Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Jul 25 2025 08:53:02 FOUS30 KWBC 250851 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 451 AM EDT Fri Jul 25 2025 Day 1 Valid 12Z Fri Jul 25 2025 - 12Z Sat Jul 26 2025 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF=20 THE CENTRAL PLAINS, MIDWEST, AND OHIO VALLEY... ....Central Plains to southern Great Lakes... Deep moisture and a front extending from the Plains to New England is the main focus for potentially excessive rainfall today and tonight...especially across the plains where surface low pressure helps focus convection along the front. However...plenty of=20 uncertainty lingers with the evolution/progression of the low...any MCV or outflow boundary that could disrupt placement/magnitude of=20 any forcing in the low levels...and a mid- and upper- level=20 disturbance hugging the Gulf coast. Despite that uncertainty...and in deference to the convective evolution Thursday night/early=20 Friday morning prior to the start of the Day 1 period combined with the amounts still expected to fall being in largely the same geographic placement...warrantied a the upgrade to a Moderate risk in the Plains. Local 1.5 to 3 inch per hour rainfall rates and 2=20 to 4 inch rainfall totals along with isolated higher maximum=20 amounts remain in the realm of possibilities. A Slight risk area=20 extended into portions of the Ohio Valley along the best moisture=20 transport vectors. Downstream from there...across portions of the Great Lakes into New England...maintained a Marginal Risk area along a corridor of 2 inch precipitable water values which should be aligned along and ahead of the cold front. The front should continue to provide a focus for showers and thunderstorms. Even though it is an=20 environment which supports isolated convection capable of=20 producing torrential downpours...the coverage of storms should be=20 much less than areas upstream and the progressive nature of=20 individual storms should be enough to mitigate concerns over a=20 widespread area. ....Northern Plains... A quick moving shortwave ejecting out of the Rockies will sweep across the Northern Plains later tonight/early Saturday morning=20 with scattered thunderstorms likely to roll through the Dakotas=20 after sunset. With precipitable water values climbing upwards of=20 +2 deviations along with ample mid-level forcing...a period of=20 enhanced heavy rainfall prospects during the time frame of impact.=20 Deterministic output remains chaotic in terms of placement and generally low in magnitude...but 1-3" of rainfall in a short=20 period of time would be sufficient for at least low-end MRGL. ....Gulf Coast... The disturbance across the northern Gulf will continue to slowly propagate west- southwestward with an attendant surface low=20 remaining situated just south of the west-central Gulf coast. Current model guidance still keeps the feature far enough offshore to preclude widespread impacts. However, the airmass surrounding=20 the disturbance will still be pretty robust with precipitable water values remaining very high (>2.3") for much of the immediate=20 coastal plain over TX back through the central Gulf coast.=20 Bann Day 2 Valid 12Z Sat Jul 26 2025 - 12Z Sun Jul 27 2025 ....THERE ARE MARGINAL RISK AREAS FOR EXCESSIVE RAINFALL OVER MULTIPLE REGIONS OF THE COUNTRY ON SATURDAY... higher posture given the isentropic lift at low levels and upper support as shown=20 ....Gulf Coast... The upper trough and associated surface low hugging the Gulf coast will remain situated across the western half of the Gulf with the main=20 area of surface reflection likely coming ashore into TX during the=20 period. Model solutions remain varied...but high precipitable=20 water and enough mid- and upper level forcing to continue producing downpours across the central and western Gulf coast with an=20 emphasis on the immediate coastal plain. ....Northern Plains... The next in a series of potent shortwave will eject northeast out=20 of the northern High Plains resulting in another round of heavy=20 precip potential with more organized convective clusters migrating=20 through the Dakotas. Isolated 2 to 3 inch rainfall maxima are possible and embedded within broader areas of lesser rainfall amounts. The pattern is fairly progressive so see little reason to move from the Marginal risk category. ....Northeastern California and Northwest Nevada... Almost a carbon copy of the prior period for convective impacts lingering across the Northern Sierra up through northeastern CA and northwest OR. The upper pattern is pretty slow to breakdown with the diffluent area in the longwave setup still situated over northern CA into NV. Instability is expected to be modest and=20 slightly above normal moisture in the terrain will offer the=20 capability for some isolated flash flood concerns within any=20 complex terrain and burn scar remnants in the above area.=20 Bann Day 3 Valid 12Z Sun Jul 27 2025 - 12Z Mon Jul 28 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE UPPER MIDWEST... ....The eastern Dakotas to northern Minnesota... Effects of a=20 shortwave trough interacting with a surface front across the Upper=20 Midwest will continue into Sunday as does uncertainty with=20 placement and timing of any convection capable of supporting heavy=20 rainfall. There are some signals in the GFS and ECMWF for possible=20 MCS development while the NAM does generate some storms but would=20 be less concerning, Given the amount of rainfall recently across=20 parts of northern Minnesota...will maintain the Slight risk in=20 deference by the GFS/ECMWF for the time being. ....The Mid Atlantic to southern New England... Mid-level flow flattens over the Great Lakes and Ohio Valley...allowing embedded shortwave energy to start digging east of there with corresponding height falls. The atmosphere will still be anomalously moist and capable of supporting convection with=20 localized downpours that produce localized flooding. ....Southwest US... Deeper moisture that made its way across parts of the Gulf and inland across Mexico should start to be drawn northwest into parts of the Southwest United States...resulting in scattered late day and evening convection across parts of New Mexico and a small portion of Arizona. Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4QlAaYAUrmW5LtqHGmr0pUAyMe6_FTME-K7csdGMhZb8= ZZVtLOYJMcxcH8nRm44prcEvH_j4MHNP2Frrm1R77bEwJvk$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4QlAaYAUrmW5LtqHGmr0pUAyMe6_FTME-K7csdGMhZb8= ZZVtLOYJMcxcH8nRm44prcEvH_j4MHNP2Frrm1R7bNczeb4$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4QlAaYAUrmW5LtqHGmr0pUAyMe6_FTME-K7csdGMhZb8= ZZVtLOYJMcxcH8nRm44prcEvH_j4MHNP2Frrm1R7CFCebqg$=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: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .