905 FOUS30 KWBC 010840 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 440 AM EDT Tue Sep 1 2026 Day 1 Valid 12Z Tue Sep 01 2026 - 12Z Wed Sep 02 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE UPPER TEXAS COAST AND FAR SOUTHWEST LOUISIANA... ...Central Gulf Coast... NHC has forecast Tropical Storm Edouard to make landfall along the Upper Texas Coast early in the period with a general consensus of moving onshore very close to Galveston Bay before lifting slowly NW through the afternoon and evening hours. The system is expected to remain compact as it organizes and comes onshore, leading to a narrow corridor of heavy rainfall thanks to PWs of over 2.25" in the accompanying tropical moisture plume. While the heaviest rain may occur along the coast and just NE of the center/track, there is potential for some inflow convergence to maintain a corridor of heavy rain even behind the system as it lifts into east-central Texas. Additionally, the forecast movement (using latest NHC forecast positions) is progged to only be around the 20th percentile of Gulf Coast systems, suggesting the potential for locally excessive rainfall where training is most pronounced and prolonged. Both the HREF and REFS ensemble suites indicate a high chance (>70%) of at least 5" in a NW oriented stripe from Galveston Bay through near College Station, with 8"/24hr probabilities exceeding 40% near the coast. This will continue to be monitored as the storm evolves. ...Four Corners and Southwest... After several days of heavy rain and substantial impacts across the Four Corners and Southwest, activity is likely to wane considerable today. Sufficient forcing and moisture for another day of local impacts will be present, especially atop the vulnerable soils impacted the last few days, thus maintaining a Marginal Risk for much of the Four Corners. Although PWs do come down, the drier air which has been progged to push east has slowed down, leaving PW anomalies of +0.5 to +1 sigma in place on Tuesday. With significant forcing remaining in place as a trough approaches from the west (leading to height falls and jet level diffluence for synoptic ascent), this will result in another day of at least scattered thunderstorm development during peak heating, or within any enhanced lift beneath weak impulses embedded within the flow. Mean 0-6km winds will remain progressive at around 25 kts, but aligned propagation vectors and continued elevated bulk shear magnitudes above 40 kts will support organization into clusters and potentially repeating cells. Hourly rainfall of 0.5 to 0.75 inches may occur. ...Great Lakes to the Northeast... Mid-level impulses tracking atop the ridge and along a wavering frontal boundary will continue to produce rounds of scattered convection from the Great Lakes through New England and the northern Mid- Atlantic states. As is typical with this convective cluster setups, there is a lot of spread in both timing and placement of the heaviest rain signatures from the available CAMs. While the guidance is in good agreement that many areas will receive periods of heavy rainfall exceeding 1"/hr as storms track steadily WNW to ESE, the duration of any of this rain may be modest due to the progressive nature of cells. However, short duration training is likely at times thanks to aligned propagation vectors/mean winds to the front, which could enhance rainfall amounts locally. In general, rainfall should be 1-2" which will only be sufficient to create isolated impacts related to flash flooding, but if any significant training/repeating could occur, locally higher rainfall is possible. This is reflected by both HREF and REFS probabilities for 3" that peak above 25%, especially across far southern New England, Long Island, and northern PA/southern NY. However, due to uncertainty in timing and placement, combined with generally elevated FFG outside of the Catskills and Tri-State area, the Marginal Risk was maintained. ...Florida... Easterly flow will draw tropical moisture onshore helping to fuel scattered afternoon convection. PW values will be nearing 2.25 inches and the mean flow across the Peninsula will be very weak suggesting cells will drift west from the sea breeze, but may converge just inland from the Gulf as the gulf breeze also pushes inland. Some short term training will be possible (limited in duration by the pulse nature of the cells) but with rainfall rates expected to be 2-3"/hr, this could create isolated flash flood impacts, especially within urban areas. Campbell/Weiss Day 2 Valid 12Z Wed Sep 02 2026 - 12Z Thu Sep 03 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PARTS OF THE NORTHEAST AND EASTERN TEXAS... ...Northern Mid Atlantic & Southern New England... A Slight Risk remains in effect for much of central and eastern new York. A stronger shortwave tracking atop the region to interact with a slowly northeast advancing warm front will result in scattered to widespread convection across the region. While the exact location of the heaviest rainfall remains uncertain, there should be amble support of training of clusters of thunderstorms with 1-2"/hr rain rates. The guidance focuses this heaviest rainfall across portions of Upstate New York, and while soil moisture is generally below normal according to NASA SPoRT, this should support up to 3" of rain in some areas leading to scattered instances of flash flooding, with more isolated responses elsewhere. ...Eastern Texas and Southwest Louisiana... Tropical cyclone Edouard will be well inland and slowly its progression while spread bands of heavy rainfall to eastern Texas and into Louisiana. Additional heavy rainfall is likely even as the central low pressure begins to dissipate. PWs of 2-2.25" will support continued heavy rain, and as 850mb inflow only slowly weakens it will drive enhanced convergence to support 2-3"/hr rain rates. While most of the rain should be around the center of the system which will be lifting slowly northward towards north Texas, there is potential for a locally enhanced inflow band on its south side which could prolong and enhance the rain across areas that receive heavy rain. The small size of the storm should limit the footprint and potential impacts, but ECENS/GEFS probabilities still indicate that at least an additional 3" of rain may fall, with locally higher amounts, leading to instances of flash flooding. Some further refinements in the Slight Risk area are expected with future updates, both to capture the latest guidance track, but also better resolve where any additional rainfall will occur on top of heavy rain from Tuesday. ...Northern Plains and Midwest... Lingering MCS activity possible early in the period across the Upper Midwest. PWAT anomalies remain elevated at times mid- week, with values of 1.5-2" forecast, however the spread in the deterministic QPF is higher than average. A broad Marginal Risk spans from Minnesota/Iowa eastward to the Great Lakes. ...Florida... Another day where the tropical moisture plume remains entrenched across Florida, reflected by PW anomalies of +1.5 sigma stretching across most of the state. Both coasts could experience slow moving storms with 2+"/hr rain rates, as well as across the inland portions of the peninsula where storm mergers/collisions can occur. A Marginal Risk was maintained for this period. Campbell/Weiss Day 3 Valid 12Z Wed Sep 02 2026 - 12Z Thu Sep 03 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PARTS OF THE NORTHEAST AND EASTERN TEXAS... ...Northern Mid Atlantic & Southern New England... Small adjustments were made to the inherited SLGT risk to account for the latest guidance. While the setup Wednesday is at least synoptically similar to both Monday and Tuesday, a more impressive shortwave tracking atop the region to interact with a slowly northeast advancing warm front will result in scattered to widespread convection. There is still some uncertainty as to the placement of the heaviest rainfall, but an improving warm sector with favorable thermodynamics along a sharp gradient should support training of clusters of thunderstorms with 1-2"/hr rain rates. The guidance focuses this heaviest rainfall across portions of Upstate New York, and while soil moisture is generally below normal according to NASA SPoRT, this should support up to 3" of rain in some areas leading to scattered instances of flash flooding, with more isolated responses elsewhere. ...Eastern Texas and Southwest Louisiana... Tropical Depression 5 will be well inland by the start of the forecast period, but with slow movement expected to continue, additional heavy rainfall is likely even as it begins to dissipate. PWs of 2-2.25" will support continued heavy rain, and as 850mb inflow only slowly weakens it will drive enhanced convergence to support 2-3"/hr rain rates. While most of the rain should be around the center of the system which will be lifting slowly northward towards north Texas, there is potential for a locally enhanced inflow band on its south side which could prolong and enhance the rain across areas that receive heavy rain on Tuesday as well. The small size of the storm should limit the footprint and potential impacts, but ECENS/GEFS probabilities still indicate that at least an additional 3" of rain may fall, with locally higher amounts, leading to instances of flash flooding. Some further refinements in the SLGT risk area are expected with future updates, both to capture the latest guidance track, but also better resolve where any additional rainfall will occur on top of heavy rain from Tuesday. ...Northern Plains and Midwest... Lingering MCS activity possible early in the period across the Upper Midwest. PWAT anomalies remain elevated at times mid- week, with values of 1.5-2" forecast, however the spread in the deterministic QPF is higher than average. A broad Marginal Risk spans from Minnesota/Iowa eastward to the Great Lakes. ...Florida... Another day where the tropical moisture plume remains entrenched across Florida, reflected by PW anomalies of +1.5 sigma stretching across most of the state. The biggest change from prior days, at least as modeled in guidance, is weaker overall flow leading to slower storm motions, and a better chance for both coasts to experience slow moving storms with 2+"/hr rain rates, as well as across the inland portions of the peninsula where storm mergers/collisions can occur. After coordination, the inherited MRGL risk was expanded to cover the entire Peninsula south of Jacksonville, with the greatest risk for impacts occurring atop urban areas. Weiss/Campbell Day 4 and Day 5 Valid 12Z Fri Sep 04 2026 - 12Z Sun Sep 06 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FRIDAY ACROSS PORTIONS OF ARIZONA... ...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 both Friday and Saturday, especially Friday across central to southeast AZ where a Slight Risk area remains from yesterday's Day 5 ERO. GEFS and ECENS PWAT anomalies increase back to 2-2.5 standard deviations above normal both Fri and Sat, however the deterministic and probabilistic QPFs per the GEFS, EC, and CMC ensembles are more supportive of the Slight Risk on Day 4 (Fri-Fri night), with the axis of best monsoonal moisture influx shifting slightly west next weekend. 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 PWAT anomaly( by Friday and over the weekend. The GFS remains too far east with the track of this feature compared to the rest of the global guidance, and it continues to trend towards the ECMWF and CMC suites. ...Northern Great Basin/Northern Rockies... Marginal Risk area from yesterday's Day 5 ERO continues in the new Day 4 outlook 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. ...Upper Midwest/Ohio Valley/Central Appalachians... Despite the current spatial and temporal spread with the current (00Z 9/1) guidance suite, expect more organized/widespread convection on Friday downwind of the upper ridge axis. 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. Hurley 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 $$