Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Mar 06 2025 15:39:34 FOUS30 KWBC 061538 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1038 AM EST Thu Mar 6 2025 Day 1 Valid 12Z Thu Mar 06 2025 - 12Z Fri Mar 07 2025 ....A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF SOUTHERN CALIFORNIA... ....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=20 the Transverse Ranges. Otherwise, thinking/rainfall totals in the=20 1-1.5" range remains on track that may result in minor flooding=20 concerns mainly after 00z.=20 Gallina ---Prior Discussion--- Trailing vorticity maxima analyzed off the=20 coast of CA will rotate around the backside of the mean trough=20 ejecting into the Southwestern U.S. A slight void in=20 precipitation, outside some lingering showers will transpire this=20 morning as the primary ascent focuses further inland. A trailing=20 mid-level shortwave will motion east-southeastward into the=20 southern portion of CA later this afternoon and evening with one=20 last enhancement for scattered to widespread convection as the=20 energy accompanies a more focused 850-700mb moisture flux as=20 progged. The heaviest precip time frame will likely occur as the=20 nose of the 700mb jet moves ashore near San Diego with the=20 streaming westerlies working inland with low- level ascent=20 maximized over the southern end of the Transverse Range down=20 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. Kleebauer 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 eastward into the Southern Plains with multiple shortwave ejections crossing out of the Gulf with steady motion through the Gulf coast. The proxy of the dynamic upper pattern will help initiate surface cyclogenesis in-of the Gulf coast with most deterministic now developing a surface low just south of LA by the end of the D3 time frame. Southerly flow ahead of the mean trough will lead to the advection of more warm, moist air northward with the northern fringe notated by a developing warm front that is depicted when assessing the sfc-850mb wind field showing convergent flow in-of the boundary. Guidance is becoming more focused along the Gulf coast for the proxy of the boundary which will be key in determining the northern extent of the instability field which will be situated south of the aforementioned front. Trends within most of the deterministic and ensembles have now shifted further south with the heaviest QPF footprint, aligning with the ML guidance over the past 24 hrs that place the more significant theta_E tongue within the proximity of the Gulf coast area extending from southeastern LA over into the FL Panhandle. PWAT anomalies are pushing towards the +2 deviation marker, a threshold typically necessary this time of year to attain any flash flood threat due to the locally elevated FFG's within this area of the CONUS. Ensemble output of 1-3" is focused within the corridor extending from the Southeastern most Parishes of LA through the I-10 corridor, including places like Mobile, Pensacola, Panama City to as far east as Tallahassee. The ECMWF has been the most consistent with this forecast over the past several runs with the other global deterministic slowly shifting south with the primary axis of heavier QPF. Considering the better instability gradient closer to the Gulf coast, the best chance for heavier convection will likely lie in that warm sector south of the warm front, and within the convergent axis just inland within the bounds of the front placement. Steering flow is likely to align parallel to the front as the west-east placement will create a funneling affect for moisture within that zone of expected impact. The previous MRGL risk was trimmed on the northern and western extent and now encompasses a smaller region along the Central Gulf Coast, including the cities referenced above. This was also agreed upon by the local MOB/TAE WFO's representing the areas in question. Will assess the trends closely in the coming days, but the prospects flash flooding remain in reason to maintain some continuity. Kleebauer Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4ZipU2y6uPyls61UR3p2yYEB5XVI13eRzNrVxuAO0pFc= fhczstRfOTeU41e0wd-DfGZkIpDjfTmMjdUwxGtgYMAbQis$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4ZipU2y6uPyls61UR3p2yYEB5XVI13eRzNrVxuAO0pFc= fhczstRfOTeU41e0wd-DfGZkIpDjfTmMjdUwxGtgq_BG1_8$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4ZipU2y6uPyls61UR3p2yYEB5XVI13eRzNrVxuAO0pFc= fhczstRfOTeU41e0wd-DfGZkIpDjfTmMjdUwxGtgHnAuE5E$=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) .