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Day 1 Outlook Convective Tornado
Hail Wind
Categorical Day1 1200Z Outlook
Images courtesy of the NWS Storm Prediction Center
 Forecast Discussion

ACUS01 KWNS 160559
SPC AC 160558

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1258 AM CDT Mon Jul 16 2018

Valid 161200Z - 171200Z


Locally severe storms are expected this afternoon and tonight from
portions of the Intermountain West into the central/northern High
Plains area, where potential for damaging winds and possibly hail
will exist.  A marginal threat for locally damaging winds is also
apparent across portions of the Great Lakes area.

Modest flow aloft will continue to prevail over the southern half of
the U.S., where upper ridging will persist.  Meanwhile farther
north, a short-wave trough crossing the Intermountain West and a
second/larger trough expanding across eastern Canada and the
northeast quarter of the U.S. will allow modestly stronger westerly
flow to evolve across portions of the northern half of the country.

At the surface, a cold front is forecast to move slowly east across
the Great Lakes region, while sagging southeastward across the
Midwest/Ohio valley and southward across the Ozarks and Oklahoma
through the daylight hours.  By Tuesday morning, the front should
extend in an arc from central Quebec southwest across the Lower
Great Lakes and Upper Ohio Valley into the Mid South, westward
across Arkansas and Oklahoma, and then northwestward across the High

...Parts of the Idaho vicinity eastward across Wyoming into western
Nebraska and surrounding areas...
As a mid-level short-wave trough moves gradually eastward out of the
northwestern U.S. into the Idaho/Wyoming vicinity, modest mid-level
cooling atop a diurnally warming boundary layer will result in
moderate afternoon destabilization.  Instability will become most
pronounced across central/eastern Wyoming and into the High Plains,
where a more moist boundary layer is anticipated in the vicinity of
the northwest-to-southeast frontal zone.  

Storm development is expected during the afternoon aided by
increasing large-scale ascent, with a few stronger cells possibly
evolving as far west as the southern Idaho/northwest Nevada region,
but likely more numerous farther east into Wyoming.  With
enhanced/30-40 kt mid-level westerlies spreading across the area
atop a low-level easterly component, shear sufficient for
organized/possibly rotating storms should evolve.  As such,
potential for locally damaging winds and possibly hail will likely
accompany stronger cells.

As a southerly low-level jet evolves over the High Plains during the
evening, most CAM output suggests varying degrees of
congealing/upscale growth of convection, possibly resulting in an
MCS shifting east-southeast out of eastern Wyoming into the
southwest South Dakota/western Nebraska and possibly northeast
Colorado area through the evening and into the overnight hours. 
Presuming this evolution manifests, potential for damaging winds may
extend into the overnight hours.

...The eastern Upper Great Lakes and Lower Great Lakes area...
Modest destabilization ahead of the slowly advancing cold front will
support considerable shower/thunderstorm development across parts of
the eastern Upper Great Lakes/Midwest region during the afternoon. 
Though stronger mid-level cyclonic flow will remain farther north
across Ontario and Quebec, 25 to 30 kt mid-level westerlies should
overspread the warm sector north of the Ohio River Valley,
supporting potential for locally stronger/organized storms.  With
both CAPE and shear expected to remain sub-optimal for a more
widespread severe risk, will maintain only MRGL/5% severe
probability across areas in the vicinity of the Great Lakes, mainly
for gusty/locally damaging wind potential.  Storms -- and limited
wind potential -- will spread eastward with time in conjunction with
the slow frontal advance, affecting portions of Pennsylvania and New
York through the evening and possibly into the overnight hours.

..Goss/Squitieri.. 07/16/2018