FOUS30 KWBC 010052 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 852 PM EDT Tue Jun 30 2026 Day 1 Valid 01Z Wed Jul 01 2026 - 12Z Wed Jul 01 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE GREAT LAKES...NEW ENGLAND...OVER SOUTHWEST TEXAS AND THE FLORIDA PENINSULA... 0100Z Update.. Given the typical strong connection with peak daytime heating, and thus the latest (diminishing_ convective trends across the Southeast, we were able to drop the Marginal Risk. Cloud tops are warming now per the longwave IR imagery, coinciding with the diminishing deep-layer CAPE trends now following sunset. Despite some weak mid- level forcing (in vicinity of weak H5 vort lobe across North FL south of the closed 594DM High), weak mid-level lapse rates (~6 C/Km) along with weak low-mid level bulk shear will inhibit any additional areas of more organized/prolonged convection. Elsewhere, made subtle adjustments to the elongated Marginal over the nation's midsection, generally to remove portions on the western flank, while expand a little farther eastward across the Central Plains based on the latest observational and CAM trends. Hurley Day 2 Valid 12Z Wed Jul 01 2026 - 12Z Thu Jul 02 2026 ..THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER THE UPPER MIDWEST... Upper Midwest and Upper Great Lakes Regions... 20Z Update: The previous forecast remains on track with the overall synoptic overview still very much in-line in run-to-run continuity. Hi-res models have been initiating heavier convection across southeastern MN with a focus on the area south of MSP towards Rochester and neighboring areas. This is likely coincident with the alignment of a sharp theta_E gradient oriented along a cold front that will bisect the region from west-southwest to east-northeast across southern MN into WI. Multiple shortwaves will ride across the northern periphery of a ridge expanding across the eastern CONUS leading to aided mid and upper forcing to couple with a primed environment positioned over the Upper Midwest. Heavy rainfall is likely with any convective core that develops leading to localized rates of 1-2"/hr as noted via the modest hourly rate probabilities from the 12z HREF. Neighborhood probabilities for >2" are running between 60-90% across all of southeastern MN into Central WI with >3" probs still a respectable 30-60% with a bullseye located just east of Rochester, MN. This was enough of a signal to expand the SLGT risk further southwest into the region and generally maintain the previous forecast over WI with some minor trimming on the northern edge of the risk as noted via trends in a slight southward shift of the frontal alignment. Kleebauer ..Previous Discussion.. The large scale flow changes little during the Day 2 period with deep low pressure moving slowly from Manitoba into Ontario while a strong and sprawling upper high remains quasi-stationary over the eastern US (except for portions of New England). That leaves a broad region of enhanced moisture-transport from the central and southern portion of the Rockies front-range and nearby High Plains to the Upper Mississippi Valley and the Upper Great Lakes region. There was a growing overlap in the models between shortwave energy rotating around the Canadian upper low and the deep-layered moisture in the channel of the moist southwesterly flow across the Upper Mississippi Valley with a corresponding increase in model QPF. The UKMET and NAM NEST were most aggressive with their QPF...perhaps from convective feedback...but even other models tended to place their QPF maximum values somewhere over or near Wisconsin. This region had precipitable water values in excess of 2.5 standardized anomalies above climatology on Wednesday afternoon/evening when daytime ML CAPE values are forecast to be in the 1000-2500 J/KG range. This environment should remain sufficient to produce a few more robust downpours with the threat for some isolated flash flooding so introduced a Slight risk area there. A broad...unfocused Marginal extended from the Upper Midwest southwestward to the Southern Rockies foothills. Weak and difficult-to-time shortwaves embedded within the broader flow can easily trigger storms capable of downpours almost anywhere within the channel. Bann Northeast US... 20Z Update: No changes were necessary across the Northeast U.S. as the forecast remains steadfast from the previous update. Pockets of heavier rain are plausible across Central NY and points north with a general maxima between 2-3" in the hardest hit locations. Best chance for those heavier totals are forecast over Northern New England with prob fields indicating modest potential for such totals over northern VT down through the Green Mountain corridor. The MRGL risk remains in effect. Kleebauer ..Previous Discussion.. Additional showers and thunderstorms are expected over parts of New England in the northwest flow to the east of the ridge axis of the upper high. Seasonably high precipitable water value should support at least some isolated heavier downpours. Antecedent conditions may also be more sensitive depending on the evolution of more widespread/potentially organized convection on Tuesday. No major changes were needed to the Marginal Risk area added on Monday. Bann Southeast Florida... 20Z Update: MRGL risk was maintained with the current update, but did trim back some on the western and northern edge of the previous update. Hi-res trends were pretty aggressive across Miami proper which correlated to elevated probs for >3" locally and even some relevant probs (30-50%) for >5" within the latest HREF output. This allowed for maintaining the MRGL risk with a chance at a targeted upgrade pending further trends. Convergence pattern across the southeast FL coast is pretty well-documented as this point in the CAMs, so there will likely be an area that receives appreciable rainfall in the region. Whether that settles over an urban zone or not will dictate the potential for flash flooding as FFG's remain high across the area. Kleebauer ..Previous Discussion.. The front which is expected to help focus showers and thunderstorms on Tuesday will continue to make its way into the southern Florida peninsula on Wednesday. Despite the front becoming weaker and more diffuse with time...the expectation is that the boundary will still act to help focus showers and thunderstorms in the unstable airmass...aided by convergence along the sea breeze along with potential for sea breeze collisions. Bann ...Louisiana... Inverted trough will maneuver around the southern periphery of a strengthening ridge positioned to the north leading to an increasing convergence pattern across the southern half of Louisiana as we move into Wednesday. Recent trends have been more aggressive with the signature over the I-10 corridor extending from the Lower Sabine through the Lake Charles to Lafayette, LA areas with the latest HREF blended mean QPF output pushing closer to 2-3" across the area. Probabilities for >3" locally are up to 40-70% within that zone along the interstate with some lower end probs for even >5" showing up between Lake Charles and Lafayette proper in the latest update. One positive in this setup is the area FFG's for all 1/3/6hr thresholds are very high given the drier antecedent soils remaining over the area. This should curb a more enhanced flash flood scenario, but still offer a modest prospect given the heavy totals in the deterministic outputs. In coordination with the local LCH and LIX WFO's, a MRGL risk was added in this forecast update to encompass the aforementioned area. Kleebauer Day 3 Valid 12Z Thu Jul 02 2026 - 12Z Fri Jul 03 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE NORTHERN PLAINS, UPPER MIDWEST INTO THE GREAT LAKES... ...Northern Plains/Upper Midwest/Great Lakes... 20Z Update: Models maintain a general convective threat across much of the Northern Plains into the Mid and Upper Midwest on Thursday as the synoptic pattern continues to promote persistent northwesterly flow around the northern periphery of a strengthening upper ridge positioned across the Eastern U.S. The general area of convection from ND down through northern IA and points north will offer the threat for isolated instances of flash flooding as models have mixed areas of QPF maxima littered across the northern tier of the CONUS. There could be an instance where heavy rainfall intersects areas hit the previous period and offer a better opportunity for flash flooding, however judgment on any targeted upgrades would need to be assessed after the previous period's rainfall. Will refrain an upgrade at this time and maintain continuity with a broad MRGL risk over the Northern Plains to Upper Midwest with a minor expansion northwest into central ND to account for the latest precip forecast indicating heavier convective potential back over the area. Kleebauer ..Previous Discussion.. A broad region of west southwesterly mid to upper level flow is expected to persist during the Day 3 period across the Northern Plains into the Upper MS Valley and Great Lakes. The area should still be located between an eastern closed upper high and a mean western trough, both of which are in the process of weakening by Saturday morning. Broadly diffluent mid- to upper-level flow associated with embedded shortwave energy moving northeastward within the west-southwest mid to upper level will support active convection, possibly organized, in an axis of slightly above average moisture across these regions. Only subtle changes were made to broad marginal risk areas which were already issued covering the period spanning from Thursday into early Friday. Confidence remains low with respect to where convection may become organized and produce heavy rainfall and isolated runoff issues, possibly linked to the changing behavior of the flow across portions of the Central and Eastern US/Canadian border and ridge strength and orientation in the eastern US. Bann Day 4 and Day 5 Valid 12Z Fri Jul 03 2026 - 12Z Sun Jul 05 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF THE NORTHERN PLAINS, MID TO UPPER MS VALLEY, GREAT LAKES, CENTRAL APPALACHIANS, AND NORTHERN MID-ATLANTIC... ...2000Z Update... On both days 4 and 5, both Marginal Risk areas were expanded a bit, based on the latest 12Z probabilistic data (including GEFS and CMC 6/12/24hr QPF 2/3/5 inch exceedance probabilities. Did broaden the areas a bit farther to the south on both days, basically 'casting a wider net' to account for the latitudinal variability in the guidance, and with the expectation that evolving MCS activity and areas of potential cell training will be able to slip farther into the ridge where low-level lapse rates will be quite high. Hurley Previous discussion... The west southwesterly mid to upper level flow that has been persistent across the Central to Northern Plains into the Upper MS Valley and Upper Lakes region will begin to become more westerly from the Northern Plains, eastward across the Lakes and into the Northeast. Broadly diffluent mid to upper level flow associated with shortwave energy moving east northeastward in this west southwest to westerly mid to upper level will support active convection, possibly organized, in an axis of slightly above average moisture across these regions. Broad marginal risk areas were depicted both day 4 and 5 to cover the current model spread for locally heavy rains and isolated runoff issues. Concerns are that with the low level flow will becoming increasingly westerly across these regions from day 4 into day 5, there will be potential for convection training for a period, likely late afternoon into the early hours each day, along and just south of the west to east oriented frontal zone expected to be moving slowly southward across the northern tier from the Upper MS Valley into the Lakes. Oravec 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 $$