Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Jun 03 2023 15:54:40 FOUS30 KWBC 031554 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1153 AM EDT Sat Jun 03 2023 Day 1 Valid 16Z Sat Jun 03 2023 - 12Z Sun Jun 04 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHERN HIGH PLAINS AND PORTIONS OF THE NORTHERN ROCKIES... ....Southern/Central Plains... Another active day of convection is expected from the Central Plains to the Mexico/Texas border, but with somewhat more diffuse organization than previous days. Mid-level troughing elongated across the Plains combined with modest left-exit jet level diffluence and a residual surface trough will drive deep layer ascent through today. This expansive lift will work across an environment with favorable thermodynamics for heavy rainfall noted by NAEFS PW anomalies of around +1 standard deviation coincident with MUCAPE of 1000-2000 J/kg, higher across southern Texas. As bulk shear increases to 30-35 kts concurrent with peak instability, this could result in some storm interactions/more organized clusters moving generally 10-15 kts as progged by the layer Corfidi vectors. Although the signal for training overall is modest today, with rainfall rates possibly reaching 2"/hr at times, any short term training or repeated rounds could quickly result in runoff issues, especially where soils are most saturated from 14-day rainfall that has been more than 300% of normal across much of west/central Texas into western OK and southern KS. Although the model signal is vague for any more organized areas of convection leading to more focused heavy rainfall, modest HREF probabilities for more than 3" invof the TX Panhandle continue to warrant the inherited SLGT risk. This is driven strongly by the antecedent conditions from recent rainfall leading to compromised FFG as low as 0.5-1.5"/3hrs which has a 20-40% chance of exceedance. Any storm that moves across this region could quickly lead to additional runoff concerns. While the rest of the area remains in a broad MRGL risk, there is potential that thunderstorms blossoming over the Serranias del Burro will congeal into an MCS with rain rates exceeding 2"/hr and push E/SE into the RGV or western TX Hill Country tonight. Some of these areas received as much as 1-3" of rain yesterday according to MRMS, but at this time the consensus signal for rainfall is a bit south of that footprint, which seems reasonable as low-level inflow is progged to back more to the south, likely resulting in any MCS diving to the southeast and missing the lower FFG to the north. There is still uncertainty into this evolution, and if it appears this MCS will track across similar areas to yesterday a targeted SLGT risk may be needed from the Big Bend to the Hill Country, but at this time the uncertainty into placement and speed precludes any upgrade. ....Northern/Central Rockies... The amplified mid-level pattern becomes a bit more strung out today as an expansive high-pressure ridge to the east expands and retrogrades slightly to the west. This will force the best meridional moisture transport and confluent flow westward from the past few days, with the best overlap of ascent and forcing shifting NW from Colorado into central/western MT and ID. There is good agreement that within this confluent flow, periodic shortwaves and associated vorticity maxima will lift northward, enhancing deep layer ascent already present through upper diffluence. With the best forcing becoming slightly displaced today from the best moisture transport, using the 850mb winds as proxy, this should result in more modest coverage of convection, with slightly less intensity. Still, PW anomalies of +1 standard deviation (+2 in MT) according to NAEFS will supply sufficient moisture for heavy rain in any of these thunderstorms today. Storms that do develop today will generally move W/NW within mean 0-6km winds of 10-15 kts, but terrain features and any storm interactions will likely lower cell translations in some areas. Rain rates progged by the HREF will generally be 0.5-1"/hr today, but could exceed 1"/hr where instability is greatest across parts of MT/ID or where any upslope can locally enhance ascent. This suggests the inherited MRGL risk is appropriate for much of the area with little change. However, the SLGT risk was trimmed from the south, to cover just areas where HREF probabilities for 1"/hr rainfall are greatest thanks to better overlap with instability, and to account for the footprint of the 24-hr MRMS QPE which has lowered FFG to just 0.25-0.75"/3hrs. ....Florida... No significant changes to the inherited MRGL risk as Tropical Storm Arlene continues to weaken and drop southward over the eastern Gulf of Mexico. NHC has this system decaying into a remnant low late tonight, and the guidance indicates the residual vorticity max associated with it will re-curve into the broad Southeast trough and move near the FL Straits before D1 is over. This subtly enhanced ascent combined with the continued modest diffluence aloft and a surface trough/convergence axis will once again provide sufficient ascent for scattered aftn/eve convection. The focus will once again be across the southern peninsula where weak bulk shear and slow storm motions will provide a setup which supports merging/interacting cells with rain rates of more than 2"/hr. This area has been very active the past few days noted by MRMS 72-hr QPE of 4-7" in a stripe from near Tampa to Miami resulting in above normal streamflow according to USGS gauges. With another similar day expected today, any slow moving convection, which will likely have rain rates above 2"/hr at times, could again lead to isolated runoff or flash flood instances. Weiss Day 2 Valid 12Z Sun Jun 04 2023 - 12Z Mon Jun 05 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHERN HIGH PLAINS... There is not anticipated to be any significant changes to the stagnant blocking mid to upper level pattern across the mid section of the nation. There will continue to be potential for widespread scattered convection in the axis of above average PW values that will stretch across much of the Southern, Central and Northern Plains and Northern Rockies. There is not a lot of confidence in any model solution, but with embedded vorts moving eastward into the Southern High Plains and north westward across the Central to Northern Plains and Northern Rockies, there will be potential for locally heavy rains. A slight risk area was introduced across the Southern High Plains to cover where there is some model consensus for additional heavy rains that will overlap with where there has been much above average totals over the past several weeks. Oravec Day 3 Valid 12Z Mon Jun 05 2023 - 12Z Tue Jun 06 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHERN HIGH PLAINS... Similar to the day 2 time period, not a lot of changes expected to the overall stagnant blocking mid to upper level flow pattern across the mid section of the nation. There continues to be some consensus for a max precip area over the Southern High Plains from northeast New Mexico into the Texas and Oklahoma Panhandle region. A slight risk was continued across this region given recent heavy rains and the potential for additional heavy rains days 1 and 2 across this area. The axis of above average PW values remains in place across much of the High Plains into the Northern Rockies, with additional shortwave energy/upper difluence maxima rotating through this high PW axis and supporting locally heavy rains.=20=20 Continued low confidence in where totals may maximize, but with some signal additional heavy rains over the Southern High Plains, felt that a continuation of a slight risk was warranted. Across the Northern Sierra...a mid to upper level low moving inland across central to southern California late Monday afternoon/Monday evening will provide a very difluent flow pattern ahead of it across the Northern Sierra into the Northern Great Basin. This will support scattered convection from the Northern Sierra into the Northern Great Basin, with locally heavy precip totals and isolated runoff issues possible. The previous marginal risk area was decreased in size and centered across the Northern Sierra where stream flows remain much above average. Oravec Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_58G-Te3-ka1hTvp3X6a_uWuk8TiYLLjKDKki42fu23Z= tW03yxrFeiro1l4hYXiHJCV12UYr6gkI9ZNKZ_ms315VBeM$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_58G-Te3-ka1hTvp3X6a_uWuk8TiYLLjKDKki42fu23Z= tW03yxrFeiro1l4hYXiHJCV12UYr6gkI9ZNKZ_msjzsLly4$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_58G-Te3-ka1hTvp3X6a_uWuk8TiYLLjKDKki42fu23Z= tW03yxrFeiro1l4hYXiHJCV12UYr6gkI9ZNKZ_ms2sIVR2c$=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) .