Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Apr 16 2025 22:34:41 FOUS30 KWBC 162234 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 634 PM EDT Wed Apr 16 2025 Day 1 Valid 01Z Thu Apr 17 2025 - 12Z Thu Apr 17 2025 Across KS and MO, the 18z HREF indicates a couple convective complexes moving across the region overnight that remain progressive. They=20 are capable of producing hourly rain totals to 1.5"" overnight=20 should there be enough cell coverage for mergers or training. Given the effective bulk shear, mesocyclones cannot be ruled out either. However, the probabilities of 2" or 3" within a 12 hour period are quite low -- all the precipitation expected could fall within an=20 hour -- and flash flood guidance values are rather high as the=20 region has seen below average precipitation in most spots over the=20 past week/two weeks/month. Therefore, the probability of rainfall exceeding flash flood=20 guidance is less than 5 percent. Roth Day 2 Valid 12Z Thu Apr 17 2025 - 12Z Fri Apr 18 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Bann Day 3 Valid 12Z Fri Apr 18 2025 - 12Z Sat Apr 19 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF CENTRAL AND NORTHEASTERN OKLAHOMA INTO SOUTHWESTERN MISSOURI... 2030Z Excessive Rainfall Update... Expanded the Slight and Marginal Risk areas a bit eastward to cover more of the possible solutions suggested by the 12Z suite of numerical guidance QPF. The expansion covers the possible rainfall enhancement from any interaction between the low level jet and the complex terrain of the Ozarks/Boston Mountains should the placement of the low level jet shift a bit in future model runs. Also expanded the Marginal risk a bit closer to the ArkLaTex region given the QPF amounts shown by the GFS/ENSQPF. Overall...the changes were fairly small (from a national perspective) and did not reflect a significant shift in forecast reasoning. Previous Excessive Rainfall Discussion... A large and very positively tilted longwave trough extending from the Northern Plains down into the Southwest/4 Corners Region will slowly press eastward towards the Southern Plains on Friday. As this forcing encroaches across the Plains, it will run into a very well established southwesterly LLJ extending from the far western Gulf (and really the Caribbean before that) northward across central Texas and then northeast into the Midwest. For much of the day Friday, the forcing to the west and the LLJ will be sufficiently separated so as to not result in much precipitation over the Slight Risk area. However, come late Friday afternoon through the overnight, that will change as the longwave trough moves east and an embedded shortwave rides the base of the trough and digs eastward, locally increasing the upper level divergence (and therefore forcing), needed to initiate and maintain both convection and a broader rainfall shield around it. Thus, expect thunderstorms to break out along and ahead of the jet with a supporting surface cold front slowly pushing southeastward. As the LLJ runs into the front, storms will rapidly develop northeastward along the front, then train northeastward one after another as the LLJ restores the moisture used up by the storms in the form of heavy rainfall. There is good agreement that the I-44 corridor from Tulsa to Joplin will be the area at greatest risk for heavy rainfall through Friday night, though storms may continue to backbuild down to the Oklahoma City metro, and will persist eastward towards St. Louis. There is good agreement in the guidance that this scenario will unfold, but less agreement on where this corridor of training storms will set up, with the I-44 corridor being the broader consensus. Thus, expect the Slight Risk area to shift with future updates. Should this corridor shift southeastward, the heaviest rain will align better with the area hard hit by the historic rainfall just 2 weeks ago, and while conditions have significantly improved due to the recent dry weather, a repeat hit may cause worsened impacts with recovery still occurring in the area. It's possible a further upgrade to a Moderate Risk may be necessary with future updates. However, should the corridor remain along I-44, urban concerns in Tulsa, Joplin, and the Fayetteville/Bentonville area may locally increase the impacts from the heavy rain. Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!84HYqRpcO48zSBGvpLbZMAkAV8hBzkAUECg5oG45QiAm= zWVysK7wV97V59o0zu2jVblr3f1ysojRA4Fsk4XPrn6ihkk$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!84HYqRpcO48zSBGvpLbZMAkAV8hBzkAUECg5oG45QiAm= zWVysK7wV97V59o0zu2jVblr3f1ysojRA4Fsk4XPc5pUubQ$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!84HYqRpcO48zSBGvpLbZMAkAV8hBzkAUECg5oG45QiAm= zWVysK7wV97V59o0zu2jVblr3f1ysojRA4Fsk4XP2SKl1YE$=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) .