Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Apr 26 2025 08:29:50 FOUS30 KWBC 260829 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 429 AM EDT Sat Apr 26 2025 Day 1 Valid 12Z Sat Apr 26 2025 - 12Z Sun Apr 27 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF NORTH AND NORTHWEST TEXAS INTO SOUTHERN OKLAHOMA... ....Summary... Based on the latest observational and guidance trends, have expanded the Slight Risk from yesterday's Day 2 ERO a little=20 farther west-southwest to include a bit more of the Rolling Plains in Northwest Texas. Otherwise, more minor adjustments were made to the surrounding Marginal Risk area. ....Southern Plains... MCS and resultant MCV currently traversing the Texas Panhandle=20 early this morning will gradually track ENE along the quasi- stationary surface frontal boundary across much of the TX-OK Red=20 River Valley today. By late morning, the weakening LLJ will allow the MCS to diminish, while later in the day (afternoon) a narrow broken line of convection develops farther upstream along the dryline=20 across Northwest TX during peak heating. This second area of convection is expected to take on a more ESE trek during the afternoon and evening, thus the southwest 'bulge' to both the Slight and Marginal Risk areas across the Rolling Plains and (for the Marginal Risk) into northern portions of the Hill Country.=20 Overnight, the surface stationary front will eventually lift=20 northeast as a warm front Saturday night, taking the more=20 organized/widespread convection with it.=20 As with yesterday's Day 2 ERO, the Day 1 Slight Risk area was adjusted to capture areas where 1-2+ in/hr rainfall rate probabilities from the HREF/RRFS ensembles are highest, while also overlapping areas where heavy rainfall has fallen over the past couple of days (wetter antecedent interviews).=20 Hurley Day 2 Valid 12Z Sun Apr 27 2025 - 12Z Mon Apr 28 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE NORTHERN HIGH PLAINS INTO THE UPPER MISSISSIPPI VALLEY... Mid-upper trough across the southern Great Basin early Sunday will lift across the central Rockies by 12Z Monday. This in-turn will=20 nudge the upper ridge axis east of the Northern Plains and Upper MS Valley late Sunday-Sunday night, with a quick onset of upper level divergence in its wake. Along with the more favorable dynamical=20 forcing (upper divergence and deep-layer ascent), deepening=20 southerly flow will tap the western Gulf and lead to an uptick in=20 low-mid layer moisture transport, with TPW values climbing to 1.3+=20 inches. Deep-layer instability meanwhile will also be ramping up,=20 to the tune of 1000-2000+ J/Kg MUCAPE per the 00Z models. To some=20 degree, the latest models indicate MCS development along the=20 western periphery of the upper ridge, tracking east to eventually=20 southeast along the 850-300 mb thickness. For the most part, the=20 forward-propagating Corfidi vectors would support a rather=20 progressive area of any organized convection that can grow=20 upscale, though much will depend on the strength of the LLJ. For=20 now, have maintained a fairly broad Marginal Risk area given the=20 potential of intense short-term (sub-3hr) rainfall rates. Hurley Day 3 Valid 12Z Mon Apr 28 2025 - 12Z Tue Apr 29 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE NORTHERN PLAINS INTO THE UPPER MIDWEST... Mid-level circulation will open into a shortwave trough across the northern Plains and Upper Midwest on Monday-Monday night. Ample pre-frontal low-mid layer moisture transport and PW values climbing to 1.5-1.75" will make for a favorable thermodynamic profile,=20 along with deep-layer instability as MUCAPEs peak between=20 2,000-3,000 J/Kg (even ~1,000 J/Kg wrapping westward into the=20 TROWAL zone). The biggest concern during this period will be with=20 cell training, especially late Monday-Monday night across the Upper Midwest with the strengthening LLJ and weakening downwind Corfidi=20 Vectors. For now, guidance spread with the heavier QPF is still=20 rather high (not well consolidated to support a Slight Risk at=20 this point). However, per the GFS/ECMWF and especially the GEM-=20 Regional, localized totals of 3-5+ inches within 12 hours would=20 appear likely in this setup. Hurley Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt= __;!!DZ3fjg!-UcQBTn_0liMEHHvybboXdRWUsQ9jVteIXIw5vkWMoIVuT14zrH86VbtiVNEw0c= 9aQA8Mkfnx0ONz1shgx-mvd6yZFM$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt= __;!!DZ3fjg!-UcQBTn_0liMEHHvybboXdRWUsQ9jVteIXIw5vkWMoIVuT14zrH86VbtiVNEw0c= 9aQA8Mkfnx0ONz1shgx-mxaARNtQ$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt= __;!!DZ3fjg!-UcQBTn_0liMEHHvybboXdRWUsQ9jVteIXIw5vkWMoIVuT14zrH86VbtiVNEw0c= 9aQA8Mkfnx0ONz1shgx-mdLb_zV8$=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) .