Severe Storm Outlook Narrative (AC)
Issued by NWS
Issued by NWS
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494 ACUS01 KWNS 091621 SWODY1 SPC AC 091620 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1120 AM CDT Sun Jun 09 2024 Valid 091630Z - 101200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF ARKANSAS...SOUTHWEST TENNESSEE...NORTHERN MISSISSIPPI...AND NORTHWEST ALABAMA... ...SUMMARY... A broad area of isolated severe hail and damaging wind potential exists today from parts of the Northwest into the High Plains, southern Plains, and lower Mississippi Valley/Southeast. A relatively greater severe threat may exist this afternoon and early evening across parts of Arkansas, southwest Tennessee, northern Mississippi, and northern/central Alabama. ...Lower Mississippi Valley/Southeast... A MCV is present over southern MO/northern AR late this morning. Outflow from this activity has spread south of the remnant ongoing convection into central AR and far western TN. A very moist low-level airmass across the lower MS Valley will continue to destabilize as strong diurnal heating occurs through the afternoon. Moderate to strong instability will likely develop across parts of AR, western TN, and northern MS, with MLCAPE values potentially reaching around 2000-3500 J/kg. Stronger mid-level flow will tend to remain displaced to the north of the warm sector today across the OH Valley, Mid-Atlantic, and Northeast in association with an upper trough/low centered over eastern Canada. Still, some enhancement to the mid-level flow due to the MCV, with gradually strengthening west-northwesterly winds at mid/upper levels, should support sufficient deep-layer shear for thunderstorm organization. Current expectations are for robust thunderstorms to develop along/near the outflow boundary in northern/central AR this afternoon, and subsequently spread east-southeastward over parts of southwest TN, northern MS, and perhaps northern/central AL through the evening. Multicell clusters will be capable of producing scattered damaging winds around 50-70 mph. Isolated hail may also occur with any marginal supercell structures that can be maintained. Convection should gradually weaken through the evening across the Deep South as it encounters a less unstable airmass and increasing MLCIN. A separate MCV is apparent over the western Carolinas based on recent visible satellite imagery. As this feature moves eastward, it may encourage isolated thunderstorms to develop through the day across parts of NC/SC. While this region will be on the southern periphery of stronger mid-level flow, sufficient deep-layer shear should be present to support modest updraft organization. Isolated hail and strong to damaging winds may occur with the more robust cores that can develop. But, generally weak instability should keep the overall severe threat fairly isolated. ...Southern/Central High Plains... With weak east-northeasterly low-level upslope flow persisting today, scattered to numerous thunderstorms should develop this afternoon over the higher terrain of the southern/central Rockies. Additional convective development is anticipated across parts of the southern Plains in the vicinity of a convectively reinforced front extending from parts of west TX into southern/eastern OK. Generally modest flow is forecast over much of these areas, which should limit thunderstorm organization to some extent. Still, a moist and moderately unstable airmass should be in place along/south of the front, and in a narrow corridor across the High Plains. Where low-level lapse rates can become steepened though daytime heating/mixing of the boundary layer, isolated severe wind gusts may occur with pulse convection and loosely organized multicell clusters. Hail may also occur with the strongest updrafts. Deep-layer shear appears too weak to support a more organized severe threat across these regions. ...Interior Northwest into the Northern High Plains... An upper-level ridge extends from the Southwest/Four Corners region into the Great Basin. Scattered thunderstorms are forecast to develop later today from parts of eastern OR to the northern High Plains on the periphery of this upper ridge. Modestly enhanced mid-level flow may support some convective organization. A deeply mixed boundary layer with inverted-v type soundings should foster an isolated threat for severe wind gusts with the strongest downdrafts. With somewhat greater low-level moisture and instability present, occasional hail may also occur over the northern High Plains as thunderstorms spread eastward this afternoon and evening. ..Gleason/Moore.. 06/09/2024 $$