Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jul 02 2023 20:09:25 FOUS30 KWBC 022009 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 408 PM EDT Sun Jul 2 2023 Day 1 Valid 16Z Sun Jul 2 2023 - 12Z Mon Jul 3 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE NORTHEASTERN UNITED STATES... ....Portions of the Ohio Valley Eastward to portions of the Pennsylvania/New York/New England.../ Was able to maintain decent amount of continuity for the period...especially from the Ohio Valley to the Appalachians and the Northeast U.S.. An upper low initially over the Mid-Mississippi Valley will continue to move eastward over the Midwest and allow for slow-moving storms early. The Slight Risk area was maintained without too many changes given the support from the SREF/GEFS and the HREF neighborhood probabilities. The one change in pulling the western boundary of the Slight westward was largely done in response to late night/early morning radar imagery suggesting somewhat more training potential over northern Ohio as opposed to areas just to the south. PWs in the Northeast are forecast to be as high as +2 to +3 standard deviations above the climatological average, when combined with forcing along the frontal boundary will likely lead to scattered areas of flash flooding. Farther to the south...the Marginal risk area was again extended a bit farther south over northern AL to account for slow-moving activity along and ahead of an approaching cold front. ....High Plains Adjacent to the Southern Rockies... Introduced a Marginal Risk again today as the numerical guidance develops another round of widely scattered to perhaps scattered coverage of late day convection in proximity to a lee side trough. Rainfall amounts look to be modest...but enough instability could form die to upwards of an inch precipitable water within a region of relatively steep mid level lapse rates to produce brief downpours. The areas most prone to any flooding would be run off from recent burn scars. Bann Day 2 Valid 12Z Mon Jul 3 2023 - 12Z Tue Jul 4 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE NORTHEAST UNITED STATES, UPPER MIDWEST/NORTHERN PLAINS, DEEP SOUTH, AND SOUTH FLORIDA... ....Pennsylvania/New York Into New England... Models still linger sufficient moisture to keep modest precipitation amounts across the region as a system pulls away from the U.S. and heads out to sea. Additional rainfall amounts after the start of the outlook period at 12Z Monday are not expected to be overly impressive, but wet antecedent conditions leading up to this time period could still yield areas with isolated flooding or problems in regions of poor drainage.=20 Therefore, the Marginal risk area in this part of the country was maintained with few modifications. Farther south, storms should exhibit enough forward motion to limit any flash flooding concerns behind a cold front. ....Montana/Wyoming Eastward to Northern Minnesota... Models indicate a cold front will drop south across the Northern Plains on Monday and Monday night as the parent surface low pressure remains north of the border. This front should provide a focus for showers and thunderstorms from south-central Montana and northern Wyoming eastward across South Dakota/Nebraska and into the Upper Midwest. Moisture pooling along and ahead of the front combined with divergence aloft from an upper level jet will create an environment favorable for storms to produce locally heavy rainfall, although highest precipitable water values only look to be modestly above 1.25 inches which may limit rates and any associated excessive rainfall potential. No major changes were needed with this forecast update. ....Mid-South... A lingering frontal boundary extending from the Mid-Atlantic to the Lower Tennessee Valley, pooling 1.75-2.00 inch PWs combined with a subtle shortwave ejecting across the central/southern Plains should allow for slow-moving storms to develop across the ArkLaMiss and extending into central/northern Alabama. Minimal low-to-mid level flow is likely to limit storm motion and could result in localized flash flooding concerns and rainfall amounts up to 2-3" within a relatively short period of time. ....South Florida... Similar to Day 1, a Marginal Risk area was added to portions of South Florida to account for slow moving cells that develop in response to sea breeze convergence, with the potential for 1-2 inches of rainfall to fall within a 30-minute time period for affected areas. The best coverage for convection is likely to be within the 18Z-00Z time period. Bann/Hamrick Day 3 The Day 3 outlook will be updated by 2030Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9LsNnhwK_XAGHGaeu9b6p2ckJcUK6GqVPj84G9PDOoWA= 9j9BbPWfhpiYRdX0v-33kFEB3ifvmWesuCcMUrThTSB5DjQ$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9LsNnhwK_XAGHGaeu9b6p2ckJcUK6GqVPj84G9PDOoWA= 9j9BbPWfhpiYRdX0v-33kFEB3ifvmWesuCcMUrThXRa1MFg$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9LsNnhwK_XAGHGaeu9b6p2ckJcUK6GqVPj84G9PDOoWA= 9j9BbPWfhpiYRdX0v-33kFEB3ifvmWesuCcMUrThPAEj4FY$=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) .