Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Nov 04 2024 15:54:55 FOUS30 KWBC 041554 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1054 AM EST Mon Nov 4 2024 Day 1 Valid 16Z Mon Nov 04 2024 - 12Z Tue Nov 05 2024 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS SOUTHEAST OKLAHOMA THROUGH THE OZARKS OF ARKANSAS AND MISSOURI... ....Texas to the Great Lakes... 16Z Update: Highly amplified flow ahead of a potent closed=20 low/upper trough axis moving through the Western CONUS will=20 continue to usher in well-above normal moisture anomalies from the=20 Gulf Coast up through the Great Lakes during the period. Heavy=20 rains overnight across OK into the AR/MO Ozarks have crashed FFG=20 indices regionally with cases of hourly FFG's now down <1"/hr=20 necessary to garner flash flood concerns. A widespread areal=20 average of 2-4" with locally as high as 7" has fallen over the=20 above area, saturating top layer soils up into the 70-85th=20 percentile as indicated via the latest NASA SPoRT output for the=20 0-10cm layer. Expectation is for the pattern to continue evolving=20 as such that another wave of heavy precip will initiate upstream=20 over OK as the nose of a 110kt 500mb jet streak rounds the base of=20 the mean trough over NM and ejects into the Southern Plains. Large=20 scale ascent will be maximized over within the time frame of 21z=20 through the remainder of the period allowing for a large cluster of showers and storms to breakout and pivot east-northeast, aided by=20 the mean flow. A theta-E tongue is well documented over Eastern TX=20 through the Lower Mississippi Valley up through the the Missouri=20 Ozarks lending to favorable instability continuing through the=20 afternoon and evening time frames.=20 CAMs have become aggressive with the QPF output given the aforementioned variables lending to a repeated pattern of heavy rainfall over areas that saw copious amounts of rain overnight. 12z HREF signals a high end probability for at least 3" within the neighborhood probability fields (70-90+%) for the Ozarks down into the Southeast corner of OK and is correlated well with a 25-50% EAS prob field for 3" with a max prob of 60% centered over South- Central MO to the east of Springfield. HREF blended mean output is elevated with 3-5" of rainfall over those areas with a max of up to 7", all of which is additional to what has transpired. Considering the expected additional rainfall with rates generally 1-2"/hr at peak intensity likely breaching the current FFG indicators for 1/3/6 hr periods, and in coordination with the TSA/LZK/SHV/SGF WFOs impacted, a Moderate Risk ERO was introduced to cover that area from Southeast OK up through North and Northwest AR into South- Central MO.=20 Further south into TX, there is a growing consensus of heavy thunderstorm genesis on the southern edge of the flanking line=20 along the axis of convergence settling within the western edge of=20 the theta-E gradient later this evening, mainly after the development of the nocturnal LLJ. The jet streak on the base of=20 the mean trough under the closed low will be juxtaposed to the=20 northwest of Central TX allowing for increasing RER dynamics within the confines of the I-35 corridor extending from DFW down into the Austin/San Antonio metros. There is consensus on the development=20 of the flanking line, but exactly where the heaviest will occur=20 depends on the CAM output. Some place the heavy core of precip near New Braunfels to San Antonio. Others place it near Austin to Waco. Regardless, the instability fields will be prime for any=20 convective initiation with PWAT anomalies sufficiently above 2=20 deviations above normal. These types of setups are sneaky with=20 regards to potential, leading to an expansion of the SLGT risk to=20 include much of that I-35 corridor and adjacent areas in the Hill=20 Country to the west of the interstate.=20 Consensus for locally heavy rainfall north of the Missouri Valley continues up into the Great Lakes as the low pressure progresses into the Midwest with the amplified flow ahead of the potent longwave trough. Lack of sufficient surface based instability caps the potential for significant rainfall totals to more of 1-2" with locally up to 3", but this would be enough to concern some urban flash flood threats for those areas extending through Illinois into Southeast WI into Western MI. The previous SLGT risk was maintained as a result with a MRGL risk encompassing.=20 Kleebauer ....New Mexico... 16Z Update: Very little change necessary for the previous MRGL risk over New Mexico as CAMs deviated very little from the overnight output. Heaviest rainfall concerns will be located within that northern periphery of the closed upper low pivoting eastward through the area as ascent remains maximized within the diffluent area north of the closed reflection, textbook synoptic scale evolution. Higher terrain will actually resolve as snow, so the main areas of concern will be the valleys and locales along the I-40 corridor.=20 Kleebauer ...Previous Forecast.. A leeside low currently over south central New Mexico will track northeast as several mesolows work to consolidate into a dominant single low over Texas and Oklahoma late today. With peak heating, some wraparound moisture and modest instability over an area with modestly depressed FFG values, steady rain with some convective cells ongoing over the area by this afternoon could result in an isolated flash flooding threat, particularly over any burn scars or other flood sensitive areas. Thus, a small Marginal Risk area was added with this update. Precipitation will be ongoing further north and into the mountains of southern Colorado but temperatures there will be cold enough for most if not all of the precip to fall as snow, precluding any flash flooding risk. Wegman Day 2 Valid 12Z Tue Nov 05 2024 - 12Z Wed Nov 06 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MISSISSIPPI AND OHIO VALLEYS... No changes were made to the inherited Marginal Risk area. The upper level trough responsible for the past few days of heavy rain across the southern and central Plains will finally retreat back into the broader jet into Ontario and Quebec. The upper level energy supporting the corridor of storms will continue supporting storms across the Mississippi and Ohio Valleys Tuesday and into Tuesday night respectively. As the energy lifts north, it will mark the end of persistent heavy rain and storms from south to north. Thus, the flooding threat will be more in the morning in Texas, and more towards the night for the Ohio Valley. Training lines of storms will move across the Mississippi Valley for much of the day. These storms will be capable of heavy rains which may cause isolated flash flooding, especially in any urban areas such as Memphis. By Tuesday night, weakening of the storms and the shift well away from any prior days' rain footprint will effectively end the flooding threat. Wegman Day 3 Valid 12Z Wed Nov 06 2024 - 12Z Thu Nov 07 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHEAST... Very few changes were needed to the inherited forecast. Deep tropical moisture will have overspread all of Florida and will be advancing into GA and SC at the start of the period Wednesday morning. A lingering front over the Southeast may act as a focus for convection across GA and SC as the deep tropical moisture moves north into the front. Potential Tropical Cyclone Eighteen (PTC18) is expected to move into the Gulf from Cuba and the northwest Caribbean as well. For the Florida Peninsula, much of the flooding threat will be determined by the eventual track of PTC18. The latest guidance has kept the center of PTC18 far enough west over the Gulf that despite shear pushing much of the rain associated therewith to the eastern side of the circulation, it will still largely remain offshore. However, with PWATs above 2.25 inches, it won't take much for daily convection to produce heavy rainfall almost anywhere in the state. A bullseye of heavier rain is currently forecast across central GA into SC. While the focus for the heavier rain will be the stalled out front, there is considerable uncertainty as to instability, which will greatly determine how strong any storms can get which could cause flooding. For now it appears much of the rain in GA/SC will be spread out through Wednesday and into Wednesday night, which should easily be handled by the antecedent dry conditions. Thus, the Marginal for this area remains in place with only minor tweaks made. The area will continue to be monitored for a potential Slight upgrade, which may not take much given the abundance of tropical moisture any storms would have to work with. Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4rsqJz5JQmuyOhOr-o08a_XA3ZM_En7YJfVLunnqBGNu= 0Q5ZlXVonjLFUna3nTiHS6oDLGE3S0Bc6ZZRN1F6hTAx4TY$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4rsqJz5JQmuyOhOr-o08a_XA3ZM_En7YJfVLunnqBGNu= 0Q5ZlXVonjLFUna3nTiHS6oDLGE3S0Bc6ZZRN1F6cSrVbjs$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4rsqJz5JQmuyOhOr-o08a_XA3ZM_En7YJfVLunnqBGNu= 0Q5ZlXVonjLFUna3nTiHS6oDLGE3S0Bc6ZZRN1F6gPCnVaM$=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) .