751 FOUS30 KWBC 300819 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 419 AM EDT Tue Jun 30 2026 Day 1 Valid 12Z Tue Jun 30 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... ...Southern High Plains to the Great Lakes... There will be a risk of excessive rainfall in various places east of the Rockies today as a deep/strong low moves slowly from Saskatchewan to Manitoba while a broad, sprawling upper high expands across the Southern Plains into the Mid- Atlantic and parts of the northeastern United States. This results in broad southwesterly flow that transports an unstable airmass with abundant Gulf moisture into parts of the Southern High Plains northeastward through the Great Lakes. Embedded shortwave energy within the larger scale flow pattern will support increasingly scattered convection with locally heavy rains and isolated runoff issues this afternoon into tonight. The concern is especially heightened over burn scars and dry washes/arroyos of the terrain near the southern Rockies. The latest hi-res guidance shows the potential for 1-3"+ of rainfall with these storms even if they remain rather short- lived and transient due to efficient downpours with rain rates of 1-2" per hour. ...New England... The latest hi-res guidance supports the maintenance/renewed development of thunderstorms in northwesterly flow over New England and portions of Upstate New York. The more widespread/organized nature of the convection would bring at least the risk of isolated flash flooding with storm total rainfall of 2 or 3 inches possible as suggested by much of the hi-res guidance. Additional refinement and possible upgrade to the risk area may be necessary with more confidence in this scenario. ...Florida... A cold front will be the focus for showers and thunderstorms as it makes its way southward into the northern Florida peninsula. The models have been maintaining their signal for convection and the storms look to be efficient rainfall producers considering the airmass will have nearly 2 inch precipitable water values already in place. As a result...maintained a Marginal risk of excessive over much the the peninsula, the panhandle and a small part of neighboring states. Bann 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... 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. Northeast US... 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. Southeast Florida... 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 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... 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 THE NORTHERN PLAINS, MID TO UPPER MS VALLEY, LOWER LAKES INTO THE CENTRAL APPALACHIANS AND NORTHERN MID-ATLANTIC... 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 $$