Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Jul 28 2023 19:29:45 FOUS30 KWBC 281929 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 328 PM EDT Fri Jul 28 2023 Day 1 Valid 16Z Fri Jul 28 2023 - 12Z Sat Jul 29 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MIDWEST... ....16z Update... No major changes were needed for the 16z update. Minor changes included expanding the slight risk slightly more into south-central Wisconsin as well as combination of the marginal risk areas along the Southeast Coast and Southwest Florida to include the central Peninsula region. Both changes were based on latest high-res guidance indicating higher totals in these regions with support from HREF probablilty fields as well. Santorelli ....Midwest/Ohio Valley/Central and Southern Appalachians... While numerous differences in the details remain, the general model consensus shows mid-level energy moving along the top of an upper level ridge, with ample moisture (PWs at or above 1.5 inches) supporting the development of isolated to scattered convection across the region during the day today. While likely to remain unorganized, these storms may still produce locally heavy amounts, which may result in isolated runoff concerns. More organized convection, with a greater threat for more widespread heavy amounts, is likely to develop during the evening and overnight hours across portions of the Midwest. Strengthening southwesterly flow ahead of a more-defined wave moving out of the northern Plains will support increasing moisture (PWs increasing to at or above 2 inches) along a front sagging south through the southern Great Lakes region. Each of the 00Z CAMs shows one or more convective complexes developing and tracking east from the mid Missouri and upper Mississippi valleys through the southern Great Lakes, to as far east as the the upper Ohio Valley overnight. These storms may produce intense rainfall rates, with the threat for repeating convection increasing the threat for localized flash flooding concerns. HREF neighborhood probabilities for amounts exceeding 2 inches are above 50 percent within much of the Slight Risk area.=20=20=20 ....Southeast Coast... As an area of low pressure over northern Florida drifts into southern Georgia, increasing onshore flow and low level convergence, coupled with divergent flow aloft, are expected to support showers and thunderstorms with heavy amounts along the Southeast Coast from northern Florida to South Carolina.=20 Convergent onshore flow is forecast to support PWs of 2.25-2.5 inches along the coast while divergence east of the upper center further supports ascent across the region. Consensus of the CAMs indicate that locally heavy amounts are likely, with the HREF showing high neighborhood probabilities for 3 inches or more within the Marginal Risk area. ....South Florida... Southerly flow in the wake of the previously noted low and along the western periphery of the subtropical ridge will continue to support above-normal moisture (PWs at or above 2.25 inches) across the southern peninsula. This is likely to support diurnal convection, with heavy downpours. This may result in an isolated runoff concerns, especially across urbanized areas. Pereira Day 2 Valid 12Z Sat Jul 29 2023 - 12Z Sun Jul 30 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE NORTHEAST AND THE CENTRAL APPALACHIANS... ....Ohio Valley/Central and Southern Appalachians to the Northeast and Mid-Atlantic... Ongoing storms across portions of the Ohio Valley into the Northeast are expected to continue through Saturday morning, with intensification possible near the associated wave and cold front as it moves across southeastern New York and southern New England during the afternoon hours. The latest model QPF amounts, along with HREF exceedence probabilities support the addition of a slight risk area across this region for the update this afternoon. Models also show the potential for storms with heavy rains to develop farther to the south along the trailing cold front as it drops through the coastal Mid-Atlantic region during the late afternoon and evening hours. Lacking a strong model consensus for where and if heavy amounts may occur, a Marginal Risk was maintained across the Mid-Atlantic for now. There remains a pretty good signal for locally heavy amounts farther to the west across portions of the central Appalachians, where mid-level energy and favorable upper jet forcing are expected to interact with the deep moisture pool along the front to produce at least locally heavy amounts. Given the relatively wet soil conditions and low flash flood guidance values, a Slight Risk was maintained across portions of West Virginia into southwestern Virginia/northeast Tennessee. ....Southeast Coast... An area of low pressure will continue drifting slowly northward continuing to fuel numerous showers and thunderstorms across the Southeast coastal region into Saturday. Ample moisture and instability will continue to support a localized flash flood threat across this region. New model guidance today allowed for the addition of a marginal risk area here for the afternoon update. ....Eastern and south-central Colorado and the Sangre de Cristo Mountains of New Mexico... Easterly low level inflow is expected to contribute to an increase in moisture and the development of showers and thunderstorms over the mountains. Weak flow aloft is expected to increase the potential for slow-moving storms, which may result in locally heavy amounts with isolated flash flooding concerns. ....Southeastern Arizona/Southwestern New Mexico... Increasing moisture ahead of a easterly inverted trough moving across northern Mexico is forecast to help support increasing coverage of showers and thunderstorms across the region. Models shows PWs returning to 1-1.5 standard deviations above normal across portions of the region, increasing the threat for showers and thunderstorms with locally heavy amounts and isolated runoff concerns. Santorelli/Pereira Day 3 Valid 12Z Sun Jul 30 2023 - 12Z Mon Jul 31 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHWEST AND THE NORTHERN PLAINS... ....Southwest... An inverted upper trough will continue to lift northeast from northern Mexico into the southwestern U.S., pushing the subtropical ridge farther to the east and allowing deeper moisture to advect across Arizona through the Four Corners region and into the central Rockies. Both the NAM and GFS show PWs increasing to over 1.5 standard deviations above normal across portions of southern Arizona and the Four Corners region on Sunday. This moisture along with decreasing heights aloft is likely to support more widespread afternoon and evening thunderstorms and an increased threat for locally heavy amounts and isolated flash flooding. ....Northern Plains... Mid level shortwaves moving off of the top of the ridge may pose a localized heavy rainfall threat as they interact with a plume of deeper moisture fed by southeasterly low level flow. These storms could pose an isolated flash flooding threat across the northern High Plains into central South Dakota before moving into the less flood prone areas of central Nebraska. While most of the guidance indicates that storms with locally heavy amounts can be expected, there is still considerable uncertainty on exactly where storms may set up. Santorelli/Pereira Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7A5J6miY3UZcIkFap7i91DCS_9BFvEzkxK1y7UvcYhMh= Qy9YoPbfq9ufRwHw9a5cIfWUBKJamSLFq90sfce0Dwrxerg$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7A5J6miY3UZcIkFap7i91DCS_9BFvEzkxK1y7UvcYhMh= Qy9YoPbfq9ufRwHw9a5cIfWUBKJamSLFq90sfce0dtnlx0w$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7A5J6miY3UZcIkFap7i91DCS_9BFvEzkxK1y7UvcYhMh= Qy9YoPbfq9ufRwHw9a5cIfWUBKJamSLFq90sfce0_6_PgbY$=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 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .