BBS: TELESC.NET.BR Assunto: HVYRAIN: Excessive Rainfall Discussion De: COD Weather Processor Data: Fri, 1 May 2026 19:55:59 +0000 ----------------------------------------------------------- FOUS30 KWBC 011955 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 355 PM EDT Fri May 1 2026 Day 1 Valid 16Z Fri May 01 2026 - 12Z Sat May 02 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN CENTRAL AND SOUTHEAST TEXAS EASTWARD ALONG THE CENTRAL GULF COAST... 16Z update... Portions of the Georgia and Alabama were removed from the Marginal Risk area given the lack of instability to maintain rainfall rates greater than 0.5 inch/hour. Otherwise the heaviest QPF and rain rates are still expected from eastern Texas to southwest/south- central Louisiana. Campbell Once again...minor reshaping of the Marginal and Slight Risk areas were made to reflect small adjustments made in the WPC deterministic QPF and the suite of 01/00Z global and CAM guidance. The axis of the heaviest rainfall still forecast to span from eastern Texas to eastern Louisiana and southern Mississippi where the best moisture convergence and instability will be present. Recent rains across the western an central Gulf states have increased soil saturation, lessening the amount of additional rainfall required for areas of flash flooding. Hourly rates of 1 to 3 inches/hr to streak from eastern Texas to eastern Louisiana. The overall evolution aloft coupled with a broad axis of formidable moisture anomalies and instability should lead to an axis of heavy rainfall across the Southern Plains from Texas over through the Lower Mississippi Valley today into early Saturday morning. A quasi-stationary front will orient itself across south- central TX down to around the Gulf coast as a wave of low pressure rides along the boundary. With precipitable water values forecast to be 1.7 inches to 2.1 inches (in the 95th percentile or higher for this time of year)...efficient warm rain processes can result in torrential downpours with resulting flash flooding especially in light of the upper divergence tied to the mid- and upper level wave making its way through the southern Great Basin early this morning. Thus there is little overall change to the forecast reasoning for a high-end Slight risk area from parts of Texas into Louisiana embedded within the broader Slight Risk area. Farther east...the Slight risk area tapers off into a Marginal Risk area where rainfall rates and amounts still have the potential to result in flash flooding but where ingredients are not as well aligned. The question in dry/drought areas always comes down to rates and resulting amounts (whether it is from training or repeat rounds). Thinking here rates may not be enough alone (with PW's generally < 1.75-ish) but some potential for training prior to frontal passage. The 01/00Z HREF neighborhood probs for 1-hr amounts at 1 in and 2 in thresholds focused generally along the LA/MS coast (admittedly sub SLGT). The RRFS..which has a tendency to be overconfident with probs and overly expansive...seemed to show its bias on its 30/18Z run but focused pretty much along the same axis. There remained some question on the latitude of the axis...considering the latest UFVS verified machine learning guidance focused a bit north of the HREF/RRFS axis closer to the support offered by an upper jet streak. Bann Day 2 Valid 12Z Sat May 02 2026 - 12Z Sun May 03 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHEAST U.S.... 21Z update... The latest QPF trends supported a minor southward nudge of the Marginal across the northern peninsula. The QPF footprint will largely span from Apalachee Bay through north- central/northeast Florida and across southeast Georgia.=20 Campbell A progressive upper trough is expected to help focus and sustain showers and thunderstorms across portions of the Southeast United States on Saturday into the early morning hours of Sunday. More importantly...the trough should result in any convection moving with minimal risk of back-building or training. The setup promotes a relatively favorable environment suitable for heavy rainfall with the stronger cell cores capable of producing rainfall rates between 1-2"/hr in a region where Flash Flood Guidance values remain high. There was enough of a signal for the possibility of some urban flooding to warrant keeping a previously-issued Marginal Risk in place with minimal amount of changes needed. Bann Day 3 Valid 12Z Sun May 03 2026 - 12Z Mon May 04 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THEM SOUTHEAST FLORIDA PENINSULA ON SUNDAY... 21Z update... Latest guidance and WPC QPF focuses the highest rainfall over portions of Palm Beach, Broward and Hendry Counties, which supported the reshaping of the western boundary of the Marginal Risk. Campbell A cold front associated with an area of low moving northeastward off the eastern US seaboard will be draped across the central portion of the Florida peninsula on Sunday...with the front separating an airmass with precipitable water values at or somewhat less than 0.5 inches in the panhandle and adjacent portions of the peninsula to values in the 1.75 inch to 2.00 inch over the southern half of the peninsula for much of Sunday and Sunday evening. Mid- and upper-level shortwave energy embedded within fast flow aloft will help focus and sustain thunderstorms that could produce 1.5 to 2.5 inch per hour along and south of the boundary. There remained enough of a signal for the potential of some urban flooding across the larger urban areas so opted to keep with the Marginal Risk area due to the high flash flood guidance. Even if the QPF remains similar in future cycles...where/how much rain falls in Days 1 and 2 will affect the flash flood guidance as Day 3 makes its way towards becoming a Day 1 outlook. Regardless...downpours and localized multiple-inch rainfall amounts in the major cities is more likely to have flood- related problems in either scenario. Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!5JMDPfAQX4EjZd0yyPEy-uBqQ8nSeq_3wN-GHcpY2ycU= 1qTM-dvzZ4uZYCKhZ6887o1dEk1fefAOT8ENxzlHAl8Q6g4$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5JMDPfAQX4EjZd0yyPEy-uBqQ8nSeq_3wN-GHcpY2ycU= 1qTM-dvzZ4uZYCKhZ6887o1dEk1fefAOT8ENxzlHNoYz6HY$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5JMDPfAQX4EjZd0yyPEy-uBqQ8nSeq_3wN-GHcpY2ycU= 1qTM-dvzZ4uZYCKhZ6887o1dEk1fefAOT8ENxzlHz7GQqpM$=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 3.28-Linux * Origin: Capitol City Online (1:2320/107) ----------------------------------------------------------- [Voltar]