Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Mar 05 2025 01:01:27 FOUS30 KWBC 050101 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 801 PM EST Tue Mar 4 2025 Day 1 Valid 01Z Wed Mar 05 2025 - 12Z Wed Mar 05 2025 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF THE MID SOUTH AND SOUTHEAST TO THE TENNESSEE VALLEY AND SOUTHERN APPALACHIANS... ....0100 UTC Update... Deep low pressure across the east-central Plains, 988 mb at the surface, is accompanied by a well-defined Warm Conveyor Belt or WCB now displaced well east of the mid-level circulation and continues a fairly rapid easterly progression. The quick eastward movement of the axis of deeper moisture (axis of 1.5"+ TPW), along with the weakening trends with time overnight (strong W-E negative TPW advection), and overall limited deep-layer instability outside of along the Gulf Coast where the convective line(s) are quite narrow, will result in a limited ERO threat during the remainder of the Day 1 period. Isolated pockets of 1.5-2.0+ inches within an hour, especially within any supercells that develop, may lead to at most localized areas of flash flooding. Hurley Day 2 Valid 12Z Wed Mar 05 2025 - 12Z Thu Mar 06 2025 ....A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF SOUTHERN CALIFORNIA AND THE NORTHEAST... 2100 UTC update...no changes made to the previous marginal risk areas over CA or the northern Mid-Atlantic into Southern New England. Oravec Previous discussion... ....Southern California... A cyclone moving towards the region at the base of an amplifying and progressive West Coast upper level trough brings precipitable water values near the coastal ranges above 1", with 0.75"+ extending into the deserts. The strength of the low-level inflow has weakened from what was seen in the guidance from 24 hours ago, except in eastern sections of the Transverse Ranges, the Peninsular Ranges, and upslope areas of the Sierra Nevada. The system has some instability to work with which could allow for hourly rain totals to reach 0.5", which would be most problematic in burn scars. Overall totals appear to be capped near 3". The inherited Marginal Risk was pared back a bit across the western Transverse Ranges and coastal ranges north of Lompoc from continuity. ....Northern Mid-Atlantic States/Southern New England... A progressive deep layer cyclone moves through the Great Lakes into Southeast Canada, bringing of shot of 60 kt inflow at 850 hPa into the region with precipitable water values rising to 1-1.25". Portions of PA, NY, and the southern coast of New England appear to have some instability to work with, as MU CAPE of 250-500 J/kg is forecast to be available. Along with low- to mid-level frontogenesis, hourly rain totals to 1.25" should be possible. While most of this area has had below average precipitation this past week, a good portion of New England north of CT/RI/southeast MA have 1-2" of snow water equivalent on the ground, so melting snow should be occurring as well, considering the strength of the warm air advection which could raise both temperatures and dew points well into the 40s. The inherited Marginal Risk both fits the most recent QPF guidance and the ideas above, so changes to the area depicted were minimal. Roth Day 3 Valid 12Z Thu Mar 06 2025 - 12Z Fri Mar 07 2025 ....A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF SOUTHERN CALIFORNIA... 2100 UTC update... No changes made to the previous marginal risk area over CA. Oravec Previous discussion... ....Southern California... Sufficient low-level inflow from the Pacific, as high as 40 kts or so, combined with small amounts of instability and precipitable water values of 0.5-0.75" appear sufficient for hourly rain totals to rise towards 0.5" an hour, so left the Marginal Risk from continuity reasonably intact. It is expected to be the relatively cold atmosphere, so heavy snow is possible within the risk area in the higher peaks. The main flash flood risk would be to areas with burn scars. Roth Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9z7sPTIoPloiqM71hAj8StRYqfRHjRgmmTd7_A1Fgco-= qjOGNZOi5tB60Ts2HxT6TUWfN-_W16_BITfb220z1GC0-xo$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9z7sPTIoPloiqM71hAj8StRYqfRHjRgmmTd7_A1Fgco-= qjOGNZOi5tB60Ts2HxT6TUWfN-_W16_BITfb220zJJG2fCI$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9z7sPTIoPloiqM71hAj8StRYqfRHjRgmmTd7_A1Fgco-= qjOGNZOi5tB60Ts2HxT6TUWfN-_W16_BITfb220zHr24bb4$=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) .