SPC AC 140537
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1237 AM CDT Tue Jul 14 2020
Valid 141200Z - 151200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE
SOUTH-CENTRAL HIGH PLAINS TO THE UPPER MIDWEST...
Strong to severe storms are expected Tuesday from the south-central
High Plains to the Upper Midwest.
Weak height falls will spread across the upper MS Valley region
during the day ahead of a short-wave trough that should extend from
the MB/ON border into the eastern Dakotas by 15/00z. Models are in
general agreement that a surface front should precede the short
wave, advancing into northwestern WI - southeast MN - western IA by
early afternoon. This boundary should serve as the focus for strong
to severe thunderstorm development during the afternoon/evening
hours. Prior to this development, substantial convection may be
ongoing across portions of eastern SD into southern MN. This
activity will likely be the remnants of ongoing convection currently
observed over western SD. Extensive cloud debris and decaying precip
shield should limit boundary layer heating across much of this
region. Even so, a narrow corridor of somewhat steeper low-level
lapse rates should evolve within the near-frontal warm sector from
southwest IA into west-central WI. This is expected to aid buoyancy
for potentially more robust convection. With a 60kt 500mb speed max
forecast to approach western WI by late afternoon, wind profiles
should support organized rotating updrafts and isolated supercells
are expected. While a few tornadoes can not be ruled out, the
primary severe risks will be wind/hail.
...South-central High Plains...
Surface pressures will rise across the northern/central High Plains
early in the period in the wake of ejecting short wave. Extensive
precipitation within the post-frontal environment across SD should
enhance the frontal surge which should advance into central KS,
arcing into southeast CO by mid afternoon. Intense surface heating
south of the wind shift will result in surface temperatures soaring
well above 100F across the OK/TX Panhandle region. Convective
temperatures will be easily breached in these areas. Frontal/upslope
convergence is expected to aid thunderstorm development across
southeast CO into the northern TX Panhandle. CAMs are reasonably
consistent in this scenario and one or more thunderstorm clusters
should spread east-southeast into the evening hours. There is some
concern that severe wind probs may need to be increased across this
region to account for high-based convection maturing downstream into
an environment that will be quite moist/unstable. This will be
considered in future updates.
...Southern New England...
Seasonally cool upper trough will shift east across New England
during the day. Latest guidance suggests low-level lapse rates will
steepen quickly beneath this trough from CT into southern VT/NH.
Forecast soundings suggest convection will develop early then drift
southeast within a weak-flow regime. While marginally severe hail
could be noted, the primary risk with this diurnally driven activity
will be locally gusty winds.
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