Subj : HVYRAIN: Excess Rain D1 To : All From : Mike Powell Date : Mon Jun 22 2026 07:52:57 FOUS30 KWBC 220945 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 545 AM EDT Mon Jun 22 2026 Day 1 Valid 12Z Mon Jun 22 2026 - 12Z Tue Jun 23 2026 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL IN EFFECT FROM NORTHERN ARKANSAS TO WESTERN TENNESSEE AND FAR NORTHWEST MISSISSIPPI... 0930Z Update... A Moderate Risk was added for northern AR to western TN and far northwest MS after assessing radar trends and latest HRRR/RRFS guidance. A mature MSC moving across eastern OK has an eastward extending wing of nearly stationary thunderstorms along an outflow boundary across northern AR into western TN and well south of the synoptic cold front to the north. The southward push of this outflow boundary is expected to compete with increasing southerly flow ahead of the MCS and strong mesovortex located in northeast OK. This all leads to an expected axis of heavy rain (hourly rates up to 3" and totals up to 6" are possible) through northern AR and into parts of western TN and northwest MS. This is just north of Little Rock, AR, but does include Jonesboro, AR and Memphis, TN. Coverage of flash flooding as well as potentially localized significant impacts prompted the upgrade to a Moderate Risk prior to the start of this day 1 forecast period (12Z Monday). This event is expected to begin diminishing by around 17Z as the MCS clears the region and weakens, but this still provides potential for around 6-hrs of intense rainfall rates and flash flood impacts. Snell Previous Discussion... ....Southern Plains to Tennessee Valley... Current WV satellite and UA analysis depicts a potent mid-level shortwave sliding southeast through the Central and Southern High Plains with eyes likely downstream into the Lower Mississippi Valley and southwestern Tennessee Valley as we move through the morning and afternoon Monday. Favorable boundary layer instability presence across much of the Southern Plains into the Southeastern CONUS will benefit periods of heavy rainfall during the period with a likely impact beginning early in the forecast period with a secondary batch likely to ensue the following evening. At the surface, surface wave will be located across OK in conjunction with an organized area of thunderstorms migrating southeast through the region overnight. A bit further east into the Ozarks and eastern OK, a slow-moving cold front will shift through the region overnight with increasing convergence likely to occur between the complex/surface wave and the front as it heads into central OK. Instability maximum over eastern OK into AR on the order of 2000-3000 J/kg MUCAPE will aid in the necessary component to initiate more thunderstorm activity as the convergence regime materializes with likely a long stretch of heavy convection orienting from south-central OK back into southwest TN by sunrise. PWAT anomalies between +1 to +2 deviations off the latest NAEFS indicate a deep moist convective environment situated over the area ahead of the front with the combination of both favorable instability and 2+ inch PWATs set to provide effective warm rain processes capable of producing efficient heavy rainfall that can spur flash flood capabilities. Recent 00z HREF outputs are pretty aggressive with scattered areas of 2-3" of precipitation anticipated in the means across the ArkLaTex through central and southern AR into southwest TN and western MS. A good portion of this rainfall is likely to occur in the first half of the period as the expected QLCS development will encroach the area and provide significant rainfall over the above locations. The disturbance over OK is forecast to utilize the positioning of the front as a focal point for the wave as model guidance agrees on the surface wave riding eastward along the front as it begins to enter eastern OK, eventually making headway into the Lower Tennessee Valley and MS Delta. Indications are for a small corridor between northeast AR through southwest TN into the Mississippi Delta to see a training episode materialize in the morning with neighborhood probs for >3" highlighting that zone with 50-70% probabilities. Some of the deterministic is very bullish within this general area noting totals of 4-6" in an isolated coverage with 2-4" more representative of an areal average. This expands back into central and southern AR as the complex of organized thunderstorms will likely slide south through Little Rock and surrounding areas creating a busy morning for flash flood prospects. This will likely expand into OK as the front location will be the main factor on where heavy precipitation would occur. In this case, the entire area is within a broad SLGT risk with a higher-end SLGT forecast across the above area between eastern OK into southwest TN and northern MS. As the complex of thunderstorms begins to peter off in the afternoon, another round of convection will spawn in-of the ArkLaTex into the eastern Red River area between OK/TX the following evening as a nocturnal LLJ develops after 23z with increasing convergence along the back edge of the front located in the area. There's still some discrepancy on the exact placement of the front, however there's enough consensus on the second round of convection to warrant attention to the prospects of flash flood potential into that area of the ArkLaTex to perhaps as far west as the I-35 corridor in southern OK towards the DFW metro. As of now, thunderstorm development is likely with training potential increasingly favored in the area as storm development will likely anchor to the front as mid-level flow aligns parallel to the boundary with surface convergence maximized along the front. A slow-moving axis of thunderstorms is a more textbook way for greater flash flood potential, especially in speaking in spatial terms as there will likely be a large area encompassed within this second round of convective development over that referenced corridor. If this were to make headway into I-20, this would likely result in numerous flash floods given the environment in place with rates between 2-3"/hr at peak intensity likely to occur. As of now, placed the region within the broad high-end SLGT forecast, but will have to monitor the CAMs closely over the course of the D1 to see if a targeted upgrade may be necessary for this band of heavy rainfall potential. ....Central Appalachians to Northeast U.S... Surface low currently analyzed over the western Ohio Valley will gradually lift to the east-northeast with an expectation for the low center to exit off the northern Mid Atlantic coast, dragging a cold front through the Mid Atlantic and Ohio Valley and lifting a warm front ahead of the disturbance. The current indications are for convection to spawn over the eastern Ohio Valley by the early- afternoon as mid-level ascent and increased surface forcing aided by the cold front and area of low pressure will trigger convective initiation just upstream of the terrain in WV and western PA. This area of thunderstorms will migrate eastward, entering a favorable environment within a modest warm sector as you move east of the Appalachian front. Shear profiles across the Mid Atlantic are anticipated to be greatest north of the Mason Dixon, however shear magnitudes are still capable for enabling stronger mid-level mesocyclones to materialize and hold as far south as I-66 leading to prospects for heavier thunderstorms to hold across the urban corridor extending from northern VA up through NYC and western LI. HREF probs for >1" are pretty high for both the neighborhood and EAS fields meaning there's a consensus for areas of heavy rainfall to impact much of the Mid Atlantic with the most pronounced signatures into the Central Appalachians and the urban centers, both are which are susceptible to flash flood concerns. Antecedent soil moisture is dry, so the initial burst of rainfall will be beneficial to those areas not tied completely by urban infrastructure, however, there's a sufficient signal in the QPF means to maintain the previous SLGT risk inherited for the region as 00z CAMs maintained their depictions on a multi-round cycle of convection moving into the area with pockets of 2-3+" forecast across portions of the aforementioned areas. ....New England... Shortwave ahead of an approaching disturbance from the southwest will enter the region by late-morning into the afternoon with scattered to widespread showers with isolated pockets of thunder for the initial wave of precipitation during the period. A second wave of precipitation with higher convective potential will enter the area by the second half of the afternoon and evening with heavier rain threat poised to impact portions of central and northern New England with southern New England likely to see more of a benefit from the approaching surface low and associated warm/cold front evolution. Areas of northern and central New England are forecast to see the most rainfall of the setup, however the instability gradient will likely be better situated south of the region as boundary layer theta_E's are likely just below the necessary magnitude to embrace a heavier convective footprint. Still, local pockets of >1"/hr are plausible over New England, north of I-90 with a greater potential for 1-2"/hr closer to the interstate and points southeast. Antecedent soils in southern New England are very dry currently with the watershed running well- below normal which should curb a more pronounced flash flood prospect with generally isolated flash flood signals in more urbanized settings. With that, the MRGL risk inherited remains forecast for much of New England. ....Front Range and Central High Plains... Defined theta_E ridge positioned over the Central to Southern High Plains will lead to an axis of relatively unstable boundary layer conditions conducive for convective generation in tandem with passing shortwaves ejecting out of the Rockies. HREF blended mean QPF depicts a smattering of elevated precipitation outputs with 1-2" totals littered across the High Plains from eastern WY and western SD down through KS/CO and portions of southwest TX. Some of the areas noted for potential impact have been hit recently, so local FFG's are lower than normal for the time frame meaning a bit easier chance at exceeding the FFG markers in place and creating isolated flash flood concerns. Threat is lower end compared to what has transpired in the past few days, but it is the beginning of what will be an active northwesterly flow pattern that could spawn multiple MCS's across the High Plains. The previous MRGL risk inherited was maintained with an extension north into the Badlands of SD and neighboring eastern WY. ....Northern Plains... Potent shortwave dropping out of western Canada will aid in regional amplification of the flow out ahead of the trough with increased ascent located within the diffluent area downstream into eastern MT and northern ND. Sufficient mid-level forcing and instability over the region will allow for scattered convection to materialize during peak diurnal destabilization, generating pockets of heavy rainfall during the late-morning into the early evening before instability wanes. Modest probs (30-50%) for >2" of rain exist within the latest 00z HREF neighborhood fields across the area of northeastern MT into the northern tier of ND with low end probabilities for >3" as some CAMs spawn supercells in-of the Northern High Plains. Previous MRGL was carried over into this update, but did expand the risk into MT to account for the heavy QPF distribution in the CAMs bleeding over into the area with similar FFG markers situated in the area. Kleebauer $$ --- SBBSecho 3.28-Linux * Origin: Capitol City Online (618:250/10) .