Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jun 14 2023 08:13:59 FOUS30 KWBC 140813 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 413 AM EDT Wed Jun 14 2023 Day 1 Valid 12Z Wed Jun 14 2023 - 12Z Thu Jun 15 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHEAST... ....Lower Mississippi Valley through the Southeast... Multiple rounds of heavy, organized activity is expected through tonight through much of MS/AL/GA as impulses and jet streaks shift east in flow parallel to the stalled frontal boundary over the Southeast. Ample Gulf moisture (PWs of 1.75 to 2") continues to pool along the frontal zone which will continue to meander north and south with the impulses given the instability pool along and north of the Gulf Coast. The westerly mean layer flow running parallel to the stationary fronts will support training and backbuilding convection over areas that are dealing with ongoing rounds of thunderstorms warranting further expansion of the Slight Risk to encompass the most likely heavy rain including areas farther south to the FL border where 1-2" fell yesterday. There remains a potential for the rounds tonight to focus over similar areas to this morning which could warrant a Moderate Risk upgrade. The risk of repeating activity roughly downstream of activity currently SW of Memphis warrants a northward expansion of the Marginal Risk into TN. ....Intermountain West and Northern Rockies onto the Northern Plains... An upper low pivoting over the Northern Rockies sends a cold front to the central portions of the Intermountain West and the renewed upper trough extending over southern CA send a surge of Pacific moisture up through this front. An axis of QPF with a risk for local 1"+ is forecast from the Sierra Nevada across the Great Basin to the CO Rockies in diurnally enhanced convection which continues to warrant a Marginal Risk. The cold front crosses the northern Rockies with lee-side convective activity in PW exceeding 1.25" by this evening (2 sigma above normal) over the already saturated central portions of Montana warrants maintenance of the Marginal Risk for much of Montana into the western Dakotas. Jackson Day 2 Valid 12Z Wed Jun 14 2023 - 12Z Thu Jun 15 2023 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHEAST... Lower Mississippi Valley through the Southeast... Further impulse activity coming across the southern tier of the CONUS in a westerly subtropical jet will continue to enhance lift along a persistent frontal zone that is anticipated to be farther south toward the Gulf coast/onto the FL Peninsula on Thursday compared to today. Continued pooling of 1.5 to 2" PWs along this frontal boundary along with ample instability and bulk shear allows for further passage of organized activity over this saturated zone from central OK ESE through southern GA/northern FL. With increased confidence in a footprint of 2-3" additional rainfall in an area with increasingly sensitive soils, the Slight Risk was further expanded across southern AL and south through the FL border. Intermountain West onto the Great Plains... The upper low over the northern Rockies today lifts northeast to the Canadian Prairies tonight while the associated troughing digs over the Intermountain West, connecting a trough axis from the northern Rockies SSW through southern CA. This will allow for a similarly placed, but greater magnitude QPF compared to today over the Great Basin to CO/WY Rockies which warrants another Marginal Risk. Farther east on the northern and central Plains, Gulf moisture drawn up ahead of the slowing cold front allows for increased PW around 1.25" (1.5 sigma above normal) and diurnal development of locally heavy thunderstorms. Slower southwesterly mean flow should allow some cell mergers, continuing to warrant a Marginal Risk. Southern Sierra Nevada... Weak instability combined with PW of 0.75 to 1" (2 to 3 sigma above normal) will support locally heavy rainfall rates in diurnal convection. Some instances of flash flooding are possible, particularly in areas where soils are overly saturated from multiple recent days of rain and in rugged terrain warranting a Marginal Risk. 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!6-HG5t-wgt4jjHSevwWDGB-1iUyBZuB_2yLJODZgDkOD= fuoJfwnXMtzBGKfsKYxsmFlkfnw7qRUquxTXTf_MyYb0IAc$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6-HG5t-wgt4jjHSevwWDGB-1iUyBZuB_2yLJODZgDkOD= fuoJfwnXMtzBGKfsKYxsmFlkfnw7qRUquxTXTf_MHpayO5A$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6-HG5t-wgt4jjHSevwWDGB-1iUyBZuB_2yLJODZgDkOD= fuoJfwnXMtzBGKfsKYxsmFlkfnw7qRUquxTXTf_M90BRmq8$=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) .