Weather Lookup

What Has Changed

Today's flood threat continues to fall as probabilities for the axis of heavier rain shifts southwest of the region. The long range outlook is fairly unchanged with variability on specific daily details limiting threat analysis. Updated for the 18Z taf issuance.

Key Messages

1) flash flood risk will continue to wane through friday morning as axis of heavier rain favors SE of the region.

2) active weather returns starting saturday into next week that could portend to increased flood risks.

Discussion

Key message 1... Latest analysis showers the main axis of low-level warm advection (around the 925mb height) that has been the focus for heavy rain shower and thunderstorm development NE of it is struggling to advance farther east than the in/oh border. Add in generally mostly cloudy skies for the region that limits the degree of destabilization, the risk for flash flooding is lowering as the next wave is more likely to produce light to moderate rain showers mainly W of i-79 and south of i-80. The threat remains non-zero given prior morning rain that saturated various localities and the continued presence of 95th+ percentile pwats, but the inability to foster additional development while maximizing their rainfall rates favors the lack of additional flooding concerns.

Surface high pressure behind the shortwave driving the oh convection currently will continue to shift north of the region through friday morning. This will push the nominal surface boundary southward and offer slightly cooler plus drier air for the rest of the day friday.

Key message 2... The reprieve in active weather will be short-lived as there is high confidence for more rounds of showers and thunderstorms starting saturday into early next week. This is due to the region generally sitting on the NE periphery of a lower mississippi to tennessee river valley high while a series of shortwaves traverse the ridge top. Additionally, warm, moist advection favors a return of the humid airmass characterized by anomalously high PWAT values ranging from 1.4"-1.9", all of which is above the 90th percentile. Though finer details vary model-to-model and day-to-day (some discussed momentarily), the broader messaging of this pattern lends to likely periods featuring showers/thunderstorm that carry an increased risk for flash flooding and, pending other environmental aspects, severe weather.

One component that can be expounded on more is the flash flood risk for the saturday night to sunday night 24-hour period. For reference, global models (notoriously weak on convective element depictions) suggest a setup that sees an mcs exiting the western great lakes towards the upper ohio river valley producing a large swath of rain. Current ensemble mean rainfall total values over this 24-hour period range from 0.75"-1.5" with the axis favoring the i-80 corridor. Pending the potential north/south re-positioning of this axis, high-end scenarios could see totals in the heaviest axis in the 2-3" range; any additional convective element boost theoretically could push that higher. Entering this period, the region already is fairly saturated with lowered flash flood guidance; any rain that develops after this initial window likely does with almost fully saturated grounds that sees a high percentage of rainfall translate to run-off (increasing flash flood likelihood). If confidence in these outcomes increase, flood watches may be issued in the coming days.

Aviation — 18Z Thursday Through Tuesday

Remnant low-level moisture across pa has kept varying MVFR decks into ports. More mixing closer to the warm sector across oh/wv has allowed for ample clearing in clouds. An area of stratiform rain is moving through central oh north of zzv but towards hlg/pit/agc. Light rain and continued MVFR restrictions have been included in these tafs. Zzv seems to be our only port with a shot remaining at thunderstorms this afternoon owing to its proximity to the warm sector. Rainfall is less certain at bvi (tempoed on the northern fringe) and lbe/mgw (prob30's late in the day possibly too far east and south). Cloud tops continue to warm on this activity and its survival into the late evening hours is in question. Rainfall likely slides south of fkl/duj where gradual cig improvement is expected this afternoon.

Rainfall is expected to dissipate and skies are expected to clear some after sunset this evening. This leaves US with clearing, light winds and a very moist surface likely opening the door for mist and fog. Models seem to favor low stratus paired with mist versus fog at this time but MVFR restrictions seem likely with drops to IFR and LIFR certainly possible.

Outlook... A gradual lifting of fog/stratus followed by improvement to VFR is likely friday under high pressure. Saturday night, restrictions are likely to return with an increased chance for showers and thunderstorms associated with an approaching disturbance.