Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Jun 24 2023 00:55:02 FOUS30 KWBC 240054 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 854 PM EDT Fri Jun 23 2023 Day 1 Valid 01Z Sat Jun 24 2023 - 12Z Sat Jun 24 2023 ....THERE IS MODERATE RISK OF EXCESSIVE RAINFALL IN SOUTHEAST PORTIONS OF MONTANA... ....Montana and North-Central Plains... A shortwave trough over Wyoming this evening will continue moving northeast to the western Dakotas tonight. Upper diffluence will continue tonight by dual left exit and right entrance region of the upper jets positioned over the Central Rockies and Canadian Prairies. Gulf-sourced moisture surging up the Plains will continue to wrap around South Dakota and through central Montana overnight with PWs reaching 1.25" over the High Plains with continued heavy rain clusters over southern/southeastern Montana rest of this evening where the Moderate Risk is maintained. Organized linear activity currently approaching the western SD border will sweep east across the state tonight with MCVs and cold pools acting to create localized swaths of repeating heavy rain as well as cell mergers from ongoing scattered activity ahead of the line. This continues to warrant the Slight Risk over SD and over the northern half of Neb. ....Central/Southern Plains to the central Gulf Coast... Widely scattered clusters of heavy thunderstorms/supercells over the central and southern High Plains this evening will continue progressing east leaving heavy streaks of rain over portions of KS/OK/TX. Areas of sensitive soils from recent activity are across this region, warranting maintenance of the Marginal Risk overnight. Scattered thunderstorms over east Texas and southwest Louisiana will continue moving southeast this evening with an isolated flash flood threat and maintenance of the Marginal Risk. ....Florida... An unstable and humid airmass is over much of FL ahead of a slow moving cold front currently approaching the northern FL border. Remnant boundaries and weak impulses rounding a trough over the eastern U.S. will allow scattered heavy convection to continue this evening. The more focused areas are progged to be away from the hard hit area east of the Big Bend, so the Slight Risk was removed there with a Marginal Risk for all but South FL. ....Mid-Atlantic... A slow northeastward drift to the upper low over the eastern OH Valley continues tonight with slow east and northward progress of the moist/unstable environment up the Eastern Seaboard into Upstate NY. Activity for the Carolinas and north has become more isolated early this evening after widespread heavy activity this afternoon. A localized flash flood threat persists, allowing the Marginal Risk to be maintained as well as expanded farther north in NY to the eastern Great Lakes. Jackson Day 2 Valid 12Z Sat Jun 24 2023 - 12Z Sun Jun 25 2023 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR MUCH OF MINNESOTA AND THE EASTERN DAKOTAS... ....ND/MN area... A deepening shortwave trough is expected to track from portions of Montana and Wyoming early Saturday morning toward central Minnesota by Sunday morning. Ahead of that feature, southerly flow in the low levels will bring northward anomalously high moisture to the region, characterized by precipitable water values to near 1.5" or +2 standard deviations above normal which could help yield rainfall amounts of 1-2 inches. The previously-issued Marginal and Slight risk areas tended to capture the area adequately, but made some adjustments to the boundaries based on the 18Z WPC QPF and 12Z runs of the HREF neighborhood probabilities combined with anticipated changes in the flash flood guidance resulting from rainfall on Day 1. Still think that isolated to widely scattered instances of flash flooding are possible, particularly across the eastern Dakotas into much of western and northern Minnesota.=20 ....Northeast... The slow moving, stubborn upper level trough will inch forward during the day on Saturday, beginning in the Ohio Valley and reaching New England by Sunday morning. The combination of anomalous moisture (PWs up to 1.5"+), warm cloud depths, and skinny CAPE profiles, efficient rainfall producing showers and thunderstorms will be capable of producing localized heavy rainfall. With the mean flow remaining somewhat parallel to the overall storm motions, some repeating rounds will be possible, supporting isolated/localized instances of flash flooding. Nothing more than cosmetic changes were needed based on the 12Z suite of numerical guidance. ....Southeast Florida... A deep axis of higher than normal moisture will position itself across South Florida this weekend and with weak flow and modest shear, higher coverage of afternoon/evening thunderstorms are expected to develop. The environment will support intense rain rates given the tall/skinny CAPE profiles and warm cloud depths. The latest guidance suggests the greatest convection may end up developing just inland away from the highly urbanized corridor, but there's enough ingredients and support in the various models to maintain the Marginal Risk in the ERO. No changes to the previously-issued Marginal Risk here. Taylor/Bann Day 3 Valid 12Z Sun Jun 25 2023 - 12Z Mon Jun 26 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE GREAT LAKES...OHIO VALLEY...NORTHEAST...AND TENNESSEE VALLEY... ....Northeast... Deep southerly flow will remain in place across the Northeast, ahead of the approaching deeper closed low tracking into the Great Lakes, and with the anomalous moisture in place (upwards of +2.5 standard deviations) and expected daytime heating/instability, scattered to widespread thunderstorms are expected across mainly the interior Northeast. Mean flow will be relatively weak (under 10-15 kts) and warm cloud depths will continue to be relatively high, supporting efficient rainfall producing thunderstorms, supporting a localized/isolated threat of flash flooding. The models have been consistent with their handling in the Northeast...so no changes were needed in this outlook cycle. ....Great Lakes to Ohio Valley... The closed mid/upper level low is expected to be across portions of Minnesota at the start of the period (Sunday morning). Ahead of that feature, an axis of higher moisture is expected to lift northward and wrap into the system, characterized by precipitable water values as high as 1.0-1.25" across portions of Wisconsin into Michigan. While higher instability will be fairly limited this far north and the showers and thunderstorms are likely to be somewhat progressive, some locally heavy rainfall will be possible, particularly by the afternoon/evening hours during peak heating across Michigan. Much of the region has been considerably drier than normal however, and the rainfall will be more welcome than concerning, but any localized intense rain rates (approaching 1"/hr) over sensitive locations and totals up to 2" possibly could lead to flash flooding. Across portions of Indiana, Ohio, and northern Kentucky, the moisture and instability will be greater with convection expected to break out late in the day but quickly drop east/southeast. Localized 1-2"/hr rain rates will be possible. This region also has had some heavier rainfall over the last 14 days, with rainfall departures near to slightly above normal in spots across Ohio and Kentucky. Little reason to change based on latest guidance. ....Tennessee Valley... The main shortwave energy tracking across the northern tier will push a cold front southward across the Plains into the ArkLaTex region. The front will be increasingly oriented west to east across the region during the period as it stalls out. In the low levels, southerly flow will allow much above normal to pool along and ahead of that front with the latest guidance indicating upwards of 2.0" precipitable water likely across portions of Arkansas into Mississippi. Convection is expected to develop late in the period (mainly overnight) on the nose of the increasing low level jet, where 850 mb flow is expected to increase to around 30-35 kts, and then dive southeast into portions of Arkansas and Mississippi. There remains some spread among the model guidance on the location and intensity of the convective complex, but the environmental ingredients support intense rain rates and heavy rainfall totals over an area that has seen above normal precipitation over the last 14 days. Taylor/Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-EVpP_HRx2s4KDKiuVLNkqe3lOZTvpBQrKjTBQiqRTa5= bPL97yTA8_mRfRTTgjcUfF5j-u_gFlat5Y8dqiB5_q-l8tQ$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-EVpP_HRx2s4KDKiuVLNkqe3lOZTvpBQrKjTBQiqRTa5= bPL97yTA8_mRfRTTgjcUfF5j-u_gFlat5Y8dqiB57f2ZAqI$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-EVpP_HRx2s4KDKiuVLNkqe3lOZTvpBQrKjTBQiqRTa5= bPL97yTA8_mRfRTTgjcUfF5j-u_gFlat5Y8dqiB51VYqvkQ$=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) .