Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jun 18 2023 08:24:51 FOUS30 KWBC 180824 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 423 AM EDT Sun Jun 18 2023 Day 1 Valid 12Z Sun Jun 18 2023 - 12Z Mon Jun 19 2023 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL OVER PORTIONS OF THE LOWER MISSISSIPPI VALLEY AND SOUTHEAST... ....Lower MS Valley into the Southeast... A 500 mb shortwave driving the ongoing convection across OK/KS/AR/MO will become detached from the main flow and slow down considerably by this evening and tonight. However, its presence along with plentiful Gulf moisture (over 1.75 inches PWATs) and impressive instability (MUCAPE values in the GFS are over 5,000 J/kg over far southern AR by this evening) will be very favorable to additional/continued thunderstorm development all throughout the Slight Risk area through tonight. For northern areas, the main driver will be that stalling out shortwave. Meanwhile, the forcing further south across central MS/AL will mainly be prior outflow boundaries and a reinvigorated nighttime low level jet (LLJ) redeveloping on 30-35 kt southwesterly mid-level winds. While the storms will be moving, Corfidi vectors of 5 kts over much of central MS/AL suggest a high likelihood of repeating convection. As usual, exactly where this axis of repeating convection sets up is the primary uncertainty at this point. Latest HRRR guidance suggests it will be over central AL, while much of the global models and other CAMs suggest MS will be the more likely target. For now just left the entire area in a Slight, but depending on how many repeating rounds of storms move over the same area, especially if there is some urbanization, it's possible locally Moderate level impacts will be seen. ....FL Peninsula... Ongoing showers and thunderstorms this morning will continue sagging south across the southern Peninsula through the day today. An isolated flash flooding threat is possible in any urbanized and poor drainage areas that get repeating rounds of convection, but given the ability for much of the region to handle the amounts of rain forecast, these will be few and far between. ....ID/MT/WY area... An upper level low and longwave trough moving into the Pacific Northwest will become more positively tilted as a vigorous shortwave trough dives southward to the west of the upper level low and trough axis, reaching northern CA by early Monday morning. This will align the upper level pattern in a southwest to northeast straight line configuration across the Marginal Risk area. An embedded 130 kt jet will round the base of the trough, putting the Marginal Risk area in a favorable left exit region of that jet streak. Somewhat anomalous moisture with PWATs approaching 0.75 inches, or 1.5 sigma above normal, along with moisture from recent rainfall will all contribute to repeating shower activity, with potential for some embedded convection, as noted on radar over western MT as of the time of this writing. The mountain ranges that are aligned orthogonal to that flow, so those with southwest facing slopes have the greatest potential to see flash flooding impacts, as upslope further enhances rainfall rates in this region. Wegman 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!59TkHy6eQ2mXSvsFEjdn1Lmbr1FPtmHzVIVv9Q_-qR4O= LhleKBbjgVSGwx6ygYA6g4NDypbWgxs9cEaCrsr8q9QR6Fg$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!59TkHy6eQ2mXSvsFEjdn1Lmbr1FPtmHzVIVv9Q_-qR4O= LhleKBbjgVSGwx6ygYA6g4NDypbWgxs9cEaCrsr8TDpQrzw$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!59TkHy6eQ2mXSvsFEjdn1Lmbr1FPtmHzVIVv9Q_-qR4O= LhleKBbjgVSGwx6ygYA6g4NDypbWgxs9cEaCrsr8TChSBhA$=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) .