Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Aug 04 2023 18:08:36 AWUS01 KWNH 041808 FFGMPD MOZ000-IAZ000-KSZ000-NEZ000-050000- Mesoscale Precipitation Discussion 0860 NWS Weather Prediction Center College Park MD 208 PM EDT Fri Aug 04 2023 Areas affected...portions of the southern Missouri Valley Concerning...Heavy rainfall...Flash flooding likely Valid 041807Z - 050000Z Summary...A wave of low pressure developing across far northeast KS will drift eastward this afternoon into Missouri. This will create expanding convection with rain rates reaching 2-3"/hr. Slow motions of these storms could produce 3-5" of rain and instances of flash flooding. Discussion...A convectively enhanced shortwave ejecting out of Nebraska is helping to amplify a wave of low pressure moving across northeast Kansas. This is evident in the regional radar mosaic as an area of circulating reflectivity. This ascent is impinging into a region of favorable thermodynamics noted by PWs nearing 2 inches, well above the 90th percentile according to the SPC sounding climatology, and a corridor of 1000-2000 J/kg MUCAPE. More concerning is that these thermodynamics are overlapped efficiently with extremely deep warm cloud depths above 10,000 ft and low nCAPE, indicating efficient warm rain collision processes will dominate. This has already resulted in radar-estimated rain rates exceeding 1"/hr according to KTWX despite reflectivity only around 35-40 dBZ. There is still uncertainty into how this will evolve through the aftn so confidence is modest, but the risk for flash flooding appears to be increasing. As the low pressure moves slowly eastward, the enhanced ascent into the favorable thermodyanmics should drive an expansion and intensification of thunderstorms. This is reflected in most of the available high-res simulated reflectivity. While SBCAPE may remain modest due to leading cloud cover, the impressive theta-e ridge rotating cyclonically around the low into a modest TROWAL should support enhanced MUCAPE, resulting in heavy rain rates. The HREF hourly rain-rate probabilities climb to as high as 40% for 2"/hr, highest in NW MO, which is well collocated with HRRR 15-min rainfall reaching 1" (brief 4+"/hr rain rates). 0-6km mean winds are going to remain quite weak in the vicinity of this low, so although there is some uncertainty into how widespread convection will become, what does develop should move extremely slowly at around just 5 kts at times. This could produce rapid and excessive rainfall accumulations reaching 3-5", with locally higher amounts noted by probabilities for 5" reaching 20-40% in both the HREF and experimental RRFS TL ensemble. Additionally, despite uncertainty in coverage, the HREF EAS probabilities for 1" reach impressive values of 20-25%, suggesting higher confidence in the placement of the heaviest rainfall. More concerning for the flash flood risk is that these slow moving, heavy rain producing cells will be occurring atop already saturated soils. AHPS 14-day rainfall is generally 150-300% of normal, leading to vulnerable soils noted by high USGS streamflow anomalies and compromised FFG. The HREF 3-hr FFG exceedance probabilities reach above 60%, reflective of the likelihood for instances of flash flooding across these sensitive soils. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_rqvh71d_AGxbzRCywQuBSrXGgW3wnpNjxTUxjwwuncWdLKo3WPRv_nI4VBQR9m0ZBeo= t2rtAwDHQwllOxL44Wbm1ic$ for graphic product... ATTN...WFO...DMX...DVN...EAX...LSX...OAX...SGF...TOP... ATTN...RFC...MBRFC...NCRFC...NWC... LAT...LON 41609429 41479336 40749232 39869176 39089164=20 38579196 38339250 38359313 38719376 39059480=20 39219561 39329613 39639672 40219685 40779656=20 41319572=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) .