect an unseasonably warm airmass into the region, setting the stage for near-record to record-breaking temperatures. NBM deterministic guidance pushes afternoon high temperatures into the upper 70s to lower 80s across the lowlands on both Friday and Saturday. Overnight lows will also be exceptionally mild, remaining in the 60s and likely exceeding record high minimum temperatures.

KEY MESSAGE 3...

The anomalous warmth and moisture will precede a potent cold front slated to cross the area Saturday afternoon and evening. Kinematic profiles are progged to be highly supportive of organized convection, with deep-layer shear parameters, such as Effective Bulk Wind Difference, approaching 40KTs across the western counties.

The primary forecast uncertainty revolves around the thermodynamic evolution. Extensive pre-frontal cloud cover or lingering morning showers could inhibit diurnal heating and limit destabilization. However, if sufficient clearing occurs and Mixed-Layer CAPE (MLCAPE) values can approach or exceed 1000 J/kg, a severe weather threat could materialize. Given the strong wind fields aloft, damaging downburst winds would be the primary hazard, exacerbated by steep low-level lapse rates and any enhanced Downdraft CAPE (DCAPE). Additionally, adequate 0-1 km storm relative helicity in the vicinity of the front would introduce a threat for an isolated tornado.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

Widespread MVFR with pockets of IFR conditions exist at this hour, with the lowest ceilings across the north. Conditions should roughly remain status quo through this evening. A nocturnally enhanced low-level jet will then trigger another wave of moderate to heavy showers and elevated thunderstorms tonight, primarily impacting PKB, but could extend as far as CRW/HTS and CKB. Visibilities will quickly drop below 3 miles in heavier convective cores, while ceilings will remain trapped around 1000 ft AGL for much of the period across all sites. Surface winds will generally remain light and variable or lightly out of the south at 5 to 10 KTs, though locally erratic and gusty winds are possible in the vicinity of thunderstorms.

FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 18Z THURSDAY... FORECAST CONFIDENCE: Medium.

ALTERNATE SCENARIOS: The exact placement and duration of the heaviest convective bands tonight remain uncertain. Terminals that experience direct hits from training thunderstorms could see visibilities drop below 1 mile for longer durations than currently anticipated.

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 17 18 19 20 21 22 23 00 01 02 03 04 EST 1HRLY 12 13 14 15 16 17 18 19 20 21 22 23 CRW CONSISTENCY H H H H H H H H H H H H HTS CONSISTENCY H H H H H H H H H H H H BKW CONSISTENCY H H H H H H H H H H H H EKN CONSISTENCY H H H H H M L H H H H H PKB CONSISTENCY M H H H H H H H M M H H CKB CONSISTENCY M H H H H H H M L H H H

AFTER 18Z THURSDAY... Unsettled conditions with periodic IFR restrictions in showers and thunderstorms will continue through Friday morning as the frontal boundary lingers.

CLIMATE

Near record maximum high temperatures and maximum low temperatures are forecast for Friday and Saturday.

RLX WATCHES/WARNINGS/ADVISORIES

WV...Flood Watch through Thursday afternoon for WVZ007>011-017-019- 020. OH...Flood Watch through Thursday afternoon for OHZ066-067-075-076- 083>086. KY...None. VA...None.