556 FOUS30 KWBC 281952 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 352 PM EDT Sat Jun 28 2025 Day 1 Valid 16Z Sat Jun 28 2025 - 12Z Sun Jun 29 2025 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTH-CENTRAL MISSOURI AND NORTH-CENTRAL ARKANSAS... 19Z Special Update... Extended the Marginal Risk farther east across central, into eastern North Carolina. PWs ~1.9 inches, along with SBCAPE 2500-3000 J/kg and weak flow aloft are supporting slow-moving storm with heavy rates (up to 2+ inches/hr in some of the stronger cells). This has resulted in areas of flash flooding in central North Carolina. The 18Z RAP indicates the environment will remain favorable for heavy rain, with additional increases in PWs and CAPE into the evening. Pereira ...Middle/Lower Mississippi Valley and adjacent southern Plains, Ohio and Tennessee valleys... Firmly in the warm sector and within a moist airmass containing widespread PWATs of 1.8-2.2" (near the 90th climatological percentile), isolated to scattered flash flooding is possible today with a potentially higher focus across parts of southern MO and northern AR tonight, where a Slight Risk of Excessive Rainfall was introduced in the 16z update. An MCV evident on morning radar and satellite imagery has already prompted a few FFWs across eastern OK and KS while gradually pushing eastward. This feature will aid in sparking widely scattered slow- moving thunderstorms throughout the afternoon while instability levels rise due to diurnal heating. Pulse thunderstorms within weak steering flow and an unstable/moist environment are also likely through much of the Ohio and Tennessee valleys today, with smaller scale scattered flash flooding possible. Current trends are for the aforementioned MCV to make it into the vicinity of southeast MO by late tonight and influence a sharp mid-level trough ahead of increasing warm air advection throughout the Plains due to a crossing shortwave in the north- central U.S. and the nighttime low- level jet. CAMs still differ somewhat in the exact location of a potential northwest- southeast oriented band of slow-moving storms, but generally converge on south-central MO and don't really develop until around 09z tonight. The 12z HREF has increased 24-hr probs (12z Sat-12z Sun) for greater than 5" of rain to 30-45% within the Slight Risk outline. Additionally, this part of the country also has relatively saturated soils already (70-100% 0-40 cm below ground relative soil moisture percentiles per NASA SPoRT) not including the likelihood of scattered thunderstorms and potentially overlapping heavy rainfall this afternoon. ...Northern Plains and Upper Midwest... Showers and thunderstorms capable of producing locally heavy rainfall rates and heavy rainfall totals have the potential to produce flash flooding as the next upper shortwave trough approaches the north-central United States. Aided by a 90kt upper level jet streak on the lee side...the upper trough will generate a compact area of fairly robust, transient deep-layer forcing over the outlook area later today and tonight. MUCAPEs are expected to soar within the warm sector prior to the surface cold frontal passage late tonight. Given precipitable water values getting near 1.75 inches...storms which form within the unstable airmass will be capable of producing rainfall rates in excess 1.5"/hr and areal average rainfall amounts of 1 to 3 inches...especially once low- level inflow accelerates to between 30 kts and 40kts at 850 mb ahead of the approaching front. The storm/mesoscale nature of the threat leads to uncertainty of a more focused corridor of higher risk, but a Slight Risk was considered in central MN where forward propagation of storms may begin slow this evening and is reinforced by the highest 12z HREF probs (20-30%) for exceeding 3" in 6 hours. ...Central Appalachians to the Northeast... There continues to be a concern for heavy to potentially excessive rainfall to develop across western Pennsylvania and surrounding areas as the frontal boundary sags southward and taps into the pooled PW values of 1.5-2". 12z CAMs are not a robust with rainfall amounts in the central Appalachians and keep things moving along in the Northeast to limit any flash flooding to isolated instances. However, the environment remains unstable and moist, so any slow- moving storms could lead to forming mesoscale boundaries that create locally intense rainfall. Farther north, the Marginal Risk was removed across northern New England given unimpressive radar trends this morning and a more progressive patter. Still, 1-1.5" of rainfall could lead to very isolated and more nuisance flooding. ...Southeast and central Florida Peninsula... Scattered pulse thunderstorms are expected across a broad warm sector and near an upper trough lingering over the region as seasonable instability develops with daytime heating. A greater focus for intense rainfall also overlaps with higher FFG across the central Gulf Coast and Florida Peninsula, where rainfall rates of 2-3"/hr are possible but should weaken quickly before convection is driven off outflow from numerous other pop-up storms. ...New Mexico... Yet another day of thunderstorms is expected across portions of southern New Mexico and west Texas with locally heavy rainfall (1-2") possible. QPF trends (coverage, intensity) are more isolated compared prior days with the moist south to southeast low-level upslope flow likely resulting in more localized areas of heavier rainfall focused across the Sacramento and Guadalupe Mtns south through the Trans-Pecos. The flash flood potential is expected to remain isolated. Snell Day 2 Valid 12Z Sun Jun 29 2025 - 12Z Mon Jun 30 2025 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL EXTENDING FROM PORTIONS OF THE CENTRAL UNITED STATES TO THE CENTRAL GULF COAST AND MID-ATLANTIC... Late-June weather pattern remains in place on Sunday with widely scattered showers/storms and isolated chances for flash flooding within the warm and humid airmass spanning from the central U.S. to the Southeast and Mid-Atlantic. Showers and thunderstorms are expected both along and well- ahead of a cold front sinking southeastward across the central Plains and Midwest, as well as associated with diurnal monsoon activity across the southern Rockies and adjacent High Plains. At the start of day 2, there's the potential for ongoing late-night convection across south- central MO as a remnant MCV and overnight low-level jet foster slow-moving thunderstorms. There remains rather high uncertainty regarding the maintenance of thunderstorm activity in this region past the 12z Sun start time of Day 2, but should greater certainty arise a Slight Risk may be needed for south-central MO and nearby regions. Meanwhile, organized convection firing along the advancing cold front across the central Plains and Midwest should provide another focus for potential slow-moving convection in the evening before activity should become more progressive under the influence of a strengthening cold pool and progressive cold front. PWs approaching 2" and near the 90th climatological percentile will provide the opportunity for intense rainfall rates scattered 2-4" rainfall totals between parts of KS, MO, and southern IA. Elsewhere within the warm sector across the Mid-South, Mid- Atlantic, Southeast, and Southern Rockies/High Plains, typical summer thunderstorms exhibiting scattered and a pulse mode are likely. These storms may contain briefly very intense rainfall rates, but see updrafts collapse quickly and become outflow dependent. Where convective clusters merge or linger near a stationary front draped across the Mid-Atlantic and central Appalachians, isolated flash flooding is possible. Snell/Bann Day 3 Valid 12Z Mon Jun 30 2025 - 12Z Tue Jul 01 2025 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHERN ROCKIES EASTWARD INTO THE MID ATLANTIC... Similar to Sunday...convection is expected to develop within a region of decent CAPE and precipitable water values in excess of 2 standard deviations above climatology. Except for some mid-level westerly flow around the Great Lakes to provide some shear there...the flow farther south should be fairly meager (but offset by steeper low-level lapse rates). This sets up the potential for some local rainfall rates in excess of 1 inch per hour that results in excessive rainfall from the Southern Rockies/Western High Plains east/northeastward into the Ohio Valley and parts of the Mid- Atlantic region on Monday and Monday night. A weakening surface boundary will help focus some of the threat for heavier rainfall but its placement is quite uncertain. One area at the moment that is being monitored for a potential upgrade to a Slight Risk are parts of the Upper Ohio Valley and central Appalachians (centered over western PA). The synoptic setup with a stationary/warm front stretching across southern PA and an approaching cold front from the west should help foster greater coverage in showers/storms within a moist environment, but storm motions within a mean column wind of 30kts could limit the flooding threat even though this area remains sensitive to intense rainfall. Therefor, a Marginal Risk was maintained to highlight the threat for isolated flash flooding. Snell/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