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Archives for the SPC Convective Outlook are updated daily (approximately) with a live map at the beginning of each article. Follow the link at the end of the article to check for current updates on the NOAA/NWS Storm Prediction Center website. Also, see Archives for Chicago's hourly weather data on CARDINAL NEWS Magazine.


Sunday, June 25, 2023

SPC Jun 25, 2023 1300 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0753 AM CDT Sun Jun 25 2023 Valid 251300Z - 261200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE GREAT LAKES/OHIO VALLEY REGION SOUTHWESTWARD ACROSS THE MID-SOUTH REGION INTO MUCH OF ARKANSAS... ...SUMMARY... Threats for at least a few tornadoes, along with scattered severe gusts and large/damaging hail, will be possible over parts of the Great Lakes/Ohio Valley region. The hail/gust threat will extend southwestward across the Mid-South region into much of Arkansas. ...Synopsis... 

In mid/upper levels, the CONUS portion of the large-scale pattern will continue to feature mean troughing in the Eastern States and near the West Coast, with ridging over the Rockies and adjoining Great Plains. This ridging will shift slowly eastward through the period as: 

1. A positively tilted synoptic-scale trough, initially located from the Canadian Rockies across the interior Pacific Northwest to offshore from CA -- moves slowly eastward. A couple weak vorticity maxima in the foregoing cyclonic flow, now over parts of OR and northeastern CA -- will pivot northeastward over ID toward the northern Rockies. 

2. A substantial cyclone -- evident in moisture-channel imagery over MN and parts of adjoining states -- intensifies while moving east-southeastward to Lower MI by 12Z tomorrow, and toward the mean-trough position. 

The combination of expansion and deepening of the associated 500-mb low will lead to height falls spreading across most of the Appalachians, Ohio/Tennessee Valleys, and even Mid-South region. At the surface, 11Z analysis showed an occluded low near MSP, with cold front across eastern IA, southeastern KS, northern/western OK, the TX South Plains, and east-central NM. A warm front was drawn over northwestern to southern IL, western portions of KY/TN, and MS, and will shift northeastward across more of the Ohio and Tennessee Valley regions throughout the day. By 00Z, the low should reach the MKE/GRB corridor, while the cold front should reach central/ southwestern IN, southern IL, northern AR, south-central OK, the Permian Basin region of west TX, and east-central NM. By 12Z, the (by then) deeply occluded low should be located near MBS, with the cold front extending from the upper Ohio Valley region across middle TN to central AR. The western segment will stall and perhaps begin moving northward as a warm front over parts of north and west TX to east-central/northeastern NM. ...Ohio Valley and vicinity... 

Scattered to numerous thunderstorms are forecast to develop in one or two organized arc or lines of lift related to: 

1. The front impinging on a destabilizing boundary layer up and down western parts of the outlook area, and perhaps 

2. A prefrontal/lake-breeze convergence zone over western Lower MI. Damaging to severe gusts and large hail are likely as activity organizes upscale following an early, discrete to semi-discrete stage.

Supercellular tornado and large-hail threats will exist along nearly the entire corridor. That said, potential for strong tornado(es) and significant/damaging-hail should be relatively maximized across the eastern IN/western OH and perhaps southern Lower MI sector, where the supporting CAPE/shear parameter space will overlap best. In that swath, large low-level hodographs will develop ahead of the main convective band, leading to 150-300 J/kg effective SRH and 40-50-kt effective-shear magnitudes. 
That will be collocated with a northward-directed corridor of afternoon destabilization and increasing buoyancy related to: 

1. Warm/moist advection behind the morning activity, 

2. Steepening low-level lapse rates from diabatic heating, and 

3. Increasing midlevel lapse rates from a combination of the northeastward-advected EML plume and large-scale ascent preceding the progressive cyclone. This should lead to a plume of MLCAPE ranging from around 3000-4000 J/kg over the lower Ohio Valley to 1500-2000 J/kg in parts of central/northern Lower MI, to where greater severe probabilities have been expanded northward. Severe potential overall should diminish with time and eastward extent tonight as activity gradually moves into lower theta-e.

Mid-South to southeastern OK... Scattered thunderstorms are expected to develop along/ahead of the surface cold front this afternoon over the Ozarks, with a least isolated to widely scattered activity backbuilding westward across western AR into stronger EML-related MLCINH and somewhat weaker/ more-mixed moisture profiles over southeastern OK. Severe gusts are possible, along with large hail (some significant/2+ inches in diameter) with any supercells. As activity aggregates and evolves upscale across parts of AR and the Mid-south region this evening, an organized MCS may develop, moving eastward to southeastward mainly from forward/cold-pool-driven propagation. This will increase the damaging-wind threat in both intensity and density this evening, with the convection weakening overnight across parts of MS/AL. Steep low-level lapse rates and favorable moisture (dewpoints 60s to low 70s F) in the warm sector will underlie large midlevel lapse rates in the EML, resulting in peak afternoon MLCAPE commonly in the 2500-3500 J/kg, locally near 4000 J/kg. Flow near the surface will be somewhat veered/southwesterly and modest in strength, limiting hodograph size. However, this area will reside under the southern rim of stronger mid/upper flow related to the height falls and tightening gradient aloft, leading to effective-shear magnitudes in the 30-40 kt range, supporting mixed multicell and supercell characteristics prior to upscale organization. 

Northern Rockies... Widely scattered to scattered, high-based thunderstorms are possible this afternoon, mainly developing over the mountains and moving northeastward across adjoining parts of central MT before weakening this evening. Isolated severe gusts will be the main concern. The approaching voracity maxima, and related increase in DCVA/large- scale lift, will coincide with diurnal heating of the higher terrain, yielding steep low/middle-level lapse rates. Though moisture will be limited, enough should persist to support MLCAPE of 300-700 J/kg over the region -- slightly larger east of the mountains where residual moisture will be greater. Gust potential will be supported by the deep, well-mixed boundary layer. ...Central High Plains... A few strong-severe thunderstorms may develop this afternoon as higher terrain and near the Laramie Range is heated amidst marginal low-level moisture, preferentially eroding MLCINH. Isolated severe gusts and/or hail are possible before convection weakens over the NE Panhandle. Near-surface flow will be weak, but with a substantial easterly component, contributing upslope lift to that needed for initiation. Forecast soundings show strong veering with height, as well as favorably vigorous mid/upper-level flow (50-80 kt through the upper 1/2-1/3 of the CAPE profile), contributing to long, nearly straight hodographs and around 35-45 kt effective-shear magnitudes. MLCAPE to around 500 J/kg should overlie a well-mixed, deep subcloud layer, until nocturnal cooling and (with eastward extent increasing MLCIN from both the EML base and decreasing low-level theta-e. ..Edwards/Mosier.. 06/25/2023 Read more CHECK UPDATE ZOOM GRAPHIC
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