Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri May 26 2023 08:11:32 FOUS30 KWBC 260811 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 410 AM EDT Fri May 26 2023 Day 1 Valid 01Z Fri May 26 2023 - 12Z Fri May 26 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE NORTHERN ROCKIES, NORTHERN HIGH PLAINS, SOUTHERN HIGH PLAINS, AND THE CAROLINA COAST... ....Carolinas... A quasi-stationary upper low upstream with rather robust upper difluence and along-stream upper divergence east of the low will favor the formation of a surface low over a favorable genesis region over the Gulf Stream waters off the concave SE US coastline. The relatively stagnant upper pattern (Rex Block with the closed upper dropping slowly through the Mid South) will make for a prolonged period of favorable deep-layer forcing and robust moisture transport, particularly across the SC and southern NC coast on Day 1 and over much of the Carolinas by Day 2. There is some spread in the guidance with respect to the QPF, though again the models confine the heaviest rainfall offshore (over the Gulf Stream) along with the more robust deep-layer instability. By the same token, the guidance brings 500+ J/Kg of MUCAPE and PWs ~1.75" closer to the coast after 00Z Sat, along with highly anomalous low-level easterly flow (50-60 kts at 850 mb by 09-12Z Sat, which is 5-6 standard deviations above normal). While the bulk of the heavy rainfall is expected to occur on Day 2 (after 12Z Sat), the rapid ramp-up in favorable deep-layer forcing and thermodynamic profiles Friday night supports a targeted Slight Risk area across coastal locations in northeast SC and southern NC. ....Great Basin-Northern Rockies-High Plains... A slightly progressive and broadening upper trough is forecast for the Western States. The deterministic and probabilistic QPF from the guidance support a localized or isolated flash flood threat possible anywhere within the broad risk area. Sufficient moisture combined with 2000+ J/kg of CAPE, and ample low-level inflow in the Plains will help aid the development of convection with heavy rainfall. A more enhanced risk lies across eastern MT, northeast WY, and western ND along/near the surface front, and over parts of eastern NM and the TX Panhandle/Cap Rock/Rolling Plains with the favorable upslope low-level flow. Both of the Slight Risk areas were expanded to account for recent heavy rainfall (including what has fallen more recently Thu night). The areas NM east into TX in particular have broad areas of 300-600% of average rainfall during this past week per the latest AHPS analysis. Hurley 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!_JlloY_P-aGgEprR2PYZOZaV3Rj5aaC_PDttC5kbJ_P4= qMr2jSBxkdTlVqE0EpWZfi1npYrQFbLYl1k45VDGOJGJT3o$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_JlloY_P-aGgEprR2PYZOZaV3Rj5aaC_PDttC5kbJ_P4= qMr2jSBxkdTlVqE0EpWZfi1npYrQFbLYl1k45VDGuK-PbrA$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_JlloY_P-aGgEprR2PYZOZaV3Rj5aaC_PDttC5kbJ_P4= qMr2jSBxkdTlVqE0EpWZfi1npYrQFbLYl1k45VDGQC1jLGA$=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) .