Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Feb 10 2024 21:34:41 FOUS30 KWBC 102134 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 433 PM EST Sat Feb 10 2024 Day 1 Valid 16Z Sat Feb 10 2024 - 12Z Sun Feb 11 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE GULF COAST STATES TO THE SOUTHEAST U.S... 16Z update... Radar imagery shows organized bands of convection are firing up across the South in locations ahead/along the surface frontal boundaries. Observations of 0.50 to 1.00 inch are common across far eastern Texas, Louisiana and southern Arkansas so far with amounts up to 0.50 elsewhere. Rainfall intensity and coverage is expected to increase by late morning along the front as it slows its progression. The northern bounds of the Marginal Risk area was adjusted a little northward to reflect the latest trends. The Slight Risk area still encompasses where the best potential for higher QPF and associated threat for flooding will be therefore no adjustments were made at this time. Campbell Convection capable of producing heavy rainfall will develop today from portions of the Gulf Coast that spreads east/northeast with time as large scale ascent increases ahead of a vigorous upper makes its way out of the southern Rockies. Between enhanced flow of Gulf moisture and increasingly difluent flow aloft... the model QPF of 1 to 3 inches with isolated maximum amounts over 4 inches seem to be reasonable along a quasi-stationary front extending across the region. With more CAMs becoming available, made a few minor adjustments to the previously issued ERO but the overall forecast reasoning has changed little. Bann Day 2 Valid 12Z Sun Feb 11 2024 - 12Z Mon Feb 12 2024 ....THERE IS A MARGINAL RISK AREA OVER PORTIONS OF THE SOUTHEAST U.S. ON SUNDAY... 21Z update... The western bounds of the Marginal Risk area was expanded westward across northern Louisiana and into far eastern Texas where additional rain will keep threat for local flooding concerns elevated. Consensus continues to focus the highest amounts for this period over the northern half of Georgia and western portions of South Carolina. Areal averages remain in the 1 to 2 inch range although locally higher accumulations may be possible. Campbell Guidance continue to depict an areal footprint of QPF across the Gulf states and into the Southeast U.S. during this period as one shortwave scoots eastward early in the period and cyclogenesis occurs vigorous shortwave trough continues to head towards the north/northeast followed by deep layered cyclogenesis over the southern Plains and southern Mississippi Valley. This reinvigorates the on-shore flow of Gulf moisture and results in the flow aloft becoming increasingly difluent. While there is some overlap with a northwest to southeast stripe in Alabama where 14-day rainfall amounts of a couple inches was observed...the axis of heaviest rain should generally be over areas that have had little or no rainfall recently. With WPC deterministic QPF generally below 2 inches...felt a Marginal risk area still adequately covers the risk of excessive rainfall. Bann Day 3 Valid 12Z Mon Feb 12 2024 - 12Z Tue Feb 13 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE SOUTHEAST U.S.... 21Z update... The area of precipitation advance to the Southeast/Mid-Atlantic region as the frontal system progresses eastward. The latest guidance continue to depict the highest amounts of 2 to 3+ inches to align near the coastal areas of North and South Carolina while locations to the west/north will be closer to 1 to 2 inches. The Marginal Risk area encompassed the part of the country that will have an elevated threat for excessive rainfall so no adjustments were needed at this time. Campbell There is a continuing threat of excessive rainfall on Monday...mainly over the Carolinas...as the large scale system moves over parts of the Tennessee Valley. At the surface...one area of low pressure forms and heads northeast over the far eastern TN/OH Valleys while a second area of low pressure forms over parts of the Carolinas...supported by the coupling of upper level jets and the associated vertical velocities supported by the upper level divergence. It is this component which results in the continued risk of excessive rainfall over the Southeast from Monday into the early-morning hours on Tuesday. Precipitable water values increase to values at or slightly above 1.75 inches ahead of a cold front sweeping across the region. Deterministic QPF from the GFS and UKMET seem better than the ECMWF and Canadian and tend to be aligned with the WPC deterministic amounts. Given high FFG numbers...especially where spaghetti plots of model QPF are 2 or 3 inches overlap...will keep the Marginal carried by the WPC Medium Range Desk yesterday. Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7_Btaq87d0RMVG5g694tGflKmtkhkxMsqE_rZDJR1gOh= 0MnBDSWOHA8eYDDAiuXN8wGk8xGO51h6uF7ywvmkwjZOKvQ$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7_Btaq87d0RMVG5g694tGflKmtkhkxMsqE_rZDJR1gOh= 0MnBDSWOHA8eYDDAiuXN8wGk8xGO51h6uF7ywvmkbW6X9t0$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7_Btaq87d0RMVG5g694tGflKmtkhkxMsqE_rZDJR1gOh= 0MnBDSWOHA8eYDDAiuXN8wGk8xGO51h6uF7ywvmkYX5BSF4$=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) .