Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Jul 01 2023 08:28:53 FOUS30 KWBC 010828 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 427 AM EDT Sat Jul 01 2023 Day 1 Valid 12Z Sat Jul 01 2023 - 12Z Sun Jul 02 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE MID MISSISSIPPI INTO THE LOWER OHIO VALLEY AND UPSTATE NEW YORK... Few changes needed from continuity as yesterday's Day 2 outlook becomes today's Day 1 outlook. Convection capable of producing heavy to potentially excessive rainfall will be forced by broad-scale ascent ahead of a trough approaching the Mid-Mississippi Valley by later today with additional convection forming along and ahead of a cold front approaching the area.=20 With forecast soundings showing favorable thermal and moisture profiles...and precipitable water values in excess of 1.75 inches across the area...convection should be fairly efficient rainfall producers that could result in instances of flash flooding due to rainfall rates between 1 and 2 inches per hour under the most active storm. Greatest concern is over parts of Kentucky which has lower flash flood guidance due to multiple rounds of showers and thunderstorms during the past couple of days. Maintained the Slight risk area over and near northern New York given the 1 to 2 inch QPF and the recent wet spell. ....Davis Mountains to the Stockton/Edwards Plateau... The models continue to advertise that a mid-level disturbance and associated moisture will be moving out of northern Mexico and enter the U.S. later today/tonight. Precipitable water values between 1.3 and 1.7 inches...which is nearly 2 standard deviations above climatology for this time of year...look to be in place by the time the energy ejects out over the high plains adjacent to the southern Rockies. This environment could result in localized downpours and associated isolated flash flooding. Bann Day 2 Valid 12Z Sun Jul 02 2023 - 12Z Mon Jul 03 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE NORTHEASTERN UNITED STATES... Even though the deterministic QPF amounts from WPC and from at least some of the global models were pretty modest...both the SREF and GEFS ensembles suggest that heavier rainfall amounts are possible which could result excessive rainfall from parts of the eastern Great Lakes/eastern Ohio Valley northeastward into parts of New England. Model spread is pretty large...but the combination of deep moisture (as shown by precipitable water values of approaching 1.75 inches/approaching 2.5 standard anomalies greater than climatology) and a developing area of low pressure and increasing isentropic have the potential to focus and enhance rainfall rates across the region. The GEFS solution favored a corridor of higher amounts across upstate New York into northern New England which has had some locally heavy rainfall in the past week to ten days...and a second area of 1 to 3 inch amounts farther south and east where the synoptc/mesoscale forcing is not as strong but the instability is greater. Was swayed to introduce the Slight risk area by the combnation of synoptic and mesoscale forcing overlapping the footprint of deeper moisture...even though the SREF was not nearly as focused with its higher-end amounts. A Marginal risk area was extended as far south and west as the Tennessee Valley where the dynamics may not be as strong as they will be in New England but the instability could still support localized downpours. Bann Day 3 Valid 12Z Mon Jul 03 2023 - 12Z Tue Jul 04 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE NORTHEAST UNITED STATES AND ACROSS PORTIONS OF THE UPPER MIDWEST/NORTHERN PLAINS... ....Pennsylvania/New York Into New England... Maintained a Marginal risk area as a system pulls away from the U.S. and heads out to see. Models still linger sufficient moisture to keep precipitation lingering across a region.=20 Additional rainfall amounts after the start of the outlook period at 12Z Monday are not expected to be blockbuster in nature...but wet antecedent conditions could still yield areas with flooding or problems in regions of poor drainage.=20 ....Montana/Wyoming Eastward to Northern Minnesota... Models show another cold front will be pushed south of the international border on Monday and Monday night as surface low pressure remains north of the border. This front should have enough support from the upper level winds to provide a focus for showers and thunderstorms from eastern Montana and northeast Wyoming on Monday which extends eastward as far as northern Minnesota by late Monday night. Moisture pooling along and ahead of the front combined with divergence aloft from an upper jet may set the stage for storms to produce locally heavy rainfall. One limiting factor may be that precipitable water values should only be in the 1.25 to 1.5 inch range and the storms may be progressive enough to prevent more than isolated problems with run-off from places with poor drainage. Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!5tBJNDOEMBzEnKDUFbMjncAIXDZnF6zHZkaOqkONkSMV= jfk2DpHsVonWvPQPAjorOq0V951W11Yc5gvq-AaQb77L5go$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5tBJNDOEMBzEnKDUFbMjncAIXDZnF6zHZkaOqkONkSMV= jfk2DpHsVonWvPQPAjorOq0V951W11Yc5gvq-AaQd8sgop8$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5tBJNDOEMBzEnKDUFbMjncAIXDZnF6zHZkaOqkONkSMV= jfk2DpHsVonWvPQPAjorOq0V951W11Yc5gvq-AaQB8DC6gw$=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) .