Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jun 02 2024 08:29:56 FOUS30 KWBC 020829 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 429 AM EDT Sun Jun 2 2024 Day 1 Valid 12Z Sun Jun 02 2024 - 12Z Mon Jun 03 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS AS WELL AS PORTIONS OF THE PACIFIC NORTHWEST.... ....Northern and Central Plains... The emergence of a low amplitude shortwave trough from the=20 northern Rockies out over the adjacent western high plains this=20 morning will set the stage for convection that produces locally=20 heavy rainfall across parts of the northern and central plains=20 later. Showers and thunderstorms should become more numerous across parts of the eastern Dakotas as a cold front becomes better=20 defined and propagates across Minnesota and Iowa later. Model QPF=20 shows convection building along the front as far south as Nebraska and Kansas during the evening. Accelerating southerly flow ahead=20 of the cold front will draw deeper moisture into the area with=20 precipitable water values ranging from roughly 1.3 inches along the international border to values approaching 1.75 inches across=20 western Iowa/eastern Nebraska and northeast Kansas by 03/00Z should be aided aloft by divergence associated with a developing jet=20 streak over the upper midwest late tonight/early Monday morning. ,,,Southern Plains... Introduced a Slight Risk across portions of the Southern Plains=20 where increasingly deep southeast flow develops and interacts with=20 a poorly defined boundary moving that move northward. Confidence in placement is below average but there are signals in various model=20 runs that point to a better than Marginal chance for excessive=20 rainfall given the moisture laden atmosphere and the passage of an=20 upper level wave ejecting eastward from the southern Rockies during the afternoon. ....Pacific Northwest... There will be a growing threat for excessive rainfall over along=20 the Coastal Range and Cascade Range from Washington and Oregon=20 southward into the mountains of far northwest California as an=20 anomalously strong mid and upper level jet usher in deep moisture=20 throughout the day. While not normally a concern in the summer=20 time...satellite imagery shows the moisture plume has its roots=20 well into the subtropics in the central/western Pacific. With the=20 arrival of strong onshore flow and precipitable water values that=20 approach 1.5 inches along the immediate coast of Oregon by late=20 this afternoon...IVT values at or above 700 kg per meter per second that is directed normal to the mountains for a rather prolonged=20 period. Only change to the previous outlook was to bring the Slight Risk areas southward into the Coastal and Cascade ranges based on=20 latest deterministic QPF amounts with isolated spots in the west=20 facing terrain potentially receiving 4+ inch amounts due to the=20 terrain influences and at least some possibility of enhanced rates=20 from embedded convective elements. The combination of rainfall and=20 snow-melt run-off from higher elevation has the potential for=20 flooding or flash flooding. Latest numerical guidance brings an=20 area of height falls...leading to the development of a trough=20 axis...which reaches the west coast towards the end of the outlook=20 period at 03/12Z. No modification was done to the changes=20 coordinated farther inland by the previous shift.=20 ....Southeast Florida... With precipitable water values nearing 2 inches ahead of an=20 approaching shortwave trough...expectation is for increasing=20 coverage of showers and thunderstorms capable of producing locally=20 heavy rainfall in a short period. The areas most vulnerable to=20 problems with run-off or ponding will be the urban corridor along=20 the southeast Florida coastline. Model QPF is not blockbuster in magnitude but the some higher amounts lurking offshore suggests=20 some possibility for a few showers with very heavy rainfall rates=20 making it onshore. Bann Day 2 Valid 12Z Mon Jun 03 2024 - 12Z Tue Jun 04 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY ACROSS PORTIONS OF THE CENTRAL/SOUTHERN PLAINS AND THE NORTHERN ROCKIES... ....Plains... The front which provided focus for showers and thunderstorms=20 capable of producing heavy rainfall will continue eastward on=20 Monday...extending from the western Great Lakes region southward=20 into the central and southern plains by Monday afternoon. The front outruns better upper support and becomes less of a driving force=20 for heavy to excessive rainfall...especially across the northern=20 tier of states. The southern portion of the front should still be=20 able to provide a mechanism for convective initiation. Exactly=20 where continues to be a big challenge...with numerical guidance=20 offering a wide range of possibilities, Introduced a Slight Risk=20 area mainly across the central and southern Plains where an upper=20 level trough moving out of the Southern Rockies should provide some upper level support. The vertical depth of this wave has been=20 fairly limited but models were beginning to show increase its=20 reach. Any convection that forms will be in a region with=20 precipitable water values over 1.75 inches being drawn towards the=20 front by southerly flow in excess of 30 knots. The GFS and CMC=20 guidance fits the Slight risk area best but nothing to preclude the northern/western solution offered by the NAM.=20 ....Rockies,,, Saw little reason to make too many changes to the outlook area=20 from Washington eastward Idaho and far western Montana as the flow=20 of deeper moisture associated with the atmospheric river continues=20 to push inland. The moisture fetch should eventually become=20 disrupted by low amplitude ridging which leads to decreasing=20 intensity and coverage from west to east. Until that happens...the=20 combination of rainfall run-off...perhaps enhanced by snow=20 melt...will continue. Bann Day 3 Valid 12Z Tue Jun 04 2024 - 12Z Wed Jun 05 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS MUCH OF THE NORTHERN AND CENTRAL PLAINS... As one cold front weakens as it progresses eastward...a second=20 front takes shape and pushes southward/eastward on Tuesday in=20 response to the sharpening of a northern stream trough on Tuesday.=20 Low level flow is forecast to back once again and draw deeper=20 moisture northward ahead of the on-coming front. It appears to be=20 two mechanism for heavy rainfall...with the southern portion of the Slight Risk being aided by weak but important shortwaves=20 supporting convection along the old front or other outflow boundary while the northern area was driven by the approaching front and=20 upper level divergence/support from the developing synoptic scale=20 system. Given the proximity of the two areas...confidence in=20 placement was not high enough to warrant two separate areas so one=20 broad Slight Risk was indicated. Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9dtVZ7UCA83W3arSuhc7R8ensT9H7aZlxVRXihxrqKHa= X37oEUBzq4VBpYsI8cA29o9BgjS7Gnc37Nb_yU1xY7iMWdI$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9dtVZ7UCA83W3arSuhc7R8ensT9H7aZlxVRXihxrqKHa= X37oEUBzq4VBpYsI8cA29o9BgjS7Gnc37Nb_yU1xwSZRo0U$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9dtVZ7UCA83W3arSuhc7R8ensT9H7aZlxVRXihxrqKHa= X37oEUBzq4VBpYsI8cA29o9BgjS7Gnc37Nb_yU1xbVILS-g$=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) .