Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Aug 16 2025 06:52:08 AWUS01 KWNH 160650 FFGMPD MNZ000-SDZ000-161200- Mesoscale Precipitation Discussion 0943 NWS Weather Prediction Center College Park MD 249 AM EDT Sat Aug 16 2025 Areas affected...South-central & Eastern SD...Southwest MN... Concerning...Heavy rainfall...Flash flooding possible Valid 160650Z - 161200Z SUMMARY...Very progressive squall QLCS will have strong moisture flux for intense rainfall production with sub-hourly totals of 1.5-2"; though best risk for flash flooding will be flanking line training for spots of 2-3" over hard/impermeable soils. DISCUSSION...GOES-E WV suite shows a compact 80kt 3H jet streak across the North/South Dakota border which continues to strengthen a compact shortwave within its broad right entrance region. 06z Surface analysis shows an inverted wave inflection along the strongest DPVA/divergent region within the southeast quadrant of the wave across central SDak. A surface stationary front extends east into west-central MN before angling north toward Duluth and is directing strong and very moist low level flow to enhance very strong moisture flux convergence. Additionally, steep lapse rates with the very rich moisture at the surface in the mid to upper 70s, supports 4500-5000 J/kg and the combination is result in very broad and strong updrafts across south-central SDAK at this time.=20 Numerous overshooting tops below -75 to -80C denotes the vigor of the updraft including their width.=20=20 As noted, the surface Tds are well above normal and loading the low-level profile to support over 2-2.25" total PWat values and given the strength of the LLJ at 30-40kts, the lower cloud moisture loading is fairly high, even though some will be lost to hail production, there will be efficient rainfall production, further increasing with time/maturity of the squall. So while the limiting factor of forward speed/propagation for duration, the broad downdrafts will allow for some overall sub-hourly totals of 1.5-2". Additionally, the strength of the bow is also supporting a veering low level profile and tight anticyclonic rotor along the southwesterly flanking line. VWP and RAP analysis suggest that flanking axis is likely to trail and has some solid angle toward the initial bow/squall line to add an additional duration of heavy rainfall. As such, an axis of enhanced totals of 2-3.5" in 2-3 hours is becoming increasingly probable across south-central into eastern SDak and eventually into SW MN. Hydrologically, the area has been in a solid drought and ground conditions well below average running at about 10-25th percentiles with 0-40cm at 10-25%. This makes the soils hard and reduce infiltration particularly in the strength of the instantaneous rates sub-hourly totals...with 03z HRRR solutions suggesting 15min totals ranging from 1.5 to as high as 2", this suggests fairly quick totals with little/no infiltration, increasing run off. As such, localized flash flooding is considered possible, especially if the flanking line repeats behind the initial line.=20=20 Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!-Vh8PTkf1F0MIOfoehoFF2Lew4lcse0AoUz4MXvZw3BLK6bC0oHDF6U3CZ4_I-m3HXcd= trvGEa8u2TMdIZfYq6fPTAo$ for graphic product... ATTN...WFO...ABR...FSD...MPX...UNR... ATTN...RFC...KRF...MSR...NWC... LAT...LON 45669531 45439422 44779398 44209493 43689625=20 43229806 43040054 43190186 44050077 44769940=20 45279730=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 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .