FOUS30 KWBC 042024 AAA QPFERD Excessive Rainfall Discussion...UPDATED NWS Weather Prediction Center College Park MD 424 PM EDT Thu Jun 4 2026 Day 1 Valid 16Z Thu Jun 04 2026 - 12Z Fri Jun 05 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER A PORTION OF THE UPPER MIDWEST... ...16Z Outlook Update... The ongoing outlook is generally on track. The Slight Risk area was expanded slightly south/southwestward across northeastern Kansas to account for latest trends in CAMs that suggest potential for convective training and prolonged rainfall generally along the I-70 corridor from Salina to Topeka and vicinity late today/tonight. Otherwise, one or more complexes of storms are expected to traverse the Slight Risk area from northeastern Kansas into Iowa from afternoon through the overnight hours, with localized training and convective mergers expected to produce isolated to scattered instances of flash flooding. Elsewhere, scattered, slow-moving convection will likely result in isolated flash flood instances especially from New Mexico/southwest Texas thorugh southeast Texas and soutwestern Louisiana. Another complex of storms should migrate eastward across South Dakota today and prompt localized training/flash flood concerns across eastern/northeastern portions of that state. Isolated/urban flash flooding is possible across southeastern Florida as well. See the previous discussion below for more information. Cook ...Previous Discussion... Circulation around a broad area of high pressure over the Northeast US and the Mid-Atlantic Region will keep an easterly flow of deep moisture over Florida and and anticyclonic flow from the Texas and Louisiana Gulf coast that becomes southwesterly from parts of the Central Plains/Upper Midwest through much of the period. An upper low over northern Mexico will help draw some of that moisture westward to support the risk of locally heavy rainfall there. ...Gulf Coast to Upper Midwest/Northern Plains... With a persistent fetch of an airmass from the Gulf Coast region into the Upper Midwest...precipitable water values increase throughout the day...exceeding 2 inches along the Texas Gulf coast to the ARKLATEX while increasing to 1.5 inches or more in a plume extending into parts of Minnesota and Wisconsin. The highest probability of heaviest rain was shown in both the operational models and the ensembles across parts of Iowa into portions of nearby Nebraska and Kansas as mid level height falls make their way out of the High Plains and as surface pressures fall. Rainfall rates of 1-2 inches per hour are possible. The 00Z runs of the HREF and the RRFS show neighborhood probabilities of 10 to 20 percent occurrence for 2 inch amounts in 3 hours for the 24 hour period ending at 12Z Friday morning. Those rates could be enough to overcome initially dry soils in parts of the area as well as be problematic in urban areas. Elsewhere along that corridor...there is sufficient CAPE to drive locally intense downpours from any convection that forms. The big problem is the relatively weak shortwave energy within the flow will be difficult to time with much lead-time. As such...left the Marginal Risk area pretty much in place with the expectation that some area may well stay rain-free. ...West Texas to Eastern New Mexico... An upper level system over Mexico will help draw some of the deeper Gulf moisture westward...keeping a risk of locally heavy rainfall and isolated instances of flash flooding. As previously mentioned...the overall organization of the convection is expected to be on the lower side, but the precipitable water anomalies and the subtle increase in the upper level difluence near the international border support potential for locally intense rain rates and the Marginal Risk. ...South Florida... Frontal boundary stalling in the vicinity of the area will remain the focus for scattered to numerous showers and thunderstorms capable of producing intense rain rates and locally heavy rainfall over the highly urbanized corridor. The risk shifts a bit farther south across South Florida compared with yesterday...mainly centering across the Miami metro. Bann Day 2 Valid 12Z Fri Jun 05 2026 - 12Z Sat Jun 06 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF EASTERN NEBRASKA INTO THE MID-MISSISSIPPI VALLEY... ...21Z Outlook Update... The Slight Risk in the previous D2 issuance has been shifted southwestward and expanded slightly based on most recent model trends. Fairly progressive convection should migrate across much of Wisconsin and Lower Michigan in the morning/early afternoon hours. During the latter parts of the forecast period (afternoon onward), Additional, surface-based convection should redevelop near the NE/IA border and migrate eastward toward the MS River/IA/IL border region. This convection should be oriented favorably for local training/backbuilding - and some of that convection (particularly in Iowa) could fall on wet soils from prior-day anticipated rainfall, creating more moist ground conditions favoring excessive runoff. The current configuration of Slight reflects most recent model depictions of heavy rainfall risk from deep convection. Elsewhere, the overall forecast is generally on track, with small spatial expansions of Marginal in New Mexico to account for potential convection in higher terrain. Scattered thunderstorms should move slowly across the entire Marginal Risk area from NM/west Texas eastward to southeast Texas. Some consideration of Slight was given for the Big Country/Hill Country with a nearly stationary mid/upper trough upstream and copious moisture content present. Instability and convective coverage were in question though and will likely be dependent on prior-day convection and the evolution of any potential complexes from west Texas that migrate through the region during the early morning hours. After collab with local WFOs, decision was made to wait another model cycle before reconsideration of a potential upgrade. Though specific timing is uncertain, a disturbance over the central Gulf will begin to migrate slowly northwestward toward southeastern Louisiana and pose heavy rainfall potential across that area and adjacent areas of Mississippi. Wet soils from prior rainfall will support excessive runoff should heavier rainfall/deep convection materialize as suggested by models. Cook ...Previous Discussion... Upper Midwest... Additional scattered thunderstorm activity is expected once again ahead of a front making its way from Iowa into Wisconsin and vicinity, spreading 1-2 inches of rain with local amounts reaching 4 inches. Storms in that area should be progressive in nature due to 20-30 knot mid/upper level flow, though localized backbuilding and mergers may increase totals locally. The Marginal Risk surrounding the Slight Risk was largely unchanged...although some of the territory was removed from the northern part of Michigan now that timing of the boundary and low level moisture fields have become handled better by the models/ensembles. Texas into New Mexico... Weak mid/upper troughing across the southern Rockies and Texas will promote another round of thunderstorm activity across a large part of Texas and southern New Mexico, with attendant flash flooding expected due to slow storm motions and abundant moisture. Coastal Louisiana... A trough of low pressure interacting with the higher moisture in place will bring a higher coverage of thunderstorms with the potential for intense rain rates and localized heavy rainfall. Spaghetti plots show more ARW core members than NMMB...suggesting that there could still be shifts in placement or QPF amounts between now and the time the outlook verifies. Bann Day 3 Valid 12Z Sat Jun 06 2026 - 12Z Sun Jun 07 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE GREAT LAKES/OHIO VALLEY AND ACROSS THE MIDDLE GULF COAST INTO THE SOUTHERN PLAINS... ...21Z Outlook Update... The overall forecast is on track with minimal changes made based on latest model trends. The Slight Risk along the Upper Ohio Valley westward to Illinois was expanded/shifted southward and westward to account for latest model trends, which develop scattered thunderstorm activity (likely in the form of clusters/linear segments) across the discussion area during the afternoon and evening. Guidance has shifted somewhat more south with precip maxima into northern West Virginia, with more isolated thunderstorm activity expected with westward extent into Illinois. Isolated instances of flash flooding appear possible in this regime. Across Texas and Oklahoma, a persistent mid-level trough will likely continue to spawn scattered to numerous shower/thunderstorm activity, with latest guidance depicting QPF maxima near the Red River and into western north Texas. Much of this evolution will depend on development and persistence of any complexes from prior- day convection, which lends uncertainty at this timeframe. Should trends hold, a Slight may be needed in portions of west Texas and the Big Country. Lastly, models are in general agreement that a Gulf disturbance will reach land over southeastern Louisiana and spread areas of heavy rainfall over Louisiana and Mississippi. Local convective training/banding may be possible depending on the organization of the disturbance. Current trends suggest additional heavy rainfall potential over wet/sensitive ground conditions from prior rainfall in the area the past couple weeks. Flash flooding is possible on at least an isolated basis. See the previous discussion below for more information. Cook ...Previous Discussion... Great Lakes/Ohio Valley... Maintained a Marginal Risk area over portions of Ohio Valley and nearby southern Great Lakes as a front become oriented along an east to west axis and flow aloft is weakly forced to lift isentropically. Maximum areal average rainfall after the start of the period at 12Z Saturday generally looks to be little more than an inch. The cumulative effect of rainfall on Days 2 and 3 suggested it was too early to entirely remove the Marginal. Texas northward into the Southern Plains... Little change in the overall synoptic pattern is expected with southerly flow of moisture continuing to be drawn into parts of the Southern Plains. Some stronger/better defined shortwave energy within the flow aloft will promote yet another round of thunderstorm activity across a large part of Texas and southern New Mexico and extending as far north as parts of Oklahoma/Arkansas and Kansas by late Saturday night/early Sunday morning, with attendant flash flooding expected due to slow storm motions and abundant moisture. Bann 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