Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Nov 09 2022 00:21:00 FOUS30 KWBC 090020 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 720 PM EST Tue Nov 08 2022 Day 1 Valid 01Z Wed Nov 09 2022 - 12Z Wed Nov 09 2022 ....THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL ACROSS THE TRANSVERSE RANGES OF SOUTHERN CALIFORNIA... ....Southern California... Curtailed both the Slight and Marginal Risk areas farther north (across the Central CA Coast), based on the latest observational trends with the southeast progression of the surface front and pre-frontal max PW plume (~1.00"). Still looking at a few more hours of more intense rainfall rates across the LA and SD metro areas, along with the southern slopes of the San Gabriels and San Bernardinos, where the Moderate Risk will continue). Per the HREF exceedance probabilities, expect the activity to taper after 04-05Z from north to south. ....Foothills of the Sierra Nevada... A Marginal Risk remains in effect across portions of central California, where per the 18Z HREF, the potential for 0.5+ in/hr rainfall rates below snow levels will persist. Areas at most risk will be burn scars from the past couple of years which dot the region highlighted with the Marginal Risk. ....Portions of the High Desert and Great Basin... No changes to the Marginal Risk area. Moisture hitting the West Coast will have a much easier than normal time getting past the mountains into interior sections of southern NV, northwest AZ, and southwest UT on Tuesday given the strong dynamics and inland advancement of the IVT plume. Looking like rainfall amounts of 1-2" will fall across this area, with localized amounts around 3" in the favored south southwest facing slopes. Not expecting much in the way of instability this far inland through 12z Wed, which should limit peak rainfall rates below 1 in/hr, but the strong IVT and orographic effects should still push hourly rainfall totals above 0.5" at times. Overall these rainfall totals and rates should not result in widespread or significant flooding impacts. However minor flooding and runoff issues are still probable with rainfall of this magnitude. ....South Florida... The center of Tropical Storm Nicole will remain offshore tonight, however the mid level low associated with this system is very broad. Embedded shortwave energy on the periphery of this broader mid level low may track across FL this period, and guidance indicates PWs potentially increasing to around 2". There remains at least some risk of convective bands moving into southeast FL during the day or overnight period, which could potentially pose a localized urban flash flood risk with tall/skinny CAPE profiles in forecast soundings and low level onshore flow of 35-45 kt / coastal convergence axis setting up. Farther north, 12Z members of the 12Z HREF showed the potential for a narrow axis of heavy rain to set up near/just north of Cape Canaveral. Potential for 3-5 inches of rain exists where onshore flow of 30-40 kt at 850 mb is forecast by the latest model consensus. However, the area potentially impacted looks fairly localized and CAPE appears as if it will focus in the lower levels due to mid-level dry air in forecast soundings. Current thinking is that a Marginal Risk need not be extended northward to include the northeastern peninsula as 14-30 day rainfall has been mostly below average...although portions of the St. Johns river valley remain in flood stage. Hurley/Chenard Day 2 Valid 12Z Wed Nov 09 2022 - 12Z Thu Nov 10 2022 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ACROSS MUCH OF THE FLORIDA PENINSULA... 2030Z Excessive Rainfall Outlook Discussion... The threat of excessive rainfall will build across much of the Florida peninsula as Nicole approaches from the east and then crosses the peninsula. Even though spread still exists in how far north or south the transit occurs, the heaviest rainfall is forecast to be along the east coast with 3 to 5 inches with isolated maximum of 8 inches. A potential upgrade to a Moderate Risk for all or portions of the First, Space, and Treasure Coasts remains a distinct possibility with future forecast updates as uncertainty diminishes. ....Upper Midwest... In coordination with WFO Duluth, maintained the Marginal Risk area in far northwest WI and a small portion along the north shore of Lake Superior. The ECMWF was on the most aggressive side in generating a 3+ inch QPF bullseye...while other guidance was generally in the 1 to 2 inch range. A plume of Gulf moisture will extend all the way up to the upper Great Lakes on Wednesday and be in place ahead of a cold front. This front will be essentially stationary, so wherever the front sets up, those areas may see multiple round of training convection. As previously mentioned, one factor that may mitigate the excessive rainfall potential will be how dry the area has been during the past few months. At this point, felt there was too much mesoscale forcing to remove the Marginal Risk at this point. Bann Day 3 Valid 12Z Thu Nov 10 2022 - 12Z Fri Nov 11 2022 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHEAST... ....2030 UTC Excessive Rainfall Outlook Discussion... Few changes needed to the on-going Day 3 Excessive Rainfall Outlook. The guidance shifted the track of Nicole westward a bit compared with the overnight guidance...but the upward tick in QPF noted in the overnight guidance persisted. Coordination with area offices, only made modest changes to the previously-issued Slight Risk area in the Southeast U.S. and the Marginal extending into the southern portion of the Mid-Atlantic. Many of the points made in the previous discussion are still valid. With the northern stream system moving a bit faster, removed some of the areal coverage of the Marginal Risk area that extended back into central Minnesota...but maintained the area farther north. Bann Previous Discussion... ....Portions of the Southeast... The circulation associated with Nicole will continue hitting portions of the Southeast on Thursday. The main areas of heavy rain continue to be focused from coastal southern South Carolina, the eastern half of Georgia, and Florida from Apalachicola east and from Tampa north. Expect an additional 3-6 inches of rain on Thursday with higher amounts locally. This area too has the potential to need additional upgrades to a Moderate Risk with future forecast updates, once the track and speed of Nicole come into better agreement in the guidance. Further north and west from northern Georgia to southwest Virginia, there has been a clear and notable wetter trend in the forecast rainfall, with some northward shift due to an approaching upper level trough. Thus, the Appalachians from GA to VA are looking particularly wetter compared with previous forecasts. Strong southeasterly to easterly flow into the mountains will upslope along the mountains, which will result in a local maximum of rainfall over this area. That being said, this area has been very dry lately, so only the Marginal Risk was expanded into this area. The Slight Risk, while expanded from inherited, is also much smaller than it otherwise would've been if the antecedent conditions weren't so dry. Thus, it remains to be seen how widespread any flooding rains are. ....Upper Midwest... A strong low will develop along a front across the Upper Midwest on Thursday. While it produces blizzard conditions across the Dakotas and northern Minnesota, on the warm side of the storm from southern MN, northern WI, and the U.P. of MI, rainfall will be ongoing from Wednesday over much of the same area, since the front focusing the rainfall will be stalled out. Once again since this area has been so dry the flooding threat is significantly diminished. However, the aggregate of multiple days of rain over this same area should result in an isolated flash flooding threat across the Marginal Risk area. Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8xof3Elqw--ZZGUnJM1V3ea71Uh4s4AEULXr2x1_l8Yg= Ax0HQs95yI7qxcH3PBanztw9640dlitZZbDzTzpv-Xnlc1E$=20=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8xof3Elqw--ZZGUnJM1V3ea71Uh4s4AEULXr2x1_l8Yg= Ax0HQs95yI7qxcH3PBanztw9640dlitZZbDzTzpvXzvnhWw$=20=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8xof3Elqw--ZZGUnJM1V3ea71Uh4s4AEULXr2x1_l8Yg= Ax0HQs95yI7qxcH3PBanztw9640dlitZZbDzTzpvZuZtquM$=20=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) .