Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Dec 18 2024 00:12:29 FOUS30 KWBC 180012 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 712 PM EST Tue Dec 17 2024 Day 1 Valid 01Z Wed Dec 18 2024 - 12Z Wed Dec 18 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ALONG PORTIONS OF THE EAST CENTRAL TO SOUTHEAST COAST OF FLORIDA... ...01Z Update.. The current synoptic pattern will yield similar convective output across the eastern FL Peninsula with low-level convergence against the coast due to prevailing easterlies within a corridor of above normal PWATs and modest low instability present. Radar and satellite composite indicate a focal point of frictional convergence along the coast near Vero Beach with a cell cluster anchored right against the coastline. Recent observations signal a local max of just over 2" within the last few hours with moderate to bordering heavy rain likely to continue until the cell finally dissipates. Recent trends within hi-res deterministic indicate isolated pockets of these types of events occurring from Coco Beach down through Fort Lauderdale into the early morning hours thanks to the unwavering easterly wind field helping to enact primed coastal=20 convergence when boundaries advecting off the nearby waters are=20 present.=20 Latest HREF neighborhood probability fields signal modest 30-50% chance of >5" across portions of FL with the max probs=20 located between Port St. Lucie down to Fort Lauderdale. Even with=20 that alignment, it's very plausible that just a slight north/south=20 displacement of the highest probs would indicate locally=20 appreciable rainfall worthy of flooding in any of the coastal urban areas of eastern FL. Considering the current radar depiction and=20 collaboration with the local offices, decided to maintain general continuity with a small extension northward given the radar trends near Viera/Coco Beach.=20 Kleebauer Day 2 Valid 12Z Wed Dec 18 2024 - 12Z Thu Dec 19 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ALONG PARTS OF THE MID-SOUTH AND LOWER OHIO VALLEY ALONG WITH THE SOUTHEAST FLORIDA COAST... ....TN into southern KY... Have included a targeted Marginal Risk in the updated Day 2 ERO across parts of western-central TN (especially northern portions) into southern KY, which would include the Nashville metro area. Amplifying upper trough to the west will allow for a more curved upper level jet streak on the lee side of the trough -- which will enhance the upper divergence and low-level moisture transport/flux into the outlook area. The latest (12Z) HREF show more elevated probabilities of 1"/hr rainfall rates between 12-18Z. In addition, especially when considering recent heavy rainfall over the past 24+ hours (1-2 inches over parts of nw TN and sw KY), the latest 1 and 3 FFG values have come down while 0-40km soil moisture percentiles per NASA SPoRT have climbed to 60-80% for most areas. As such, the HREF neighborhood probabilities of 3 hourly QPF exceeding 3 hour FFG peaks between 25-40% between 12-15Z Wed, when in that short 3-hour window most areas should see additional rainfall of 1-1.5" while some (isolated) locations receive closer to 2+ inches. ....Southeast FL... Basically carrying over the Marginal Risk area from Day 1 into the Day 2 period, as much of the 12Z high-res CAMs show lingering convective clusters along the se FL coast (mainly south of Vero Beach). Continued favorable (onshore) low-level moisture flux/convergence and sufficient deep-layer instability on Wed will maintain elevated short-term rainfall rates, likely 1-2+ in/hr at times during the day 2 period per the HREF probabilities. The 12Z HREF meanwhile also indicates 50-70% 40km neighborhood probabilities of at least 5 inches of additional rain during Day 2 (12Z Wed-12Z Thu), with 30-50% probs of 8+ inches. The NAM-CONUS Nest, ARW1, and 12Z HRRR in particular are leading to these high HREF probabilities. Hurley Day 3 Valid 12Z Thu Dec 19 2024 - 12Z Fri Dec 20 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Hurley Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_NgqMpb88PXqjkJx9n9dNWlUDnQVs0ew7DBQVtyMs5iF= 1ZE6xYclFrbYeLc06se9k3VEm8cdOCpAW7vZ5xsnoF18qkQ$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_NgqMpb88PXqjkJx9n9dNWlUDnQVs0ew7DBQVtyMs5iF= 1ZE6xYclFrbYeLc06se9k3VEm8cdOCpAW7vZ5xsnXKMlbx8$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_NgqMpb88PXqjkJx9n9dNWlUDnQVs0ew7DBQVtyMs5iF= 1ZE6xYclFrbYeLc06se9k3VEm8cdOCpAW7vZ5xsn5tU4hBI$=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) .