Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jun 29 2025 08:28:45 FOUS30 KWBC 290828 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 428 AM EDT Sun Jun 29 2025 Day 1 Valid 12Z Sun Jun 29 2025 - 12Z Mon Jun 30 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL EXTENDING FROM=20 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.=20 As Day 1 begins, late-night convection lingering across parts of=20 Missouri should be about to fade with the weakening of a low level=20 jet. With models showing renewed convection later today and tonight across western Missouri/eastern Kansas that extends northward into portions if Iowa...did introduce a Slight Risk area to the=20 outlook where organized convection from overnight approached the=20 area from the north. Precipitable water values approaching 2" and=20 near the 90th climatological percentile will provide the=20 opportunity for intense rainfall rates scattered 2-4" rainfall=20 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. Bann/Snell Day 2 Valid 12Z Mon Jun 30 2025 - 12Z Tue Jul 01 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS=20 OF THE SOUTHERN ROCKIES EASTWARD INTO THE MID ATLANTIC... Similar to today...convection is expected to develop within a=20 region of decent CAPE and precipitable water values in excess of 2=20 standard deviations above climatology. Except for some mid-level=20 westerly flow around the Great Lakes to provide some shear=20 there...the flow farther south should be fairly meager (but offset=20 by steeper low-level lapse rates). This sets up the potential for=20 some local rainfall rates in excess of 1 inch per hour that results in excessive rainfall from the Southern Rockies/Western High=20 Plains east/northeastward into the Ohio Valley and parts of the=20 Mid-Atlantic region on Monday and Monday night.=20 A weakening surface boundary will help focus some of the threat=20 for heavier rainfall but its placement remains quite uncertain.=20 One area that is still being monitored for a potential upgrade to a Slight Risk are parts of the Upper Ohio Valley and central=20 Appalachians (centered over western PA). The synoptic setup with a=20 stationary/warm front stretching across southern PA and an=20 approaching cold front from the west should help foster greater=20 coverage in showers/storms within a moist environment, but storm=20 motions within a mean column wind of 30kts could limit the flooding threat even though this area remains sensitive to intense=20 rainfall. Therefore, a Marginal Risk was maintained to highlight=20 the threat for isolated flash flooding. Snell/Bann Day 3=20 Valid 12Z Tue Jul 01 2025 - 12Z Wed Jul 02 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER A PORTION OF THE MID ATLANTIC... The boundary that helps focus some of the threat for heavy to potentially excessive rainfall on Day 2 will continue to shift=20 eastward and provide the focus for another round on Day 3. The flow aloft becomes more supportive over the Northeast US as=20 divergence aloft increases in response to a digging trough aloft=20 and low level convergence increases along the boundary. Portions=20 of the Mid-Atlatic have suppressed Flash Flood Guidance from a=20 period of above normal rainfall making that area a bit more susceptible to excessive rainfall...while faster cell motions should preclude more than isolated instances of flash flooding across the Northeast US. Farther south/west along the boundary...convection is expected to be develop within a region of decent CAPE and precipitable water=20 values in excess of 2 standard deviations above climatology. With weaker flow aloft...locally heavy rainfall totals could result in isolated instances of excessive rainfall.=20 Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!5Z4WwZjNFsQ92uhxLAlvBmpjrq68qQXIJyB-1ilV77Ry= gJOWrtZSCpYvkXTFlj7sA_NPX8viLO7NWgSoWEfc1IOI7wM$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5Z4WwZjNFsQ92uhxLAlvBmpjrq68qQXIJyB-1ilV77Ry= gJOWrtZSCpYvkXTFlj7sA_NPX8viLO7NWgSoWEfcpV8So14$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5Z4WwZjNFsQ92uhxLAlvBmpjrq68qQXIJyB-1ilV77Ry= gJOWrtZSCpYvkXTFlj7sA_NPX8viLO7NWgSoWEfcAbzbCRQ$=20 =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. 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