Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jul 02 2023 04:30:09 AWUS01 KWNH 020430 FFGMPD ILZ000-MOZ000-IAZ000-021030- Mesoscale Precipitation Discussion 0619 NWS Weather Prediction Center College Park MD 1228 AM EDT Sun Jul 02 2023 Areas affected...North-Central IL...Northeast MO...Southeast IA Concerning...Heavy rainfall...Flash flooding likely Valid 020430Z - 021030Z Summary...Slow moving showers and thunderstorms with rainfall rates of 1-3"/hr will likely lead to renewed instances of flash flooding overnight. Discussion...A broad area of low pressure and an associated frontal zone is gradually consolidating across portions of the Midwest tonight, driven by a parent shortwave trough hanging back (just upstream) across the intersections of IA/MO/NE/KS. Multiple rounds of showers and thunderstorms have occurred in the general vicinity of the MPD over the past 24 hours, with totals (per MRMS estimates) being most significant (swath of 2-6 inches) across northern MO into west-central IL. This has resulted in some local reduction in Flash Flood Guidance (FFG), generally ranging from 1.5-2.0" for 1-hr guidance, and 2.0-2.5" for 3-hr guidance. The mesoscale environment is currently characterized by MU CAPE of 500-1000 J/kg (largely surface-based), PWATs of 1.6-2.0 inches (near or above the 90th percentile, per ILX sounding climatology), and effective bulk shear of 20-30 kts. Convective activity is fairly disorganized at the moment, but updrafts have occasionally strengthened locally with those flareups coinciding with MRMS estimates rainfall rates of 1-3"/hr (largely aggravated by slow storm motions, as the 850-300 mb flow to the north and west of the surface low is a paltry 5-10 kts). Going forward tonight, convection is expected to remain fairly disorganized given relatively low levels of instability and shear (both near the median for this time of year, per ILX sounding climatology). However, the tropospheric column is certainly anomalously moist, and the aforementioned slow storm motions are the primary concern for any renewed flash flooding overnight. The 00z HREF guidance helps contextualize these concerns, as 40-km neighborhood probabilities for 3" exceedance indicate a broad area of 20%+ (with values peaking between 30-50% from far southeast IA into west-central IL). That said, totals in excess of 3" overnight are expected to remain highly localized.. as depicted by both the HREF probability-matched mean (PMM) and ensemble agreement scale (EAS) products (with hourly HRRR runs since 22z also suggesting highly localized 3"+ totals). Conceptually this makes sense, thus localized (i.e. relatively isolated) instances of flash flooding are considered likely overnight (with any heavy downpours over already saturated soils of particular concern, which could lead to a significant instance or two of flash flooding). Churchill ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!8Fq-n3RmwEKrzweQMfuQgW_g1nSJ5dAhsaJ9s3OFyHpA-5yqVvNWeBq0xgAgpUzRKsU_= pBO5MRIrE-xbSXQrb5tEPaI$ for graphic product... ATTN...WFO...DMX...DVN...EAX...ILX...LOT...LSX... ATTN...RFC...MBRFC...NCRFC...OHRFC...NWC... LAT...LON 41668975 41618792 40918763 40318895 39719006=20 39659122 40349284 41179293 41599104=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) .