Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jun 27 2023 01:13:18 FOUS30 KWBC 270113 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 912 PM EDT Mon Jun 26 2023 Day 1 Valid 01Z Tue Jun 27 2023 - 12Z Tue Jun 27 2023 ....THERE ARE SLIGHT RISKS OF EXCESSIVE RAINFALL ACROSS PORTIONS MID-ATLANTIC... ....Great Lakes...Eastern and Southern U.S.... Scattered showers and thunderstorms were in progress from the Great Lakes and New England, southward into the Carolinas. While some areas have been worked over by convection during the day, a broad swath of MLCAPE of 500 to 2000+ J/kg remained from the southern Mid-Atlantic into the Northeast at 00Z. Anomalous moisture remained with synoptic and mesoscale ascent present beneath and ahead of a large closed low/mid-level trough over the eastern third of the CONUS. Favorable kinematics remain across many areas for training and repeating of thunderstorms with 1-2 in/hr (locally higher) rainfall rates. Adjustments to for the 01Z ERO included breaking the Slight within and south of the D.C. metro where a gap in thunderstorm coverage has occurred and questions remain as to the development of heavy rain overnight. =46rom Baltimore and locations northward into southern NY/NJ, as well as portions of VA into NC, ongoing clusters of thunderstorms pose a risk for flash flooding with some overlap of antecedent wet conditions playing a role in flash flood potential. ....Southern Montana into Northern Wyoming and Western South Dakota... Adjustments to the existing Marginal Risk were made to account for radar trends and the past few cycles of the HRRR. Ongoing thunderstorms with localized 1-2 in/hr rainfall rates are expected to continue for several more hours while gradually shifting eastward into the northern High Plains, with additional development possible ahead of an approaching shortwave and upper level jet streak from the southwest. While 2-3 inches is likely an upper bound for maximum rainfall totals overnight, these totals should remain highly localized. Portions of the area are more prone to flash flooding given anomalously wet antecedent conditions. ....ArkLaTex into Lower Mississippi Valley... Adjustments to the previous Marginal Risk were made to include portions of southeastern OK into the Lower MS Valley where nocturnal flareup of convection is expected near a lingering frontal boundary that stretched westward across AL/MS into southern AR and the Red River Valley. Moderate to large CAPE values were noted on area 00Z soundings and PWs nearing 2 inches. Increasing magnitude of southwesterly low level flow and diffluent flow aloft will likely bring about scattered thunderstorm development after 06Z. While coverage is a bit uncertain, flow favors the potential for at least some training and repeating of cells, atop portions of the ArkLaTex into the Lower MS Valley that received heavy rain Sunday night/early Monday morning. ....Northern Cascades... Scattered thunderstorms were ongoing across the Washington Cascades with slow movement due to weak steering flow. An isolated flash flood risk, focused most on recent burn scar areas, will remain until convection weakens with the loss of instability and increasing convective inhibition through 06Z. ....Southeastern Florida... Earlier convection has dissipated and thunderstorms are not expected to impact land overnight. The previous Marginal Risk has been removed. Otto Day 2 Valid 12Z Tue Jun 27 2023 - 12Z Wed Jun 28 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE NORTHEAST AND THE MID-ATLANTIC, AND THE NORTHERN ROCKIES AND PLAINS... ....Northeast/Northern Mid-Atlantic... The upper low moving across the upper Great Lakes on Day 1 is forecast to transition to an open wave and slow as it moves across the lower Great Lakes on Day 2. Deep southerly flow ahead of the trough will continue to support ample moisture, with precipitable water values remaining around 1.5 inches along much of the Mid-Atlantic and Northeast seaboards. Models show ongoing convection, potentially producing locally heavy amounts and isolated flash flooding concerns early in the period across portions of New England. Then later in the day, destabilization and mid-level energy lifting along the leading edge of the trough are likely to support the redevelopment of showers and storms back to the west across the Mid Atlantic into Upstate New York, which may also produce some additional isolated flash flooding concerns. Still enough uncertainty about how much rain falls on Day 1...and where...at this point to preclude a Slight Risk. ....Northern Rockies and Plains... A slow-moving trough in the west and sufficient moisture will support another day of showers and storms developing over the mountains of western Wyoming and Montana. Farther to the east, leading energy moving out of the trough, interacting with deepening moisture along a strengthening low level jet is expected to support showers and storms developing along and ahead of a front dropping southeast through the High Plains. Although widespread heavy amounts are not expected, locally heavy amounts may produce an isolated flash flooding threat, especially given the wet antecedent soils. Pereira/Bann Day 3 Valid 12Z Wed Jun 28 2023 - 12Z Thu Jun 29 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE NORTHEAST, UPPER MIDWEST, AND THE NORTHERN ROCKIES... Overall...the 12Z suite of numerical guidance maintained decent run to run consistency so nothing more than a few costmetic adjustments were made.=20 Bann Previous Excessive Rainfall Discussion... ....Northeast... An upper trough will linger for yet another day over the Northeast, channeling both deep moisture and mid-level energy across portions of the region. Daytime heating is likely to help support additional showers and thunderstorms, with locally heavy amounts possible, especially across portions of eastern Update New York into New England. ....Upper Midwest... Mid-level energy emanating from the trough in the West, along with an amplifying trough approaching from the northwest over central Canada is expected to support an increasing chance for rain across portions of the region on Wednesday into early Thursday.=20 Deepening moisture (PWs increasing to around 1.5 inches), along with some potential for southwest-northeast training, may produce at least some locally heavy amounts from northern Minnesota to the western U.P. of Michigan. ....Northern Rockies... With an upper trough remaining positioned to the west and a relatively moist airmass still in place, isolated to scattered showers and storms are expected to develop once again across the region. These may produce locally heavy amounts and generate isolated flash flooding concerns, especially given the wet antecedent conditions. Pereira=20 Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_de7X9KL89mVoxamN0Mp1fk8KbwrZcqR95XLWQHNNqSB= bR6CBQ8cZrfBs85EZCx80ltivaWQI2ejTYOP88fHN5V_4T0$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_de7X9KL89mVoxamN0Mp1fk8KbwrZcqR95XLWQHNNqSB= bR6CBQ8cZrfBs85EZCx80ltivaWQI2ejTYOP88fH1reX3xY$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_de7X9KL89mVoxamN0Mp1fk8KbwrZcqR95XLWQHNNqSB= bR6CBQ8cZrfBs85EZCx80ltivaWQI2ejTYOP88fHSlZydoU$=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) .