Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jun 13 2023 08:12:33 FOUS30 KWBC 130812 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 411 AM EDT Tue Jun 13 2023 Day 1 Valid 12Z Tue Jun 13 2023 - 12Z Wed Jun 14 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE ARKLATEX INTO SOUTHWESTERN GEORGIA... ....ArkLaTex Through Southeast... Low level convergence north of a warm front over central TX in a moist and unstable environment should trigger rapid development of heavy thunderstorms around the Red River early this morning. This activity develops and shifts east in the 40kt westerly mean layer flow, likely spreading across the AR/LA border by midday and then central MS/AL into GA this afternoon. This will approach or cross areas that had heavy rain yesterday, particularly near the northern FL Panhandle borders with AL/GA. A shortwave impulse currently over the Desert Southwest reaches the southern Plains by this evening and tracks over the stationary frontal zone and into AR producing a second round of heavy thunderstorms over a similar area to this morning from northeast TX along the AR/LA border. Through this time, precipitable water values of 1.5-2" will be maintained along the frontal zone with ample instability (CAPE of 3000-4000 J/kg) will persist just south in the warm sector. There should be enough low-level inflow and effective bulk shear to organize convection with cell training in WNW-ESE motion and occasional mesocyclone formation leading to hourly rain totals up to 2.5". 00Z guidance and now the 06Z HRRR guidance maintains a consistent signal for local 3-5" totals among the two rounds from northeast TX into MS. The Slight Risk was expanded west to northeast Texas where the threat of two rounds is greatest. Farther southeast over AL into GA there is less confidence in the CAM consensus, but conceptually the presence of the front draped across this area along with scattered areas that received heavy rain yesterday warrants maintenance of the Slight Risk farther east. ....Great Basin/Northern Intermountain West to the Southern Plains... An upper trough currently off the BC coast will amplify and close into an upper low as it digs southeast to the northern Rockies tonight. This will enhance divergence aloft over the northern Great Basin into the northern Rockies. Pockets of 0.75-1.25" PWs combined with diurnal max of 1000+ J/kg of MLCAPE will allow for convection to develop in the afternoon and evening hours. Hourly rain totals to 2" are possible within such an air mass where cells merge and/or train. 00Z guidance QPF continues to indicate a localized 2" risk. Diurnal convection over the CO Rockies will spill onto the High Plains where above normal moisture persists in southerly low level flow. Maintained the Marginal Risk for from the Sierra Nevada through the northern Intermountain West and over the CO Rockies through southwestern KS into the OK/TX Panhandles. Jackson Day 2 Valid 12Z Tue Jun 13 2023 - 12Z Wed Jun 14 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHEAST... ....Lower Mississippi Valley through the Southeast... Ongoing activity from Tuesday night should be across MS/AL/GA as an impulse shifts east along the stalled frontal boundary over the Southeast. Ample Gulf moisture (PWs of 1.5 to 2") continues to pool along the frontal zone which will continue to meander north and south ahead and behind this first and subsequent impulses given the instability pool along and north of the Gulf Coast. Expect redevelopment Wednesday night over potentially the same areas from the AR/LA border and east. Therefore, the Marginal Risk was shifted west over much of southern AR while the inherited Slight Risk matches up well with the 00Z consensus. There remains a risk for this repeating heavy activity to focus over similar areas in MS/AL/GA to the FL Panhandle as today which may warrant an eventual Moderate Risk upgrade. ....Intermountain West and Northern Rockies onto the Northern Plains... An upper trough pivoting over the Northern Rockies sends a cold front to the central portions of the Intermountain West and a renewed upper trough extending over southern CA allows an elevated surge of Pacific moisture up through this front. An axis of QPF from the Sierra Nevada across the Great Basin to the CO Rockies is forecast with a risk for local 1"+ precip in diurnally enhanced convection warrants a Marginal Risk. The cold front crosses the northern Rockies with lee-side convective activity over the already saturated central portions of Montana warrants maintenance of the Marginal Risk into the western Dakotas. Jackson Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!70YIHUNFQ_pjRcQPD61-35nSzr0Sp0g6gkB-f__XfEdH= V6v7hHSm-JOXnu5PSHYuhRytwbKIF1-s2BSbOC3b_0UCx4I$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!70YIHUNFQ_pjRcQPD61-35nSzr0Sp0g6gkB-f__XfEdH= V6v7hHSm-JOXnu5PSHYuhRytwbKIF1-s2BSbOC3b_JhSrB8$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!70YIHUNFQ_pjRcQPD61-35nSzr0Sp0g6gkB-f__XfEdH= V6v7hHSm-JOXnu5PSHYuhRytwbKIF1-s2BSbOC3bZQtSt-k$=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) .