FOUS30 KWBC 232030 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 430 PM EDT Tue Jun 23 2026 Day 1 Valid 16Z Tue Jun 23 2026 - 12Z Wed Jun 24 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN EFFECT OVER PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS TO LOWER RED RIVER VALLEY AS WELL AS SOUTHEAST VIRGINIA... ...Central and Southern Plains through Lower Mississippi Valley... As of 16Z...Organized heavy rain over OK from strong southerly flow over a frontal zone. Prior extreme rainfall near Texarkana has shifted to the northeast into OK, but may get impacted again this overnight from organized activity originating from storms currently along the western Neb/KS border. That may be progressive, so a Moderate does not seem needed at this time. Southern/central OK is under imminent heavy rain concern through early afternoon given thunderstorm clusters along the TX Panhandle/OK border shifting south-southeast while the activity from Texarkana over southeast OK propagates north-northeast. This area is considered to be an enhanced area in the Slight Risk, but also not a Moderate at this time. Will note that 12Z CAMs are struggling with the western OK/TX Panhandle activity, so for now the Slight Risk was expanded west a bit. Northwest flow around the high centered over far west Texas will drive the aforementioned MCS activity tonight across KS, OK through the lower Red River Valley. This should be progressive, but could further complicate excessive rainfall concerns over areas hit by heavy rain through this afternoon. Further activity from the Front Range/northern Sangre de Cristos will shift onto the high plains overnight as well. The Slight Risk was expanded west and north a bit. Meanwhile the Marginal was removed from northeast Nebraska based on 12Z CAMs and radar trends. ...Central North Carolina through Eastern Virginia and the DelMarVa... Scattered heavy thunderstorms in central NC shift northeast through the afternoon and perhaps hang on around Hampton Roads this evening, this activity is ahead of a mid level trough axis over the VA/NC Piedmont. Expanded the Marginal Risk to cover the current activity into NC and expanded north into southern NJ based on 12Z and later CAMs. A forthcoming MPD (#507) will have further details. Given the urban areas and PW at least two sigma above normal, the Slight Risk was maintained. Jackson Day 2 Valid 12Z Wed Jun 24 2026 - 12Z Thu Jun 25 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN EFFECT FROM THE CENTRAL HIGH PLAINS THROUGH THE MID-SOUTH TO THE CENTRAL GULF COAST... ...Central High Plains to Central Gulf Coast... Northwesterly flow persists north of the high centered over west Texas, maintaining the active pattern from the Front Range through the Mid-South with organized convection shifting farther southeast to the central Gulf Coast/Florida Panhandle through the day Wednesday. Complex organized activity ongoing over the southern Plains/Oklahoma still makes for uncertainty with convective focus areas tonight/Wednesday, so amendments are expected. For now, the Slight Risk was expanded farther than before - northwest into the Nebraska Panhandle and southeast to the Florida Panhandle. The sensitive area around Texarkana is in the threat area, so the Slight Risk was maintained and is considered more enhanced than normal Slight Risks given the extreme rainfall this morning, potential for more this evening, and Day 2 QPF from the 18Z HRRR which has its highest rainfall QPF in southeast Arkansas. Otherwise the heavy rainfall focus is over the central High Plains from west Kansas through the southern Neb Panhandle and down toward the central Gulf Coast per 12Z CAM consensus. The southeast activity would be hold over/redevelopment through the afternoon from what crosses the Mid-South tonight. Portions of the Southeast/Gulf Coast would have PW around 2 sigma above normal along a stalling frontal boundary, so the ingredients for heavy rainfall are present. The High Plains threat would be evening convective initiation that spills onto the Plains through Wednesday night. ...Southwest U.S... Anomalous mid and upper level moisture advects up from the Sea of Cortez tonight through Wednesday, crossing southern Utah in time for peak heating Wednesday. Most 12Z CAM guidance has hardly any development south of Las Vegas, but the anomalous moisture (3 to 4 sigma above normal) and terrain should enable at least some heavy thunderstorm development. Greater confidence is in afternoon convective development with a repeating threat from southern NV through southern UT (including slot canyons). The Marginal Risk was maintained/expanded east through the San Juan Mtns of CO for Wednesday night activity. Jackson Day 3 Valid 12Z Thu Jun 25 2026 - 12Z Fri Jun 26 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN EFFECT OVER PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS TO MID-MISSISSIPPI VALLEY... ...Plains to Mid-Mississippi Valley... Increasing troughing down the West Coast from a low over the eastern Gulf of Alaska has the downstream effects of suppressing the west Texas high pressure, making for more zonal flow over the Rockies, Plains, and Mid-South into the Midwest. At the surface, a quasi- stationary front from southern KS through MO and the Midwest. Still expecting a strong mid-level vort to eject east from the Central Rockies, allowing lee cyclogenesis over OK by Thursday evening. Areas east-northeast will have a front and an increasing LLJ to support widespread organized/heavy convection from KS/OK east through MO and eventually southern IL Thursday night. Main uncertainty is latitudinal with some models like the UKMET trending north while others like the EC-AIFS holding steady. Given PW anomalies of 2 to 3 sigma above normal, wanted to retain a broad Slight with the only expansion being farther east for the overnight convection that may last into southern Indiana/western KY. The 12Z RRFS favors the southern section of this zone which is reasonable given increasing instability to the south, but it will come down to the frontal placement. This area is likely to need an embedded Moderate Risk eventually. ...Four Corners States... Increased troughing down the West Coast Thursday should enable afternoon/evening terrain-initialized convection over the Four Corners states including slot canyon areas over western CO into UT. The Marginal Risk was expanded south through southeast AZ/southwest NM where southwesterly flow aids enhanced moisture advection into that area of terrain. ...Southeast/Central Gulf Coast... There is enough signal for an impulse over the Southeast to warrant raising a Marginal Risk along the Central Gulf Coast through southern GA for Thursday. Higher res models like the 12Z RRFS have this impulse coming from activity tonight over the Mid- South. Any remnant convective impulse would tap into Gulf moisture and have surface troughing to focus convection on. Jackson Day 4 and Day 5 Valid 12Z Fri Jun 26 2026 - 12Z Sun Jun 28 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE MID-MISSISSIPPI VALLEY AND OHIO VALLEY ON FRIDAY AND FOR PARTS OF THE NORTHERN PLAINS AND OHIO VALLEY ON SATURDAY... Day 4... 2030Z Update... The daytime guidance did not present any reason to make significant changes, therefore the update reflects only minor adjustments. Previous Discussion... Deepening upper trough over the Pacific Northwest on Friday increases downstream ridging within a mostly zonal flow regime east of the Rockies to the start the forecast period and shifts the heavy rainfall threat along the a quasi- stationary frontal boundary east-northeast from the Ozarks to the Upper Ohio Valley. PWs are expected to be modest around 2" and between the 75th-90th percentile. Ensemble clusters 75th percentile QPF are generally 1-3", but with some spread in location between a focus over the Midwest or over the upper Ohio Valley and central Appalachians. NBM and ECENS probabilities for at least 1" of rain are between 30-60% between MO and southwest PA. Additionally, westerly mid-level flow parallel to the aforementioned boundary does bring the potential for training thunderstorms and increases the risk for at least scattered flash flooding. A MRGL risk was maintained for now given some lingering location uncertainty at this range, but an upgrade to a SLGT risk is possible with future updates. Day 5... 2030Z Update... Previously noted boundary is forecast to lift north through the mid Mississippi Valley while lingering over portions of the Ohio Valley and central Appalachians. The boundary is expected to remain a focus for anomalous moisture -- remaining 1.5-2 std dev above normal according to the GFS and ECMWF. This moisture interacting with low-amplitude energy moving along the boundary may support additional periods of heavy rain. A Marginal Risk was added from the Indiana/Kentucky border east into West Virginia. While there are numerous detail differences, models generally indicate this will be a pivot location for the front, supporting the potential for repeating activity. Both the ECMWF/NBM show higher probabilities for amounts over an inch. Further raising the threat for flash flooding may be the heavy amounts occurring the previous day, as well as the area's complex terrain. Only minor adjustments were made to the Marginal Risk over the northern Plains. Previous Discussion... By Saturday the trough over the Pacific Northwest deepens significantly (below the 1st climatological percentile per the 00Z ECMWF) and further increases the upper ridging downstream over the Midwest/Great Lakes. Heavy rainfall remains possible along the frontal boundary draped over the Ohio Valley, but even more uncertainty exists at this range given the western edge of the front will be lifting northward. However, more certainty with respect to potentially heavy rain exists over the northern Plains as a leading shortwave ejects north-northeast over the region and within the left-exit region of a strengthening upper jet streaking above the northern Rockies. A warm front is also expected to remain nearby and extend from the northern High Plains to the Midwest. This will allow for thunderstorms to potentially focus along or become elevated to the north-northeast of the boundary and tap into PWs above 1.5". Global deterministic guidance depicts 2-4" of rainfall is possible, with NBM and ECENS probabilities for at least 1" in 24-hrs around 30-70% (highest in ND). This prompts a MRGL risk and allows for potential upgrades should confidence increase in amounts above 3" and greater location certainty. Pereira/Snell 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 $$