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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http://dlvr.it/SrCKbv
