Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri May 10 2024 08:18:27 FOUS30 KWBC 100818 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 418 AM EDT Fri May 10 2024 Day 1 Valid 12Z Fri May 10 2024 - 12Z Sat May 11 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF=20 THE SOUTHEAST U.S.... ....Summary...=20 Multiple rounds of convection ahead of a slow moving cold front=20 will pose a Marginal Risk of excessive rainfall today across parts=20 of the Southeast. Very minor changes were made to the outlook area=20 from yesterday's Day 2 ERO.=20 ....Southeast AL-Southern GA-Far Southern SC-FL Panhandle-North FL...=20 The advancing frontal boundary across the Southeast U.S. will be=20 the primary focus for deep convection Friday into Friday afternoon. Unseasonably robust upper level jet streak (110-130kts at 250 mb)=20 will traverse the Mid Atlantic region Friday. This would put the=20 outlook area in the right-entrance region of jet streak for a=20 little while, allowing for an uptick in divergence aloft/large- scale ascent along with low-level frontogenesis ahead of the=20 approaching cold front. Into the early evening hours, pre-frontal,=20 mixed-layer CAPEs will average between 1500-2500 J/Kg over most=20 areas per the guidance, which along with the anomalous PW profile=20 (1.75-2.00"), will support isolated 2-2.5"/hr rainfall rates=20 underneath the strongest cells. Simulated reflectivity forecasts=20 per the CAMs do show the potential for some cell training; however, they all show fairly fast cell motions along with quick forward=20 propagations of more organized clusters per the Corfidi Vectors. As a result, while the probabilities of 3" in 6 hours are fairly=20 decent (spotty 30-40+ probs per the HREF and RRFS), the=20 probabilities of 5+ inches drops precipitously to 10% or less.=20 Therefore expect some localized heavier rain totals and rain rates=20 to pose an isolated flash flood risk today within the Marginal Risk area. Hurley Day 2 Valid 12Z Sat May 11 2024 - 12Z Sun May 12 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF=20 THE SOUTHERN HIGH PLAINS INTO SOUTH-CENTRAL TEXAS... ....Summary...=20 Vigorous upper level shortwave trough moving slowly across the=20 Four Corners region and southern Rockies will lead to a quick=20 influx of deep-layer forcing and moisture across the southern High=20 Plains in eastern NM, much of the TX Cap Rock-Rolling Plains, and=20 into the TX Hill Country/South-Central TX. The Marginal Risk of=20 excessive rainfall from yesterday's Day 3 ERO was expanded across=20 these areas based on the latest guidance trends, where the=20 potential exists for isolated instances of flash flooding. ....Eastern NM into portions of Western and Central TX... Ahead of the approaching upper shortwave trough, a gradual uptick=20 in difluence aloft will ensue across the outlook area.=20 Strengthening low-level moist S-SE inflow will also take place Sat- Sat night along and east of the dryline, as 850 mb moisture flux=20 anomalies peak between 2-3 standard deviations above normal.=20 Convection forming off the terrain will obtain quite a bit of=20 forward propagation given the strong deep-layer shear profile,=20 therefore cell training is not a concern per the simulated=20 reflectivity guidance form the models. However, available deep-=20 layer instability (MUCAPEs at least ~1000 J/Kg over the northern=20 portion of the Marginal area...1500-2500+ J/Kg south) along with=20 PWs averaging 2 standard deviations above normal will favor maximum rain rates of 1-1.5"/hr and 1.5-2.0"+/3hr underneath the strongest cores. Supported by the latest CSU ERO first guess guidance,=20 runoff from these stronger storms will pose an isolated or=20 localized risk for flash flooding, even with the antecedent dry=20 soils over parts of the outlook area.=20 Hurley=20 Day 3 Valid 12Z Sun May 12 2024 - 12Z Mon May 13 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF=20 CENTRAL AND EASTERN TEXAS INTO MUCH OF LOUISIANA AND SOUTHWEST=20 MISSISSIPPI... ....Summary... Mid-upper level trough traversing the Central-Southern Plains=20 north of the Red River will lead to a surge of deepening=20 instability and moisture from the western Gulf of Mexico as a warm=20 front pushes into eastern TX and southwest LA. Favorable dynamic=20 and thermodynamic profiles will result in widespread convection=20 across central-eastern portions of TX into parts of the Lower MS=20 Valley, where a high-end Slight Risk of excessive rainfall is=20 anticipated Sunday and Sunday night. ....Central-Southern Plains and Portions of the Lower Mississippi=20 Valley to the Mid-Upper TX and western LA Gulf Coast... For now at least, just a modest kinematic response is noted from=20 the guidance during day 3 ahead of the the approaching shortwave.=20 850 mb wind anomalies for instance are currently modeled to be=20 around 1-1.5 standard deviations above normal (while at the same=20 time 850-700 mb moisture flux anomalies top out between +2-2.5).=20 The absence of a a more robust subtropical jet streak is the likely culprit; however, the presence of the 90-100 kt upper jet streak=20 traversing the Southern Plains and TN Valley will be felt by way of subtle right-entrance region forcing (focused area of upper=20 divergence/deep-layer ascent and low-level frontogenesis). This=20 will enhance the fgen along the leading edge of the surface warm=20 front, while also retarding it's east-northeastward motion. Largely elevated, convection will become more widespread downwind of the=20 warm front in a favorable deep- layer warm/moist advection pattern=20 off the western Gulf of Mexico. The lingering low-level=20 frontogenesis/slow progression of the surface front will allow for=20 some cell training, especially across parts of central-eastern TX=20 which had received quite a bit of rain over the past week. Over=20 this region eastward through central LA and southwest MS, feel the=20 ERO risk will be more of a "high end" Slight (i.e. at least 25%=20 risk of rainfall exceeding FFG within 25mi of a point). 00Z models=20 show pockets of 3-5+ inches of rain during day 3 within this area,=20 with the past 2 ECMWF and UKMET runs consistently wetter than the=20 other models. Hurley Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8MVWWXfV17m3r7yGfEsF8qnAZqrLjHXAzXdMOMdCtmre= D9J8njX_k0qUFTmJUL9xwbYhclkgAQD53A8zBYyqZrzuxqI$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8MVWWXfV17m3r7yGfEsF8qnAZqrLjHXAzXdMOMdCtmre= D9J8njX_k0qUFTmJUL9xwbYhclkgAQD53A8zBYyqe3ZJDdg$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8MVWWXfV17m3r7yGfEsF8qnAZqrLjHXAzXdMOMdCtmre= D9J8njX_k0qUFTmJUL9xwbYhclkgAQD53A8zBYyqJbOlElI$=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .