Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Jul 27 2023 21:26:28 AWUS01 KWNH 272126 FFGMPD MIZ000-WIZ000-MNZ000-280330- Mesoscale Precipitation Discussion 0798 NWS Weather Prediction Center College Park MD 525 PM EDT Thu Jul 27 2023 Areas affected...Upper Midwest into the Western Great Lakes Concerning...Heavy rainfall...Flash flooding possible Valid 272130Z - 280330Z Summary...Thunderstorms will increase in coverage and organize into clusters ahead of a cold front this evening. Rainfall rates of 1-3"/hr are possible, which could result in 2-3" of rain with locally higher amounts. Flash flooding is possible. Discussion...The regional radar mosaic this aftn shows an area of convection expanding across northern WI and eastern MN. This convection is being driven by an approaching 700-500mb shortwave noted in the GOES-E WV imagery which is also driving a WPC analyzed cold front eastward. This is working in tandem with an upper jet streak positioned across Canada to drive deep layer ascent across the Upper Midwest. Thermodynamically, the environment is extremely favorable for heavy rainfall rates noted by PWs exceeding the 90th percentile according to the SPC sounding climatology, and MUCAPE of more than 4000 J/kg. The overlap of this ascent and robust thermodynamics is resulting in rainfall rates estimated by KDLH of 1.5"/hr. FLASH responses to this rainfall have been modest so far, likely due to generally fast forward motion on 850-300mb mean winds of 25-30 kts. This motion is progged to remain through the evening, but with continued thermodynamic advection on pre-frontal SW flow and increasing effective bulk shear around 40 kts to help organize storms, rainfall rates could rise to 3"/hr. This is reflected both by HREF neighborhood probabilities and the HRRR 15-min rainfall showing up to 0.75" at times. Despite the fast motion, these rain rates could overwhelm soils to drive rapid runoff, especially in urban areas or atop the most vulnerable areas that received 1-2" of rain earlier today. Additionally, mean 0-6km winds are forecast to become more closely aligned to the approaching cold front, which could pose an enhanced training threat to the SW as storms develop into the greater instability and lift northeast through the evening. This is reflected by a SW to NE extension of higher HREF probabilities for 3", as well as some modestly higher EAS probabilities for 1" indicating better model agreement in this evolution. Soils across this area generally feature near normal moisture due to variable rainfall and USGS streamflow anomalies that feature spotty above normal values. However, FFG in some areas, especially across less permeable urban corridors and across the western U.P. that received heavy rain this morning, is as low as 1.5"/3hrs which has a 20-40% chance of exceedance. Instances of flash flooding will likely be isolated this evening, but could occur anywhere the most intense rain rates train, or fall atop the more vulnerable soils. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!45h42tX6Drhtv-tK4_KBdiIcRK5fWff77hhjoiHKswwCb6HBiV5XaFecQ4oxpWWFfAs2= wRz5bLZQKyRNSxQzJwwgLYY$ for graphic product... ATTN...WFO...ARX...DLH...FSD...GRB...MPX...MQT... ATTN...RFC...NCRFC...NWC... LAT...LON 47248801 47198784 46778721 46068732 45528811=20 45298873 44968952 44519048 44229159 44019300=20 43929424 43949507 44459530 45279497 45999431=20 46629316 46969220 47239003=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) .