Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jan 02 2023 00:37:00 FOUS30 KWBC 020036 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 735 PM EST Sun Jan 01 2023 Day 1 Valid 01Z Mon Jan 02 2023 - 12Z Mon Jan 02 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Hurley Day 2 Valid 12Z Mon Jan 02 2023 - 12Z Tue Jan 03 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE MID-MISSISSIPPI VALLEY TO EASTERN TEXAS... On Monday, a deep upper level trough over the Four Corners region will eject northeastward onto the Plains, reaching the eastern Dakotas/MN by Tuesday morning. Upper jet will mostly lift to the northeast, placing the Mid/Lower-MS Valley into the Mid-South in the right entrance region of the jet, with another jet streak nosing in off the Gulf Coast. This will provide broad-scale lift to the region in the warm sector in advance of a cold front from the west. In addition, a plume of Gulf moisture will be drawn northward up the MS River Valley through the day. This plume will contain PWs exceeding 1.5 inches in some areas, which is as much as +5 sigma. The cold front will act as the forcing mechanism for numerous thunderstorms of varying types across the middle MS River Valley Monday afternoon through the overnight, as they develop in the aforementioned plume of Gulf moisture. More on the severe threat can be viewed on the Storm Prediction Center's summary of the active weather. As far as excessive rainfall, much of the guidance suggests a series of squall lines and cell mergers are likely across the Slight Risk area. This will increase the potential for training thunderstorms. Thus, the primary flash flooding threat will be from short bursts of heavy rain from thunderstorms, rather than a long duration of widespread moderate to occasionally heavy rain. The Slight Risk outline basically covered the intersection of GEFS probs for higher QPF and at least some instability, and is also near the CSU First Guess outline. Where recent heavy rain occurred in northwestern LA, there may be a higher risk of flash flooding, but the guidance shows a split in higher QPF probs to the south of northeast of this area. Can re-evaluate with the next CAM cycle. CSU First Guess fields based on a machine-learning algorithm were attuned to this sensitivity. Wegman/Fracasso Day 3 Valid 12Z Tue Jan 03 2023 - 12Z Wed Jan 04 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE FLORIDA PANHANDLE AND THE SOUTHERN APPALACHIANS... On Tuesday, the eastward progression of the upper level longwave trough will slow as compared with Monday as it lifts northeastward. A 120 kt upper level jet streak will race eastward from IA into the MS Valley by Wednesday morning. This jet and associated shortwave will reintensify convection across the Southeast overnight Tuesday night after potentially multiple rounds of thunderstorms in this same area during the day Tuesday with the initial cold front. PWs are progged to surge to around 1.50" or +2.5 sigma (supported by high GEFS probs). Two Slight Risk areas were maintained in the afternoon update: along the Gulf Coast in the FL Panhandle where recent 7-day precip anomalies are over 200% and over the southern Appalachians where a couple rounds of higher rainfall rates are possible. Both areas may see pre-frontal convection in addition to higher rates with the frontal passage in association with a surge in moisture on 40-50kt SW flow at 850mb. Combination of heavier rainfall in successive waves could result in some flash flooding concerns. Fracasso/Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6PcQkQnyOTZWumTjUAqyLtbiBxI06ZtD--VaIskfLV7w= dQK3PU7cp745tLfZbtYmGcVmIARTRkQRxkR858IekpWyMwM$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6PcQkQnyOTZWumTjUAqyLtbiBxI06ZtD--VaIskfLV7w= dQK3PU7cp745tLfZbtYmGcVmIARTRkQRxkR858IeF-ARao0$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6PcQkQnyOTZWumTjUAqyLtbiBxI06ZtD--VaIskfLV7w= dQK3PU7cp745tLfZbtYmGcVmIARTRkQRxkR858IeWu52Huc$=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) .