Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Jun 13 2025 07:01:19 AWUS01 KWNH 130701 FFGMPD WIZ000-MNZ000-SDZ000-NDZ000-131200- Mesoscale Precipitation Discussion 0426 NWS Weather Prediction Center College Park MD 300 AM EDT Fri Jun 13 2025 Areas affected...south-central MN and some surrounding portions of far northeast SD, southeast ND, and western WI Concerning...Heavy rainfall...Flash flooding likely Valid 130700Z - 131200Z Summary...Bands of slow moving heavy rainfall with localized hourly totals of 1-2" may result in 5"+ totals through 7am CDT. Isolated to scattered instances of flash flooding are likely (and may be locally significant). Discussion...Bands of slow moving heavy rainfall are taking shape early this morning across portions of far northeastern SD and south-central MN, in response to strengthening isentropic ascent (concentrated on 295-300K surface) amid veering low-level (925-850 mb) flow. While the low-level jet is actually expected to weaken a bit over the next several hours (from 30-35 kts to 25-30 kts), the moisture transport (and more importantly the resulting isentropic ascent) will conversely become stronger and more pronounced (as the flow orients perpendicular to the isobars on the 300K isentropic surface). The resulting conditional symmetric instability (CSI) is driving the convective heavy rainfall threat this morning (even though MUCAPE of 250-500 J/kg is underselling the threat) with anomalously high wet bulb zero heights (~11k feet), 850 mb mixing ratios (~10 g/kg), and precipitable water (~1.5") all near the 90th percentile (per MPX sounding climatology). Hi-res CAMs have so far struggled to appropriately model what is ongoing, as impressive slow moving bands of heavy rainfall are indicated to be producing 15-min totals nearing 1" and hourly totals approaching 2" (per MRMS estimates). While modest low-level flow is producing these bands, the flow aloft within the layer of skinny CAPE from 700-500 mb is from the west at only about 10-20 kts. These slow moving heavy rainfall bands will tend to train form west-to-east (while gradually lifting north a bit), and while some of the CAMs do hint at localized 2" hourly totals (primarily the ARW2 and NAM-nest) they're likely underestimating the scale of the potential (given ongoing observational trends, which are occurring meaningfully south and east of the main model signal). Even still, the post-processed statistical data from the 00z HREF is hinting at the relative high-end potential from this event with 40-km neighborhood 6-hr probs for 3" and 5" exceedance of 25-45% and 5-15%, respectively. This corresponds with relatively high odds of 6-hr FFG exceedance (25-35%), as well as a chance (20-40%) of 10-yr ARI exceedance and a slight chance (up to 10%) for 100-yr ARI exceedance. Overall the HREF solutions are considered to be underestimating the threat, and therefore isolated to scattered instances of flash flooding are considered likely (and may be locally significant, given that training 1-2"/hr rainfall rates may result in localized 3-6 hour totals of 5"+). Churchill ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9GeO2Y_p77Jj9o2SbODDn2-XHhR37R_OH3EPWgoHh1cIuV3EhMFJSjsO1IGuvGB0qT-J= TYOT9z_2w22QGOGiRuATaDY$ for graphic product... ATTN...WFO...ABR...ARX...BIS...DLH...FGF...FSD...MPX... ATTN...RFC...KRF...MSR...NWC... LAT...LON 46489497 46459367 46079266 45309223 44499244=20 44089316 43979412 44399572 45099743 45719854=20 46389765 46459629=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) .