Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Dec 13 2022 20:20:39 FOUS30 KWBC 132020 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 319 PM EST Tue Dec 13 2022 Day 1 Valid 16Z Tue Dec 13 2022 - 12Z Wed Dec 14 2022 .....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM FAR EAST TEXAS INTO THE LOWER MISSISSIPPI VALLEY... 16Z update... An organized line of thunderstorms are tracking across the Southern/Central Plains and Midwest this morning. MPD #1157 goes into further detail on the environment and associated flooding risk with these storms as they pass through eastern Texas, Oklahoma and Arkansas. The nature of the storms are fairly progressive at least over portions of Oklahoma, Kansas, and Missouri so the risk is somewhat less than those further south; the storms that will trek through far eastern Texas, Louisiana and southern Arkansas still have the potential to produce hourly rates of 1 to 2+ inches. The 1 hr/3 hr flash flood guidance is as low as 1.5 inches/hour which could be quickly surpassed with these expected rainfall intensities. The Slight Risk area had minor expansions to the east and north to reflect the latest trends in the CAMs. Campbell Broad mid-upper low will migrate into the central-northern Plains later Tue and Tue night, as a 130+ kt southern stream jet streak develops across North-Northeast TX. As this occurs, favorable broad scale/elongated along-stream forcing will push into much of the Mississippi Valley, with more focused (enhanced) exit-region forcing (upper difluence and divergence) across the Lower MS Valley out ahead of the aforementioned upper level jet streak. The guidance continues to depict higher areal-average QPF totals over this region, with areal-average amounts of 1-2" along with isolated 3-5" amounts, owing to the enhanced deep-layer forcing (robust moist southerly inflow/moisture transport) and more favorable thermodynamic setup. PW values peaking between 1.5-1.75", low-mid layer moisture flux anomalies 3 to 4+ standard deviations above the mean, and MUCAPEs 500-1000 J/Kg will allow for spotty 1.5-2.0"/hr and 2.5-3.0/3hr rainfall rates within the Slight Risk area. Hurley Day 2 Valid 12Z Wed Dec 14 2022 - 12Z Thu Dec 15 2022 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FROM THE SOUTHERN LOUISIANA TO CENTRAL ALABAMA... 21Z update... The latest guidance is suggesting that there will be redevelopment across southern Louisiana once the initial line passes. This will reinvigorate convection across the Lower Mississippi Valley/Central Gulf Coast region allowing hourly rates to flourish from 1 to 2.5 inches/hour while slowing their eastward progression. A broad area of 1 to 3 inches will extend from the Central Gulf Coast to as far north as the southern Ohio. There is a growing signal for an axis of 2 to 4 inches to align from south-central Louisiana to central Alabama with very isolated maximums of 6 to 8 inches possible. A Moderate Risk was hoisted over portions of southern/eastern Louisiana, southern Mississippi and western Alabama given the favorable environment for sustained, slow moving convection and enhanced moisture supply. The Marginal and Slight Risk areas were expanded further north to reflect the latest WPC QPF and latest trends. Campbell A broad slight risk area was maintained with some minor modifications over the upcoming day 2 period from the Central Gulf coast, northeastward into the southern Appalachians-southern OH Valley. The day 1 heavy precip event stretching from the eastern portions of the Southern Plains into the Lower to Mid Mississippi Valley will continue its eastward march during day 2, stretching from the Central Gulf coast into the Southern Appalachians. The overall favorable large scale pattern for organized frontal and pre-frontal convection will continue during day 2, with strong frontal convergence and well defined upper difluence continuing in the axis of above average PW values, along with continued anomalous 850-700 mb moisture flux coming off the central to eastern Gulf of Mexico ahead of the associated eastward moving cold front. We contemplated upgrading to a moderate risk area for portions of far northeast Mississippi, northern Alabama into northern Georgia where recent heavy rains have increased stream flows and lowered flash flood guidance values. Our concerns are that models may still be too far to the north with their respective max precip areas. The greatest instability for the day 2 time period is expected farther to the south and closer to the immediate Gulf coast. This may support the heaviest precip falling farther to the south than models suggest, across areas that have not had as much precip recently and subsequently have lower stream flow and higher flash flood guidance values. For these reasons, no changes were made with the risk level, keeping it at slight for the time being. Hurley/Oravec Day 3 Valid 12Z Thu Dec 15 2022 - 12Z Fri Dec 16 2022 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Campbell Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_fHwEKlDAU5fLIcXXJ7156WHtfL6uYT3N6Nx1xOsgrAA= a30A1JCvD8-rjFrcRxytoMcTeLjWms05GZNQNukfFbRubiY$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_fHwEKlDAU5fLIcXXJ7156WHtfL6uYT3N6Nx1xOsgrAA= a30A1JCvD8-rjFrcRxytoMcTeLjWms05GZNQNukfFkRi6v8$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_fHwEKlDAU5fLIcXXJ7156WHtfL6uYT3N6Nx1xOsgrAA= a30A1JCvD8-rjFrcRxytoMcTeLjWms05GZNQNukfR9CO9LU$=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) .