Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Jun 16 2023 08:28:37 FOUS30 KWBC 160828 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 427 AM EDT Fri Jun 16 2023 Day 1 Valid 12Z Fri Jun 16 2023 - 12Z Sat Jun 17 2023 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR THE EASTERN GULF COAST AND FOR PORTIONS OF EASTERN COLORADO INTO WESTERN KANSAS... ....High Plains... A positively tilted longwave trough over the Intermountain West will gradually drift eastward between the polar jet over Canada and the subtropical jet over NM and extending eastward to LA/AR. In the subtropical jet, a southwesterly jet streak will be in place from the northern Baja California peninsula northeastward to the OK/TX Panhandles. The left exit region of this jet streak in close proximity to the aforementioned longwave trough will create and area of strong upper level diffluence across CO. Highly anomalous moisture will be in place along the CO/KS border, with PWATs approaching 1.25 inches. This is above the 95th percentile in the climatology, or over 2.5 sigma above normal. This will favor strong and moisture-laden thunderstorms across the area. CAMs guidance suggests multiple rounds of moderately fast moving storms will develop along the Front Range in central CO and move ENE into eastern CO and western KS. There is decent agreement that the storms will train over these same areas, generally from Denver and the I-70 corridor south, with much less rainfall expected further north. Antecedent conditions are quite favorable, with portions of CO at over 600% of climatological normal for rainfall for the past 2 weeks. Thus, the chances of flash flooding are considerable, with widely scattered flash flooding impacts possible. This is considered a higher end Slight risk area, particularly from the Palmer Divide east. The storms will continue northeastward into eastern NE while weakening as they track into far eastern SD. The Marginal Risk area covers these somewhat lower risk areas due to weaker storms and less favorable antecedent conditions. In the mountains, there will be a potent shortwave trough that may result in more scattered storms across portions of WY, so the Marginal Risk was expanded. Finally, there is a nearly stationary front that extends westward from CO into southeastern CA. A few flash flooding reports have been reported in southeast CA near Death Valley, and the drifting rainband may impact the Las Vegas area. Meanwhile, the convection may move over the slot canyons of southern UT, which are particularly vulnerable to localized flash flooding. ....MS River Valley and into FL... The inherited Slight Risk area along the eastern Gulf Coast was expanded southeastward into portions of north central FL with this morning's update. A stationary front with access to ample Gulf moisture is causing extreme flash flooding in the Pensacola area this morning. The front will continue to act as a "train track" of sorts for developing thunderstorms to train along. While FFGs in these areas are very high, as the stationary training thunderstorms near Pensacola have shown, these can be overcome. Since the same front will still be in the same area, with the Gulf moisture not going anywhere, and Corfidi vectors will remain parallel to the northwest to southeast oriented front, it remains probable that renewed rounds of storms will develop again this afternoon. PWATs will be steady around 1.75 inches, which while not unusual for this time of year, the addition of the extreme heat ongoing across Texas will lead to extreme instability. The extreme instability will support the continued thunderstorms over this region. ....Northeast... A strong upper level shortwave will slowly track eastward from western PA to off the Jersey Shore through the day today. Ahead of this forcing, a bit of additional Atlantic moisture will track northward up the coast, increasing PWATs to around 1.25 inches. This will be enough moisture for showers with a few embedded thunderstorms to develop across much of New England and the northern Mid-Atlantic. Some of these areas have seen enough rain the past couple weeks that the antecedent soil conditions may support isolated flash flooding, particularly where any slow-moving or training storms can move over the same areas. There is a local maximum of rainfall forecast for southeastern PA through southern NJ, then curving northward into coastal New England. The inherited Marginal Risk area was expanded quite a bit to now include much of New England and the northern Mid-Atlantic. Areas at greatest risk for isolated flash flooding are urbanized and poor drainage areas. Wegman Day 2 The Day 2 outlook will be updated by 0830Z. 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!5f_c73X_x7ZqXss-1uEyNrmc-nQ6YJSSvhcb9fN4F5r9= cEo9R9Eh7RCVQCpqNllVxxJpE82YfX7akkl-thwze7g2FK4$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5f_c73X_x7ZqXss-1uEyNrmc-nQ6YJSSvhcb9fN4F5r9= cEo9R9Eh7RCVQCpqNllVxxJpE82YfX7akkl-thwzCKMrn2A$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5f_c73X_x7ZqXss-1uEyNrmc-nQ6YJSSvhcb9fN4F5r9= cEo9R9Eh7RCVQCpqNllVxxJpE82YfX7akkl-thwzsl2aQ8o$=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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