Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Feb 21 2024 20:05:09 FOUS30 KWBC 212005 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 304 PM EST Wed Feb 21 2024 Day 1 Valid 16Z Wed Feb 21 2024 - 12Z Thu Feb 22 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. ....Southern California... The passage of a mid-level shortwave across southern California near 12Z this morning has lowered IVT values below 250 kg/m/s into the Transverse and Peninsular Ranges. While weak instability and low level onshore flow will likely continue to promote occasional showers tracking from west to east into far southern California and the Peninsular Ranges into the afternoon, the threat for flash flooding has fallen below the 5 percent threshold and the Marginal Risk has been removed with this update. Otto Day 2 Valid 12Z Thu Feb 22 2024 - 12Z Fri Feb 23 2024 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE OHIO VALLEY... Areas of heavy rain and embedded thunderstorms are expected to be ongoing over portions of northern Indiana into Ohio at the start of the period (12Z Thursday), located north of a weak warm front within a corridor of weak (<500 J/kg) MUCAPE. A surface low will track eastward across northern Indiana into Ohio during the day on Thursday with a trailing cold front extending southwestward. Precipitable water values are forecast by the 12Z model consensus to peak in the 1.0 to 1.2 inch range across the Ohio Valley (standardized anomalies of +2) with 850 mb winds exceeding 50 kt at times within the warm sector. The latest guidance shows left exit region ascent at the nose of a 130-150 kt jet streak aloft, translating eastward from the central Plains into the Tennessee Valley between 12Z Thu - 00Z Fri. Mean west-southwesterly flow in the LFC-EL layer and at 850 mb will have similar magnitudes, supporting the potential for repeating and training of any convective cells that develop. There is a broad, but low end threat for rainfall to exceed flash flood guidance from the confluence of the Mississippi and Ohio Rivers, eastward into much of Ohio and West Virginia to the west of the spine of the Appalachians. Peak rainfall rates of 0.5 to 1.5 in/hr will be possible (with the higher end of that range to the south and west where better instability will be present) and 3 hour totals of 1 to 2+ inches. Relatively modest total precipitable water and weak instability (MLCAPE generally less than 500 J/kg, MUCAPE generally less than 1000 J/kg area wide) should limit the potential for a greater flash flood risk. The threat looks to wane in the 00-06Z time frame on Friday as the cold front sweeps through the Ohio and Tennessee Valleys. Otto Day 3 Valid 12Z Fri Feb 23 2024 - 12Z Sat Feb 24 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Otto Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_JpaqpMiZBww0iyl6fkP2baktf5r5FwdenkS-qUeicYX= GyFxRXVWy1LRPvMCIG4hnUWvdvSo8AswiOWdiLkyUjZ2uak$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_JpaqpMiZBww0iyl6fkP2baktf5r5FwdenkS-qUeicYX= GyFxRXVWy1LRPvMCIG4hnUWvdvSo8AswiOWdiLkyF5ibTPI$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_JpaqpMiZBww0iyl6fkP2baktf5r5FwdenkS-qUeicYX= GyFxRXVWy1LRPvMCIG4hnUWvdvSo8AswiOWdiLkyHBUJ7kw$=20 $$ =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .