Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Dec 04 2022 20:18:56 FOUS30 KWBC 042018 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 317 PM EST Sun Dec 04 2022 Day 1 Valid 16Z Sun Dec 04 2022 - 12Z Mon Dec 05 2022 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHEAST ARIZONA AND FAR SOUTHWEST NEW MEXICO... Most of Arizona and New Mexico remains beneath the divergent right-entrance region of a ~110 knot 250mb jet streak while, simultaneously, an upper low off the Pacific Northwest coast continues to funnel rich subtropical moisture overhead. NAEFS climatological percentiles remain exceptionally high over southeast Arizona and much of New Mexico this morning and afternoon with PW values above the 99th climatological percentiles in some cases. The IVT also remains quite robust as the upper low off the Pacific Northwest coast and the ridge over the Gulf of Mexico work in tandem to generate IVT values of 400-500 kg/m/s, which is also around the 99th climatological percentile through 00Z this afternoon. However, similar to what was observed on Saturday, any sufficient instability to help garner heavier rainfall rates remains absent, thus keeping a lid on rainfall rates from becoming too heavy. The lack of instability is what keeps the Excessive Rainfall threat capped to a very localized area, which is surprising given how anomalous this amount of atmospheric moisture is over the region. Southern Arizona and far southwest New Mexico has been picking up steady rainfall since Saturday and soil moisture has been growing increasingly saturated. NASA SPoRT-LIS soil moisture percentiles in the 0-40cm layer have ballooned to as high as 90-98% in some cases and has a noticeably larger footprint across the region compared to this time yesterday. The Marginal Risk remains in place given the increasingly more sensitive soils, but any potential flash flood threat will be very localized. Areas that have received as much as 1-2" of rainfall in the last 24 hours, as well as typically dry washes and areas along complex terrain, are most prone to potential flash flooding through this afternoon. The bulk of today's heaviest rainfall is likely to occur before 03Z. It is possible that the Marginal Risk may be adjusted further or removed in the 01Z update later today as the axis of anomalous moisture presses east of the current Marginal Risk area overnight. Mullinax Day 2 Valid 12Z Mon Dec 05 2022 - 12Z Tue Dec 06 2022 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR FAR SOUTHERN TENNESSEE, NORTHERN ALABAMA, NORTHEAST MISSISSIPPI, AND NORTHERN GEORGIA... High pressure over the East Coast will work in tandem with low pressure over the Southern Plains to generate a southwesterly 850mb moisture moisture fetch out of the western Gulf of Mexico beneath an expansive 120 kt southwesterly jet over much of the country. Meanwhile, there is also a lingering 850mb moisture feed emanating out of the tropical East Pacific set to be oriented at the Mid-South on Monday. By 18Z Monday and lasting through Monday night, NAEFS shows an expansive swath of PWs from Texas to the TN Valley that ranges generally between 90-97.5 climatological percentiles and PW values >1.5" in the Lower Mississippi River Valley. In addition, IVT values of 500-750 kg/m/s are oriented across North Texas and through the Mid-South, which are also in the 90-97.5 climatological percentile range. While there is no shortage of anomalous atmospheric moisture and moisture transport, the key in generating excessive rainfall rates is squarely on instability. Most operational guidance focuses the highest values of MUCAPE closer to western Tennessee and northern Mississippi Monday night with values ranging as high as 500-1,000 J/kg. Farther east, instability is tougher to come by, but PWs and upslope flow into the higher terrain of northern Alabama, northern Georgia, and eastern Tennessee allow for additional precipitation rate enhancement. Soils are generally closer to normal when it comes to soil saturation, despite the swath of 300-400% of normal rainfall across northern Alabama. There is still an impressive swath of anomalous moisture available, and the westerly 850-300mb mean flow is likely to run quasi-parallel to the warm front lifting north through the Mid-South Monday evening. This could support training segments of heavy showers and/or thunderstorms if sufficient instability is available. Have opted to maintain the current Slight and Marginal Risks over the Mid-South, making subtle adjustments based on latest QPF forecasts. Mullinax Day 3 The Day 3 outlook will be updated by 2030Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_xOBu_8yOlCrBaBnq_UBDllvRq_HNdHx5Jo4Ho9p9tAd= 4bYCEPkgphjcthA-Zmly3zlJduPCcqNLp5j7wHLqVK_AnLQ$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_xOBu_8yOlCrBaBnq_UBDllvRq_HNdHx5Jo4Ho9p9tAd= 4bYCEPkgphjcthA-Zmly3zlJduPCcqNLp5j7wHLqFZfmnsg$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_xOBu_8yOlCrBaBnq_UBDllvRq_HNdHx5Jo4Ho9p9tAd= 4bYCEPkgphjcthA-Zmly3zlJduPCcqNLp5j7wHLqP44OYJM$=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) .