Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Aug 27 2024 00:06:37 AWUS01 KWNH 270006 FFGMPD MIZ000-WIZ000-MNZ000-270600- Mesoscale Precipitation Discussion 0932 NWS Weather Prediction Center College Park MD 805 PM EDT Mon Aug 26 2024 Areas affected...Southeast MN...Northwest WI...Western UP of MI... Concerning...Heavy rainfall...Flash flooding possible Valid 270005Z - 270600Z SUMMARY...Very intense short-duration thunderstorms to produce 1-2" in less than an hour with developing QLCS. Additional stalled/stationary downstream thunderstorms along effective stationary front may result in longer duration heavy rainfall and widely scattered flash flooding as well. DISCUSSION...GOES-E 10.3um EIR loop depicts a broadening cirrus canopy indicative of an upscale growing MCS across central MN, with embedded overshooting tops to -75C. RADAR further confirms expanding arch/QLCS pattern west of the Twin Cities along and south of well defined stationary front that extends northeastward along the west coast of Lake Superior. Surface analysis also notes that Lake breeze becoming the effective FGEN forcing mechanism along the southern coast into NW WI, northern U.P. of MI has sharpened localized convergence is breaking out a few isolated cells as well. Very unstable environment of 3000-5500 J/kg of MLCAPE will support the MCS/QLCS driven by modest mid-level drying and solid lapse rates. As such very strong updrafts will support the primary severe weather hazard (see SPC MCD 2004 for more details). However, ingested low level moisture in the mid to upper 70s Tds and overall depth over 2.0" of total PWat will result in very strong moisture convergence and rapid conversion to intense rainfall rates. Instantaneous rates will be well over 2"; closer to 4-6"/hr, but with dry air mixing and Downdraft CAPE values over 1500 J/kg, forward propagation will limit residency to 15-45 minutes likely resulting in 1-2" totals as it passes. Increased potential exists along the northern and southern rotor/bookend vorticies; with the northern one will have higher potential of tracking along/near southern Lake Superior along the aforementioned effective stationary front. This may collect/merge with those isolated downstream cells or track through their rain-foot further increasing the potential for a spot or two of 2-3" through 06z. As noted, this will result in the greatest potential for localized flash flooding; however, the shear short-term magnitude may still result in localized flash flooding, especially in urban or hydrophobic ground conditions. So while, risk across the overall area of the MPD of flash flood inducing rainfall rates/totals is limited, there remains a sizable risk for these isolated possible incidents accompanying the increasing severe weather risk. Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9C80ZmZ1bt0RGefMOIFlD-tPVPT3ctMRjRxmtxoFROuXvyrqxgf6mMxYmjAE4gtWy04j= CnLxehwvKaOrxk6SxiQZBRA$ for graphic product... ATTN...WFO...ARX...DLH...GRB...MPX...MQT... ATTN...RFC...NCRFC...NWC... LAT...LON 46768816 46628762 46118754 45348873 44548886=20 43998988 43749145 43819327 44159422 44789389=20 45429350 45899339 46239299 46509180 46539098=20 46648988=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) .