Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Mar 03 2025 00:36:01 FOUS30 KWBC 030035 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 735 PM EST Sun Mar 2 2025 Day 1 Valid 01Z Mon Mar 03 2025 - 12Z Mon Mar 03 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. An instance or two of flash flooding may occur over and in the=20 immediate vicinity of fresh burn scars across portions of California mainly this evening as widely scattered showers capable of=20 producing rainfall rates in excess of one-quarter of an inch per=20 hour move across the area. Forward speed of the showers and limited rainfall rates should preclude concern for excessive rainfal away=20 from those areas with hydrologic sensativity. Bann Day 2 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 Monday night across portions of north central TX into central OK along a cold front. As impressive forcing (strong mid level shortwave and upper level divergence) overruns this front convection should quickly develop by 06z. Activity will likely organize into a line pretty quickly and then track eastward across north TX and OK. The expected quick eastward motion of the cold front will likely limit the extent of the flash flood risk. However with a 50-60kt south southwesterly low level jet developing and deep layer flow largely parallel to the front...there should be some opportunity for brief convective training. Not a long duration of training, but possibly enough to locally exceed 2" in an hour rainfall. More often than not setups like this tend to overachieve rainfall wise, and think that will likely be the case this time as well. Thus tend to think the 12z HREF guidance is too dry, and would expect to see an uptick in model QPF in future runs...with totals in the vicinity of the 12z Gem Reg (currently one of the wetter models) quite possible. Overall, not anticipating a significant flash flood threat, but localized, mainly urban, flash flooding is a possibility. Chenard Day 3 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 LOWER MISSISSIPPI VALLEY AND TENNESSEE VALLEY... 20z Update: Cut back some on the northern end of the Slight risk over portions of MO/KY and TN with this update where forecast rainfall magnitudes and rates are trending downward. The new Slight risk area is confined to where the better potential for higher convective rainfall rates is expected to reside. Even here this likely remains a lower end Slight risk given limited instability and fast forward convective motions. However enough large scale forcing and low level moisture transport to still support the potential for some 2"+ per hour rainfall rates within the stronger convective line, which could begin to locally approach/exceed FFG. The Slight risk over IA and MO was slightly realigned and trimmed back on the northwest side where a transition to snow is likely. Overall this risk area also remains lower end given weaker instability and rainfall rates. However there is some opportunity for greater than 0.5" per hour rainfall Tuesday as some elevated instability works into the area, followed by a prolonged period of steady rainfall. With event total rainfall of 2-3" possible, some minor flood issues could arise. Chenard ....Previous Discussion... 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 are expected across two general regions, near the Mid-South (primarily in associated with precipitation from the broad open warm sector and subsequent cold frontal passage) and much of IA into northern MO (mainly from the pivoting low pressure center as it occludes/matures). 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 motion, the very dynamic nature of the system is likely to bring strong convection with localized totals nearing 2" in a short period (though a portion of the QPF over IA is likely to be in the form of snow on the back-end of the low). Barring any major changes in the forecast strength and progression of the storm system, impacts are likely to be capped at the Slight threshold with better refinement of the areas impacted with the addition of CAM data over the next couple of days. Churchill Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7fn-BiNBBrNPdQwKdydmhcwArnz3op4223KZS_SBBcQS= BkD-9aYtFnxV4odPNOJtkoR_P5xFbqGjm1kyo4-sSSHkIiM$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7fn-BiNBBrNPdQwKdydmhcwArnz3op4223KZS_SBBcQS= BkD-9aYtFnxV4odPNOJtkoR_P5xFbqGjm1kyo4-sDzIlSA4$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7fn-BiNBBrNPdQwKdydmhcwArnz3op4223KZS_SBBcQS= BkD-9aYtFnxV4odPNOJtkoR_P5xFbqGjm1kyo4-sR0KEE24$=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) .