Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jul 03 2024 04:57:04 AWUS01 KWNH 030456 FFGMPD ILZ000-MOZ000-IAZ000-KSZ000-031055- Mesoscale Precipitation Discussion 0545 NWS Weather Prediction Center College Park MD 1255 AM EDT Wed Jul 03 2024 Areas affected...much of central and northern MO...adjacent portions of west-central IL and far northeast KS Concerning...Heavy rainfall...Flash flooding possible Valid 030455Z - 031055Z Summary...Additional isolated to scattered instances of flash flooding are possible as MCS slowly wanes/progresses. Some flash flooding may be locally significant (particularly if convection backbuilds further in northern MO). Discussion...A mature squall line has gradually transitioned into a more consolidated MCS (mesoscale convective system) over the past several hours, as surface based instability has been completely exhausted over portions of the Upper Midwest (from southeast IA into northwest IL). While some elevated instability (500-1000 J/kg of MU CAPE) remains across this region, the much more favored locations going forward are to the south and west (central/northern MO and downstream portions of west-central IL), where rich surface ThetaE air (350K+) is resulting in SB/ML CAPE of 1500-2500 J/kg (despite relatively mediocre low-level and mid-level lapse rates of 5.5-6.0 degC/km). The most impressive deep tropospheric moisture is also centered over central and northern MO, with precipitable water values of 2.2-2.5 inches (well above the max moving average of SGF sounding climatology, remarkable given the site nearly 200 miles south). But perhaps the most concerning development is the backbuilding of convection occurring over northwest MO (much closer to a surface cold front which significantly trails the bulk of the convection to the east), as a 30-35 kt low-level jet (LLJ) provides ample moisture transport and convergence. And while the aforementioned lapse rates are rather lacking for upper-level thermodynamic support, the combination of an MCV (mesoscale convective vortex, which originated from convection near the OK/KS border earlier today) and strong diffluence/divergence aloft (via the right-entrance region of a 100 kt jet streak over northern WI/MI) is supporting convection in this crucial upstream region. The latest hi-res guidance is a bit messy, given the complicated mesoscale evolution of convection that has taken place. Overall, the HREF signal is clearly displaced too far northeast with the QPF maxima (given the observational trends), but the more recent runs of the HRRR have done a good job assimilating and reflecting a southwest shift. When accounting for this southwest shift (as well as a reduction in the QPF magnitude from prior cycles of the HREF, which may be a bias due to the assimilation struggles), additional localized totals of 2-4" are expected across the region. These amounts would clearly be most problematic across the northern tier of the outlooked region (i.e. across portions of northern MO), but this is also where the forecast is most uncertain (as it is dependent on continued backbuilding of convection into an area that is relatively worked over with 3-hr ML CAPE reductions of 1000-1400 J/kg). Should convection continue to backbuild due to the many other favorable factors, then localized significant instances of flash flooding may occur (over these areas that have already received 2-4" over the past 3-6 hours). Farther south (where the heaviest rainfall and expected 2-4" localized totals are most likely), antecedent conditions are much drier (with 3-6 hour FFGs generally ranging from 2-3"). As a result, isolated to scattered instances of flash flooding are possible (and only conditionally likely farther north). Churchill ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!4nQGZL2LUCO4udRpc7Qne1YY28EO7DafJx6EIkMwB6AmUpAcSA9ESh-Dp6Q1PwlND5xN= dozf6i8noXH8ZdoG1tIGtD0$ for graphic product... ATTN...WFO...DVN...EAX...ILX...LSX...SGF...TOP... ATTN...RFC...MBRFC...NCRFC...NWC... LAT...LON 40429142 40359071 40039035 38979041 38189138=20 37989287 38789461 39599540 40269374 40419249=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .