Subj : HVYRAIN: Excessive Rainfa To : All From : Mike Powell Date : Tue Oct 17 2023 09:15:00 FOUS30 KWBC 170708 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 308 AM EDT Tue Oct 17 2023 Day 1 Valid 12Z Tue Oct 17 2023 - 12Z Wed Oct 18 2023 A vigorous shortwave trough will exit southwestern Canada into the northern plains later this afternoon/evening continuing through the end of the D1 period. Locally heavy rainfall is possible within the northern periphery of an eventual closed upper-level reflection across North Dakota leading to totals possibly exceeding 1" in a 3-6 hr span over northern and eastern ND. Lack of sufficient buoyancy will negate the potential for heavier rainfall that would induce a flash flood concern, even for the flood plain along the ND/MN border. ARI exceedance probabilities continue to be near or at 0% within the area of expected rainfall, thus will maintain the void in any excessive rainfall risk areas. The probability of rainfall exceeding flash flood guidance is less than 5 percent. Kleebauer Day 2 Valid 12Z Wed Oct 18 2023 - 12Z Thu Oct 19 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Kleebauer Day 3 Valid 12Z Thu Oct 19 2023 - 12Z Fri Oct 20 2023 Despite a marginally better convective scheme for Thursday evening across the Tennessee Valley and portions of the Southeast U.S, the probability of exceeding guidance within the 1,3, or 6 hr time frames for flash flood exceedance intervals is very low with even the 75th percentile of PQPF for the NBM blend still falling well-short of the expected FFG guidance within the above area. Modest theta-E advection regime and deep layer ascent from a digging shortwave on the backside of the mean trough is still falling short of what would be necessary to "improve" any flash flood threat, but it will be a period to monitor for trends once we get into the range of CAMs and hi-res ensemble probabilistic forecasts. The probability of rainfall exceeding flash flood guidance is less than 5 percent. Kleebauer $$ --- SBBSecho 3.14-Linux * Origin: Ilink: CCO - capitolcityonline.net (454:1/105) .