Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jul 05 2023 00:45:12 FOUS30 KWBC 050045 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 844 PM EDT Tue Jul 04 2023 Day 1 Valid 01Z Wed Jul 05 2023 - 12Z Wed Jul 05 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE CENTRAL PLAINS... ....Southeast... Stationary boundary remaining draped across the region will continue to act as a focus for slow moving thunderstorms through the late evening, particularly across portions of the Mid-MS Valley where current radar shows multiple clusters of deep convection continuing and satellite imagery showing cooling cloud tops. The 18Z HREF suggests that area stands the greatest probabilities of seeing localized heavy rainfall exceeding 1-1.5"/hr through about 04-06Z before dissipating. Elsewhere across the Southeast, convection is likely to diminish further with the loss of daytime heating but locally heavy rainfall could linger for a few more hours. ....Front Range into the Plains... Shortwave energy ejecting out of the Rockies this evening combined with a frontal boundary draped across the Plains will drive multiple areas of deep convection through the overnight hours. Vigorous deep convection igniting along the frontal boundary in the Plains will work with the higher than normal moisture and expected instability and relative lower mean winds to produce intense rain rates and hourly totals up to 2" at times. Further to the west, as the shortwave energy comes out of the Rockies, more organized convection will likely track across portions of northeast Colorado into western Kansas while additional convection develops on the rose of the strengthening low-level jet across central/eastern Kansas. Altogether, multiple areas in the Slight Risk could see concentrated areas of 2-3"+ through 12Z and the Slight Risk was only minimally adjusted for the latest trends. Taylor Day 2 Valid 12Z Wed Jul 05 2023 - 12Z Thu Jul 06 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE MIDWEST, CENTRAL MISSISSIPPI VALLEY, CENTRAL/SOUTHERN PLAINS, AND EASTERN/COASTAL PORTIONS OF THE CAROLINAS... ....2030Z Update... No major changes were made with this afternoon's update. Uncertainty remains high regarding where the core of the heaviest rain is forecast for Wednesday. Just since last night the primary area of the highest probabilities has shifted from central MO to near the junction of I-35 and the KS/OK border. Due to that uncertainty and wild shifts in where the heaviest rainfall totals are expected, the Marginal Risk has been left in place for the Plains through MI. Likewise, only cosmetic changes were made to the Marginal Risk area for the eastern Carolinas, where isolated flash flooding is possible with the most persistent heavy rains with near stationary cells or cell mergers. There is some possibility the southern Appalachians of NC through GA may need to be added to the Marginal Risk with a future update, but the signal there is weak enough that it was left out of the western Carolinas for now. Wegman ....Previous Discussion... ....Upper Midwest/Mississippi Valley into the Central/Southern Plains... The unseasonably strong frontal system that has been discussed in the Day 1 ERO will gradually push southeastward, with the bulk of the forcing for convection following suit. Anomalously high moisture pooling along the front will present the risk for localized flash flooding across a rather large area, but there remains insufficient clustering/agreement to introduce any Slight Risk areas at this time (though central MO is situated near the highest probabilities). As the remainder of the CAM guidance covers the entirety of the Day 2 period later today, this will be further evaluated. Right now, the Marginal Risk area was maintained from the prior Day 3, and generally encompasses areas with the potential for localized 2" exceedance (per the available CAM guidance). ....Eastern/Coastal Carolinas... Maintained a Marginal Risk area again across the Carolinas as well, with the potential for short-term localized 2" exceedance (per the available CAM guidance). The tail end of a lingering frontal boundary (from the system ejecting into the Atlantic from the Northeast) will likely help to enhance afternoon sea breeze convection, and given prior days rainfall a Marginal Risk seems appropriate (despite the sandier soils and relatively high FFGs). Churchill Day 3 Valid 12Z Thu Jul 06 2023 - 12Z Fri Jul 07 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE CENTRAL PLAINS... ....2030Z Update... The only change worth noting was an expansion of the previous Slight Risk area southeastward into northwestern and north-central OK. With the D2/Wednesday area of heaviest rain now shifted into OK, the local maximum of forecasted rainfall expected for D3/Thursday in many of the same areas of OK was enough to increase the confidence that similar flooding impacts as expected in KS will also spread into OK. Elsewhere, typical summertime convection is likely from the lower MS Valley to the Mid-Atlantic, so few changes were needed to the inherited Marginal Risk area. Wegman ....Previous Discussion... ....North/Central High Plains into the Central Plains... The inherited Slight Risk area was maintained across much of western and central KS, as the global guidance continues to remain in rather good agreement with regard to the potential for 2-3" totals (with the deterministic ECMWF, GFS, UKMET, CMCreg, and the ECENS being the strongest contributors). Given the expected strong low-level return flow behind the departing system that has been discussed during Days 1-2, would expect robust diurnal convection to develop along the Front Range and North/Central High Plains, propagating upwind into KS/OK. While the exact location may need tweaking for future updates, the overall model agreement provides higher than usual confidence at this range. ....Ohio Valley into the Mid-South, Deep South, and Gulf Coast... The inherited Marginal Risk area was broadened a bit for this cycle, owing to some timing differences with the progression of the front across the global model suite. The unseasonably strong nature of the front is expected to locally enhance what would otherwise be typical pulse convection summertime storm mode, and thought an expansion of the Marginal was appropriate given this. That said, any meaningfully organized signal from the global models is currently lacking, and this area will need to be refined as we get into the range of the CAMs. ....Coastal Carolinas southward into Coastal Georgia and Northeast Florida... A Marginal Risk area was maintained and expanded a bit southward into Day 3, largely continuing the meteorological reasoning from Day 2 (as the tail end of a lingering coastal front may help to enhance diurnal sea breeze convection in the afternoon). The global guidance does a poor job resolving these largely mesoscale features at this range, and the risk area may need to be adjusted with future updates. Churchill Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9Vhl8JB4CPx0vAhjlzWCnuCEPJramqvgJ6uJK7L2im-Y= YOKNJcTRCwHva0qnLG06Z06kcL7U8tyX-4eoxMZUnHJCYII$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9Vhl8JB4CPx0vAhjlzWCnuCEPJramqvgJ6uJK7L2im-Y= YOKNJcTRCwHva0qnLG06Z06kcL7U8tyX-4eoxMZUELebeWc$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9Vhl8JB4CPx0vAhjlzWCnuCEPJramqvgJ6uJK7L2im-Y= YOKNJcTRCwHva0qnLG06Z06kcL7U8tyX-4eoxMZUrOiv8yc$=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) .