Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Jun 03 2023 08:13:34 FOUS30 KWBC 030813 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 412 AM EDT Sat Jun 03 2023 Day 1 Valid 12Z 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 FROM PORTIONS OF THE NORTHERN ROCKIES INTO THE NORTHERN HIGH PLAINS... ....Southern High Plains... For the day 1 time period there is an overall weakening to the favorable convective pattern across the Southern Plains, reflected by the model consensus of less precip potential. However, with several days of heavy rains, lowering ffg values and raising stream flows to anomalously high levels, there will continue to be a threat for flash flooding. While the mid to upper level trof that has been across the Southern High Plains is expected to be weaker day 1 compared to previous days, additional height falls and upper difluence maxima will support additional convective development from eastern New Mexico into northwest Texas and western Oklahoma from Saturday afternoon into Saturday evening.=20 The previous slight risk area was expanded eastward into western Oklahoma and far southwest Kansas to cover the overlap area between heavy rains over the past 24 hours and additional heavy rain potential Saturday afternoon into Saturday evening. The slight risk fits well with the latest HREF neighborhood probabilities for 1"+ amounts, which are high, 60-90% across this region. Probabilities do drop off significantly for 2"+ totals, with a more narrow axis of 40-60% probabilities over northwest Texas. Models do show potential for widespread convection and locally heavy rainfall amounts across the remainder of the Southern to Central Plains day 1. The consensus max precip areas from the Lower Rio Grande, northeast Texas through, eastern Oklahoma, central to western Kansas and eastern Colorado do not overlap with recent heavy rains, so for the time being, the threat level was maintained at marginal. ....Northern Rockies into the Northern High Plains... The blocking mid to upper level pattern will persist day 1 from the Upper Lakes, Upper Mississippi Valley Northern Plains into the Northern Rockies. Upper difluence maxima on the west side of the closed upper high will continue to enhance uvvs through the Northern Rockies. This will be especially so with the lead vort which is forecast to maintain a well defined comma head deformation precip band early day 1 across central to west central Montana. This will be followed by weaker vorts pushing northwestward on the western side of the closed upper high, supporting addition convection Saturday afternoon into evening.=20 With PW values remaining very anomalous, 2 to 2.5+ standard deviations above the mean from northeast Colorado, across much of Wyoming and Montana, additional heavy rain totals are possible. A slight risk area was introduced for areas from northwest and north central Wyoming, northward into west central Montana. Recent heavy rains over the past 24 hours have lowered ffg values significantly. HREF neighborhood probabilities are high for 1"+ amounts in the slight risk area, dropping off significantly for 2"+ amounts. ....Florida... The latest NHC forecast track for Arlene continues to show weakening as the storm pushes south southeastward and stays well off of Southwest Florida and the Keys. The mid to upper level trof that is pushing Arlene southeastward Saturday will also continue to favor widespread scattered convection to its east across much of central to South Florida. With HREF neighborhood probabilities high for 1, 2 and 3"+ totals, no changes were made for the broad marginal risk area. The primary concerns will continue to be urban flash flooding across Southeast and Southwest Florida where localized hourly rainfall rates of 1 to 2" are possible. Oravec 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 Sun Jun 04 2023 - 12Z Mon Jun 05 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!_wRtqMrkGNqvpMs8YV5iE10cJ_DZBIrLtF3EDWOi6v22= vyW9x7wWMwvlxEV39TYGa-UTDgJ35yDtslhX4YvofIbpF18$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_wRtqMrkGNqvpMs8YV5iE10cJ_DZBIrLtF3EDWOi6v22= vyW9x7wWMwvlxEV39TYGa-UTDgJ35yDtslhX4Yvo2JpdD9s$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_wRtqMrkGNqvpMs8YV5iE10cJ_DZBIrLtF3EDWOi6v22= vyW9x7wWMwvlxEV39TYGa-UTDgJ35yDtslhX4YvoGvlI4-I$=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. 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