Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Jul 28 2023 01:24:31 AWUS01 KWNH 280124 FFGMPD WVZ000-OHZ000-KYZ000-INZ000-280630- Mesoscale Precipitation Discussion 0799 NWS Weather Prediction Center College Park MD 923 PM EDT Thu Jul 27 2023 Areas affected...Parts of the Ohio Valley Concerning...Heavy rainfall...Flash flooding possible Valid 280122Z - 280630Z Summary...Showers and thunderstorms developing along a low-level convergence axis will persist and drift southward tonight. Rainfall rates at times may reach 2"/hr, resulting in 1-3" of rainfall in some areas. Flash flooding is possible. Discussion...The regional radar mosaic this evening shows scattered slow moving thunderstorms developing along a west-to-east oriented axis from southern IN through central WV. These storms have struggled to organize due to minimal effective bulk shear, but impressive PWs around 2 inches as measured by GPS and a ribbon of extreme 3000-4000 J/kg MUCAPE is supporting repeated pulse convection. Storms this evening have generally been occurring along residual outflow boundaries and storm mergers, which within these favorable thermodynamics is producing radar-estimated rainfall rates above 2"/hr according to KILN. This has produced mesonet observed rainfall as much as 2 inches in a few locations resulting in localized CREST unit streamflow as high as 500 cfs/smi. The high-res guidance is high variable in its evolution tonight, so confidence is modest in the evolving flash flood threat. However, 850mb inflow of 20-25 kts is drawing the impressive PW/MUCAPE northward and driving efficient confluence into the low-level convergence axis noted in 850mb wind fields. This resupply of thermodynamics should allow for convection to continue to develop along outflow boundaries and within storm mergers where ascent will be locally enhanced despite weak mid and upper level forcing. With effective bulk shear progged to remain below 15 kts, pulse storms with limited temporal duration are expected, but any of these cells could have rain rates exceeding 2"/hr according to HREF neighborhood probabilities and HRRR sub-hourly fields as they generally drift southward. Additionally, where storm mergers or outflow collisions occurs, brief upticks in intensify and lengthening of rainfall duration are possible. While some of the high res indicates storms congealing into an MCS and diving southward, limited shear for organization suggests this is unlikely, and storms should remain pulse until instability gets exhausted overnight. This suggests that while most rainfall will be around 1 inch, there could be local maxima as high as 3 inches tonight, before instability finally exhausts overnight. A few flash flood warnings are already in effect, and this is where heavy rainfall has occurred atop pockets of more sensitive soils due to 7-day AHPS rainfall that is 150% of normal causing elevated USGS streamflow anomalies. 1-hr and 3-hr FFG is in some places as low as 1.5-2 inches, for which the HREF indicates has a 15-25% chance of exceedance. Flash flooding will remain possible across the area for several more hours, with the greatest chance occurring during any storm mergers, especially over any sensitive terrain features or urban areas. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_hULQry7ziI6554JT_Y6R2-aSWafH4Tsf892_cuydphM29Jghie3EXx45CLlbIZ-UjQg= jPPfRvyLlALMB5Vh-COg3og$ for graphic product... ATTN...WFO...ILN...IND...JKL...LMK...PAH...RLX... ATTN...RFC...OHRFC...NWC... LAT...LON 39458484 39418364 39268270 39038207 38538140=20 37998150 37918235 37568364 37278478 37128579=20 37138668 37368754 37708781 38468728 39268592=20 =20=20=20=20=20=20=20=20=20=20=20=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) .