Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Mar 03 2025 07:10:38 FOUS30 KWBC 030710 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 210 AM EST Mon Mar 3 2025 Day 1 Valid 12Z Mon Mar 03 2025 - 12Z Tue Mar 04 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHERN PLAINS... Robust convective development is expected tonight across portions=20 of north central TX into central OK along a cold front. As=20 impressive forcing (strong mid-level shortwave and upper-level=20 divergence) overruns this front convection should quickly develop=20 by 06z. Activity will likely organize into a line pretty quickly=20 and then track eastward across north TX and OK. The expected quick=20 eastward motion of the cold front will likely limit the extent of=20 the flash flood risk. However with a 50-60kt south southwesterly=20 low-level jet developing and deep layer flow largely parallel to=20 the front, there should be some opportunity for brief convective=20 training. While the duration of training will not be very long, it may locally be enough to exceed 2" in an hour of rainfall. Setups=20=20 like this tend to overachieve rainfall wise, and that will likely=20 be the case this time as well. Thus we still tend to think the new 00z HREF guidance is too dry (with the PMM suggesting localized totals of ~1.5"), and there may still be an uptick in model QPF in future runs (with totals in vicinity of one of the wetter models, the 00z GEM-Reg, still quite possible). Overall, not anticipating=20 a significant flash flood threat, but localized, mainly urban,=20 flash flooding is a possibility. Churchill/Chenard Day 2 Valid 12Z Tue Mar 04 2025 - 12Z Wed Mar 05 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE UPPER MIDWEST AND PORTIONS OF THE MID-SOUTH INTO THE SOUTHEAST... A pattern change will bring widespread precipitation to much of the Central and Southeast CONUS, as a cut-off low/upper-level trough and associated surface cyclone progress across the middle portion of the country. QPF maxima continue to be expected across two=20 general regions, in and around the Mid-South (primarily in=20 associated with precipitation from the broad open warm sector and=20 subsequent cold frontal passage) and much of IA into northern MO=20 (mainly from the pivoting low pressure center as it occludes).=20 While flash flood impact coverage should remain somewhat limited in both areas (low-end Slight risk probabilities) with relatively dry antecedent conditions and a rather progressive storm system=20 motion, the very dynamic nature of the system is still likely to=20 bring periods of strong convection with localized totals nearing=20 2". While a portion of the QPF over IA is likely to be in the form of snow on the back-end of the low, the expected 2" total will also be relatively long duration, as rates will be limited to 0.5"/hr=20 with a relative lack of instability. Over the Mid-South and Southeast, any localized 2" totals could occur over a much shorter period of time (as little as an hour) as instability which be much more plentiful. Barring any major changes in the forecast strength and progression of the storm system, impacts are likely to be=20 capped at the Slight threshold with continued refinement to the=20 outlook with the addition of more CAM data over the next day or so. Churchill Day 3 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... ....Southern California... A cyclone moving towards the region at the base of an amplifying=20 and progressive West Coast upper level trough brings precipitable=20 water values near the coastal ranges above 1", with 0.75"+=20 extending into the deserts. While the strength of the low-level=20 inflow is modest -- 25+ kts -- the system has some instability to=20 work with which could allow for hourly rain totals to reach 0.5",=20 which would be most problematic in burn scars. Overall totals=20 appear to be capped near 3". The inherited Marginal Risk appears=20 reasonable, so changes to the area depicted were minimal. ....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=20 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=20 the most recent QPF guidance and the ideas above, so changes to the area depicted were minimal. Roth Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4kyLDl3EZNXdXusUn3_Y81wJqMLJHWKLHdX4Vnpleuh2= Gdz3lQyKQR1-ZQO1mQ0za0PYSUHOJKBhU6Pb_qYu7_U5fDs$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4kyLDl3EZNXdXusUn3_Y81wJqMLJHWKLHdX4Vnpleuh2= Gdz3lQyKQR1-ZQO1mQ0za0PYSUHOJKBhU6Pb_qYuN3iDCO0$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4kyLDl3EZNXdXusUn3_Y81wJqMLJHWKLHdX4Vnpleuh2= Gdz3lQyKQR1-ZQO1mQ0za0PYSUHOJKBhU6Pb_qYuRTk4XfE$=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) .