Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu May 18 2023 08:16:08 FOUS30 KWBC 180816 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 411 AM EDT Thu May 18 2023 Day 1 Valid 12Z Thu May 18 2023 - 12Z Fri May 19 2023 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS OF THE CENTRAL/SOUTHERN PLAINS COASTAL SOUTH CAROLINA... ....Central/Southern Rockies to the Plains... A surface front sandwiched between a closed upper-level low positioned over the Upper Midwest and separate closed upper-level low over northern Baja California will focus a risk of heavy rain from the High Plains of southeast Colorado/northeast New Mexico to north-central Oklahoma and south-central Kansas. Modest moisture is expected to help generate scattered convection growing upscale into a potential MCS further east across the Central Plains by the evening. Recent rains have increase soil saturation across the Rockies and adjacent High Plains region, with 3-hr FFG as low as 1 inch in the higher terrain. There has been widespread severe to exceptional drought across western and south-central Kansas, as well as western and north-central Oklahoma. This has the potential to limit any long-duration flooding and contain the risk to any immediate flash flooding due to overlapping thunderstorms with rainfall rates up to 2"/hr. The sensitivity of the soils will be more prone to flooding across southeast Colorado and within any urban areas. The widespread drought conditions remain the limiting factor within much of the Slight Risk area over Kansas and Oklahoma, however model consensus shows the potential for 1 to 4" with potential local maximums nearing 6 inches. The greatest excessive rainfall risk will likely be near a northern bookend vortex associated with an organized MCS. The most likely location for this within recent model guidance is along and just south of the western/central Kansas-Oklahoma border. Maintained the Slight and Marginal Risks for this period. ....Southeast... There will be a stalled frontal boundary draped across the Southeast today with a surface low developing near the Georgia/South Carolina Coast. Convection should remain widely scattered and unorganized, while also occurring over parts of the country where soils can handle brief periods of heavy rain. FFG across much of the Lowcountry is n the 3-5" range, urban areas and typically prone low-lying regions will be most at risk to the isolated flash flood threat. The latest guidance is depicting higher QPF closer to the coastline/slightly inland coinciding with high tide. Some of the CAMs are showing areal of 3 to 5+ inches with a couple even higher, in the 5-7+ range. With minimal movement of the low or the frontal boundary, the rainfall could be very efficient and quickly become excessive. In coordination with the local forecast offices a Slight Risk was hoisted for much of coastal South Carolina and extreme North Carolina. Elsewhere, the Marginal Risk was also expanded further north across central South Carolina and southern North Carolina. Campbell/Snell Day 2 Valid 12Z Fri May 19 2023 - 12Z Sat May 20 2023 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS OF THE CENTRAL/SOUTHERN ROCKIES AND CENTRAL ARIZONA, AS WELL AS, THE SOUTHERN PLAINS/LOWER MISSISSIPPI VALLEY... ....Southern/Central Rockies into Central Arizona... During this period a cold front is expected to slow/hang in the vicinity of the Central/Southern Rockies on Friday, with upslope flow on its backside in an environment with anomalous moisture. Increased soil sensitivity combined with high streamflows will maintain an elevated threat for excessive rainfall and isolated areas of flash flooding. The latest guidance continues to forecast up to 2 inches over this part of the country. Localized flooding and exaggerated flooding where snowmelt comes into play. The Marginal Risk area spans from the Mogollon Rim (Arizona) to south-central Colorado and eastern New Mexico. ....Lower Mississippi Valley to Southern Plains... Farther east, ongoing convection from early Friday morning across eastern OK and southern KS may contain elevated rain rates continuing to nudge into portions of far eastern Oklahoma, Arkansas, and southern Missouri, leading to the Marginal Risk area. The front continues to appear progressive during this period which will should not allow for too much training of storms. Storms along the cold front extending into the Ohio Valley and the Great Lakes should also be progressive enough to limit the flash flood potential. The Marginal risk was expanded a little further southwest over central TX. ....Coastal North Carolina.. The latest guidance show a large spread on where the QPF will be and how much as a compact surface low pressure system lifts north on Friday near far eastern North Carolina. PWs potentially exceeding 1.5" combined with frontogenesis associated with the surface low and associated warm front could support a narrow corridor of intense rainfall possibly exceeding 4-5", but this rain could very well occur offshore or over areas with very high FFGs along the immediate coastline. Will continue to monitor the excessive rainfall potential should trends shift the heavy rainfall amounts further inland. The threat for excessive rainfall is non-zero, especially along the coast. Campbell/Snell Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4j6BIBUg17zWQrbtk1aBMAsHWPxalPbEI9lnQn4IrPgC= U9pe65BfaYEJSAZjJoGd_zDXeRw0Jgv-5iPPpkIBNohhQuM$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4j6BIBUg17zWQrbtk1aBMAsHWPxalPbEI9lnQn4IrPgC= U9pe65BfaYEJSAZjJoGd_zDXeRw0Jgv-5iPPpkIB52ZQCNo$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4j6BIBUg17zWQrbtk1aBMAsHWPxalPbEI9lnQn4IrPgC= U9pe65BfaYEJSAZjJoGd_zDXeRw0Jgv-5iPPpkIBx4HHfVk$=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) .