ACUS01 KWNS 271257
SWODY1
SPC AC 271256

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0756 AM CDT Thu Jun 27 2024

Valid 271300Z - 281200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PORTIONS
OF THE CENTRAL AND NORTHERN HIGH PLAINS...

...SUMMARY...
The greatest severe-thunderstorm threat is over parts of the
northern/central High Plains this afternoon and evening. Gusts near
80 mph, damaging hail greater than 2.5 inches and a few tornadoes
are possible.

...Synopsis...
The mid/upper-level pattern will feature a progressive northern
stream, with troughs initially located over the inland Pacific
Northwest and over the Northeast. A series of phased vorticity
maxima extend from the Northeastern trough southwestward across the central/southern Appalachians to parts of MS/LA in recent moisture-
channel imagery. This feature should shift eastward to the eastern
Carolinas, southern GA and coastal MS by 00Z, becoming stationary
tonight across GA and the Gulf Coast east of LA, but moving offshore
from NC and SC.

The Northwestern trough will move eastward astride the international
border, with a closed 500-mb low forming and moving over extreme
southern parts of AB/SK tonight. By 12Z tomorrow, the trough should
extend from the southern SK low across central MT to southern ID.
Though the flow will remain nearly zonal well to its southeast over
the central High Plains, height falls are expected to extend as far
south as parts of the OK/TX Panhandles.

At the surface, the 11Z analysis showed a cold front across western
MT, central ID and northern CA, and a warm front from near HVR
across east-central MT, western/southern SD and northern NE.
Cyclogenesis will continue over MT through the day, shifting
eastward. By 00Z, the main low should reach the MT/ND border area
roughly between GDV-DIK, with cold front southwestward across
northwestern WY, southeastern ID and central NV. A dryline should
sharpen over the High Plains through the day, and by 00Z, extend
from near the MT/SD line across eastern CO to the western TX
Panhandle. The warm front should extend from the low southeastward
over the western Dakotas and central parts of NE/KS, becoming
diffuse and fragmented farther southeast. A lingering segment of a
separate front should be quasistationary and act as a surface trough/convergence zone across southern parts of AL/GA and the
central/eastern Carolinas.

...Great Plains...
Scattered thunderstorms are expected to develop in multiple episodes
over the northern/central Plains, probably leading off with
cold-frontal initiation from late morning through afternoon across
parts of western/central MT, where large-scale lift will be
strongest with the approach of the northwestern trough aloft. This
activity -- which may arise from the same vertical-motion field now
associated with convection in higher elevations of southwestern MT
-- should move generally eastward over the Plains, with upscale
organization possible. Severe gusts (some exceeding 70 mph) and
sporadic hail (some exceeding 2 inches diameter) will be the main
concerns. Subsequent development is expected closer to the surface
low, dryline and warm front over the northeastern MT/western Dakotas
area this afternoon/evening, also posing a threat for large to very
large hail and severe gusts. Tornado potential will be relatively
maximized with any discrete or embedded supercell(s) moving into the
plume of greatest low-level moisture and backing of surface flow
near the low and warm front (east of the dryline).

Deep-layer shear should strengthen throughout the day ahead of the
cold front, across the central/northern High Plains, while heating
gradually weakens MLCINH, and regional lift increases in relation to
low-level cyclogenesis. This will combine with a plume of favorable
low-level moisture (dewpoints generally in the 60s F by mid/late
afternoon) to support a corridor of MLCAPE in the 1000-2000 J/kg
range near and just west of the warm front. Effective-shear
magnitudes in the 40-55-kt range (strongest on the northern areas)
will support supercell potential, with longer hodographs west of the
warm front favoring destructive-hail production. One or more storm
clusters may evolve and grow upscale into MCS activity this evening,
further reinforcing the wind potential, with support from moisture
transport and enhanced storm-relative flow of a 40-50-kt LLJ.

Convection should be more isolated southward down the dryline and
lee trough into the western KS/OK Panhandle region, with deep shear
also weakening southward. However, intense surface heating and
somewhat high LCL will foster boundary-layer conditions suitable for
at least isolated severe gusts and hail. Some clustering and
mesobeta-scale cold-pool aggregation may occur to maximize
severe-wind potential for a few hours sub-regionally.

...UT and western parts of CO/WY...
Widely scattered to scattered thunderstorms are expected to form
atop a seasonally moist, well-heated and weakly capped boundary
layer this afternoon, offering locally severe gusts, isolated large
hail, and a marginal/conditional tornado threat. This activity
should develop as height falls spread over the area related to the
Northwestern trough, along/ahead of the surface cold front. Diurnal
heating will reduce MLCINH substantially, especially in the presence
of moisture characterized by 50s F surface dewpoints remaining in
many basins/valleys through the heating mixing cycle, while
orographic forcing also aids lift locally. That moisture, combined
with steep low/middle-level lapse rates, will support MLCAPE of
500-1500 J/kg, atop favorable subcloud thermal profiles to support
downdraft accelerations to severe levels. Although environmental
flow should be nearly unidirectional through most of the
troposphere, terrain-forced backing will enhanced deep shear
locally, with effective-shear magnitudes generally in the 25-40-kt
range. Mostly multicells and a few supercells are possible.

...Southeast...
Widely scattered to scattered thunderstorms should develop this
afternoon into early evening, from the NC Coastal Plain
southwestward to southern portions of AL/GA. Damaging to isolated
severe gusts will be the main concern. Activity should develop most
densely near the remnant front/convergence zone as the mid/upper
trough closely approaches, as well as along sea-breeze, outflow and differential-heating boundaries south/southeast of the front.
Despite weak midlevel lapse rates, a combination of strong diurnal
heating and rich low-level moisture (with surface dewpoints commonly
in the upper 60s to mid 70s F) should yield MLCAPE in the 1500-2000
J/kg range. Weak low/middle-level flow will limit vertical shear substantially, and convection should be multicellular in nature with
some clustering and local cold-pool development possible. Though
moist-, subcloud layers nonetheless should be well-mixed, supporting strong/locally severe downdrafts.

..Edwards/Bunting.. 06/27/2024

$$
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ACUS01 KWNS 021253
SWODY1
SPC AC 021251

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0751 AM CDT Tue Jul 02 2024

Valid 021300Z - 031200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
SOUTHERN IOWA...NORTHERN MISSOURI...NORTHEASTERN KANSAS...AND
EXTREME SOUTHEASTERN NEBRASKA...

...SUMMARY...
Damaging thunderstorm winds, a few tornadoes, and large hail are
most likely this afternoon and early evening over southern Iowa,
northern Missouri, and northeastern Kansas.

...Synopsis...
Broadly cyclonic flow in mid/upper levels will persist from the
Pacific Northwest across the central/northern Rockies to the Upper
Great Lakes. Within that, a series of shortwave troughs were
apparent, the most prominent over the CONUS being located initially
across WY and northeastern UT. This perturbation should move
eastward to eastern SD and central NE by 00Z, cross the upper
Mississippi Valley overnight, and reach parts of WI and the Upper
Peninsula of MI by the end of the period. As that occurs, a
persistent subtropical high over the Arklatex region will shift
eastward over the Delta region, but with attached ridging expanding
back across central and west TX to near ELP. Another attached ridge
will shift eastward across the Ohio Valley and Lower Great Lakes.

At the surface, 11Z analysis showed a surface low near HLC, with
cold front southwestward across extreme southeastern CO and northeastern/north-central NM. A warm front arched from the low
across southeastern NE, then southward near the KS/MO and AR/OK
borders. The warm front should move northeastward to the mid
Mississippi Valley today while the low moves northeastward and
weakens. Meanwhile, by 00Z, the cold front should reach western IA, northeastern through south-central KS, and the northern TX
Panhandle. becoming a warm front into a deepening low over
southeastern CO. By 12Z, the cold front should reach northern IL, central/southwestern MO, north-central OK, then into the low, which
will have sagged into the northern TX Panhandle.

...IA/MO/northeastern KS and vicinity...
A swath of decaying convection and associated cloud shield are
ongoing from Lower MI to IA and parts of southeastern NE and
northwestern MO. This plume of clouds/precip should continue to
shift east-northeastward and erode through the day, but leave behind
an outflow/differential-heating boundary that, southwest of the
synoptic warm front, should act as the primary convective influence
ahead of the cold front. Convergence near these boundaries, and
strong heating in the richly moist warm sector between, will support
scattered afternoon thunderstorms. This will include the potential
for a few supercells with tornado and large-hail threats, whether
relatively discrete early in the convective cycle, or embedded in
subsequent quasi-linear evolution. That upscale convective
organization also will maximize severe-wind potential from late
afternoon into early evening, before activity encounters a
more-stable, nocturnally cooling airmass farther east near the
warm-frontal thermal gradient.

In the preconvective warm sector, 70s F surface dewpoints should be
common, as a Gulf-origin airmass blends with areas of
evapotranspirative moisture contribution. Though mid/upper-level
lapse rates will be modest, strong low-level destabilization will
combine with a deep troposphere to contribute to MLCAPE in the
2000-3000 J/kg range. Effective-shear magnitudes will have a large
range -- roughly 35-55 kt based strongly on boundary effects upon
near-surface winds. Boundary-layer shear/hodographs will be
greatest near the warm front and along any mesoscale boundaries
between the fronts, locally maximizing supercell organization in low
levels.

...Central/southern High Plains...
Widely scattered to scattered thunderstorms are forecast to develop
this afternoon over western portions of this area -- initially over
relatively high elevations of southeast WY, east-central/
southeastern CO and northeastern NM, where diurnal heating will
preferentially erode MLCINH. This activity should move generally
eastward onto the adjoining High Plains, offering sporadic severe
gusts and hail. The greatest concentration of convection (and
associated severe potential) still appears most probable over
southeastern CO, growing upscale as a complex and moving into parts
of southwestern KS this evening.

Vertical shear will be most favorable for supercells north of the
front, where a substantial easterly component of boundary-layer flow
will contribute to enhanced low-level shear, greater storm-relative
low-level winds, upslope lift, and moist advection (to offset
mixing-related moisture loss somewhat). The northern lobe of the
(marginal) outlook area will be under the greatest mid/upper-level
flow and strongest deep shear, but also will have weaker low-level moisture/theta-e and less buoyancy than farther south, with similar mid/upper-level lapse rates under a monsoonal plume as closer to the subtropical ridge. In the Arkansas River Valley region, activity
moving into 50s to low 60s F surface dewpoints, with a strongly
heated boundary layer, will encounter peak diurnal MLCAPE of
500-1500 J/kg across southeastern CO, and 1000-2000 J/kg into
southwestern KS, amidst 45-55 kt effective-shear magnitudes, and
long/nearly straight low-level hodographs favoring large hail with
any discrete supercells. However, a well-mixed subcloud layer
should support severe outflow and aggregation of outflows, leading
to upscale clustering for a few hours before activity encounters too
much CINH to remain severe over southern/central KS. Farther south,
along and south of the front, deep-layer flow and shear will be
weaker, as will buoyancy (due to drier, deeper mixed layers), but
convection still may pose a threat for isolated severe downbursts.

..Edwards/Kerr.. 07/02/2024

$$
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