Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Aug 10 2024 00:52:11 FOUS30 KWBC 100051 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 851 PM EDT Fri Aug 9 2024 Day 1 Valid 01Z Sat Aug 10 2024 - 12Z Sat Aug 10 2024 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF=20 NEW ENGLAND, THE CENTRAL AND SOUTHERN ROCKIES/HIGH PLAINS... ....01Z Update... With the center of Post-Tropical Cyclone Debby now moving into southern Quebec, the threat for widespread heavy rain and flash flooding is now greatly diminished across the Northeast. Therefore, the previous Moderate Risk has removed. The threat for locally heavy rainfall remains along the trailing inflow band, which currently extends from New Hampshire and western Maine back into southern New England. A Slight Risk was maintained where HREF guidance indicates another 1-2 inches may occur before rainfall rates diminish and the band shifts further to the east later this evening. Further to the south, deepening moisture along the=20 trailing cold front may fuel isolated to scattered storms from the=20 Northeast back into the Carolinas. These storms may produce some=20 locally heavy amounts, which may produce isolated flash flooding=20 concerns especially in areas recently impacted by heavy amounts. =46rom the central and southern High Plains and Rockies back into=20 the Southwest, made smaller adjustments based on recent=20 observations and hi-res guidance -- maintaining a Slight Risk=20 covering much of southern Colorado, northern New Mexico into the=20 Panhandle Region. Guidance continues to indicate that the greatest=20 threat for heavy rainfall accumulations this evening into the=20 overnight will center over northeastern New Mexico into the=20 Panhandles. Confluent steering flow along with upstream low level=20 easterly flow will continue to support training storms across this=20 region, with the HREF guidance indicating that amounts of 2-3=20 inches are likely. Pereira Day 2 Valid 12Z Sat Aug 10 2024 - 12Z Sun Aug 11 2024 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHWEST, CENTRAL ROCKIES INTO THE PLAINS, AND THE COASTAL CAROLINAS... ....20Z Update... The previous forecast MRGL risks are still within reason with only minor changes to each respective risk for the period. The heavy rain signal across the Eastern Carolinas is more diffuse compared to previous days with a magnitude lower in the probability fields for heavy precip values, mainly anything above 3". There is still a formidable signal for isolated pockets of 2-4" in some storms as they move slowly within the mean flow. HREF neighborhood probabilities for 3" remain elevated 50-80% but have a significantly lower output for anything above 5". Best chance for flooding remains within those urbanized areas confined to the coastal plain, but with elevated small stream responses lingering from the past few days of heavy rainfall, some areas usually not as susceptible may be under a better opportunity for flash flooding if a heavy thunderstorms settles overhead. Across the Plains and Western U.S, the signal for widespread heavy rainfall remains underwhelming, however another complex ejecting into the Southern Plains could offer a chance at a low-end SLGT upgrade if the mean QPF signal improves. The current indication is some scattered heavier cores within a progressive complex leading to modest probabilistic output within the 12z HREF. The area has been parched for precipitation the past several weeks, so the initial surge of rainfall will be a welcomed site with the FFG indices running very high for all 1/3/6 hour markers. The best threat for excessive rainfall will lie within more urban settings with some CAMs indicating a better chance within the OKC metro as well as a secondary batch just north of the DFW metro. Both areas lie within the MRGL risk threshold, but are not enough to warrant an upgrade given the antecedent conditions. Thus, maintained general continuity. Kleebauer ....Previous Discussion... ....Southwest, Central Rockies, and Plains... A rather broad MRGL Risk was maintained extending from the Southwest to the central/southern Plains as diurnal heating and monsoonal moisture will keep showers and thunderstorms developing during the afternoon and evening hours for much of the Four Corners region. Meanwhile, an area of more organized convection triggered by shortwave energy from the D1 period will be making its way eastward into the foothills and spreading out into the high Central/Southern Plains. There is a fair amount of uncertainty with how far east into the Plains the convection reaches, location of heaviest amounts and the overall accumulations. Most of the consensus is suggesting 1-3 inches however a couple models have maxes near/over 4 inches. A Marginal Risk covers much of the Four Corners, eastern Wyoming, western Nebraska and Kansas, Oklahoma, northern Texas, southwest Missouri and northwest Arkansas. If amounts trend up then a Slight Risk area may be need with further updates. ....Coastal Carolinas... A lingering frontal boundary and diurnal sea breeze convection will continue chances for scattered thunderstorms across the Southeast and more specifically the eastern Carolinas on Saturday. Soils should remain saturated after prior heavy rainfall, increasing the flash flood threat across an area that isn't usually as prone to flash flooding. CAMs depict localized totals from pulse thunderstorms could reach 1-3", which is supported by PWs over 2". Snell Day 3 Valid 12Z Sun Aug 11 2024 - 12Z Mon Aug 12 2024 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHWEST, FOUR CORNERS, CENTRAL ROCKIES INTO THE PLAINS, AND THE EASTERN CAROLINAS... ....20Z Update... The best signal for heavy rainfall in the period continues to point towards the Southern Plains to Ozarks region with a fairly robust MCS potentially developing beginning early Sunday evening and moving eastward into the Ozarks area and Northeast OK by the back half of the forecast period. The potential for 2-4" of rainfall has been indicated via some deterministic, but the area has been void of precipitation for a while meaning some of the antecedent conditions favor some priming before a more significant flash flood threat can ensue. The ensemble bias corrected QPF is fairly aggressive and there's some consensus growing with the specific location, however we have seen these setups shift inside 48 hours in the past as a lot is contingent on the evolution of the previous days pattern. As of now, have maintained a MRGL risk, but the addition of a SLGT is high somewhere in-of the Southern Plains to the Mid-Mississippi Valley, pending the eventual track of the future complex. Elsewhere, the Eastern Carolinas may see yet another round of enhanced convection, only this time the signal is for lower coverage and decreasing magnitude in the potential. The latest ensemble QPF output was lower within the southern half of Coastal SC leading to some trimming of the southern edge of the previous MRGL risk forecast. The remainder of the risk area was maintained with the best signal located across Eastern NC. Expect totals closer to 1-2" with upwards of 3" in the stronger cores this time around, a much lower threat compared to the previous several days. Kleebauer ....Previous Discussion... ....Four Corners, Southwest, and Central Rockies... A deepening western U.S. trough by D3 will allow for another round of diurnal monsoonal convection across the Southwest and Four Corners region, with GEFS and ECENS depicting PWs above the 75th climatological percentile. Opted to maintain the MRGL Risk for now given the limited QPF signal in available guidance and the possibility for fast storm motions. ....Plains and Mid-Mississippi Valley... Northwest flow aloft and a gradually lifting warm front over the Southern Plains will support MCS potential into the overnight period on D3 along with increasing mid-level flow, which could produce training and intense rainfall rates within convection. Relatively high uncertainty remains with the exact placement of heaviest rainfall (greatest potential currently near the western Ozarks into northeast OK and southeast KS), which prompted the MRGL Risk as opposed to a SLGT for now. Additional convection is possible over SD and NE, with similar uncertainty in placement. ....Eastern Carolinas... Another day of diurnal convection along a nearby frontal boundary could be enhanced by an approaching shortwave diving over the Ohio Valley around a deep upper-level low over SE Canada. Similar to D2, rainfall amounts of 1-3" appear possible and are likely to occur over saturated soils. Snell Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_vNVEQ5muHcHJJJjFCOm-qwrl_0jCxNK5tL-rmXD7x9D= VJsfVQ4Kn7485qsM1uB0SH0GRrZw0Jr2_Xsv3EeOQpaWsTs$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_vNVEQ5muHcHJJJjFCOm-qwrl_0jCxNK5tL-rmXD7x9D= VJsfVQ4Kn7485qsM1uB0SH0GRrZw0Jr2_Xsv3EeOgx79EmQ$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_vNVEQ5muHcHJJJjFCOm-qwrl_0jCxNK5tL-rmXD7x9D= VJsfVQ4Kn7485qsM1uB0SH0GRrZw0Jr2_Xsv3EeO1IjbtgQ$=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) .