Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon May 15 2023 08:25:27 FOUS30 KWBC 150825 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 424 AM EDT Mon May 15 2023 Day 1 Valid 12Z Mon May 15 2023 - 12Z Tue May 16 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHERN TEXAS AND THE MO/OK OZARKS REGION... ....Texas... Confidence on exactly where convection will fire up across South Texas during this period remains a uncertain. Moisture and instability is expected to be in place with various boundaries/vort centers passing through that would support convective development. The recent multiday wet period has lowered local FFGs across the region- with much of the state in the 2-2.5 inch range for 3-hr FFG with values as low as 0.50 inch in the vicinity of the Houston metro. South TX appears to be the most likely location for this...both with potential convection moving in from Mexico, and with any convective vort center moving inland out of the Gulf of Mexico. These features are all pretty subtle in nature and will be hard to pin down at this lead time. The Slight Risk area was maintained at this time albeit likely on the lower end of a Slight. ....Ozarks Region... Shortwave energies are expected to traverse northward as a cold front drops south into southern Missouri/northern Arkansas. With the west-east orientation establishing across the central states, and the steady influx of moisture and instability, the convection should become more organized while increasing the rainfall efficiency and threat for flash flooding. The latest runs of the guidance continue to have some latitudinal spread but the more favorable location will be the Ozarks and into eastern Oklahoma. The Slight Risk area was maintained and the encompassing Marginal Risk area had minor reshaping to account for the latest QPF trends. ....FL Panhandle Region... The latest CAMs and global guidance show a signal for locally heavy rainfall across portions of the Florida Panhandle into far southern Georgia, with consensus of 1 to 2 inches with isolated maxes of 3+ inches. While plenty of Gulf moisture and instability will be present, the area remains in a Marginal Risk (largely for flood sensitive areas such as urban Tallahassee) as FFGs in this area are very high, so flash flooding should be isolated at best. Campbell Day 2 Valid 12Z Tue May 16 2023 - 12Z Wed May 17 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE OHIO AND TENNESSEE VALLEYS TO THE CENTRAL AND SOUTHERN APPALACHIANS... ....Ohio and Tennessee Valleys and the Central and Southern Appalachians... With plenty of instability (over 2,000 J/kg, and PWATs to 1.5 inches to the south of the front, there will be plenty of moisture, instability and forcing for heavy rain. Although the nature of this boundary will be more on the progressive side, there will be some upper jet support to work with by this time, with the right entrance region moving across the region. This enhanced lift should result in robust convective development over wet antecedent conditions. Most of the 3-hr FFGs from eastern Missouri to the Mid-Atlantic Coast is in the 1.0 to 2.5 inch range, with the lowest being near the areas of higher terrain. The inherited Slight Risk continues to highlight the areas were the threat for areas of excessive rainfall and flash flooding are more elevated so no adjustments were needed at this time. ....Mogollon Rim of Arizona... Recent runs of the guidance has depicted abnormally high amounts of atmospheric moisture, as high as 4 sigma above normal in this region, though there was initially no forcing to help get storms to form. However they are hinting that weal forcing will be present during this period that could be sufficient in triggering convective activity that could produce heavy rain and isolated flash flooding, especially on any old burn scars, slot canyons, and dry washes. The Marginal Risk area was maintained for this period. ....Intermountain West... A Marginal Risk area remains in effect from the Okanogan Highlands of northeast Washington east to the western Montana Hi-Line. A strong shortwave trough will skim well northeast of the area, but the combination of plenty of antecedent moisture, topography helping with forcing, and 500-1,000 J/kg of CAPE should be enough for some isolated flash flooding, especially along the mountains. The area around Great Falls, Montana is currently in the bullseye for the most rainfall, but that is subject to change. Campbell 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!66p0g0FDJQ109jSDrRi73bvyoMSTTLiW6bxk90IT3Rwf= W6sEPj7xyU_FbjLansASnCSvbIkcnomwYzL453chrVm-BcE$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!66p0g0FDJQ109jSDrRi73bvyoMSTTLiW6bxk90IT3Rwf= W6sEPj7xyU_FbjLansASnCSvbIkcnomwYzL453chA190RCA$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!66p0g0FDJQ109jSDrRi73bvyoMSTTLiW6bxk90IT3Rwf= W6sEPj7xyU_FbjLansASnCSvbIkcnomwYzL453cha1rEP3A$=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. 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