357 FOUS30 KWBC 202024 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 424 PM EDT Mon Jul 20 2026 Day 1 Valid 16Z Mon Jul 20 2026 - 12Z Tue Jul 21 2026 ...THERE ARE SLIGHT RISKS OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHWEST AND NORTH CAROLINA... ...Southwest... 16Z Update...little change, more Marginal in western CO. Monsoonal moisture continues to stream across the Southwest into the Great Basin with renewed diurnal convective coverage again today. The eastern end of the threat area is bounded by a shortwave low over west Texas. Elevated moisture with PW of 2 to 2.5 standard deviations above normal and limited cloud cover from overnight allows good coverage of convection. Focus of heavies along the Mogollon Rim, southeast AZ and southern NM. West Texas is less certain for needing a Slight given ongoing clouds/precip this morning. ...Southern Mid-Atlantic to southern Appalachians... A warm front on leaving edge of deep tropical moisture plume extending northeastward from the tropical depression in the Gulf. The front will provide enough forcing across much of eastern North Carolina to allow for a renewed round of widespread showers and thunderstorms in the area. Soils remain generally dry over most of the area, despite storms impacting some of eastern North Carolina yesterday. Above normal moisture for the storms to work and the front providing some forcing warrants continuation of the Slight Risk. Trimmed southern NC from the Slight given consensus in the 12Z HREF/REFS. ...Gulf Coast... The outermost western periphery of Tropical Depression Two continues to impact the Gulf Coast of Florida, through the Panhandle into southern Georgia, and over to southeastern Louisiana. Banding is occurring, so localized multiple inch per hour rates. Regardless, the center remains far enough offshore, with drier air aloft working to significantly cut down on the overall coverage of storms. Considering the dry soils and high FFGs typical of the immediate Gulf Coast, even periods of heavy rain should only result in isolated instances of flash flooding. Thus, there was little change to the Marginal Risk area. ...Midwest... The Marginal Risk across much of the Midwest and upper Great Lakes also remains largely intact with updated progression for ongoing activity. There remains considerable uncertainty as to coverage of storms impacting the area today into tonight. It appears the most likely areas to be impacted this afternoon/tonight are from central Iowa east across northern Illinois. Dry soils highlight this area, so this being the height of the growing season should mitigate the flash flood risk. Jackson Day 2 Valid 12Z Tue Jul 21 2026 - 12Z Wed Jul 22 2026 ...THERE ARE SLIGHT RISKS OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHWEST AND THE MID-ATLANTIC TO THE OHIO VALLEY... ...Intermountain West... Monsoonal moisture continues to arrive over the Southwest from the sub-tropical Pacific around a mid-level high centered over Colorado. A shortwave trough will track from southwest NM into eastern AZ which will promote increased convective coverage over both AZ and UT into NV. The Slight Risk area was further expanded to include most of UT through central NV. The greatest convective coverage and most impactful flash flooding is still expected from southeast AZ up through the Mogollon Rim to the Grand Canyon which is considered a more "enhanced" Slight Risk. A fair amount of convective coverage tonight over AZ may cause some opaque stratus to persist into Tuesday which could at least locally disrupt the diurnal trend in activity. The PW anomaly reaches 4 standard deviations above normal over the Sierra Nevada on Tuesday. This should promote vigorous diurnal convection up the High Sierra to Lake Tahoe. A Slight Risk may be warranted, but for now an expanded Marginal Risk is drawn. ...Mid-South through the Ohio Valley and Mid-Atlantic into New England... A strong cold front pushing south across the Midwest will run into plentiful tropical moisture being drawn north from Tropical Depression 2 in the Gulf. The front will act as a catalyst for numerous segments of mostly fast moving thunderstorms across the Ohio Valley and Interior Northeast through the Mid-Atlantic on Tuesday, likely holding together for the into New England Tuesday evening. PW of 2 to 2.25" ahead of the front and sufficient instability will allow for heavy rainfall through this area, possibly as far west as the Mid-South (per the RRFS and the 12Z HRRR) and as far east as the New England coast up through Down East Maine. Mean layer Wly to SWly flow of 40-50kt will keep activity moving, but the threat for backbuilding and training storms as well as the book ends of any segments could cause widely scattered instances of flash flooding. The Slight Risk was expanded per 12Z (and 18Z HRRR) CAM consensus along with chats with WFO PHI/OKX through the northern Mid-Atlantic into Connecticut. ...Gulf Coast... Tropical Depression 2 is still forecast to gradually drift west with the center offshore until reaching southern Louisiana early Thursday. Northerly shear and dry air entrainment will continue to focus most associated precip south of the center with the banding seen today east and north of the track over FL diminishing tonight and having less coverage for Tuesday. This is in spite of this being a tropical cyclone with PWATs up to 2.5 inches. Therefore, the Marginal Risk for the Florida Panhandle through southeast Louisiana remains in place with few changes. Jackson/Wegman Day 3 Valid 12Z Wed Jul 22 2026 - 12Z Thu Jul 23 2026 ...THERE ARE SLIGHT RISKS OF EXCESSIVE RAINFALL FOR THE SOUTHERN MID-ATLANTIC TO THE SOUTHERN APPALACHIANS, MUCH OF THE CENTRAL ROCKIES, AND LOWER SOUTHEAST LOUISIANA... ...Mid-Atlantic to Tennessee Valley... The cold front that reaches much of the Mid-Atlantic on Tuesday will stall over the Delmarva through southern Virginia and the southern Appalachians on Wednesday. Abundant Gulf moisture will continue streaming northeastward from Tropical Depression 2 ahead of the front with PW spiking above 2.25". Westerly mean layer flow becomes parallel to this front on Wednesday which will promote training activity and repeating heavy thunderstorms. This places the focus farther north than the prior forecast with areas from the Delmarva through North Carolina at risk where the Slight Risk was redrawn. There remains a more "enhanced" Slight Risk over southeast VA (including Hampton Roads) down toward Raleigh. The Slight Risk was trimmed on the south end including over southern NC and most of SC. Since much of this area should get a break in heavy rain on Day 2, a Moderate Risk was not considered at this time. However, this stalled front will only slowly move south Wednesday to Friday which may open the door to a Moderate Risk at some point over the southern Mid-Atlantic/Carolinas. ...Central Gulf Coast... Tropical Depression 2 is forecast to be drifting west toward the mouth of the Mississippi on Wednesday. Northerly shear will remain a concern to development of precip on the north side, keeping most of the heaviest rains over the Gulf. The 12Z consensus for heavy rain is even farther south than the previous forecast, well south of New Orleans in an area that is not flash flood prone. Out of an abundance of caution (a wise approach with tropical systems) and in coordination with WFO LIX, the Slight Risk remains in effect for lower southeast Louisiana. Some banding east and north of the low center looks to track into the central Gulf Coast where the Marginal Risk was expanded a bit. ...Intermountain West onto the Central Plains... The shortwave trough tracking north from AZ on Wednesday should focus the heaviest rain ahead of it over UT/CO up through WY and eastern ID. The Slight Risk was expanded over these areas based on the 12Z QPF consensus and in coordination with WFO BOU. Much of the Rockies terrain is covered by a Slight Risk. High pressure centered over MN brings some return flow across Nebraska which warrants continuing the Marginal Risk there with an expansion into northeast KS per the 12Z consensus. The PW anomaly drops below 3 standard deviations for the Sierra Nevada, but enough moisture remains to warrant another Marginal Risk. Jackson Day 4 and Day 5 Valid 12Z Thu Jul 23 2026 - 12Z Sat Jul 25 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE CENTRAL PLAINS TO LOWER MISSOURI VALLEY, THE CENTRAL TO WESTERN GULF COAST, AND THE EASTERN CAROLINAS ON DAY 4... ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE LOWER MISSOURI AND MID MISSISSIPPI VALLEYS, AND THE EASTERN CAROLINAS ON DAY 5... 2030Z Update... Removed the Slight Risk area from the Texas portion of the Day 4 Excessive Rainfall Outlook based on the forecast soundings along and near the path of the system making its way along the Gulf coast in the shorter periods. Based on NHC guidance available on Monday afternoon...the system should have transitioned to an extra- tropical system by then which would facilitate the advection of unsaturated/drier air from the land. Elsewhere changes tended to be pretty modest and still largely fit the previous discussion. Bann Previous Discussion... ...Southeast... A moisture-laden front will continue to sink slowly south across the region. While the overnight guidance continues to present differences on the timing of the front and corresponding precipitation, there remains a strong signal for additional heavy amounts impacting parts of the region, especially for portions of the Carolinas. Precipitable Water values remaining around 2.25 inches along with periods of enhanced ascent will raise the threat for additional heavy amounts most likely centered over eastern North Carolina into northeast South Carolina Thursday into early Friday. Due in part to model differences and forecast uncertainty, maintained a Slight Risk. However, this has the potential to be a second day in-a-row, and the fourth day this week for heavy rains impacting parts of the region. Therefore, if forecast confidence increases and the signal for a multi-day heavy rainfall event holds, future upgrades may be required. For Friday into early Saturday, it remains a question whether the front will continue to push south, bringing drier conditions into the Carolinas as the GFS/UKMET indicate, or continue to hang up well to the north as shown by the ECMWF and Canadian. Opted for a Slight Risk on for the Day 5, centered similar to the Day 4 area, which presents a compromise between the two camps and lined up with the higher probabilities from the most recent ECENS. ...Gulf Coast... Shear across Tropical Depression Two is expected to keep the heaviest rainfall amounts associated with the system mostly south of the center and offshore. However, cannot rule out the threat for onshore flow supporting some locally heavy amounts along the coast, especially if the trends support a stronger system and more northerly track. Therefore, the a Slight Risk was maintained along the Louisiana to the upper Texas Coast on Day 4. A Marginal Risk was drawn for Day 5 from the upper Texas Coast inland toward south-central Texas, where heavy amounts are possible if the storm remains organized and continues to track west. ...Central Plains to the Mid Mississippi Valley... Models continue to show a well-defined shortwave sliding southeast off of the top of the western U.S. ridge through the northern Plains and into the mid Mississippi Valley on Day 4. Organized heavy rain may develop late Thursday into early Friday as this energy interacts with a deepening moisture pool fed by a strengthening southwesterly jet. A Slight Risk was maintained on Day 4 over parts of southeastern Nebraska into adjacent parts of Kansas, Iowa, and Missouri, where models indicate the deepest moisture, better forcing and greater potential for localized training will center. Storms continuing through Friday morning and possibly redeveloping later in the day downstream will extend the threat across across a greater part of the mid Mississippi Valley on Day 5. ...Southwest/Great Basin/Central and Southern Rockies... Monsoon moisture will continue to fuel diurnal activity, however the footprint is expected to diminish especially by Day 5 as moisture anomalies drop off and heights build across the Southwest. Pereira 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 $$