Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue May 23 2023 07:49:50 FOUS30 KWBC 230749 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 349 AM EDT Tue May 23 2023 Day 1 Valid 01Z Tue May 23 2023 - 12Z Tue May 23 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHEAST, SOUTHERN PLAINS, NORTHERN PLAINS, AND INTERMOUNTAIN WEST... ....Southeast... Heavy rainfall will be likely again across portions of the Southeast Tuesday into Tuesday night as the upper flow remains broadly difluent, while at the surface a boundary remains draped quasi-stationary across the region. Moisture will continue to be above normal with the favorable easterly flow bringing in PWs 1.75"+ around the stationary boundary. While the deep-layer forcing will remain rather diffuse, 0-6km bulk shear values averaging 25-30 kts per the guidance will favor more widespread, multi-cellular cluster convection during and after peak daytime heating, with the more intense rainfall rates lasting a bit longer than the more typical pulse-type convection. As a result, upwards of 2-3+" within an hour will be likely underneath the strongest cells, as slow storm motions and colliding boundary interactions may also play a factor into the rain totals, which could top 3-5+" in places for the period. For the time being, what is preventing a higher risk (i.e. Slight) is the absence of more focused deep-layer forcing, which is leading to quite a bit of spread among the CAMs with respect to the QPF maxima given how much influence the more chaotic mesoscale processes/convective evolution have. Meanwhile, some overlap is possible with respect to heavy rain areas yesterday and again today, which may lead to a more enhanced risk (i.e. Slight) with subsequent updates to the Day 1 ERO. Otherwise, anticipate more isolated instances of flash flooding, particularly for the more susceptible locations and urban areas. ....Southern Plains... Another round of dry-line induced showers and thunderstorms is expected Tuesday into Tuesday night, a bit displaced to the east compared to today's expected convection. The latest guidance shows a better/strong low level jet upwards of 30-35 kts at 850 mb along with a large pool of higher moisture across the region. The 00Z guidance remains on track for showing potential of 1-2" areal average totals in the risk area with some signal for higher amounts possible and the Marginal Risk was only minimally changed for this update. ....Intermountain West into the Northern Plains... A very slow moving longwave trough over the West Coast will direct a large stream of moisture northeastward in advance of the trough. Embedded within the trough is an upper level low that will be over the BC/AT border north of WA/ID. A shortwave disturbance pinwheeling south of the low will approach the intermountain west Tuesday. This will locally increase the forcing (ribbon of upper divergence) over the Marginal Risk area across northeast NV and northern UT into eastern ID and the northern Rockies. Anomalous moisture will still be in place, with PWATs up to 0.75 inches are over 3 sigma above normal. This will support training storms tracking northeast from NV through UT and into ID. The storms that are forced by the local mountains may stay more stationary, which will locally increase the flash flooding potential. Meanwhile, scattered to numerous showers and thunderstorms are likely to develop across portions of North Dakota into northern Minnesota late this afternoon into the evening as a cold front approaches from Canada and intercepts a low level southeasterly jet of 25-30 knots that will be advecting deeper moisture into the region. Localized 1-2" totals are expected based on the latest forecast guidance and although the areal coverage of heavy rainfall isn't expected to be high, the storms that do form will be capable of producing intense rain rates that could be great enough to cause isolated instances of flash flooding.=20 Hurley/Taylor 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!9QXE5z_pRK1Rc078dPkv2ERSFxDl6L7QEal7gLahSWC4= kT8m7bjFORv87dQ5iR6Y2FzXaiRp3vFa5jZo24BM7ztP2Mk$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9QXE5z_pRK1Rc078dPkv2ERSFxDl6L7QEal7gLahSWC4= kT8m7bjFORv87dQ5iR6Y2FzXaiRp3vFa5jZo24BM116pbRk$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9QXE5z_pRK1Rc078dPkv2ERSFxDl6L7QEal7gLahSWC4= kT8m7bjFORv87dQ5iR6Y2FzXaiRp3vFa5jZo24BMQWsUZM0$=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) .