Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Dec 18 2022 19:19:03 FOUS30 KWBC 181918 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 218 PM EST Sun Dec 18 2022 Day 1 Valid 16Z Sun Dec 18 2022 - 12Z Mon Dec 19 2022 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Campbell Day 2 Valid 12Z Mon Dec 19 2022 - 12Z Tue Dec 20 2022 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY AND CENTRAL GULF STATES... 21Z update... Overall the environment remained nearly the same from the previous forecast cycle however the QPF along the immediate Gulf Coast did increase and expand west-east from southeast Texas to the Mississippi Delta. Additionally, there was a broadening of the QPF swath across eastern Texas, northern Louisiana and central Mississippi along and near where the frontal boundary is expected to reside. The WPC QPF trended upwards with areal averages of 1 to 3+ inches. As such, the Marginal Risk was expanded westward while reshaped/reduced slightly across western Alabama. Campbell Previous discussion... Maintained the Marginal Risk area with few changes from when it was issued on Saturday. Once again...guidance has trended in incrementally higher along the immediate coast across parts of southeast Texas and southern Louisiana while maintaining a separate QPF swath maximum centered over north-central Louisiana closer to a front that is forecast to be just offshore. While there has been some run to run adjustments in the placement and the amounts...the overall picture remains similar (including surface based instability creeping closer to the coast from southeast Texas to extreme southern Alabama and northern to northern Louisiana and central Mississippi. Bann Day 3 Valid 12Z Tue Dec 20 2022 - 12Z Wed Dec 21 2022 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE FLORIDA PENINSULA... 21Z update... Very minimal adjustments made to the inherited Marginal Risk area that was already in affect across the Florida Peninsula to reflect the latest WPC QPF. Campbell Previous discussion... Upper level support of the right entrance region of a 110 to 135 kt upper level jet over the Southeast U.S. and difluent flow aloft over the Florida peninsula and the northeast Gulf of Mexico will support a blossoming area of showers over the northeast Gulf of Mexico that will make its way inland on Tuesday and Tuesday night/early Wednesday morning. The EC ensembles have precipitable water values increasing to more than 1.8 inches across the southern half of the Florida peninsula by early Tuesday evening which is around the 95th percentile while the GEFS are only slightly less in PW magnitude and between the 90th and 95th percentile at the same time. In the broadest sense, both the ECMWF and GFS show maximum rainfall on the order of 3 inches or greater along the east coast and west coast with scattered to broken coverage of 2+ inch amounts inland. Focused this area for the Marginal Risk...while not going for a Slight Risk area in part given the timing differences shown by the NAM and UKMET, Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6IRXjtu_5YOgGZQLcdoWl3QL4YZ2baJameF3oEGu9gKp= 33g-6nEkvPAFNX50hu8vYPR7SV8P3g_uHi9Vaf0yrMj7w-s$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6IRXjtu_5YOgGZQLcdoWl3QL4YZ2baJameF3oEGu9gKp= 33g-6nEkvPAFNX50hu8vYPR7SV8P3g_uHi9Vaf0yP0YOMNo$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6IRXjtu_5YOgGZQLcdoWl3QL4YZ2baJameF3oEGu9gKp= 33g-6nEkvPAFNX50hu8vYPR7SV8P3g_uHi9Vaf0yKL-Lvt0$=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 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .