741 FOUS30 KWBC 030021 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 821 PM EDT Wed Sep 2 2026 Day 1 Valid 01Z Thu Sep 03 2026 - 12Z Thu Sep 03 2026 ...THERE IS A HIGH RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHEAST TEXAS... ...East Texas... A High risk remains for a small area of southeast TX, primarily across the Big Thicket into the Piney Woods region, where ongoing heavy rain south of Edouard remnants is over areas most impacted this morning. The center of Edouard is slowly shifting north, but inflow is still converging over similar areas as earlier today as the center received less convergent focus. This southern area should run its course/diminish overnight with potential new development farther north per recent CAMs. However, inflow from the Gulf will allow some additional convection over the areas hardest hit today into Thursday. Minimal changes to the existing outlook areas including the High Risk which were well placed. Please see latest MPD (soon to be 1178) in east Texas for further information. ...Eastern Great Lakes into Mid-Atlantic & New England... Low over central Quebec will continue to deepen and drift east tonight. Warm sector convective line progressing through western NY may have some followup activity overnight with some activity ahead warranting a larger Slight Risk over western NY and central PA. Trimmed the Marginal Risk a bit over New England based on the 18Z HREF while expanded over the Shenandoah Valley and southern MI for ongoing activity. Please see MPD 1177 for further details on NY/PA. ...Florida... Ongoing activity has consolidated south of Tampa Bay and should continue a downward trend this evening. The Marginal Risk was shrunk. ...Arizona... Earlier monsoonal activity over southern has waned with a fair amount of convective inhibition present. Removed the Marginal Risk. Jackson Day 2 Valid 12Z Thu Sep 03 2026 - 12Z Fri Sep 04 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF EASTERN TEXAS... 20z Update: Upgraded to a Slight and Moderate risk for portions of east TX. An axis of training convection should be ongoing at 12z Thursday to the south and Southeast of the remnant circulation of Edouard. Given the system will be weaker by this time, we are not expecting the flash flood threat to be as extreme as what occurred Tuesday night into early Wednesday. However, the low level vort center should be defined enough to focus another round of nocturnal training/backbuilding convection by later Wednesday night into Thursday morning. This activity should persist past 12z and into this day 2 period...but should weaken towards 15z. The MDT 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. Chenard ...Previous Discussion... ...Southwest... A Slight Risk remains in effect across southern Arizona and into New Mexico for this period. An uptick in moisture should result in increased convective coverage and a scattered flash flood risk. This region will continue to be monitored over the coming days. ...Texas, Gulf Coast and Florida... The remnant vort center of Edouard should be less defined by this time, but still present over east Texas with lingering tropical rain over sensitive soils. It could still help focus some organized convective clusters, and thus an isolated flash flood risk could linger into Thursday. 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. ...Upper Midwest to Mid-Atlantic... While the details on where the heaviest rain will occur there continues to be a signal for one or more rounds of organized convection to track trough portions of this area through the day into Thursday night. Parts of this region have had recent rains to lower FFG and increase sensitivity to additional heavy rainfall. A Marginal Risk was maintained from Minnesota/Iowa to Del-Mar-VA and New Jersey. ...California into the Intermountain West... A Marginal Risk continues from northern California into Idaho. During this period a strong synoptic system will bring an axis of heavy rainfall 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. Campbell/Chenard Day 3 Valid 12Z Fri Sep 04 2026 - 12Z Sat Sep 05 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FRIDAY ACROSS PORTIONS OF ARIZONA AND NEW MEXICO... 20z Update: The Slight risk over the Southwest was realigned based on model trends. The better moisture/instability axis is forecast farther east than previously forecast, with the Slight risk shifting in that direction as well. Still seeing a decent convective signal in the guidance, including the 12z RRFS, over this Slight risk area, and thus isolated to scattered flash flooding is expected. A Marginal risk was added from southeast TX, along the Gulf Coast and into FL. Lingering moisture and instability along this corridor could result in a continued localized flash flood risk. Chenard ...Previous Discussion... ...Northwest/Northern Rockies... Marginal Risk area is in effect across portions of the interior Northwest, particularly the area surrounding the northern Idaho Panhandle. This area will be much closer to the upper level trough, so forcing should be much better than in the Southwest. However, moisture and instability will be much lower, resulting in more likelihood of stratiform rainfall. Despite this, the rainfall should still have modest amounts of instability to work with in a generally dry, and therefore flash flood prone, area of the country. ...Southwest/Four Corners/Central-Southern Rockies... The signal for the return of heavy rain areas across the Southwest into the Four Corners and central-southern Rockies remains strong GEFS and ECENS PWAT anomalies increase back to 2-2.5 standard deviations above normal with the axis of best monsoonal moisture influx shifting slightly west. 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. ...Upper Midwest/Ohio Valley/Central Appalachians... Expect more additional organized/widespread convection downwind of the upper ridge axis. 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 West Virginia. Campbell/Hurley Day 4 and Day 5 Valid 12Z Sat Sep 05 2026 - 12Z Mon Sep 07 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL SATURDAY AND SUNDAY ACROSS PARTS OF THE SOUTHWEST... A deep upper low persists over the Pacific Northwest through Saturday before shifting south to far northern California for Sunday. The trough around this low and a strong upper high centered over the southern Plains U.S. will direct southwesterly flow into the Desert Southwest and mover much of the Intermountain West on Sunday. Confidence has increased on a more southward suppressed moisture and instability axis that extends farther east from southern California through central New Mexico. The Day 4 Marginal Risk is trimmed from Utah and expanded east through the Sangre de Cristo/Sacramento Mtns. That said, a connection to a tropical moisture plume from Marie is present, so this area will continue to be closely monitored. The farther south closed low into far northern CA on Sunday should direct tropically sourced moisture up through the Intermountain West to the central Rockies. The Day 5 Marginal Risk is expanded farther east through western Colorado and New Mexico. Moisture may end up lifting farther north and some 12Z guidance has decent QPF in Montana, so please monitor future updates. Jackson 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 $$