Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Aug 28 2024 00:59:41 FOUS30 KWBC 280059 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 859 PM EDT Tue Aug 27 2024 Day 1 Valid 01Z Wed Aug 28 2024 - 12Z Wed Aug 28 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS=20 OF THE SOUTHWEST AND FROM THE CENTRAL PLAINS TO THE GREAT LAKES... ....01Z Update... Removed the Marginal Risk that previously covered much of the upper Great Lakes. Storms now pressing south across Lake Erie into the Ohio Valley are expected to remain progressive, with rain rates decreasing as these storms moving into a more stable airmass.=20=20 There remains a threat for isolated flash flooding further to the west from southern Lower Michigan back through the mid Mississippi and lower Missouri valleys into Kansas. Ample moisture and=20 instability ahead of a slow-moving boundary will continue to=20 support showers and storms, with areas of heavy rain possible=20 through the evening. While widespread heavy amounts are not=20 expected, the HREF does indicate locally heavy amounts of 2 inches=20 or more are possible, with the highest probabilities centered along the northern Kansas-Missouri border, the northern Missouri-=20 Illinois border, and along the Indiana-Michigan border. Made only minor adjustments to the Marginal Risk in the Southwest. Monsoon showers and storms are expected to continue. The greatest threat for heavy amounts is expected to center across southeastern Arizona and southwestern New Mexico, where the HREF is showing high neighborhood probabilities for accumulations of 1-2 inches through the remainder of the evening into the overnight. The threat for heavy amounts further to the north across northern New Mexico is=20 expected to remain more isolated, however cannot rule out the threat for flash flooding, especially across the vulnerable burn scar areas. Pereira Day 2 Valid 12Z Wed Aug 28 2024 - 12Z Thu Aug 29 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE SOUTHWEST, NORTHERN PLAINS TO UPPER MISSISSIPPI VALLEY, AND PARTS OF THE MIDWEST INTO THE OHIO VALLEY AND NORTHERN MID- ATLANTIC... ....2030z update... See previous discussion. ....Summary... Compared to yesterday's Day 3 ERO, the Southwest and northern-tier Marginal Risk areas were largely unchanged. However, based on the 00Z guidance suite, the Marginal Risk across the northern Mid Atlantic Region was expanded westward to include much of the OH Valley and parts of the Mid MS Valley. ....Southwest... Guidance mid-level vorticity progs continue to support a more north-south outlook area compared to Day 1, though nonetheless still quite similar. Instability and moisture parameters (afternoon and evening CAPE and PW profiles) remain similar, and thus the anticipation of more isolated/localized instances of flash flooding than otherwise, particularly after 18Z coinciding with peak diurnal heating. ....Upper Midwest... Strong, deep-layer warm and moisture advection ahead of the next vigorous mid-upper level trough (closed 500-300 mb low) and associated surface fronts will favor more organized/widespread elevated convection by Wed night ahead of the advancing low-level warm front. Models are still indicating spread with the QPFs, enough to keep the ERO risk level at Marginal for now. Later shifts will need to assess the need to upgrade at least a portion of the outlook area to Slight however, as the heavy rainfall signal exists given the degree of dynamical forcing and thermodynamical profiles. 00Z ECMWF and regional GEM in fact indicates localized totals of 3+ inches between 00-12Z Thu. ....Eastern Portions of the Mid Mississippi Valley-Ohio Valley- Northern Mid Atlantic... W-E frontal boundary will sink southward on Wednesday, then remain quasi-stationary Wed night as the mid- upper trough traverses the central-northern Rockies and High Plains. Deep-layer moisture and instability will be sufficient for areas of heavy rainfall along this boundary, while the easterly storm motions (parallel to the low-mid level fronts) would support the risk of cell training. Outside of the 00Z Regional GEM, the guidance at this point isn't overly robust with the QPF within the outlook area, at least not yet, despite some uptick in right- entrance region forcing from the upper level jet streak over northern NY-New England. Thus for now, have kept the ERO risk at Marginal. Hurley Day 3 Valid 12Z Thu Aug 29 2024 - 12Z Fri Aug 30 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM PARTS OF THE CENTRAL PLAINS INTO THE UPPER MIDWEST, ALONG WITH THE MID ATLANTIC REGION... ....2030z update... See previous discussion. ....Summary... Few changes were made to yesterday's Day 4 ERO Marginal Risk areas across the Central Plains to Upper Midwest and over the Mid Atlantic. ....Eastern Portions of the Central Plains into the Upper Midwest... Aforementioned upper trough and associated surface cold front will continue eastward on Thu-Thu night, though with the mid-upper low lifting north into western Ontario by 12Z Fri. This will keep the bulk of the deep-layer forcing north of the U.S., however sufficient low-level frontogenesis will persist ahead of the mid- upper shortwave well south of the main mid-upper low. Much cooler/drier post-frontal airmass will lead to a fairly tight moisture gradient along the front, with strengthening negative PW advection behind it. Given the anticipated swift movement of the front (strong deep-layer shear), for now it would appear any organized, more widespread linear convective segments ahead of the front will too be rather progressive. Therefore, have maintained the Marginal Risk area. ....Mid Atlantic Region... Lingering quasi-stationary boundary across the Mid Atlantic will couple with increasing right entrance region forcing via an upper level jet streak traversing NY-New England. Over time, the CAD signature becomes evident from the guidance -- i.e. cooler/more stable low-level air and a south-southwest dip in the surface boundary occur along and near the Mid Atlantic Coast. However plenty of deep-layer instability should linger west of the DelMarVa, which along with the forcing, should allow for more widespread/organized convection and a localized flash flood threat. Hurley Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!5cIvkXps-eEN6fTrQcDXrV6mfeHT95GeBOkw97kHQTMO= ufkazdf4eed9PNBSoth0M3bVKeRSxRHB-1QRRAlUrmtDvlQ$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5cIvkXps-eEN6fTrQcDXrV6mfeHT95GeBOkw97kHQTMO= ufkazdf4eed9PNBSoth0M3bVKeRSxRHB-1QRRAlUk75OmcI$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5cIvkXps-eEN6fTrQcDXrV6mfeHT95GeBOkw97kHQTMO= ufkazdf4eed9PNBSoth0M3bVKeRSxRHB-1QRRAlUF-_mANg$=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) .