Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Mar 07 2025 00:25:51 FOUS30 KWBC 070023 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 723 PM EST Thu Mar 6 2025 Day 1 Valid 16Z Thu Mar 06 2025 - 12Z Fri Mar 07 2025 ....A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF SOUTHERN CALIFORNIA... ....01Z update... Radar/satellite imagery indicate gradually increasing rain rates across portions of the Transverse Ranges in southern California. These rates increase somewhat while translating southeastward toward San Diego County and adjacent areas of the Peninsular Ranges as a stout mid-level wave migrates toward the region. The forecast remains on track, with areas of 1-1.5 inch rainfall totals expected (highest in terrain-favored areas). Minor flooding may result in a few areas. Cook ....16z update... Based on 12z Hi-Res solutions and trending for most direct impact/core of moisture flux mainly across San Diego county and points south in Mexico into the Peninsular Range, trimmed back the Marginal Risk exclude much of the LA Basin and lower foothills of the Transverse Ranges. Otherwise, thinking/rainfall totals in the 1-1.5" range remains on track that may result in minor flooding concerns mainly after 00z. Gallina ---Prior Discussion--- Trailing vorticity maxima analyzed off the coast of CA will rotate around the backside of the mean trough ejecting into the Southwestern U.S. A slight void in precipitation, outside some lingering showers will transpire this morning as the primary ascent focuses further inland. A trailing mid-level shortwave will motion east-southeastward into the southern portion of CA later this afternoon and evening with one last enhancement for scattered to widespread convection as the energy accompanies a more focused 850-700mb moisture flux as progged. The heaviest precip time frame will likely occur as the nose of the 700mb jet moves ashore near San Diego with the streaming westerlies working inland with low- level ascent maximized over the southern end of the Transverse Range down through the Peninsular Range just east of San Diego proper. Latest CAMs output is pretty consistent with the areal max hovering between 1-2" across the above locations with the highest situated closer to the Baja border just east of the SD metro. This is mainly due to the forecast orientation of the 700mb jet co-located within this small zone, a consistency among most of the deterministic suite this evening. PWATs will be generally near to just above seasonal for the anomalies (0.6-0.9"), but considering the previous period of rainfall with remnant burn scars being impacted currently, the continued rainfall will only maintain the potential for low-end flash flood exceedance. With the 00z HREF EAS/neighborhood probs nestled between 70-90% for at least 1" over the hardest hit locations in the Peninsular/Transverse domain, a continuation of the MRGL risk was still relevant given the characteristics above. Kleebauer Day 2 Valid 12Z Fri Mar 07 2025 - 12Z Sat Mar 08 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Otto Day 3 Valid 12Z Sat Mar 08 2025 - 12Z Sun Mar 09 2025 ....A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE CENTRAL GULF COAST... A fairly robust upper-low over the Southwestern U.S will pivot=20 eastward into the Southern Plains with multiple shortwave ejections crossing out of the Gulf with steady motion through the Gulf=20 coast. The proxy of the dynamic upper pattern will help to organize a surface low during the day on Saturday with most deterministic=20 depicting a low somewhere between the Sabine River to roughly the middle Texas coast for 00Z Sunday. Southerly flow ahead of the=20 mean trough will lead to the advection of warm, moist air=20 northward with the leading edge of deepest moisture at/near the=20 surface likely returning northward through the central and eastern=20 Gulf but not quite making it to land. Precipitable water values are forecast to rise into the 1.5 to 1.9" range along the east-central Gulf Coast on Saturday into Saturday night (standardized anomalies becoming 2+ for early March). Meanwhile, a well-defined cold front is expected advance southward through the lower Mississippi Valley and Gulf Coast states into=20 the northern Gulf from Saturday to Sunday morning. Low level=20 convergence at the leading edge of 925-850 mb moisture transport is forecast to align with the mean steering flow from west to east=20 along or near the Mississippi/Alabama coasts into the Florida=20 Panhandle. Forecast consensus of MUCAPE shows values of 500-1000=20 J/kg along the coast to ~150-200 miles inland which could support rainfall rates of 1 to 2 in/hr. Lift will likely be aided by upper level divergence within the right-entrance region of a 140-160 kt=20 upper level jet located from the lower Mississippi Valley to the=20 Mid-Atlantic coast. The GFS remains a northern outlier with the QPF max likely related to its faster and farther north depiction of a 500 mb low moving over Texas and Oklahoma compared to the remaining non GFS/GEFS based guidance. Trends with most of the deterministic models have=20 been south with QPF, aligning with the ML guidance placement. Deterministic QPF output is in the 1 to 3 inch range for the 24 hour period ending 12Z on the 9th, but the ECMWF has maxima closer to 4 inches. Meanwhile, the ensembles have been relatively=20 consistent over the past 24 hours of runs with only the GEFS=20 focusing QPF farther north.=20 Only minor adjustments were made to the previous Marginal Risk across the region with fairly dry antecedent conditions and typical higher flash flood guidance values a consideration for keeping the risk no higher than Marginal at this time. Localized flash=20 flooding will remain possible across this region but further=20 adjustments to the risk area will be likely as the event draws=20 nearer and hires model QPF becomes available. Otto/Kleebauer Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-WJ0TPekXujR19sQj_s0k5En4U7ul098jpxQO3IO43HR= qgRZtOjBrxu5dqoX---uxg6ZygT79yuEJh9dlI3ZbgJ-01w$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-WJ0TPekXujR19sQj_s0k5En4U7ul098jpxQO3IO43HR= qgRZtOjBrxu5dqoX---uxg6ZygT79yuEJh9dlI3ZoR_1_Hc$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-WJ0TPekXujR19sQj_s0k5En4U7ul098jpxQO3IO43HR= qgRZtOjBrxu5dqoX---uxg6ZygT79yuEJh9dlI3Zm9VhGY4$=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .