Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Mar 15 2024 00:31:15 FOUS30 KWBC 150031 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 831 PM EDT Thu Mar 14 2024 Day 1 Valid 01Z Fri Mar 15 2024 - 12Z Fri Mar 15 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS AREAS FROM=20 NORTHEAST TEXAS INTO THE MID-SOUTH, AND ACROSS PARTS OF ILLINOIS AND INDIANA... ....0100 UTC Update -- Added a rather narrow/targeted Slight Risk area across parts of southern IL into central IN, basically encompassing the training line of convection along the forward=20 flank oriented wsw-ene of the surface low. MUCAPES of 1000-2000 J/Kg within this region early this evening will drop to 500 J/Kg or below towards midnight. However until then, given the favorable forcing within the right-entrance region of the upper jet, along with the aforementioned deep-layer instability and PWs of 1.1 to 1.3", hourly rainfall rates of 1-1.5" or greater from training cells will allow for a more enhanced risk for flash flooding in this corridor. Otherwise, minimal changes were made to the previous Day 1 ERO, mainly to trim the NW-W-SW edges of both the Slight and Marginal Risk areas based on the latest observational and guidance trends. Hurley Day 2 Valid 12Z Fri Mar 15 2024 - 12Z Sat Mar 16 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN AND NEAR SOUTHEAST TEXAS AND PORTIONS OF THE SOUTH... ....20:30z Update... The overall synoptic, moisture and instability setup remains mostly the same. Non- GFS/NAM guidance continues to keep the QPF max over northern/central Alabama, while the 12z CAMs and ECMWF are spread=20 back into Mississippi on Friday. This continues to be the main uncertainty and is likely directly tied to the timing/speed of the surface cold front propagating from the northwest. The 12z HREF=20 mean still has 0.25-0.5/hr rates over southeastern Texas where the other Slight Risk area is currently drawn. Kebede ....Previous Discussion... A cold front begins to accelerate to the southeast across the Southeast as a broad upper level trough gains real estate across=20 portions of the Great Lakes and Upper Midwest, with the front=20 moving slower to the south into the Southern Plains as a cold low=20 in the Desert Southwest shows minimal movement and keeps the upper level flow southwest to west- southwesterly which should slow the surface boundary's progression. This combination of systems=20 flattens the ridging across the Southeast and Gulf Coast.=20 Temperatures at 700 hPa suggest that the heaviest rainfall should=20 be north of southern TX, where temperatures are <6C, based on GFS=20 forecasts and ML CAPE should rise to ~3000 J/kg. An axis of=20 anomalous PW values, 1.5-1.75", will be seen near the front.=20 Another day of potentially widespread heavy rainfall is expected, as hourly rain totals to 2.5" and local amounts to 4" remain=20 possible. There is the typical amount of spread with respect to the position and maxima within the heavy rainfall axis, but the=20 overall model consensus suggests potentially heavy rains. Some=20 heavy rainfall is expected across areas of Mississippi, Alabama and Georgia that have had above average precip over the past week or=20 two, resulting in higher stream flows and greater soil saturation=20 which continues to be the reason for the Slight Risk, over other=20 considerations. The Slight Risk area was split in two to depict the bimodal distribution of the heavy rainfall pattern in the=20 southern tier of the country, with the eastern portions associated with the progressive frontal zone/850 hPa confluence early on more northerly and the western portions associated with the slow- moving boundary shifting more southerly. A separated Marginal Risk remains in and near portions of WV which is typically more sensitive to heavy rainfall and where flash=20 flood guidance values remain relatively low near a progressive section of the front. Hourly rain totals to 1" and local amounts=20 to 2" are possible there, which could exceed the flash flood=20 guidance values.=20 Roth Day 3 Valid 12Z Sat Mar 16 2024 - 12Z Sun Mar 17 2024 ....A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS ACROSS PORTIONS OF=20 SOUTHERN TEXAS... ....20:30z Update... The southward trend in QPF guidance noted in the previous discussion continues into this update. The cold front extending from the Carolina Coast will stall out just south of southern Texas. A potential surface wave over the Texas Gulf Coast may enhance inflow into the state. Synoptic, moisture and instability remains similar to what was forecast overnight. Small details will dictate where the axis of max QPF sets up. Kebede ....Previous Discussion... Difluence aloft ahead of an upper level low moving slowly across=20 Arizona teams up with a sagging front in southern TX to continue=20 the potential for heavy rainfall in the front's vicinity. The=20 guidance has shifted southwest, which has led to a similar shift=20 in the excessive rainfall areas. Temperatures at 700 hPa imply that the heavy rain threat should be mainly north of Deep South=20 TX, based on GFS forecasts. Inflow at 850 hPa from the Gulf should pulse up to 25-30 kts at times, importing ML CAPE of 2000 J/kg or=20 so. Effective bulk shear should be sufficient for organized=20 convection, capable of producing hourly rain totals to 2" and local amounts to 4". Roth Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9-IV1m4HI5ek38xl2IYgh44v76lwjDWLqs42CUwVPgnD= GTLi0ZL6wHgbONknFxyF-Ppq-9Y9mOd6hNBgf12tIObisjk$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9-IV1m4HI5ek38xl2IYgh44v76lwjDWLqs42CUwVPgnD= GTLi0ZL6wHgbONknFxyF-Ppq-9Y9mOd6hNBgf12tEpyk9zQ$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9-IV1m4HI5ek38xl2IYgh44v76lwjDWLqs42CUwVPgnD= GTLi0ZL6wHgbONknFxyF-Ppq-9Y9mOd6hNBgf12tGSwcftE$=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. 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