Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Mar 31 2024 00:55:25 FOUS30 KWBC 310055 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 855 PM EDT Sat Mar 30 2024 Day 1 Valid 01Z Sun Mar 31 2024 - 12Z Sun Mar 31 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS SOUTHERN CALIFORNIA AND PARTS OF THE SOUTHWEST... 0100 UTC Update -- Pared quite a bit of the Marginal Risk area across CA, based on the latest observational and guidance trends. Latest 18Z) HREF continues to show spotty neighborhood probabilities between 20-40% of hourly rainfall rates > 0.50" associated with the spiral bands east of the deep low offshore. Convective component is relatively weak (MUCAPEs generally aob 500 J/Kg), however sufficient to cause localized runoff issues overnight, especially over burn scars.=20 Hurley 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... 20Z Excessive Rainfall Discussion... Previous outlook for a Marginal Risk of excessive rainfall still looks to be on track as several shortwave troughs embedded within the broader flow pivot around the filling/weakening mid/upper level system. QPF from many of the models and the WPC QPF have been fairly consistent in terms of amounts and placement so only minor nudges were needed. Bann 08Z Excessive Rainfall Discussion... 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=20 appears justified based on the lack of a true focus for sustained,=20 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... 20Z Excessive Rainfall Discussion... The 12Z set of models still indicated a fairly broad range of solutions with respect to rainfall amounts and placement from portions of=20 Oklahoma/Missouri eastward across portions of the Ohio Valley. NCEP models still show best instability on the western periphery of the precipitation field. The previous outlook had that pretty well handled...but felt that the potential for sufficiently intense rainfall rates were possible a bit farther east based on the instability and the coupling of upper level jets so the Slight Risk was expanded into parts of=20 eastern Missouri. Farther east...instability was not as great and=20 looks to be more elevated in nature being north of a quasi-stationary front and air with lower thetae values being advected in at low levels north of the front...think the rainfall rates will be lower and less prone to result in flash flooding given recent dry conditions. It=20 remains a possibility that a localized risk upgrade will be needed in later outlooks but was not done with this issuance. Bann 08Z Excessive Rainfall Discussion... ....Oklahoma into Missouri... Although some uncertainty exists with respect to specific frontal and low-level cyclone position, some consensus exists in a fairly 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=20 convective training and locally higher rainfall rates especially in the Slight Risk area. Any excessive runoff concerns may be mitigated by initially dry ground conditions, although storms should eventually traverse into more favorable terrain for flash flooding (across the Missouri Ozarks and vicinity) with time through the evening hours. It is worth noting that the locations of peak flash flood risk may shift in future forecast cycles pending eventual location of the=20 surface 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:=20 https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt= __;!!DZ3fjg!_omoDxoodzcy1NcMJtl0Jia6xo86PBzuas7HgA1JeoCMltlPcsYB0f_UooJ-0BO= gLXpPBubP3GODZqM4gxAE4XD5GiA$ Day 2 threat area:=20 https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt= __;!!DZ3fjg!_omoDxoodzcy1NcMJtl0Jia6xo86PBzuas7HgA1JeoCMltlPcsYB0f_UooJ-0BO= gLXpPBubP3GODZqM4gxAE8UIL-QE$ Day 3 threat area:=20 https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt= __;!!DZ3fjg!_omoDxoodzcy1NcMJtl0Jia6xo86PBzuas7HgA1JeoCMltlPcsYB0f_UooJ-0BO= gLXpPBubP3GODZqM4gxAE__b4fsk$=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) .