Severe Storm Outlook Narrative (AC)
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Issued by NWS
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115 ACUS01 KWNS 031255 SWODY1 SPC AC 031253 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0753 AM CDT Wed Jul 03 2024 Valid 031300Z - 041200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF THE CENTRAL/NORTHERN HIGH PLAINS... ...SUMMARY... A threat for all severe hazards is possible this afternoon into evening over portions of the central/northern High Plains. Damaging to severe gusts may occur near a separate front, mainly from the Ozarks to Ohio. ...Synopsis... In mid/upper levels, broadly cyclonic flow will continue over much of the northern CONUS from the Pacific Northwest to the Upper Great Lakes, with numerous embedded vorticity maxima and shortwaves of varying amplitudes. Of those, the most important for this outlook will be a shortwave trough now apparent in moisture-channel imagery over northern Rockies. This feature should dig southeastward to southwestern ND, southeastern MT, northwestern WY and southeastern ID by 00Z. By the end of the period (12Z), the trough should extend diagonal across SD, then to southeastern WY and northwestern CO. Subtropical ridging will persist over the Gulf Coast States and portions of southern CA/AZ, with a height weakness in between, over northwestern MX and NM. At the surface, 11Z analysis showed a cold front across Lake Michigan, northwestern IL, central MO, and southeastern KS, becoming quasistationary across northwestern OK and the TX Panhandle to northeastern NM. By 00Z, the front should move to Lake Huron, northwestern OH, southern IN, southern MO, while drifting southward again to northeastern and west-central OK and the southern Panhandle/northern South Plains region of TX. By 12Z, the front should extend over western parts of NY/PA, eastern/southern KY, and north-central AR, becoming a warm front over north-central/ northwestern OK. Cyclogenesis is forecast late this afternoon through this evening along a lee trough over east-central CO, with a cold front developing from the NE Sandhills into northeastern/ central CO by 06Z. By 12Z, the low should migrate to central NE, with warm front over southern IA, and cold front southwestward across western KS to northeastern NM. ...Central/northern High Plains and vicinity... Isolated to scattered thunderstorms are expected to develop this afternoon -- initially over higher terrain near the Palmer and Cheyenne Ridges and near lee trough, increasing in coverage while moving eastward to southeastward over the High Plains. Large hail (some 2+ inches in diameter) and damaging wind (some gusts over 70 mph) are expected over the north-central High Plains, and a couple tornadoes also are possible, mainly in and near western NE where some overlap of favorable moisture and low-level shear is expected. As the mid/upper trough approaches, expect a favorable strengthening of large-scale lift, winds aloft, deep shear, and mass response leading to northward moisture advection/transport, to the north of the southern frontal zone. Optimal moisture return may be precluded by effects of ongoing clouds/precip to reinforce the baroclinic zone over the southern Plains; however, boundary-layer moisture should be sufficient to support development as heating of higher terrain preferentially erodes MLCINH. Steep low/middle-level lapse rates will contribute to development of 1000-2500 J/kg MLCAPE in a corridor from eastern CO and northwestern KS to southwestern SD, decreasing from there westward toward the Bighorns and southward into less-unstable conditions of the Panhandles and northeastern NM. Veering of winds with height east of the lee trough will contribute to favorable vertical shear for supercells and organized/upscale- coalescing multicells, the latter being most commonly progged over parts of eastern CO and northwestern KS (where wind probabilities are relatively maximized). Low-level hodographs should be relatively maximized in size over western NE, and rather elongated over a broader swath of the central High Plains, supporting large to significant hail production. ...Lower Ohio Valley region... Widely scattered to scattered, multicell thunderstorms are expected to develop this afternoon and focus mainly near the front and prefrontal outflow/differential-heating boundaries, from northern OK to the Lower Great Lakes. The greatest concentration of convection is still expected over the area from the Ozarks to central OH from late afternoon into early evening. Forecast soundings suggest that diurnal heating and rich boundary-layer moisture, represented by upper 60s to lower 70s surface dewpoints, will offset modest mid/upper-level lapse rates enough to support peak/preconvective MLCAPE in the 2500-3500 J/kg range over the Ozarks, to 1000-2000 J/kg in OH. Conversely, low-level and deep-layer shear will be fairly weak overall, and decreasing with southwestward extent. Damaging to severe gusts will be the main concern. A few short- lived convective clusters are possible, with locally maximized potential for severe gusts. ..Edwards/Kerr.. 07/03/2024 $$