Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Jun 01 2023 08:13:17 FOUS30 KWBC 010813 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 412 AM EDT Thu Jun 01 2023 Day 1 Valid 12Z Thu Jun 01 2023 - 12Z Fri Jun 02 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE SOUTHERN-CENTRAL PLAINS AND MUCH OF EAST-CENTRAL MONTANA INTO NORTH-CENTRAL WYOMING... ....Central and Southern Plains... Based on continued CAM trends and short-term wet antecedent soils, maintained an adjusted Slight Risk area largely based on the new HREF and associated neighborhood exceedance probabilities (suggesting high odds of localized 2" exceedance across the region). This includes a small portion of northeast NM, much of the TX/OK Panhandles, and into north-central OK and south-central KS. Another active day of convection looks likely, with some additional lift being provided by the northward moving aforementioned mid-upper low and associated vort max. While convection overall should be less organized than on Day 2, there could be multiple rounds of heavy rainfall with convection likely still lingering from overnight into the morning, in addition to the anticipated initiation from daytime heating in the afternoon/evening. Further increasing confidence, the latest machine learning CSU First-Guess fields continue to depict a broad Slight Risk area as well. ....Northern/Central Rockies and Plains... Things start to get a little more interesting across the Northern Rockies and High Plains today, as a remnant mid-upper low and associated vorticity maxima eject northward from the Four Corners region. This should provide broad ascent via DPVA, along with modest diffluence aloft and sufficient instability (rising to 750-1500 J/kg of SB CAPE, per the HREF). The 00z HREF also suggests relatively high neighborhood probabilities for exceedance of both 2" and 3", with the best probabilities over south-central MT (near and west of Billings). PWATs are expected to increase to as high as 1.25" (which is +3.0 SD, or approaching the 95th percentile climatologically per the GEFS.. near or above the max moving average per TFX and GGW sounding climatology). Have once again maintained (and modified) the inherited Slight Risk and this area based on the new guidance. Farther south into the Central Rockies and into the Great Basin, any flash flooding is expected to be localized with much less organized convection (and largely tied to small-scale terrain forcing). Machine learning CSU First-Guess fields are also depicting a broad Slight Risk for this area (though offset seemingly a bit too far east). ....Central and Southern Florida... Continued the Marginal Risk for much of central/southern FL going into today, given the potential for a surface low to become more coherent and track toward this area. Aloft, a very slow-moving upper-trough over the Gulf will finally make its way directly overhead the Florida Peninsula with the strength/track of its surface reflection still uncertain. This should act to enhance typical diurnal convective activity across the region, with strong mid-level lapse rates allowing for more intense updrafts with tropical-like rainfall efficiency (given PWATs ~2.0" and wet bulb zero heights of ~15K feet). There may be a banded type feature as well oriented from northwest to southeast, which may allow for some training of heavy rates as well. Any localized flooding impacts are most likely across urbanized metro areas with poor drainage. Churchill/Pereira/Hurley/Fracasso Day 2 Valid 12Z Fri Jun 02 2023 - 12Z Sat Jun 03 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PARTS OF MONTANA-WYOMING AS WELL AS THE SOUTHERN-CENTRAL PLAINS... ....Central and Southern Plains... Overall pattern again shows little change given the degree of mid-upper level blocking. One notable difference is that by Day 2 (Fri-Fri night), the models show the main southern stream shortwave (north of the weakening subtropical jet streak) dropping a bit farther south across the southern Plains -- i.e. south of the Red River across North-Central TX. This will result in a small southward expansion of the more widespread, organized convection and heavier areal-average rainfall totals. Only minimal changes were made to the Slight and Marginal Risk areas inherited from yesterday's Day 3 ERO. Given the overlap of Slight Risk areas on Days 1 and 2 across parts of the TX-OK Panhandles into north-central OK and south-central KS, an upgrade to a Moderate Risk may be needed at some point somewhere within this region given the amount and coverage of heavy rainfall from the previous day(s). At this point, all current CSU First-Guess fields depict at most a Slight Risk. ....Northern/Central Rockies and Plains... Stagnant, blocky upper-level pattern also supports an excessive rainfall risk on Day 2 very similar to that on Day 1, as lingering DPVA and diffluence aloft look to persist from the mid-upper low being forced northward due to the ridging. The biggest difference compared to Day 1 is across northern WY, as the risk looks to shift west into the terrain a bit more (covering more of northwestern WY). In addition, the CSU First-Guess fields depict a Slight Risk as well. ....Central and Southern Florida... Models show the mid-upper trough across the eastern Gulf of Mexico flattening a little upon traversing the FL Peninsula and Cuba on Day 2. This would likely lead to a weakening trend with the low-level inflow and moisture transport/flux convergence, although continued favorable thermodynamic parameters (deep-layer moisture and instability) along with slow storm motions will likely maintain an isolated/localized flash flood threat, especially over urban areas. Therefore, will continue to maintain a Marginal Risk across Central and South FL. ....Northern New England... 'Breaking' northern stream shortwave will drop south across Quebec, east of the closed mid-upper high, and reach far northern New England by the end of the forecast period (late Fri night). Given the amplification aloft, strong along-stream upper divergence will pivot across northern New England during Day 2, which along with the uptick in deep-layer instability (mixed layer CAPEs climbing between 1000-1500 J/Kg with the steepening 700-500 mb lapse rates coinciding with the diurnal heating Fri afternoon and evening), will lead to pockets of 1-3+" rainfall totals within a 3-6 hour period across northern New England. This may lead to localized short-term runoff issues, and as such have maintained the Marginal Risk area inherited from yesterday's Day 3 ERO. Churchill/Pereira/Hurley 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!5rR7Hpykm8_ckE1A6YWqHBy4s5RbywgBXpgl-Wr48m5v= oMh2pYMrZJfgnaux7Y2_9T9_792cns5P4GElooc6isHCJto$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5rR7Hpykm8_ckE1A6YWqHBy4s5RbywgBXpgl-Wr48m5v= oMh2pYMrZJfgnaux7Y2_9T9_792cns5P4GElooc6nuXGMcY$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5rR7Hpykm8_ckE1A6YWqHBy4s5RbywgBXpgl-Wr48m5v= oMh2pYMrZJfgnaux7Y2_9T9_792cns5P4GElooc6vPouS68$=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) .