Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Aug 01 2023 12:55:21 ACUS01 KWNS 011255 SWODY1 SPC AC 011253 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0753 AM CDT Tue Aug 01 2023 Valid 011300Z - 021200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE CENTRAL HIGH PLAINS AND MUCH OF NORTH DAKOTA TO NORTHWESTERN MINNESOTA... ....SUMMARY... Severe-thunderstorm gusts are most probable over parts of the central High Plains and much of North Dakota to northwestern Minnesota, along with at least isolated large hail. ....Synopsis... In mid/upper levels, the longstanding Southwestern anticyclone has shifted eastward over the southern Plains, with ridging extending west-southwestward over northwestern MX, northwestward over the central/northern High Plains, and east-southeastward over the mouth of the Mississippi River. These synoptic features should move little through the period, though the Plains ridge will be traversed by several low-amplitude shortwaves. One is apparent in moisture- channel imagery over eastern parts of CO/WY, with some vorticity enhancement from yesterday's Colorado convection. This feature should cross parts of NE and SD through 00Z, with the northeastern fringe becoming caught up in strong northwest flow across IA this evening. A weaker perturbation is evident over the northern MT border in the GGW area, and should move eastward across ND and southern parts of SK/MB today. Elsewhere, a synoptic-scale trough will move offshore from the Atlantic coast today, leaving behind strongly difluent northwesterly flow aloft across areas from the Carolinas to FL. At the surface, 11Z analysis showed a cold front offshore from the Carolinas to near SAV, becoming quasistationary across parts of AL, northern MS, AR, and KS. This boundary generally will move little through the day, and should serve as a northern delimiter to the hottest, most intensely mixed boundary-layer air mass in KS. Another cold front -- initially drawn over extreme northern MT -- is forecast to move east-southeastward through 00Z, reaching from northern ND through a weak low over northeastern MT, to north- central/northeastern WY. ....Northern Plains.. The large-scale DCVA/UVV plume preceding the shortwave trough, and sufficient available low-level moisture, are supporting widely scattered thunderstorms over portions of northeastern MT this morning. Isolated severe hail and gusts will be the main concerns in the near term. As this activity and/or the related ascent plume impinge on diurnally destabilizing boundary layer across ND through the day, additional thunderstorms are possible along and near the front, with potential for surface-based supercell(s) and multicell convection and some upscale clustering possible. Conditional but increasing potential exists for an initially separate area of thunderstorms forming over southeastern MB or nearby parts of ON to move southeastward into the MN Arrowhead this afternoon, with at least isolated/marginal wind and hail potential as well. Low-end unconditional probabilities have been extended into that area, and may need further upgrade if confidence increases based on 12Z guidance and subsequent mesoscale trends. The air mass southeast of the front over ND and northwestern MN will be favorably moist, with surface dewpoints in the 60s F and diurnal heating contributing to a plume of 2000-3000 J/kg MLCAPE, locally near 3500 J/kg. Weak low-level flow will limit hodographs and boundary-layer shear in the warm sector, though strong upper/ anvil-level winds should aid in storm organization. ....Central Plains... Widely scattered to scattered thunderstorms should develop readily this afternoon in the Front Range and adjoining foothills, as strong heating of higher terrain preferentially removes CINH. Heating to at or above convective temperature, in modified RAOBs and forecast soundings, also indicates isolated diurnal thunderstorm potential farther east across KS, though this threat is more conditional and prone to entrainment problems. The CO activity will stand the greatest chance of aggregating outflows and organizing into a cold-pool-driven complex and moving eastward to east-northeastward with ambient mid/upper flow, across the High Plains of eastern CO, northwestern KS and southwestern NE. Though isolated hail is possible, severe gusts will be the main threat, given the strongly heated, deeply mixed boundary layer and near dry-adiabatic lapse rates, fostering large DCAPE in its projected path. Despite the vertical mixing, sufficient low-level moisture will remain to support a corridor of 1500-2500 J/kg preconvective MLCAPE from northeastern CO eastward. Given the pattern, the thermodynamic profile and good agreement among convective progs for an MCS crossing the CO/KS/NE tri-state region into this evening, will boost wind probabilities into categorical "slight" range on this outlook cycle. Remnants of this activity may reach the lower Missouri Valley region late in the period, prior to 12Z tomorrow, and link with the warm-advection plume discussed below. ....Lower Missouri Valley... Scattered thunderstorms are ongoing in a plume oriented south- southeast/north-northwest across central MO, related to an elevated, persistent, low-level warm-advection/moisture transport plume and associated isentropic ascent to LFC. While strong northwest flow aloft will help to maintain supercell-favorable deep-layer wind profiles through the period, a decrease in LLJ-supported inflow later this morning should contribute to weakening of this convection, though isolated hail cannot be ruled out in the meantime. A similar regime should develop again tonight across parts of northern/central MO -- and perhaps nearby parts of northeastern KS, southeastern NE and southwestern IA -- again supporting early-stage hail potential and isolated strong-severe gusts while shifting southeastward. ....Atlantic Southeast... Although convection should be more numerous well offshore, ahead of the trough aloft, widely scattered to scattered thunderstorms are expected to develop today, amidst favorable low-level moisture/ destabilization, and a broad area of low-level convergence. Isolated damaging to marginally severe downdrafts are possible. Sea-breeze and outflow boundaries should help to focus initiation on the mesobeta and smaller scales. Surface dewpoints commonly in the upper 60s to low 70s F, diurnal heating, and weak CINH are expected, with MLCAPE ranging from around 2000-2500 J/kg in northern FL to 500-1000 J/kg over northern fringes of the outlook area. Weakness of both deep-layer flow and vertical shear should limit organization of convection to multicellular with pulse downdrafts. ...Edwards/Broyles.. 08/01/2023 $$ = = = 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) .