FOUS30 KWBC 220033 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 833 PM EDT Tue Jul 21 2026 Day 1 Valid 01Z Wed Jul 22 2026 - 12Z Wed Jul 22 2026 ...THERE ARE SLIGHT RISKS OF EXCESSIVE RAINFALL FOR MUCH OF THE SOUTHWEST AND GREAT BASIN AS WELL AS MUCH OF THE OHIO AND TENNESSEE VALLEYS THROUGH THE MID-ATLANTIC AND INTO NEW ENGLAND... ...Ohio and Tennessee Valleys, Mid-Atlantic, into the Northeast... Strong cold front under a potent upper trough continues to push across the Ohio River with prefrontal activity training at times early this evening over West Virginia and Kentucky. This activity shifts over the Mid-Atlantic and Tennessee rest of this evening and lingers over the Delmarva and probably eastern Virginia overnight. Ample moisture that streamed up from Bertha is present over the region with PW over 2", peaking at 2.5" over north-central TN as of 00Z. Most activity has been progressive, but orientation to direction of motion has been problematic. Scattered flash flooding continues for the Mid-Atlantic, southern Appalachians, and Tennessee overnight where a Slight Risk remains. This is considered to be a higher end (or "enhanced") over the central Mid-Atlantic and over middle/eastern Tennessee. There is some activity back with the surface front back over central Ohio, so the Slight Risk is maintained behind the prefrontal activity. Poleward motion ahead of the front/upper trough maintains some activity over the northern Mid-Atlantic and southern New England where a general Slight Risk remains in effect. Recent HRRR and RRFS runs seem to be on track with the activity across this region. MPDs will continue to be issued, so please consult them for further information overnight. ...Southwest and Great Basin... Monsoonal activity continues this evening, most vigorously over the Mogollon Rim in Arizona and over southeast Utah which is downstream of a persistent mid-level low over the central AZ/NM border. Earlier activity along the Sierra Nevada has shifted east onto the Great Basin with more isolated flash flood threats there through northern Utah into the northern/central Rockies overnight. Recent HRRR/RRFS runs have a decent handle on activity with MPDs continuing to be issued for the notable threats. ...Gulf Coast/Tropical Storm Bertha... Thin bands of rain continue overnight for the Florida Panhandle up into southern MS/AL and for southern Louisiana. Ample moisture is present with PW of 2.2" to 2.4" along the central Gulf Coast, so isolated flash flood threats persist overnight with the Marginal Risk still in affect. Jackson Day 2 Valid 12Z Wed Jul 22 2026 - 12Z Thu Jul 23 2026 ...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL OVER PORTIONS THE TIDEWATER OF VIRGINIA AND NORTH CAROLINA... ...Carolinas, Southern Virginia, and Northern Georgia... 21Z update... Given the steady influx of tropical moisture from T.S. Bertha northeastward into the sinking strong cold front, widespread convection with embedded heavy rainfall will focus over North Carolina and Virginia Tidewater region. There is a signal for 2 to 4 inches for this part of the country and rainfall rates could easily exceed 1.5/2 inches per hour. Training/repeating of storms expected along the frontal boundary therefore a Moderate Risk was raised for this period. Campbell A strong cold front running into highly anomalous moisture being siphoned from the circulation of Tropical Storm Bertha will exacerbate the gradient of moisture along the frontal interface through the day across the Carolinas and into southeastern Virginia. This will work to keep any forward progress of the front minimal. Storms will train along the front, especially across northeastern North Carolina and into southeastern Virginia. This area remains in a higher-end Slight Risk and with the stalled out front remaining to guide the frequent development of additional storms, a Moderate Risk upgrade in areas where the storms focused in the Day 1 period remains a distinct possibility. Guidance has been laser focused in this area and so forecast changes have been minimal. Further south and west, however, guidance has become increasingly optimistic on storms developing further west into the southern Appalachians. As such, the Slight Risk was expanded west to include this region from north of Atlanta through the western Carolinas. ...Intermountain West... 21z update... Minor expansions of the Marginal Risk were made across north-central Arizona and eastern Kansas to reflect the new WPC QPF placement. The latest CAMs indicated a modest uptick in convection for north-central and southeast Wyoming and northeast of Boulder Colorado, which was just outside the inherited Slight Risk area. Therefore eastward adjustments were made to the Slight Risk area. Campbell Highly anomalous amounts of atmospheric moisture associated with the monsoon over the Intermountain West will be activated by rapid height falls as an upper level and highly negatively tilted trough pushes east from off the coast of Washington and Oregon. Meanwhile, separate upper level energy undercutting the ridge will also provide additional forcing further east across eastern Idaho and Wyoming. Once again, numerous thunderstorms will form in the anomalous moisture and for many areas, will be tied to the local topography. Few changes were needed with this update. The greatest amounts of rain look to concentrate in western Wyoming, where any storms south of Yellowstone could necessitate a higher-end Slight for some of those areas, as well as for the Uintas of northern Utah. With nearly all of the forcing further north, the Marginal Risk into southern Arizona and southern New Mexico was trimmed significantly with this update, as ridging quickly overtakes this area and limits convective potential south/west of the Mogollon Rim as a result. ...Tropical Storm Bertha/Gulf Coast... Strengthening shear across the circulation will continue to keep any organized convection and meaningful rainfall out over the open waters of the Gulf. The immediate coastline could still see amounts greater than an inch, but the rainfall footprint continues to shift off the coast. In coordination with LIX/Slidell, LA forecast office, the inherited Slight Risk for this region was downgraded with this update, with the overall area of the surrounding Marginal remaining little changed. What little rainfall does impact land areas remains with the potential to be locally heavy, so unfortunately no changes to the Marginal Risks can be made so long as Bertha remains a tropical entity. Wegman Day 3 Valid 12Z Thu Jul 23 2026 - 12Z Fri Jul 24 2026 ...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL OVER PORTIONS NORTH CAROLINA... ...Southeast... 21Z update... The heavy rainfall mentioned for the Day 2 period will persist across North Carolina and surrounding locations as the tropical moisture continues to interact with the stalled frontal boundary. Training/repeating of storms will focus an additional 2 to 4+ inches over North Carolina and portions of southern/southeast Virgina bringing the 48-hr forecast of 4 to 9+ inches for the region. There will likely be a fair amount of overlap in the QPF footprint from the D2 period, which will already be well saturated prior to this period. A Moderate was also raised central and east/northeast North Carolina as scattered to widespread instances of flash flooding is expected. Campbell The stalled out front that has remained across the Southeast will continue to plague the area with very heavy rainfall, as the continuous stream of Gulf moisture from the Gulf funnels northeastward along the front. Yet another day of heavy rain is expected to impact the Carolinas as a result. The front may drift ever so slightly further south and east which should clear all but the Hampton Roads area of far southeast Virginia from the heavy rainfall threat by Thursday, but for much of eastern North Carolina, much of South Carolina, and portions of northern Georgia, generally from Atlanta east, the heavy rainfall threat will continue through Thursday. Once again, potential for very heavy rainfall totals in many areas as are expected to see heavy rain from Wednesday could mean further upgrades to the risks may be needed, especially across eastern North Carolina. Ultimately, where the heaviest rain falls both today and Wednesday should dictate if further upgrades will be needed. ...Central Plains... An MCS is expected to impact a portion of northeast Kansas, southeast Nebraska and the Kansas City and St. Joseph metros on Thursday. The heavy rainfall footprint has drifted south and west, so the Slight Risk has been adjusted accordingly. As with many MCS's the location of the heaviest rain is likely to continue shifting with future updates, most likely towards the south, so stay tuned for further updates. Periods of heavy rain may continue to impact Wyoming into Colorado as well, where upgrades to a Slight are also probable, depending on where the heavy rains from Wednesday overlap with Thursday's forecast. ...Bertha... 21Z update... Rainfall trends across far southeast Texas have trended down with the latest guidance thus the threat for isolated flash flooding has reduced as well. The Marginal Risk was trimmed out of Texas for this period. Campbell Bertha, who may no longer be a tropical cyclone by Thursday, and likely to be in a weakening state, should continue to keep any associated rainfall off the coast. The immediate coast remains with the best chance for seeing anything over an inch of associated rainfall. FFGs are significantly higher than that in all areas. Given this, and with very good consistency in this scenario in the guidance, the inherited Slight and Marginal for a portion of the Texas and Louisiana Gulf coasts was removed with this update. The Marginal Risk has been downgraded to under a 5% risk for the upper Texas Gulf Coast, as well as the Slight for coastal Louisiana downgraded to a Marginal with this update. Wegman Day 4 and Day 5 Valid 12Z Fri Jul 24 2026 - 12Z Sun Jul 26 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MISSOURI ON DAY 4 AND FOR PARTS OF THE CAROLINAS DAYS 4 AND 5... ...Southeast... The multi-day rainfall event continues into the weekend, with additional heavy rains likely, especially for the Carolinas. The focus for these rains will be a slow-moving, moisture-laden front that is forecast to linger across the region through at least the first half of the weekend. Southwesterly flow ahead of a shortwave trough moving through the Ohio/Tennessee valleys will further fortify the already moisture- rich airmass, with models showing PWs increasing in excess of 2.25 inches (+2 to 3 sigma). This moisture, along with pockets of enhanced ascent afforded by mid- level energy, will support periods of heavy, highly-efficient rainfall. While areas of heavy rainfall are likely, forecast confidence regarding their placement remains limited due to continuing model spread with regards to the placement of the front, which will have impacts on where the heaviest amounts occur. Slight Risks are expanded west to include both central and eastern sections of the Carolinas for both Days 4 and 5. ...Missouri to the Tennessee Valleys/Southern Appalachians... There should be some ongoing activity over Missouri Friday morning with greater confidence on a more vigorous setup over much of Missouri after peak diurnal Friday afternoon/evening. PW increases to 2-2.25 inches with support from southwesterly low level inflow and potential frontal boundaries. The Day 4 Slight Risk was expanded a bit over Missouri. Farther south, frontal forcing will help focus diurnal convection over northern AL/GA east into South Carolina with a Day 4 Marginal Risk now connected from Missouri to the Carolinas along this frontal boundary. The Day 5 Marginal Risk was refocused to be along the continued frontal boundary from southeast Missouri through the Tennessee Valley instead of to the Gulf Coast. Given this larger change, please be on the lookout for further refinement. ...Southwest/Great Basin/Central and Southern Rockies... A downward trend in convective coverage and potential flash flooding late is forecast for Friday with a Marginal Risk limited to terrain around the Four Corners. Moisture anomalies then increase again for Saturday which along with mid level energy moving around the southwestern periphery of a broad high will help expand afternoon and evening storm coverage. A broader Marginal is in effect for Day 5, including the southern Arizona deserts and the majority of the Four Corners states into eastern Nevada. WFOs ABQ and EPZ were concerned about mid level warmth/capping when asked about a Day 5 Slight for the Sangre de Cristo/Sacramento, so that remains a Marginal at this time. ...Gulf Coast... Confidence has increased on heavy rain associated with Bertha remaining away from the Texas and Gulf Coasts on Friday to warrant removal of the Day 4 Marginal from Texas. Further more, frontal related rainfall both Friday and Saturday is now focused far enough inland to not have A Marginal Risk on the coast for either day. Jackson/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 $$