


Quantitative Precipitation Forecast
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935 FOUS30 KWBC 100556 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 156 AM EDT Thu Jul 10 2025 Day 1 Valid 0553Z Thu Jul 10 2025 - 12Z Fri Jul 11 2025 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHERN NEW ENGLAND... Special update based on radar trends and new 00z CAM guidance to introduce a SLGT risk for portions of southern New England. See upcoming MPD #633 for more detailed information. Elsewhere, maintained MRGL risk areas for where some lingering rainfall is still ongoing across portions of the Mid-Atlantic (though convection continues to rapidly wane). The MRGL in place for portions of the Central/Northern Plains was shifted east a bit based on observational trends. Churchill Day 2 Valid 12Z Fri Jul 11 2025 - 12Z Sat Jul 12 2025 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MID ATLANTIC AND SOUTHEAST... ...Mid Atlantic and Southeast... 20Z Update: Conditionally unstable airmass will remain situated across the Eastern Seaboard with a general instability maxima and deep moist layer situated over the Southern Mid Atlantic through SC/GA. A lee trough over the Piedmont of VA down through SC will align with a formidable theta_E axis outlining an area of focus for diurnally driven convection as we break into Thursday afternoon. Forcing will be weak in the grand scheme, so the loss of sufficient kinematics will mute the threat compared to Wednesday, but a fairly buoyant environment and strong diurnal heat flux will remedy the lack of large scale forcing and initiate a scattered to widespread convective regime mostly driven via thermodynamic processes and focused convergence within the lee trough center. 12z HREF blended mean QPF depicted a smattering of maxima with 2-4" signals extending over Eastern GA up through the Carolina Piedmont into VA. Northern periphery of the best convective threat aligns with the Potomac Basin as drier above 600mb advects through the Central Mid Atlantic curbing some of the greater potential as you move into MD/PA, so the prospects of heavier rainfall will lie south of the shifting environment. Maintain general continuity from previous SLGT issuance, but extended the SLGT further south and west to account for the favorable convective regime through the period with stronger convective cores still capable of local 2-3"/hr rates causing concern within any compromised areas from prior periods, and urbanized settings where run off capabilities are highest. Kleebauer ...Northern and Central Plains into the Upper Midwest... 20Z Update: The synoptic evolution over the Plains and Midwest is still very much advertised for late-Thursday afternoon through early Friday morning with a likely organized convective window transpiring downstream of an approaching shortwave trough. Strongest signal within the CAMs remains parked over IA with some expansion westward into Eastern NE where the organized multi-cell pattern will likely occur after cells initiate upstream across the Sandhills and High Plains of NE. 12z HREF EAS is actually relatively robust across Central IA where CAMs are in excellent agreement on a regional maxima positioned near Des Moines overnight Thursday into Friday. This is coincident with the progression of nocturnal complex expected to materialize over NE with the mean flow likely to orient the complex on a west to east trajectory near/over I-80. LLJ introduction will aid in supplemental low-level moisture advection maintaining suitable MCS maintenance for a time before the system collapses as it exits IA into IL. Pending forward propagation speed, it`s plausible the complex can reach North- Central IL by the time the period ends with some remnant heavy rain cores moving into the I-39 corridor. This potential evolution has merit within the 12z EC AIFS Ensemble with a low-end prob for heavier QPF output to the west of the Chicago metro. In this case, the previous SLGT risk was modified a bit more to the east to cover for higher probabilities for >2 and >3" outputs via the HREF and to account for the AIFS ensemble depiction which has a pretty solid track record with handling convectively driven disturbances inside 48hrs. Kleebauer ..Previous Discussion.. By Thursday the persistent ridge aloft over the Southwest U.S. begins to break down, as an upper-low off the northern CA coast opens up into a shortwave trough on Wednesday and ejects eastward ahead of a digging longwave trough over western Canada. These two features look to interact over the Northern and Central Plains, but there are still substantial differences between models in how these features evolve and interact. PWs of 1.5"+ are expected (near the 90th percentile for the region) with ample instability and dynamics for organized convection and subsequent high rainfall rates (as this shortwave trough looks much more potent relative to the expected shortwave on Day 1). Maintained an inherited Slight risk area that was adjusted based on the new consensus guidance. Churchill Day 3 Valid 12Z Sat Jul 12 2025 - 12Z Sun Jul 13 2025 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE MIDWEST... ...Midwest into Mid-Mississippi Valley... 20Z Update: Secondary vorticity maxima migrating through a relatively low amplitude portion of the mid-level regime will eject eastward in a similar path to the previous disturbance, only this time encountering a more suitable environment with a deeper IVT pulse being advected poleward ahead of the mean trough. A stronger shortwave will also be digging south of out Canada allowing for a better meridional push of deep layer moisture into the Upper Midwest while also creating a more defined RER jet dynamic thanks to a strengthening 250mb jet streak ~110kts positioned over the Dakotas to Northern MN. Models have come into agreement on a west- southwest to east-northeast oriented heavy convection regime with some multi-cellular organization likely given increasing shear and large scale forcing instigating the pattern. Totals between 2-4" are being forecast already within the global deterministic with the ensemble mean QPF firmly between 1-2" over a large area encompassing Eastern NE, much of IA, Southern MN, and Western WI. This correlates well with the forecast alignment of the stronger IVT advection being pumped into the area due to the increasing meridional state of the synoptic field. This setup has a pretty robust indication via ML output as well, so the confidence has grown enough to warrant a broad SLGT as the threat could be in overlap of some hard hit areas the period prior. This will be an evolving threat and the positioning of the risk could change in the coming days, but wanted to align with consensus on initial thinking. Further south, a bit more complexity in the potential with less agreement within the deterministic suite on potential heavy convection across portions of MO/IL to the south of the pattern evolving over the Midwest. Instability will be suitable overall, but could be missing some elements to help push this threat to a higher risk. Still, a fairly robust PWAT forecast and solid thermodynamic structure should provide some modest risk for isolated flash flooding, at a minimum. Maintained continuity of a MRGL in the area to account for the potential and will be monitored for targeted upgrade opportunities if the signal increases in magnitude and/or coverage. Kleebauer ...Mid-Atlantic and Southeast... 20Z Update: No changes necessary to the previous forecast as the pattern remains favorable for isolated heavy rainfall across much of the Southeast into the Southern Mid Atlantic. Kleebauer ..Previous Discussion.. As mid-level troughing becomes more established in the Northern Plains into Day 3, ridging builds in response downstream and may finally begin to suppress convection more significantly across the northern Mid-Atlantic into the Northeast. While there are no clear signs of significant convective organization at this juncture into the Southeast and southern Mid-Atlantic, convective initiation with scattered convection and locally high rainfall rates appears likely (where ridging will be insufficient to fully suppress convection). Churchill ...Rockies into the Central and Southern High Plains... 20Z Update: A slightly better signal is being depicted across the Front Range on Friday with a chance for a stronger convective complex to initiate off the WY/CO Front Range and migrate east- southeast along as the 850-300mb mean flow orients out of the west-northwest in-lieu of a digging trough dropping out of Canada to the north. A cold front trailing a surface low maturation over the Central Plains would only entice a focal area for not only heavy rainfall, but increasing prospects for back-building and training behind any complex. The environment for locally enhanced rainfall from any diurnally driven convection within a narrow lee trough across the Southern High Plains and anticipated cold front approach from the north will also lead to isolated flash flood prospects from Southwest KS down into the Upper Trans Pecos. This threat is on the lower end of the MRGL threshold, but still has credence when assessing the overall environment. The MRGL will remain in place from previous forecast, but will be keeping an eye on perhaps a targeted upgrade in-of the migrating complex anticipated off the Front Range. Kleebauer ..Previous Discussion.. As the Southwest ridge continues to break down for a second day, the global guidance signal for more substantial convective initiation within the terrain of the Rockies increases into Friday (and particularly so farther north into the northern/central Rockies of WY/CO). Localized 1-2" totals (as indicated by both downscaled deterministic GFS/ECMWF solutions and ensemble 1" exceedance probabilities) in the sensitive terrain may lead to localized flash flooding concerns, and more substantial convective organization in association with shortwaves/vorticity maxima rounding the ridge and coming off the terrain may allow for more organized convection into the evening/overnight in the Central and Southern High Plains. Churchill 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