Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Jun 08 2023 07:05:48 FOUS30 KWBC 080705 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 305 AM EDT Thu Jun 08 2023 Day 1 Valid 12Z Thu Jun 08 2023 - 12Z Fri Jun 09 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE NORTHERN ROCKIES INTO THE INTERIOR PACIFIC NORTHWEST...=20 =20 =20 ....Northern/Central Rockies into the Pacific Northwest...=20 Closed low over the Great Basin will weaken while lifting north and northeast. This puts the Northern Rockies in the path, with divergence aloft over an area of plentiful moisture and instability to lead to widespread convection on Thursday, with rates likely eclipsing 1"/hr in many areas. Effective bulk shear in the area reached 25-35 kts which should lead to convective organization. One week rainfall has been as much as 600% of normal (highest in MT). This all supports the existing Slight Risk. Even though the ID Stovepipe has had below average rainfall this past week and streamflow is below average, the ingredients in place support hourly rain totals to 2" where cells merge and/or train, which would be problematic even there. Changes made to the risk areas was minimal this cycle.=20 =20 ....Northern Plains...=20 A weakening stationary front will dissipate during Thursday ahead of a secondary cold front approaching from Canada late in the period. This forcing moving across a region of elevated PWs of +1 to +2 standard deviations according to NAEFS collocated with a ribbon of MUCAPE reaching as high as 2000 J/kg will support hourly rain totals which at times may reach 2"/hr based upon the ingredients available. Although Corfidi vectors reach 20 kts, they are aligned to the mean wind suggesting some training potential, while bulk shear of nearly 30 kts indicate the potential for convective organization. These together could result in pockets of heavier rainfall as repeated rounds of storms occur, with locally 3" possible. Overall the flash flood risk looks isolated, with the Marginal Risk shifted to where the guidance indicates the best potential for heavy rainfall. ....Portions of CA & NV...=20 As the closed low opens and drifts northward, sufficient moisture with PWs of 0.75-1 inch and MUCAPE of 500-1000 J/kg supports a Marginal Risk of excessive rainfall/flash flooding, with the potential of hourly rain totals to 1.5" where cells merge and/or train. Convective coverage will be the main reason for the low risk in this region, as any heavy rain-related issues are expected to be isolated. Additional rainfall could reach 1-3" in some areas. If it occurs over the same areas impacted earlier this week, rapid runoff and isolated flash flooding could ensue.=20=20=20 =20 =20 ....Southern Florida...=20 A shortwave aloft lifts through northern FL on Thursday, providing another day of favorable ascent for scattered showers and thunderstorms across the southern FL peninsula. Sufficient moisture, with PWs above 1.75 inches, collocated with a ribbon of 2000 J/kg MUCAPE will fuel 2.5"/hr rain totals within the convective activity. Storms that do develop are progged to move progressively to the northeast on 20-25 kts of mean 0-6km winds, but aligned Corfidi vectors and 25 kts of bulk shear indicate that training/convective organization is likely, which could enhance both the rain rates and rain duration. The highest risk for heavy rainfall occurs within a region that has been more than 200% of normal rainfall during this past week. While the greatest risk for any isolated flash flooding appears to be along the urban Gold Coast where sea breeze pinning is more likely to occur, any place across South Florida that experiences training could see instances of flash flooding.=20 ....South-Central to Southeast TX... A system moves across portions of central and eastern TX today, and is expected to interact with a moisture gradient across central TX which could spur development farther to the east and southeast with an uncapped air mass. PWs are ~1.5" and CAPEs should rise to 2000+ J/kg. Low-level inflow is weak but cyclonic. Effective bulk shear appears to be sufficient for some level of convective organization, so any bigger issues could end up being closer to the origination point of convection midday local time before cold pools form and forward propagation commences. Hourly rain totals to 1.75", with local amounts of 2-4", are expected within the new Marginal Risk area. Flash flood guidance values are lower to the west and higher to the east. However, urban areas around Houston and the Golden Triangle of Southeast TX could have localized flooding with these sort of amounts. Coordination with EWX/the New Braunfels TX forecast office led to this new Marginal Risk area. ....Kansas into Arkansas... A southward propagating piece of the polar front at 850 hPa is expected to instigate convection today within an uncapped air mass. PWs are 1.5-1.75", while CAPEs rise to 2000+ J/kg or so.=20 There are some pieces of guidance indicating local 2-4" amounts in this area. Since hourly rain totals could rise to 2", this would be a problem in any urban areas or within any problematic local topography, despite relatively high flash flood guidance values.=20 As issues are expected to be isolated, the new threat area is considered Marginal Risk. Roth/Weiss 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!5SdixdnrzGNETvj9uth6dthA9ynbyvKpr1HK70YQj6DY= 2cei0xF8R1YZ38GxMud-804TMBtfOBwvIhfzfsJGY6xRQek$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5SdixdnrzGNETvj9uth6dthA9ynbyvKpr1HK70YQj6DY= 2cei0xF8R1YZ38GxMud-804TMBtfOBwvIhfzfsJGMMfFea8$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5SdixdnrzGNETvj9uth6dthA9ynbyvKpr1HK70YQj6DY= 2cei0xF8R1YZ38GxMud-804TMBtfOBwvIhfzfsJGhBZrUmw$=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) .