Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Feb 14 2023 20:20:27 FOUS30 KWBC 142020 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 319 PM EST Tue Feb 14 2023 Day 1 Valid 16Z Tue Feb 14 2023 - 12Z Wed Feb 15 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. ....16Z Update... In coordination with the FSD/Sioux Falls, SD; DMX/ Des Moines, IA; ARX/ La Crosse, WI; and MPX/Minneapolis, MN forecast offices, opted against an upgrade to a Marginal Risk with this morning's update. The concern is rainfall falling onto snowpack with anywhere from 2 to 5 inches of snow water equivalent would lead to isolated instances of flash flooding. However, temperatures in the upper 30s should hinder snowmelt rates enough that while there certainly will be rises on area rivers and streams with today's/this evening's rainfall, the flash flood threat remains low as they should be gradual rises. Urban flooding due to clogged storm drains specifically in the Twin Cities metro remains the highest chance in the area of seeing any flooding. Wegman Day 2 Valid 12Z Wed Feb 15 2023 - 12Z Thu Feb 16 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY, WESTERN TENNESSEE VALLEY, AND LOWER OHIO VALLEY... ....2030Z Update... Very few changes were made with this afternoon's update. The Marginal Risk area was trimmed on the southern end a bit with a focus on northwestern LA across northern MS. The guidance is in good agreement that thunderstorms will develop along an axis from northwestern LA through northern MS. Thus, with increased certainty as to where the convection will develop, the confidence allowed the narrowing of the Marginal Risk area. Meanwhile further north, there were no changes to the previous risk area, and the previous discussion below remains in effect. Wegman ....Previous Discussion... Upper level jet streak and associated shortwave energy will round the base of the longwave trough on Wednesday, then lift northeast along the eastern periphery late Wed-Wed night as the the trough begins to phase with the northern stream shortwave. At the surface, the guidance is fairly well clustered with the lee-side low emerging across the TX Panhandle by midday Wed, and are now in more decent alignment with the track and timing through Wed night (GFS and NAM still a bit faster than the non-NCEP consensus, however both are trending closer to the ECMWF). Wed night into Thu morning, as the upper level jet streak and associated shortwave energy lift across the Central Plains and Lower MO Valley, the longwave trough will be nudging eastward across the southern High Plains. The increasingly difluent flow aloft, combined with the right-entrance region forcing from the upper jet streak to the north, will strengthen the low-mid layer moisture transport and deep-layer ascent across the outlook area Wed night into Thu morning. Per both the GEFS and SREF, 850-700 mb moisture flux anomalies climb between 3-4 standard deviations above normal between 00-12Z Thu, as 850 mb SSW flow increases to 40-50 kts. Increasingly favorable thermodynamic environment in evolving warm sector will also include PWs increasing to 1.5-1.6 inches and MUCAPE values between 500-1500 J/Kg. The dynamic and thermodynamic setup will favor 1-2" hourly rainfall rates Wed night underneath the stronger convective clusters, however at this point it appears there will be enough low-mid layer shear to maintain forward propagation, at least through 12Z Thu, especially over eastern portions of the outlook area. Because of this and overall later timing of the heavier rain (latter half of the outlook period/after 00Z Thu), will maintain the Marginal Risk from yesterday's Day 3 ERO with the anticipation of at most isolated/localized short-term runoff issues.=20 Hurley Day 3 The Day 3 outlook will be updated by 2030Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9ipJCHg5UtReowg7txdvTxr2S4wpJLpPtcipDYRIDrGb= 3qfTNeW4h7dhbVb_9xM5Xe2vhqTYmlPgPfc3H3tEQbxP8Ss$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9ipJCHg5UtReowg7txdvTxr2S4wpJLpPtcipDYRIDrGb= 3qfTNeW4h7dhbVb_9xM5Xe2vhqTYmlPgPfc3H3tEleMV3eE$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9ipJCHg5UtReowg7txdvTxr2S4wpJLpPtcipDYRIDrGb= 3qfTNeW4h7dhbVb_9xM5Xe2vhqTYmlPgPfc3H3tEbNNyWVU$=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) .