Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue May 30 2023 07:52:34 FOUS30 KWBC 300752 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 351 AM EDT Tue May 30 2023 Day 1 Valid 12Z Tue May 30 2023 - 12Z Wed May 31 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE WEST, MIDWEST, AND PLAINS... ....Northern CA northeast across ID and southwestern MT/northwestern WY... Mid-Upper low off the Central CA Coast to start Day 1 (12Z Tue) will slowly wobble through SoCal during the period. Favorable upper-level diffluence north of the compact mid-upper low, south of the digging northern stream upper trough/height falls across the Pacific NW, will generate favorable broad-scale forcing across the outlook area Tue-Tue night. PWATs meanwhile are expected to climb between 0.75-1.00", which is ~1.5 standard deviations above normal for the end of May (per the GEFS) and plenty for heavy rain concerns at elevation. Modest uptick in deep layer forcing and moisture, along with at least some diurnal instability (mixed layer CAPEs peaking between 500-1000 J/Kg) will allow for scattered to more numerous showers/storms within the outlook area -- a few will be capable of hourly or sub-hourly rainfall rates of 0.50-1.00" which is around FFG values. 12Z HREF neighborhood probs max out around 35% for exceeding these FFG values, though perhaps overdone at nearby lower elevations. Nevertheless, this will pose a localized flash flood risk for yet another day, especially over any recent burn scars into northeast CA and southern OR and/or over areas that have received recent appreciable rainfall. ....Northern and Central Plains into Midwest... A pair of mid/upper level shortwave troughs are expected to pivot across eastern portions of the Northern Plains and across the far northern MS Valley today. Models do show some low-level frontogenetical response with these features, along with pockets of upper level divergence which are likely convectively enhanced.=20 PWATs look to peak around 1.3" (near the 75th percentile, per TOP sounding climatology), with SB CAPE rising to as high as 3000 J/Kg into the outlook area. Low-level inflow and effective bulk shear appear sufficient to organize convection that forms. While HREF neighborhood exceedance probabilities continue to suggest the potential for locally extreme amounts (3-5"+), it is too difficult to pinpoint a specific area within this broad region (as indicated by HREF EAS neighborhood probabilities for 1" exceedance, which only peak at 15% for southwest KS/OK Panhandle and the IA/NE/MO border region, respectively). Should the 12z HREF come into better agreement, a targeted Slight Risk upgrade (or two) are possible. ....Southeast OK into Northeast TX and Ark-La-Tex... Precipitable water values of 1.5"+ (near the 90th percentile, per SHV sounding climatology) with SB CAPE expected to increase to 1000-3000 J/kg. Low-level inflow appears weak, only on the order of 10-15 kts, but the mean 850-300 hPa winds are virtually null (which suggests minimal if not chaotic storm motion and better rainfall efficiency than average). Effective bulk shear may be as high as 25 kts on the western edge of the MRGL risk area, which may help to organize storms (and would potentially organize a complex, should upscale growth be sufficient). Even so, FFG values are quite high in this area so any excessive rainfall concerns should remain isolated. Churchill/Fracasso/Roth Day 2 The Day 2 outlook will be updated by 0830Z. Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6YaCjfh3XkDYZpsa2NytCPETYcycsl1TbRc0N6dMRnlD= c3slfh2gU7Fxz922-J25j_lkwfpeKHCWEDrGMBBRaV0bdDY$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6YaCjfh3XkDYZpsa2NytCPETYcycsl1TbRc0N6dMRnlD= c3slfh2gU7Fxz922-J25j_lkwfpeKHCWEDrGMBBRutowHeU$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6YaCjfh3XkDYZpsa2NytCPETYcycsl1TbRc0N6dMRnlD= c3slfh2gU7Fxz922-J25j_lkwfpeKHCWEDrGMBBRfpCuuPw$=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) .