Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jun 01 2025 08:31:00 FOUS30 KWBC 010830 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 430 AM EDT Sun Jun 1 2025 Day 1 Valid 12Z Sun Jun 01 2025 - 12Z Mon Jun 02 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE SOUTHWEST... Impressive closed low off the northern Baja coast will gradually=20 fill and start to shift northeastward today.Downstream of this=20 low, southerly flow will strengthen, drawing increased moisture=20 and instability northward into the Southwest United States. This=20 will support impressive thermodynamics as precipitable water values=20 surge to 1.25-1.5 inches, above the 99th percentile according to=20 NAEFS (and in some areas above anything measured in the 06Z CFSR=20 climatology). Given the amount of overlap with MUCAPE climbing to=20 250-750 J/kg, convection is expected to blossom rapidly and then=20 organize through 25-35 kts of bulk shear. This organization within=20 the favorable thermodynamics and upper level dynamics will support at least briefly heavy rain rates that may exceed 1"/hr (10-20%=20 chance). With storm motions slowing as the upper low pivots=20 overhead later this evening/tonight, this could produce pockets of 1-2" of rain, especially in the low deserts of AZ. Farther east,=20 aligned Corfidi vectors with the mean flow will allow for repeating rounds of convection to lift northward, producing other areas of=20 1-2" of rain despite the faster progression. Saw little reason to make too many changes to the previously issued Slight and/or=20 Marginal risk areas. Bann Day 2 Valid 12Z Mon Jun 02 2025 - 12Z Tue Jun 03 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE CENTRAL HIGH PLAINS AND CENTRAL PLAINS AND OVER THE SOUTHEAST FLORIDA PENINSULA... ....Central High Plains and Central Plains... The mid-level low initially over Baja will continue to weaken and=20 shear out as it becomes embedded within pinched westerlies south of a trough diving out of Montana. This will result in expanding deep layer lift through height falls and modest deformation expanding=20 from the Four Corners through the Northern Plains as well as=20 additional ascent occurring as the northern stream trough drives a=20 cold front southeastward. This synoptic setup will produce an expansive area of lift into increasingly robust thermodynamics, and it is likely that a large area of showers and thunderstorms will develop on Monday...with=20=20 southerly low- level flow increasing to as much as 40-50 kts at=20 850mb helping boost precipitable water values increase to 1.00 to 1.25 inches. This overlaps with MUCAPE rising to 250-1000 J/kg,=20 sufficient to produce rainfall rates of 0.5"-1"/hr. While there is=20 still some uncertainty in the placement of the heaviest rainfall,=20 the guidance is in general good agreement in a maximum of 2-3", or=20 locally higher as reflected by <10% probability for 3"/24 hrs from=20 the ECENS/GEFS, from eastern CO and WY through parts of southeast South Dakota or eastern/northeastern Nebraska as well as in parts of west Texas that form along the dryline.=20 Over parts of the Intermountain region...residual moisture from=20 Day 1 is expected to still be in place which enhances the prospect=20 for downpours from any slow moving storms which develop during the late day or evening. This region is sensitive due to the variety=20 of slot canyons and other sensitive terrain, which feature FFG that is as low as 0.5"/1hr.=20 ....South Florida... The 01/00Z model runs tended to show an uptick in the coverage and rainfall amounts over southeast Florida...resulting in the introduction of a Slight Risk area focused along the urbanized corridor. As an upper trough digs south along the FL Panhandle and into the peninsula, it will push a weakening cold front and=20 shortwave southward, enhancing ascent across the area before stalling and potentially getting deflected northward. With PWs=20 approaching 2" overlapped with MUCAPE above 2000 J/kg, this will=20 support scattered to widespread heavy- rain producing convection on Monday with the HRRR and RRFS showing the potential for amounts of 3 inches. Bann Day 3 Valid 12Z Tue Jun 03 2025 - 12Z Wed Jun 04 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE CENTRAL US AND OVER A PORTION OF THE SOUTHERN FLORIDA PENINSULA... ....Texas to the Great Lakes... The front pushing south- and eastward from the Northern Plains=20 will continue to encounter a moist airmass extending from Texas=20 northward towards the western/central Great Lakes region...with=20 maximum precipitable water values approaching 2.2 inches pooling=20 ahead of the front over northern Texas and eastern Oklahoma by late Tuesday evening and values approaching 2 inches nearing the=20 southern Great Lakes by the end of the outlook period.=20 Thunderstorms forming in this airmass should be capable of=20 producing 1 to 2 inch per hour rates. While the storms should be=20 progressive...the alignment of the mean winds with the orientation=20 of the front does open up the potential for repeat convection or=20 training of cells and the associated risk of flash flooding.=20 ....Southeast Florida... Embedded impulses rotating around a building Atlantic ridge will result in showers and thunderstorms lingering across parts of the=20 southern Florida peninsula...although the guidance was struggling=20 with placement. Given their handling of the evolution on Day 2...a=20 small Slight Risk area was embedded within a broader Marginal Risk=20 area and placed based on spaghetti plots of SREF/GEFS 2 and 3 inch amounts.=20 Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!86Cn40BKojC5fRAceIiL6dPwBwllPtQfbowNjXTir9G9= jFwY562zH_aHVJ1MEd86nfTqoVwrtNkfrbryI0UhGDR315w$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!86Cn40BKojC5fRAceIiL6dPwBwllPtQfbowNjXTir9G9= jFwY562zH_aHVJ1MEd86nfTqoVwrtNkfrbryI0UhbpBjImU$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!86Cn40BKojC5fRAceIiL6dPwBwllPtQfbowNjXTir9G9= jFwY562zH_aHVJ1MEd86nfTqoVwrtNkfrbryI0UhFAIa_iU$=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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