Subj : HVYRAIN: Excessive Rainfa To : All From : Mike Powell Date : Sun Jan 05 2025 10:04:00 FOUS30 KWBC 050815 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 315 AM EST Sun Jan 5 2025 Day 1 Valid 12Z Sun Jan 05 2025 - 12Z Mon Jan 06 2025 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHEAST AND CENTRAL GULF COAST... An impressive deep layer cyclone is taking shape over the central US early this morning, originating from a potent shortwave trough digging through the Central Rockies over the past couple of days. The trough is in the process of cutting off into an upper-low as it emerges from the Rockies into the central Plains. Strong DPVA in association with the trough will interact with the right- entrance region of a broad phased jet structure (~140 kt jet streak @ 250 mb over the Mid-Atlantic, and a smaller ~100 kt jet streak near the Ozarks). A substantial low-level jet (850 mb of 40-60 kts) is expected to form as a result of deep cyclogenesis, stretching from the Central Gulf Coast to the Mid-South, ushering in highly anomalous tropospheric moisture (for this time of year) with precipitable water values nearing 1.5" (between the 90th percentile and max moving average, per JAN/BNA/BMX sounding climatology). Most hi-res CAMs continue to suggest localized 1-2" totals in association with combined totals from scattered convection in the open warm sector and the following primary squall line in association with the approaching cold front, though a couple of solutions (FV3 and CMCreg) suggest localized streaks of 2-3" totals (from northeast LA through north/central MS into northwest AL). While much of these totals may occur over a relatively short period (with any flash flooding conditions more likely due to storm mode and sub-hourly rates and totals of 1-2"), 00z HREF 40-km neighborhood probabilities for 2" exceedance over 3 hours barely peak at 20-30%. Therefore the progressiveness of this system (and the limited window of time in the afternoon to take advantage of destabilization, with SB CAPE from east TX and southern LA to the Mid-South reaching 500-2000 J/kg) should largely preclude any organized flash flood threat. Have maintained the inherited Marginal risk area once again, generally encompassing the expected warm sector of the system (while excluding areas farther north where more impressive broad QPF exists, as this precipitation will mostly occur in the form of ice and snow). Churchill Day 2 Valid 12Z Mon Jan 06 2025 - 12Z Tue Jan 07 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Churchill Day 3 Valid 12Z Tue Jan 07 2025 - 12Z Wed Jan 08 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Churchill $$ --- SBBSecho 3.20-Linux * Origin: ILink: CCO - capitolcityonline.net (454:3/105) .