FOUS30 KWBC 031606 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1206 PM EDT Thu Sep 3 2026 Day 1 Valid 16Z Thu Sep 03 2026 - 12Z Fri Sep 04 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF EASTERN TEXAS... ...Texas, Gulf Coast and Florida... 16z Update: No changes were made to the ERO outlook over Texas and the Gulf Coast region. Over Texas, the Moderate Risk ERO will be extended into the afternoon with heavy rainfall ongoing and active flash flood warnings. A slow moving cluster of storms is producing hourly rainfall rates of 1-3 inches a hour with radar estimated accumulations of 3-6 inches in the past 3 hours. The complex of storms will continue through the afternoon with an additional 3-5 inches possible today as highlighted in HREF guidance. Some locally higher rainfall totals are possible. Farther south across eastern Texas in the Slight Risk, flash flooding was ongoing across a line of storms streaming in from the Gulf. This area is still sensitive from the previous rounds of heavy rainfall and may continue to see a flash flood risk this afternoon. High PWATS and an enhanced coverage of storms courtesy of a mid- level low could bring isolated areas of flash flooding or water ponding along the Florida Peninsula and Gulf Coast region. Wilder ..Previous Discussion: An axis of training convection and backbuilding located to the south and Southeast of the remnant circulation of Edouard will be persist from the overnight hours and should weaken towards 15z. The Moderate risk may be able to be removed with the 16z update tomorrow, but the expectation is for a locally significant flash flood risk to be ongoing to start the period Thursday morning. Some models indicate another possible uptick Thursday night into Friday morning, but this is lower confidence given more uncertainty regarding the state of the remnant vort center by this time. Elsewhere onshore flow within the pooled high PW values and stalled boundary could trigger convection along the coastline and across the Florida Peninsula leading to isolated areas of flash flooding/ponding. A Marginal Risk spans from eastern Texas to Florida. ...Southwest... 16z Update: A pool of PWATS around 1-1.5 inches is present over southern Arizona and southwest New Mexico with CAPE values on the order of 1000 J/Kg. This will help fuel locally heavy thunderstorms with high probabilities of exceeding an inch per hour rainfall rates. This could lead to flash flooding in sensitive terrain, such as burn scars and dry washes. A Slight Risk ERO remains across southern Arizona and southwest New Mexico this afternoon. Wilder ..Previous Discussion: Moisture will be increasing over the region during this period to help fuel diurnal convection across Arizona and New mexico, leading to a scattered flash flood risk. This region will continue to be monitored over the coming days. A Slight Risk is in effect for southeast Arizona and extreme southwest New Mexico while a Marginal covers portions of eastern Arizona and nearly the western half of New Mexico. ...Upper Midwest to Mid-Atlantic... 16z Update: A Slight Risk was added for portions of northeast Ohio and northwestern-central Pennsylvania. Rounds of storms have saturated the soils and lowered flash flood guidance to an inch to half an inch in some places. Additional energy rounding the Great Lakes will bring rounds of storms this afternoon and evening that could result in 1-3 inches of additional rainfall. Scattered flash flooding is possible as a result. A broader Marginal Risk extends from the upper Midwest to portions of the Northeast as storms ride along an instability and moisture axis associated with a draped stationary front. Some heavier precipitation is possible across Wisconsin today, but the drier antecedent conditions and progressive storm motion should mitigate the flood risk. Wilder ..Previous Discussion:One or more rounds of organized convection is forecast to track trough the region today and into the overnight hours. Antecedent rains have left portions of the area sensitive to flooding. The axis of heaviest with the heaviest precipitation will likely focus over Wisconsin. A Marginal Risk is in effect from North Dakota to southern New England/northern Mid- Atlantic. ...California into the Intermountain West... 16Z Update: The forecast remains on track and no changes were made. A plume of moisture streaming ahead of an upper-level trough in the West may bring 1-2 inches of rainfall across portions of the Great Basin and the interior Northwest. Flash flooding is most likely in sensitive terrain, primarily burn scars. Wilder ..Previous Discussion:strong synoptic system will bring an axis of heavy rainfall to to the region. Not much instability, but just enough showing up in model forecasts to suggest some potential for localized higher rates and an isolated flash flood potential. A Marginal Risk is in effect for northern California, eastern Oregon, eastern Washington, Idaho and far western Montana. Campbell/Chenard Day 2 Valid 12Z Fri Sep 04 2026 - 12Z Sat Sep 05 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF ARIZONA AND NEW MEXICO... ...Southwest... PW anomalies raise back to 2-2.5 standard deviations above normal during this period. Still remains to be seen how much influence the eventual tropical system that ultimately pulls west of Baja will have in terms of the upper level moisture (potential uptick in the PW anomaly). A Slight Risk was maintained for Arizona while a broad Marginal covers southeast California the Four Corner as this is where the signal for better moisture/instability axis aligns. Isolated to scattered flash flooding is expected. ...Gulf states... Lingering moisture and instability along this corridor could result in a continued localized flash flood risk. A Marginal Risk was maintained from eastern Texas to southern Georgia and Florida. ...Upper Midwest/Ohio Valley/Central Appalachians... Additional organized/widespread convection to develop downwind of the upper ridge axis today. Precipitable water values are high enough with sufficient instability that embedded cells could produce local downpours and isolated flooding. This will likely start over eastern portions of the Upper Midwest, where the upper jet streak to the northeast is expected to strengthen as the pivoting northern stream trough impinges on the broad-scale ridge to the south. Have essentially traced the Marginal Risk area southeast along the mean 850-300 mb thickness fields, where the upper level forcing along/ahead of the surface front will be most supportive of more organized activity. A Marginal Risk is in effect from Wisconsin to Virginia and eastern North Carolina. Campbell/Chenard Day 3 Valid 12Z Sat Sep 05 2026 - 12Z Sun Sep 06 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF THE SOUTHWEST... Moisture southwesterly flow will be directed into the Southwest between a deep upper low/trough over the Pacific Northwest and a strong upper high centered over the Southern Plains. A suppressed moisture and instability axis will likely be positioned from southern California through central New Mexico. There is connection to a tropical moisture plume from Marie so this area will continue to be closely monitored. For now, a Marginal Risk covers the level of threat for excessive rainfall and spans from southern California across southern Nevada, Arizona and New Mexico. Campbell/Jackson Day 4 and Day 5 Valid 12Z Sun Sep 06 2026 - 12Z Tue Sep 08 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM SOUTHERN CALIFORNIA, ACROSS THE SOUTHWEST, GREAT BASIN, INTO THE NORTHERN ROCKIES AND EASTWARD INTO THE NORTHERN PLAINS/UPPER MISSISSIPPI VALLEY AND ACROSS PORTIONS OF THE SOUTHEAST... ...Southern California/Southwest, Great Basin into the Northern Rockies... The anomalously strong western mid to upper level trof will continue to be very slow moving during the upcoming day 4 and 5 period. There is consensus that this trof will be able to transport anomalous PW values in the vicinity of Marie northeastward from Southern CA/Southwest, into portions of the Great Basin, and Northern Rockies. Widespread scattered convection, locally heavy rains and localized flash flooding possible across this area. A more widespread qpf and excessive rainfall footprint expected day 4, with a decrease in threat area day 5, confined to eastern AZ/western to central NM into southwest CO. A slight risk area is possible in future updates when confidence in details of potential heavy rain axes increases. ...Northern Plains into the Upper Mississippi Valley... Shortwave energy moving northeastward in the broadly diffluent upper flow pattern across the Northern Plains/Upper MS Valley region will also support potential for organized convection along and to the northeast of the northwest to southeast oriented frontal zone across the Northern Plains. Anomalous PW values, 2-3+ standard deviations above the mean, expected across this region, supporting potential for heavy rains and isolated runoff issues both day 4 and day 5. ...Southeast/North Florida... Widespread scattered convection likely both day 4 and 5 in the vicinity of the slowly southward moving frontal boundary across the Southeast/North Florida. Low confidence in qpf details in the vicinity of this front, but with PW values 1.75-2.00", locally heavy rains and isolated runoff issues possible. Oravec Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt $$