Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jun 11 2023 07:09:23 FOUS30 KWBC 110709 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 308 AM EDT Sun Jun 11 2023 Day 1 Valid 12Z Sun Jun 11 2023 - 12Z Mon Jun 12 2023 Day 1=20 Valid 12Z Sun Jun 11 2023 - 12Z Mon Jun 12 2023=20 =20 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF COLORADO & THE TENNESSEE VALLEY...=20=20 =20 =20=20 Great Lakes/Midwest/Ohio Valley/Tennessee Valley...=20=20 A broad area of locally heavy rainfall is expected in the eastern portion of the country -- much of it welcome because of recent dryness -- as a deepening closed cyclone drops into the Great Lakes and phases with a shortwave moving eastward from the southern Plains. The best signal for heavy rainfall is in the TN Valley, where strengthening low-level inflow, CAPE of 2000+ J/kg, and PWs of 1.5-2" are forecast. There appears to be enough effective bulk shear for convective organization. These ingredients allow for hourly rain totals to 2.5". The guidance has a good signal for local 3-4" amounts. Outside of northernmost GA, the region has seen much below rainfall over the past week, if not two months. However, with the rain rates expected, particularly in urban areas, widely scattered to scattered instances of flash flooding are expected despite the recent dryness. The Slight Risk has been shifted southeast to best fit the available guidance.=20=20 =20 To the north, a front moves in while 1.5"+ PWs pivot in and around portions of the OH Valley, quite a different look than seen in the guidance 24 hours ago. Increasing 850 hPa frontogenesis, and the low-level inflow exceeding the mean 850-400 hPa wind are expected to lead to better than average rainfall efficiency. Outside of portions of southern IL, southern IN, and perhaps southwest OH, residence time of the highest moisture in OH is a bit more limited than seen on last night's guidance. Within this region that's been dry, some areas for quite a while, there's a concern that in some spots soils will be hard/brick-like initially, with rainfall all running off until soils can soften and allow infiltration.=20 Hourly rain totals to 2" should be possible, which would be problematic in urban areas. In order to avoid constant flip-flopping on the risk area in this region, and due to the moderately large mass field change over the past 24 hours, have left the level at Marginal in the Ohio Valley.=20 =20=20 =20=20 In and near Colorado...=20=20 Upslope flow behind a frontal zone imports moisture from the southern and central Plains into eastern Colorado, with PWs exceeding 1" in easternmost CO in a col point in the mid-level flow. CAPE is expected to rise towards 1000 J/kg. With the mid-level flow opposing the low-level flow, enough effective bulk shear should exist for organized convection, which could allow hourly rain totals to rise to 2" where cells train and/or merge.=20 Once cold pools becoming dominant, organized convection should plow east to southeast into the low-level flow, increasing storm scale inflow. The guidance has a good signal for local amounts of 2". Flash flood guidance is rather low, so a scattered risk of flash flooding is anticipated as both hourly and three hourly flash flood guidance values are exceeded. The Slight Risk area remains similar to continuity and matches the overnight model guidance.=20=20 =20=20 =20=20 Remainder of the West...=20=20 An anomalously deep closed low pivoting through southern CA into southern NV will help cause pockets of 1000+ J/kg of CAPE and PWs of 0.75-1.25". This is expected to cause isolated heavy rain concerns particularly at elevation across portions of the West and northern Rockies. Where cells train and/or merge, hourly totals of 1.5" are possible. Considering recent wetness, the existing Marginal Risk area looks reasonable at this time as cell coverage should not be dense enough to cause scattered flash flood issues.=20 Some expansion was made to the Marginal Risk area to account for the 00z HREF guidance.=20 =20=20 Roth Day 2 The Day 2 outlook will be updated by 0830Z. Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6vxPrFxP-BGH0PVi6oETBwQvrv0ooo4VAfL8Ftidlh4i= hRG2j5IE34oBZRJyWJBwElfmF1hHCB4fNAuQiUPqigUPPlc$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6vxPrFxP-BGH0PVi6oETBwQvrv0ooo4VAfL8Ftidlh4i= hRG2j5IE34oBZRJyWJBwElfmF1hHCB4fNAuQiUPqXr5tQWk$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6vxPrFxP-BGH0PVi6oETBwQvrv0ooo4VAfL8Ftidlh4i= hRG2j5IE34oBZRJyWJBwElfmF1hHCB4fNAuQiUPqVgmgDWA$=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) .