Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
SPC AC 091634
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1134 AM CDT Sun Jul 09 2017
Valid 091630Z - 101200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER THE UPPER
MISSISSIPPI VALLEY REGION...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
ENHANCED RISK OVER THE UPPER MIDWEST...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER THE UPPER
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM COASTAL
CAROLINAS INTO SOUTHERN GEORGIA...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER SOUTHERN
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER THE
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM TEXAS TO
THE LOUISIANA COAST...
Severe thunderstorms are expected late this afternoon into tonight
across the Upper Midwest, particularly across central and southern
Minnesota, northeast Iowa, southwest Wisconsin and northwest
Illinois. Strong thunderstorms may also impact portions of the south
Atlantic coast into southern Georgia, southern Arizona, and portions
of the northern Rockies this afternoon and evening.
...Upper Mississippi Valley region...
Morning clouds and scattered weak convection over parts of the upper
Midwest are associated with a lead short wave trough moving across
the area. This is expected to shift eastward over the next few
hours in advance of a stronger perturbation evident in water vapor
imagery moving southeastward over far southern Manitoba. This
latter feature is forecast to progress into the upper Mississippi
Valley this afternoon and tonight contributing to an increased risk
of severe storms that will continue through much of the overnight
Low-level moisture is expected to increase northward into the region
this afternoon and evening as a southwest low-level jet strengthens
from western Iowa into southern Minnesota. A plume of steep
mid-level lapse rates is forecast to spread into the upper
Mississippi Valley this afternoon and contribute to an increasingly
unstable environment by later this afternoon and evening with MLCAPE
of 1500-3000 J/kg in place into the region.
Model guidance suggests the cap associated with the EML plume will
delay primary storm development until late this afternoon and
evening over parts of central Minnesota. Strong veering wind
profiles with height associated with the southwesterly low-level jet
and northwest flow in the mid/upper levels will result in 40-50 kt
deep layer shear, supportive of supercell characteristics in initial
discrete storms. Very large hail and a tornado or two will be
possible. With time the activity is expected to grow upscale into
one or two bowing QLCS systems that will accelerate southeastward
into the overnight hours. The primary severe risk is expected to
evolve into primarily a damaging wind threat tonight with potential
for one or more swaths of wind damage occurring across the immediate
Mississippi Valley region. A severe threat may persist through much
of the overnight hours and the severe risk areas have been extended
southeastward into northern parts of Illinois and Indiana to reflect
A modest weakening of the Four Corners vicinity upper-level ridge is
forecast today with expectations for somewhat weaker easterly
steering flow, in addition to what may be sub-optimally timed
ridge-peripheral disturbances. Even so, where isolated storms do
develop/slowly propagate this afternoon and evening, a hot/deeply
mixed boundary layer will support the possibility of locally strong
wind gusts and blowing dust, mainly across parts of
...Coastal portions of the Carolinas and Georgia...
Along and east of a weak slow-moving/stalling front, a moist air
mass featuring 70s F surface dewpoints and ample precipitable water
(in excess of 2 inches) will linger today mainly in coastal areas of
the Carolinas and southern Georgia. Heating and front/sea
breeze-related convergence aside, thunderstorm development will be
favorably influenced by cyclonic flow aloft. While
low/mid-tropospheric winds will be weak (less than 20 kt),
sufficiently steep low-level lapse rates and ample moisture
conducive for water loading could yield some strong to locally
severe downdrafts this afternoon/early evening.
...Portions of southern Plains/Ark-La-Tex to the Gulf Coast...
Pockets of locally stronger heating/destabilization should occur
today near and south of a convectively modulated/decaying front.
While overall forcing for ascent and vertical shear will remain
weak, sufficient moisture/destabilization could allow for a few
instances of downbursts capable of very localized wind damage.
A western states ridge-peripheral disturbance, in addition to height
falls over the Pacific Northwest, should influence thunderstorm
development across the region aside from adequate moisture and
orographic lift. Storms should initially develop and intensify this
afternoon across eastern Idaho/southwest Montana into western
Wyoming. Adequate moisture/buoyancy in the presence of as much as
25-35 kt of effective shear could yield a few instances of
marginally severe hail, while a relatively warm/well-mixed boundary
layer could support severe downdrafts this afternoon through early
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