Severe Storm Outlook Narrative (AC)
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000
ACUS03 KWNS 230730
SWODY3
SPC AC 230730

Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0230 AM CDT Sun Jul 23 2017

Valid 251200Z - 261200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE NORTHERN PLAINS EASTWARD TO WESTERN PORTIONS OF THE UPPER GREAT
LAKES...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
SLIGHT RISK AREA...

...SUMMARY...
Strong/locally severe thunderstorms will be possible across portions
of the north-central U.S. Tuesday.

...Synopsis...
As an upper trough moves slowly east across the northeast U.S. Day
3/Tuesday, a second trough/weak low will move very slowly inland
over the West Coast region.  Meanwhile, the southern fringe of a
trough/low crossing the Canadian Prairies will affect the northern
Plains and upper Great Lakes area.  Elsewhere, between the western
and eastern troughs and south of the Canadian system, upper ridging
will prevail over much of the country.

At the surface, a cold front advancing steadily southeast across the
north-central U.S. with time will be the main feature with respect
to severe convective potential this period.

...The north-Central U.S. from the high Plains to the Great Lakes...

Afternoon heating of a moistening boundary layer is expected across
parts of the northern Plains and upper Mississippi Valley, ahead of
an advancing cold front.  While low-level capping will hinder storm
development into the afternoon hours, ascent focused near the cold
front should support isolated mid- to late-afternoon storm
development, as mixed-layer CAPE values exceed 2000 to 2500 J/kg.
With low-level southerly winds beneath increasingly strong westerly
flow aloft, shear will be supportive of updraft
organization/rotation.  Along with resulting potential for large
hail, locally damaging winds and possibly even some tornado risk
should evolve across this area.

While storms should remain isolated into the evening with
southwestward extent across the South Dakota vicinity, a tendency
for upscale growth toward linear bands and/or an MCS is indicated,
with storms likely to spread east across the upper Mississippi
Valley and possibly southeast into parts of the upper Midwest into
the evening and overnight.  Along with hail potential, damaging
winds could become an increasing threat into the overnight hours.

..Goss.. 07/23/2017

$$


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