Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Mar 09 2024 20:17:34 FOUS30 KWBC 092017 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 316 PM EST Sat Mar 09 2024 Day 1 Valid 16Z Sat Mar 09 2024 - 12Z Sun Mar 10 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE SOUTHEAST U.S TO SOUTHERN MAINE .... 16z UPDATE... The organize line of storms moving across the Southeast are starting to weaken. The latest hi-res guidance do depict hourly rates up to 1.5/2 inches/hr persisting a few more hours bur will be moving quickly through areas with higher FFGs. Therefore the Slight Risk area was removed from portions of Florida, Alabama and Georgia along with the western boundary of the Marginal Risk area reduced from Florida to North Carolina. With the stronger convection focused more over the Southeast, the convection tracking through the eastern Carolinas are not as heavy and are expected to move offshore in the new few hours. The Slight Risk that was in place for portions of South and North Carolina was also removed. Campbell Southeast U.S.... Given radar trends seen early this morning...introduced a Slight Risk area over portions of the Southeast U.S. mainly to cover the period from 09/12Z until about 09/16Z or so. Convection was responding to continued influx of moisture and instability off of the Gulf of Mexico...and the alignment of this convection is such that training of some intense downpours will continue beyond 12Z.=20 The presumption is that the rates will begin to weaken early in the new Day 1 period as flow off the Gulf gets disrupted and less unstable Atlantic moisture gets drawn into the system. Bann ....0830Z Excessive Rainfall Discussion... Maintained the Slight Risk area in the Carolinas...although shrunk the areal coverage in the western portion of the area given the trends in short-range QPF guidance....while radar trends suggested the need to hold back the western boundary of the Marginal Risk area near the Gulf coast due to convective trends near the cold front. In terms of the Slight Risk area...while there was enough confidence to trim the western portion of the area there was still a larger than usual spread for a Day 1 period in the north/south placement of the QPF in the Carolinas. Higher rates may be more expected in the southern portion of the Slight Risk area given the proximity of moisture/instability...the northern portion of the area (e.g. North Carolina coinciding with the Piedmont to Coastal Plain transition), Flash Flood Guidance was generally lower.=20 Given the 09/00Z HREF signal for neighborhood probabilities reaching 10 percent...maintained the Slight Risk area another cycle with minimal adjustments northward or southward. Mid Atlantic into the Northeast... A strong low tracking northeast from the Ohio Valley will spread a broad shield of precipitation towards the Eastern Seaboard throughout the day and tonight., Maintained the Marginal Risk area...although continued to minimize overlap of the excessive area with winter weather concerns. The latest WPC QPF continued to focus an area of 0.75 to 1.5 inch amounts over portions of the Mid-Atlantic into southern portions of New England...roughly coincident with where the latest HREF probabilities showed 30 to 50 pct of 1 inch rainfall in 3 to 6 hours. This could result in some instances of urban and small stream flooding over parts of the area where antecedent conditions have kept stream flows elevated and not much recovery time from moderate to heavy rain a few days ago. Bann Day 2 Valid 12Z Sun Mar 10 2024 - 12Z Mon Mar 11 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF COASTAL NEW ENGLAND ON SUNDAY... 21Z update... With the latest trends focusing the bulk of the rain near Downeast Maine opted to reduce the western edge of the Marginal over western Maine. Campbell Maintained a Marginal Risk area...mainly confined to eastern Maine...as an area of low pressure pulls away from the region.=20 Areal average rainfall continues to be on an order of 1 to 1.25 inches...enough that there could be isolated problems from flooding/ponding given the antecedent conditions over the past few weeks. Confined the Marginal Risk areas to lower elevations where rainfall is the expected to be the primary precipitation type and attempted to limit the overlap inland where the precipitation type is expected to be snow. The threat of excessive rainfall should be tapering off across the outlook area during the afternoon and evening as dry air filters in behind the departing system and the terrain acts to block too much wrap around precipitation. Bann Day 3 Valid 12Z Mon Mar 11 2024 - 12Z Tue Mar 12 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Campbell Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9PV8bMaiUbhWCujo4aIoTcVjeHh9CzyFQztkHdNmQins= EKgj_bZjcrgKlnLmp64PJSKvbviOa3Qqxw0zbC8CwseZ5WU$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9PV8bMaiUbhWCujo4aIoTcVjeHh9CzyFQztkHdNmQins= EKgj_bZjcrgKlnLmp64PJSKvbviOa3Qqxw0zbC8CtWjiiTM$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9PV8bMaiUbhWCujo4aIoTcVjeHh9CzyFQztkHdNmQins= EKgj_bZjcrgKlnLmp64PJSKvbviOa3Qqxw0zbC8C0z6mQKo$=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .