Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Jun 13 2025 01:01:04 FOUS30 KWBC 130100 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 900 PM EDT Thu Jun 12 2025 Day 1 Valid 01Z Fri Jun 13 2025 - 12Z Fri Jun 13 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF=20 THE NORTHERN PLAINS AND UPPER MISSISSIPPI VALLEY... ....Mid-Upper Texas Coast into the Lower-Mid Mississippi Valley... 01Z Update: As the shortwave slowly pivots towards and eventually=20 east of the ArkLaTex, broad-scale subsidence/NVA will push into the area from the west. This along with the general airmass=20 stabilization following the MCS earlier today will lead to a more=20 limited flash flood risk heading into the overnight period -- even=20 with some return low-level flow off the Gulf (albeit weak). The=20 latest CAM guidance, including recent HRRR and RRFS runs, are=20 fairly light with additional rainfall overnight along areas hit=20 hard earlier (Mid-Upper TX Coast); however, given the heavy=20 rainfall earlier and thus low FFG values, will maintain a Marginal=20 Risk area over what was a Moderate. Elsewhere, downstream of the slow-moving upper trough do anticipate a localized risk of flash flooding within the diffuse, secondary Warm Conveyor Belt off the Gulf and into the mid-level deformation axis/comma head pivoting across northern AR and southern MO.=20 Hurley ....Northern Plains... 16Z Update: Only minor adjustments necessary for the inherited SLGT and MRGL risk areas across the northern tier of the CONUS. The forecast remains steadfast overall with little deviation in the expected heavy rain axis to be located within the northern periphery of a strong 850mb FGEN band situated west to east across the Northern Plains into the Upper Midwest. 12z HREF EAS prob fields for at least 2" is pretty high (40-60%), which is a testament to the agreement within the CAMs suite on the placement of the heavier precip threat. Rainfall rates between 1-2"/hr will be common in the strongest convective cores, and with training potential elevated due to parallel alignment of the mean wind to the surface/low-level based forcing mechanism(s), this will lead to a narrow axis of 2-4" with locally up to 5-6" plausible over the course of the late-afternoon and evening time frames when the event takes shape. Isolated flash flood concerns will extend as far northwest as MT with remnant shortwaves and modest instability maintaining a persistent convective presence during the course of the period with the best chances likely developing after 19z. Kleebauer ....Southeast U.S... A combination of elevated moisture across the Southeast and strong differential heating away from the coastal plain will lead to a corridor of enhanced SBCAPE on the order of 2500-3500 J/kg across GA up through the Continental Divide in the Southern Mid Atlantic. Scattered to numerous thunderstorms with relatively slow storm motions will enhance locally heavy rainfall capabilities with rates between 2-3"/hr plausible in a few of the stronger cores. Urbanized zones within the region referenced above will be the most susceptible for flash flooding prospects with some of the latest CAMs going as high as 4-5" in some of the greater outputs anticipated. A MRGL risk is in place for the areas above with a minor expansion on the southern and western edge of the inherited risk. Kleebauer Day 2 Valid 12Z Fri Jun 13 2025 - 12Z Sat Jun 14 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF ARKANSAS... ....Arkansas/Mid-South... Slowly-moving upper low will be centered over the Ozarks Friday morning and drifting northeastward amid a very moisture-laden environment. Instability will remain modest as the cool core passes through, which will support another round of afternoon storms (following rainfall today) with rainfall rates of 1-2.5"/hr. Increase in LLJ overnight tomorrow night may again enhance some rainfall over the area, and have maintained the Slight Risk for excessive rainfall over the region with a small extension eastward/northeastward into the stronger IVT zone. Soils are wet and FFG values will lower today/tonight, leaving the area (especially in the hillier terrain) more susceptible to localized/scattered instances of flooding. With the wettest soils in Arkansas from about Little Rock west, this area was maintained in an internally-denoted higher-end Slight Risk. ....Mid-Atlantic/Carolinas... Expanded the Marginal Risk northward to near the PA border and westward into eastern West Virginia given an increase in QPF from the 12Z guidance. Frontal boundary sinking southward will stall over the region, acting as a focus for heavier rain and rates (1-2"/hr) where it has been rather wet coming out of May. Over VA into the Carolinas, PW values will remain elevated (1.75-2.00") and some localized flash flooding is possible. CSU Machine Learning ERO guidance shows a small Slight Risk area from near the DC Metro area southward, so this area will need to be watched further. ....Northern WI/Michigan U.P.... Area of low pressure moving eastward through MN may help drive a small risk for heavier rainfall over northern WI into the U.P. Friday morning, but instability is limited. ....Northern Rockies/Western High Plains... The Marginal from Montana to northeast Colorado was maintained with minimal changes along the western interface of the deeper moisture over much of the Plains. Fracasso/Wegman Day 3 Valid 12Z Sat Jun 14 2025 - 12Z Sun Jun 15 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM CENTRAL ARKANSAS THROUGH NORTHERN MISSISSIPPI... ....Arkansas through Alabama... After multiple days of shower and thunderstorm activity in this area, there should be some decrease in the organization of the overall shower and thunderstorm activity expected Saturday from Arkansas east through Alabama. Despite that decrease, very wet soils through Mississippi and a lingering frontal boundary providing some forcing should still lead to enough organization to support widely scattered instances of flash flooding. The Slight Risk area was maintained for Arkansas and Mississippi to capture the early morning rainfall potential and due to previous expected rainfall (and lower FFG values). Plentiful moisture over 1.5 inches of PWAT will still support any storms that do form to be capable of heavy rainfall. ....Mid-Atlantic... Maintained the Marginal Risk area much of the Midwest to Mid- Atlantic that remains in a moisture-laden environment near and south of a frontal boundary. Targeted upgrades to Slight Risks may be warranted pending rainfall distribution over the next two days (especially over areas that have above normal soil moisture). CSU Machine Learning ERO guidance does show a Slight Risk over northern VA so this will be monitored in future shifts. Fracasso/Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4xt_EiXqjGMNeX0mjrHnOcl4CZ6nN2zNWWTCkco5B8gI= 40EbKGw4WFsrOq6PfCJrvWv-vAIFs7kWmCXydtZOhM-WDQg$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4xt_EiXqjGMNeX0mjrHnOcl4CZ6nN2zNWWTCkco5B8gI= 40EbKGw4WFsrOq6PfCJrvWv-vAIFs7kWmCXydtZOQU1WjrE$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4xt_EiXqjGMNeX0mjrHnOcl4CZ6nN2zNWWTCkco5B8gI= 40EbKGw4WFsrOq6PfCJrvWv-vAIFs7kWmCXydtZOgYp0rQs$=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) .