Subj : DAY1SVR: Day 1 Convective To : All From : Mike Powell Date : Fri Jun 30 2023 15:08:00 ACUS01 KWNS 301946 SWODY1 SPC AC 301944 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0244 PM CDT Fri Jun 30 2023 Valid 302000Z - 011200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF THE SOUTHERN AND CENTRAL HIGH PLAINS EASTWARD INTO THE TENNESSEE VALLEY... ....SUMMARY... Scattered damaging winds and large hail, along with a couple tornadoes will be possible into this evening from the Mid-Mississippi to Tennessee Valleys and across the central to southern High Plains. ....20Z Update... Much of the previous forecast remains on track, with severe hail and wind producing storms most likely to develop around the periphery of the upper ridge (centered over the southern Plains) this afternoon into tonight. One main change to this outlook was to expand tornado probabilities in area across western Kansas. At least a couple of landspout tornadoes have already occurred over central CO with storms aided by the ascent of a passing mid-level impulse. Additional storm development into KS is likely along a baroclinic zone, where a few additional tornadoes (likely landspouts in nature) may occur later this afternoon. However, any tornado potential that becomes realized should be brief since upscale growth into one or more MCSs should follow only a few hours after convective initiation. The second change made to the outlook was to expand the 5 and 15 percent wind probabilities ahead of a persistent damaging-gust producing MCS along the AL/GA border, where additional damaging gusts are possible through the afternoon. Please see MCD 1356 for more details. ...Squitieri.. 06/30/2023 ..PREV DISCUSSION... /ISSUED 1130 AM CDT Fri Jun 30 2023/ ....Mid-MS to the TN Valley... The composite outflow from yesterday's MCS is still fairly well defined from near I-70 in MO southeastward into western KY, with a relatively cooler air mass farther northeast. Elevated storm clusters are ongoing within two weakening warm theta-e advection regimes, one across west-central IL and the other near the GA/TN/AL border area. Neither regime is expected to greatly intensify as activity loosely parallels the more pronounced CAPE gradients to their south and west, respectively. Later this afternoon into early evening, it appears the primary focus for at least isolated thunderstorm development will be along the composite outflow boundary, but with uncertainty on exactly where. Vertical shear will be on the lower margins for sustained supercells, though continuing steep mid-level lapse rates and large to extreme buoyancy will favor a cluster or two capable of producing locally significant damaging wind and hail. There is uncertainty regarding whether or not broader upscale growth will evolve and persist into tonight given relatively weak low-level flow, and how far east/southeast any such cluster could move with an attendant threat for damaging winds. ....Central/southern High Plains... A lower-amplitude shortwave trough will move eastward from the central Rockies to the central Great Plains through tonight. 50s surface dew points across eastern CO within a post-frontal environment, steep mid-level lapse rates, and strong surface heating in cloud breaks will result in moderate buoyancy with MLCAPE of 1000-2000 J/kg. Thunderstorm coverage will increase this afternoon just east of the Front Range and over the Raton Mesa, and storms will subsequently spread east across the High Plains. Effective bulk shear of 40-45 kts with relatively straight hodographs will initially support a few supercells capable of producing significant severe hail and perhaps a couple tornadoes, especially over east-central CO. Upscale growth into clusters/line segments appears likely by late afternoon. The potential for occasional severe outflow gusts/isolated large hail will persist through this evening as storms spread eastward into KS/southern NE. Farther south, a weak surface trough/dryline will focus scattered thunderstorm development this afternoon across the southern High Plains. Deep-layer vertical shear will weaken gradually with southward extent, but be sufficient to support a mix of multicell clusters and transient supercells capable of producing isolated strong-severe outflow gusts and large hail later this afternoon into the evening. $$ --- SBBSecho 3.14-Linux * Origin: Ilink: CCO - capitolcityonline.net (454:1/105) .