Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Mar 30 2024 07:39:14 FOUS30 KWBC 300738 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 338 AM EDT Sat Mar 30 2024 Day 1 Valid 12Z Sat Mar 30 2024 - 12Z Sun Mar 31 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTHERN CALIFORNIA... Heavy to excessive rainfall should be ongoing associated with a landfalling atmospheric river across Transverse Ranges (and adjacent areas) of southern California at 12Z Saturday. This atmospheric river will shift southeastward in tandem with southeastward movement of an anomalously deep low centered about 200 mi west of the California coastline. The southeastward shift of the atmospheric river will spread areas of 0.25-0.5 inch/hr rain rates across coastal ranges and areas from Los Angeles to San Diego through around 00Z Sun. Thereafter, the cold upper low and continued onshore flow will aid in shower and isolated=20 thunderstorm redevelopment across the western and central areas of the Slight Risk (including the Transverse Ranges) from 21Z through the end of the forecast period. This redevelopment could also trigger flash flooding amid wet ground conditions from prior rainfall. Farther east, CAMs indicate low-end potential for isolated thunderstorm development across the Lower Colorado River Valley that could result in brief, locally heavy rainfall at times. The Marginal Risk area was broadened slightly to include more of western Arizona where this risk is maximized. Cook Day 2 Valid 12Z Sun Mar 31 2024 - 12Z Mon Apr 01 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS SOUTHWESTERN CALIFORNIA AND PORTIONS OF ARIZONA... The anomalously deep upper low near southwestern California at the beginning of the D2/Sun forecast period will transition into an open wave while progressing eastward toward the Lower Colorado River Valley. This pattern will continue to support scattered shower/isolated thunderstorm activity amid upslope flow in southern California and cooling aloft associated with the upper low. Only a Marginal risk appears justified based on the lack of a true focus for sustained, multi-hour heavy rainfall potential in favorable terrain. Occasional heavy rainfall could materialize across central through southeastern Arizona during the forecast period, which could result in isolated/spotty flash flood concerns especially in the afternoon and early evening. Cook Day 3 Valid 12Z Mon Apr 01 2024 - 12Z Tue Apr 02 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF NORTHEASTERN OKLAHOMA INTO SOUTHWESTERN/CENTRAL MISSOURI... ....Oklahoma into Missouri... Although some uncertainty exists with respect to specific frontal and low-level cyclone position, some concensus exists in a fairly=20 focused area of deep convective initiation generally from north-central/northeastern Oklahoma into central Missouri from Monday afternoon onward. The initial convection will potentially align along the synoptic surface boundary and parallel to deep southwesterly flow aloft to support areas of convective training and locally higher rainfall rates especially in the Slight Risk=20 area. Any excessive runoff concerns may be mitigated by initially=20 dry ground conditions, although storms should eventually traverse=20 into more favorable terrain for flash flooding (across the Missouri Ozarks and vicinity) with time through the evening hours. It is=20 worth noting that the locations of peak flash flood risk may shift=20 in future forecast cycles pending eventual location of the surface=20 front and mesoscale details that support/foster convective=20 training. ....Illinois eastward through West Virginia and vicinity... A couple of factors support potential for at least spotty/isolated excessive rainfall potential across these areas Monday into early Tuesday: 1) Potential for multiple rounds of scattered convection to migrate west-to-east along a warm frontal zone located across the Ohio Valley vicinity and 2) Repeating rainfall, with ground conditions likely being moistened by antecedent rainfall in some areas during the prior forecast period (D2/Sun). Despite the favorable overall pattern for increasing rainfall (and spots of 2+ inches), models vary with respect to specific locations of heavier rainfall from training convection. Furthermore, some uncertainty exists on the degree to which inflow parcels into convection will be surface-based (with an attendant heavier rainfall threat). These mesoscale details could necessitate a localized risk upgrade in later update cycles. Cook Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!5uplCK0WQBaOHuWKktc0g9o-Ijd0oI44C2YRwjk-l3t9= 1jVmiMi_hjbeEEbneoJi9cop9s_oSiwD3LZ5GnUfkGHcpG0$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5uplCK0WQBaOHuWKktc0g9o-Ijd0oI44C2YRwjk-l3t9= 1jVmiMi_hjbeEEbneoJi9cop9s_oSiwD3LZ5GnUffC04n-w$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5uplCK0WQBaOHuWKktc0g9o-Ijd0oI44C2YRwjk-l3t9= 1jVmiMi_hjbeEEbneoJi9cop9s_oSiwD3LZ5GnUfHiKlA38$=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .