Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Apr 01 2024 00:42:06 FOUS30 KWBC 010041 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 841 PM EDT Sun Mar 31 2024 Day 1 Valid 01Z Mon Apr 01 2024 - 12Z Mon Apr 01 2024 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTHERN CALIFORNIA, SOUTHERN ARIZONA, AND FROM CENTRAL-NORTHERN ILLINOIS INTO THE OHIO VALLEY... 0100 UTC Update -- Some expansion to the Marginal Risk areas were made across southwestern AZ and over northern portions of IL-IN-OH, based on the current observational trends (radar especially) along with most recent HRRR/HREF guidance. Otherwise across So. Cal., no changes were made. In all areas, the latest (18Z) HREF shows much higher areal probabilities of >.50"/hr rainfall rates, yet <25% probs of 1"/hr rates. Therefore, continue to expect any flash flooding to be isolated at best and more likely over the more flood prone areas (locations with locally lower FFG values), including burn scar areas over southern CA-AZ. Hurley Day 2 Valid 12Z Mon Apr 01 2024 - 12Z Tue Apr 02 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL EXTENDING FROM THE OZARK REGION NORTHEASTWARD ACROSS THE MID MISSISSIPPI VALLEY INTO THE OHIO VALLEY... 20Z Excessive Rainfall Discussion... Expanded the Slight Risk area a bit southward along the west face of the Appalachians where the combination of instability and low level orographic forcing may act to enhance rainfall amounts on Monday and Monday night. This occurred in spite of a fairly large north/south spread in QPF placement...so overall confidence is modest at this point but felt enough to warrant southward expansion. Still think the better chance for intense rainfall rates will be farther west in Missouri into parts of Oklahoma. Thinking was that dynamics that far and west should keep storms progressive enough to prevent more than isolated to widely scattered occurrences of excessive rainfall. Bann 08Z Excessive Rainfall Discussion... A well-defined shortwave moving through the base of the broader- scale trough in the Southwest will lift northeast, reaching the central High Plains by Monday evening. Amplifying southwesterly flow ahead of the wave will support increasing moisture advection into a region a strong ascent afforded by favorable upper jet forcing. The western portion of the outlook remains much the same, with training storms expected to develop initially along an axis of strong southwesterly inflow centered from eastern Oklahoma into Missouri and then further east along a slow-moving west-to-east boundary that will remain centered near the I-70 corridor. As the evening progresses, guidance indicates that convection will become more widespread along the front, with storms training through the Ohio Valley into the central Appalachians overnight. Deep southwesterly flow ahead of the wave will support increasing moisture through the evening, with PWs climbing to near 1.5 inches from the mid Mississippi into the Ohio Valley during the evening into the overnight hours. The models continue to move into better agreement, with several deterministic members showing a solid stripe of 1-2 inch areal average amounts extending from Missouri to northern West Virginia. Therefore, with confidence increasing, continued to bring the Slight Risk further east with this package, extending it along and north of the Ohio River into West Virginia. Pereira Day 3 Valid 12Z Tue Apr 02 2024 - 12Z Wed Apr 03 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE MID ATLANTIC AND ALONG THE CENTRAL AND SOUTHERN APPALACHIANS... 20Z Excessive Rainfall Discussion... Even though forecast reasoning remains similar as before, did expand the Marginal Risk area across portions of the Appalachians given uncertainty in whether or not there will be time for the atmosphere to recover for additional heavy rainfall given the sharp trough aloft. Also nudged the southern periphery of the Marginal southward. Overall, the progressive nature of the convection should limit the overall threat for widespread heavy rainfall and associated flash flooding concerns. Bann 08Z Excessive Rainfall Discussion... Models show the last of the convection developing over the Midwest on Day 2, moving east of the Ohio Valley and across the central Appalachians into the Mid Atlantic Tuesday morning into the afternoon. As these storms move offshore, a sharp trough will remain to the west, with strong, deep southwesterly flow supporting PWs increasing upward of 1.5 inches along a cold front trailing a rapidly deepening low that will be lifting into the Great Lakes. This will fuel the potential for heavy rainfall rates as storms develop and advance east from the Tennessee Valley into the Appalachians Tuesday afternoon into the evening. While heavy rainfall rates are expected, the progressive nature of the front will limit the threat for widespread heavy accumulations and flash flooding concerns. Pereira Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4bU75TWEEat8-2qgYVz97lwmHXsAJk-nBI4iDOOPHKcB= yWWvZEjQYG55pxyG2LDzSL-RhUolHA_hygkMUjg9SLeW0iM$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4bU75TWEEat8-2qgYVz97lwmHXsAJk-nBI4iDOOPHKcB= yWWvZEjQYG55pxyG2LDzSL-RhUolHA_hygkMUjg9f3C3oEs$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4bU75TWEEat8-2qgYVz97lwmHXsAJk-nBI4iDOOPHKcB= yWWvZEjQYG55pxyG2LDzSL-RhUolHA_hygkMUjg94cSS_K0$=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) .