Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Jun 22 2023 12:41:38 ACUS01 KWNS 221241 SWODY1 SPC AC 221240 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0740 AM CDT Thu Jun 22 2023 Valid 221300Z - 231200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL AND SOUTHERN HIGH PLAINS... ....SUMMARY... Widely scattered severe thunderstorms are forecast mainly this afternoon into the evening across parts of the central and southern High Plains, with a threat of large hail (possibly in excess of 2 inches in diameter), severe wind gusts, and a tornado or two. ....Synopsis... Although mean mid/upper-level troughing over the eastern and western CONUS will be maintained, some deamplification is likely through the period in response to these processes with the two most prominent attached cyclones: 1. A broad circulation initially apparent in moisture-channel imagery off the coast of north-central CA, forecast to pivot inland and reach NV as a strong but deamplifying shortwave trough by 12Z tomorrow. Ahead of this feature, difluent southwest flow will remain over the central Rockies and adjoining High Plains. The eastern segment of a weak/preceding shortwave trough now over central/northern AZ should reach southeastern WY and eastern CO around 00Z. 2. An even broader vortex -- orbited by several vorticity lobes of varying strength/size -- is centered initially over the BNA/HSV area. Associated cyclonic flow extends from eastern OK to the coastal Carolinas. The low should move slowly north-northeastward over middle TN and central KY, reaching southwestern OH by the end of the period, while heights rise slightly over most of the Southeast in response. However, broadly cyclonic flow will be maintained over the region. At the surface, the 11Z chart showed a weak low over southeastern AL, with warm front northeastward across the coastal plain of the Carolinas. As the low moves/redevelops northeastward along the boundary through 00Z, the warm front should reach the Piedmont southwest of RIC, and the southern Delmarva Peninsula. The western part of this boundary is more diffuse today, and modulated/displaced by prior MCS activity over the southern Plains, but was drawn roughly from central LA across northwest TX to a low near ROW. A dryline was drawn in the Front Range and southward to near LVS, then erratically south-southeastward into the Big Bend region. This boundary should move little through the day, with a relatively moist boundary layer staying banked up against the eastern foothills from LVS up through CO. A wavy, mostly cold frontal zone was drawn from a low over eastern ND across central SD, and the NE Panhandle, to another low near CYS. This boundary should move slowly eastward across northern MN and eastern SD today, while becoming diffuse and perhaps retreating northwestward over the southeastern WY region. ....Central/southern High Plains... An ongoing, slow-moving band of thunderstorms over the southern KS/CO border vicinity is moving through nocturnally minimized boundary-layer lapse rates and maximized MLCINH, but still is accessing enough low-level moisture to be maintained with strong/ isolated marginally severe gust potential and isolated large hail. Veering and speed reduction of foregoing 850-mb flow is apparent in the DDC VWP, though enough storm-relative flow may persist to maintain the complex for a few more hours toward northwestern OK, given a relative weakness in MLCINH apparent that way. This afternoon into evening, just ahead of the subtle/lead perturbation aloft, isolated to scattered thunderstorms should develop on the eastern rim of the elevated terrain between southeastern WY and northeastern NM. Activity should move generally northeastward over WY and northeastern CO, eastward elsewhere over CO, and eastward to southeastward over the northeastern NM/western TX Panhandle region -- loosely in keeping with the difluent streamlines of mean-wind vectors. A few supercells are possible, offering large to significant (2+ inch diameter) hail, locally severe gusts, and the threat for a couple tornadoes. A cluster or two may organize upscale from initial multicell and supercell aggregation over the corridor, offering a more-prolonged wind potential into tonight. Heating of higher elevations in western parts of the outlook area should lead to preferential erosion of MLCINH, and earliest convective initiation today. The downshear inflow layer will be characterized largely by convectively processed air from yesterday and this morning -- but still, sufficient low-level moisture and diurnal destabilization to support deep buoyancy and severe potential. 50s to 60s F surface dewpoints should be common on the adjoining High Plains, leading to MLCAPE around 1500-2000 J/kg. 30-40 kt 500-mb flow should be common over the I-25 corridor near and south of I-70 by late afternoon, increasing this evening. This, along with near-surface southeasterlies veering with height, should contribute to effective-shear magnitudes around 35-45 kt. ....West to south TX... Farther southeast across much of west to south TX, the convective picture is more muddled and almost randomized, amidst a broad area of subtle forcing, a multitude of residual boundaries, long/strong diurnal heating in most of the region, and interspersed pockets of both original/undisturbed Gulf boundary layer (with very rich moisture) and convectively perturbed air masses that are more-easily diurnally mixed/dried. These variabilities on mesobeta and smaller scales largely will drive convective development and at least some upscale clustering potential where corridors of highest inflow-layer buoyancy can be accessed. While conditional, highly localized risk exists for up to significant-severe hail and wind, the threat still appears too poorly focused for more than a broad-brushed, marginal unconditional area at this time. Mesoscale trends may elicit greater specificity in subsequent outlook updates. .....Southeast... Episodes of isolated to scattered thunderstorms are expected throughout the period, but peaking in the midday to evening time frame, offering the threat of damaging to isolated severe gusts and a tornado or two. Activity should move roughly eastward across the FL Peninsula, and northeastward to northward over the Atlantic Coast States part of the outlook, in keeping with the ambient/deep- tropospheric cyclonic-flow field. Marginal severe potential is expected to spread northward from the eastern Carolinas into the Hampton Roads and adjoining lower Chesapeake Bay/southern Delmarva region through the afternoon, in step with the motion of the warm front; the outlook has been expanded northward somewhat to accommodate this. An ongoing band of convection over the northeastern Gulf should shift onto the north-central peninsula through the remainder of the morning, with the boundary layer destabilizing both to its north and south (inflow region). Sea-breeze processes and subsequent smaller- scale outflow boundaries to its south over the peninsula also should contribute to convection, in an environment characterized by rich low-level moisture, with dewpoints commonly 70s F and 2500-3000 J/kg afternoon MLCAPE. Though winds will veer with height, speeds should be modest (generally 20 kt or less except slightly stronger in the 400-600-mb layer), keeping effective-shear magnitudes less than 35 kt. Farther north, weak low/middle-level lapse rates will keep buoyancy somewhat less over that portion of this outlook from GA to the Tidewater region, but with MLCAPE still potentially reaching 1000-2000 J/kg. At this distance from the northward-shifting mid/ upper low, around 30-35 kt midlevel flow will contribute to similar effective shear magnitudes, but with enough hodograph curvature (especially near the warm front) to support transient supercell character. ...Edwards/Jewell.. 06/22/2023 $$ = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .