Subj : HVYRAIN: Excessive Rainfa To : All From : Mike Powell Date : Fri Sep 12 2025 09:25:56 FOUS30 KWBC 120805 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 405 AM EDT Fri Sep 12 2025 Day 1 Valid 12Z Fri Sep 12 2025 - 12Z Sat Sep 13 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTH FLORIDA, SOUTHWESTERN COLORADO THROUGH CENTRAL NEW MEXICO, AND THE NORTHERN PLAINS... ....South Florida... Stationary front persists over far South Florida today with the positive moisture anomaly focused over the Miami metro with the eastern coast likely to get more slow moving heavy thunderstorms in the light mean layer flow. The Slight Risk is shrunk to be closer to the Miami-Palm Beach metro area with the Marginal Risk still extending up the east coast nearly to Jacksonville. ....New Mexico and Colorado... The positively tilted upper level trough from an upper low over northern NV will pivot to neutral tilt this afternoon. Therefore, expect a more south to north oriented axis of heavy rainfall, stretching from south-central New Mexico to across much of western Colorado. Moisture from the Pacific will also be drawn northward into eastern Arizona and western New Mexico with PW anomalies of +1.5 to 2 sigma, resulting in a rather large QPF footprint. Diurnal convection is the main focus at play today, though guidance continues to suggest repeating rains over southeast AZ and southern NM into the overnight. The Slight Risk is maintained over southwest CO and central NM. ....Northern Rockies onto the Northern Plains... The upper low center shifts north to MT by late tonight. Notable activity ahead of the low/trough looks to focus over the western Dakotas into eastern MT per 00Z CAM consensus where a Slight Risk has been raised. PW anomalies of 1 to 2 sigma remain over northern ID/western MT where the Marginal Risk is maintained. ....Upper Midwest... Ongoing activity over eastern ND and northern MN should shift southeast by 12Z and track to northern WI. Then diurnally driven convection looks to cross a similar path. Given the advance of moisture over the upper ridge axis extending over eastern IA, it was worth adding a Marginal Risk to northern MN/WI and the western U.P. of MI. Jackson Day 2 Valid 12Z Sat Sep 13 2025 - 12Z Sun Sep 14 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM WESTERN KANSAS TO FAR WESTERN TEXAS, THE MIAMI METRO, AND WESTERN NORTH DAKOTA... ....Central High Plains through Southern Rockies... The upper level trough over the Intermountain West becomes negatively tilted on Saturday with the monsoonal moisture axis over NM during the day shifting to the southern High Plains overnight. The position of this trough will enhance the low level jet on the High Plains Saturday night and draw deeper Gulf moisture north over the Panhandles and eastern New Mexico and through western Kansas. This will encourage diurnally developing lines of storms from New Mexico terrain to press eastward onto the High Plains. Given the +2 sigma PW anomalies and overall slow storm motion, the Slight Risk area was expanded a bit over western KS and down into far western Texas. ....South Florida... The front will push south from Florida during the day Saturday with anomalous moisture lingering in the morning over the Miami metro where A Slight Risk persists. The Slight Risk still looks generous given the decreasing moisture profile through the day, but is maintained for now. ....Northern Plains... The upper low center over central MT will allow the focus for heavy convection to shift north a bit from Friday with both morning and diurnal max activity looking to focus on western ND. Given good overlap in heavier precip among available CAMs and the EC-AIFS, a Slight Risk is raised over western ND. Pivoting of the low without much lateral movement is expected, prolonged heavy rainfall is possible with. Jackson Day 3 Valid 12Z Sun Sep 14 2025 - 12Z Mon Sep 15 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN THE DAKOTAS... ....Central and Northern Plains... Negatively-tilted trough axis lifting up the central Plains Sunday should provide a narrow focus to convective development over the western or central Dakotas. This activity will be heavy given PW anomalies of +3 sigma persist over this area. Further development is expected from central KS up through the Dakotas where a generous Marginal Risk remains in effect. Jackson $$ --- SBBSecho 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (618:250/1) .