Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS01 KWNS 230058
SWODY1
SPC AC 230057

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0757 PM CDT Fri Sep 22 2017

Valid 230100Z - 231200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER A PORTION OF
NORTHERN MINNESOTA...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE
SOUTHERN HIGH PLAINS INTO THE CENTRAL PLAINS AND UPPER MISSISSIPPI
VALLEY REGION...

...SUMMARY...
Severe storms remain possible this evening over northern Minnesota
with a threat for a few instances of large hail and damaging wind.
Elsewhere, isolated strong to severe storms will persist through mid
evening over a portion of the southern into the central High Plains,
but this activity should weaken by 03Z.

...Upper Mississippi Valley area...

This evening a warm front extends from northwest MN to a surface low
in southeast ND. A cold front extends from the low through eastern
SD into northern and southwest NE. A very moist boundary layer with
dewpoints around 70F resides in the warm sector across MN. However,
both International Falls and Aberdeen RAOB data show a stout capping
inversion with temperatures around 11-12C at 700 mb. Latest HRRR
runs continue to suggest storms will increase/intensify over
northern MN primarily within zone of increasing isentropic ascent
north of the warm front as the low-level jet strengthens this
evening. Recent radar trends continue to show an increase in storm
coverage over northwest MN. Given presence of the warm layer aloft,
LFCs will probably remain closer to the international border. These
storms should remain slightly elevated north of the warm front, but
may become capable or producing damaging wind and large hail.

Cluster of storms that initiated earlier along cold front continues
moving through warm sector from southeast SD into southwest MN.
Increasing convective inhibition suggests these storms will probably
continue to weaken as updrafts become increasingly detached from the
boundary layer.

...Southern High Plains into the central Plains...

Isolated storms that developed along the dryline persist from
southeast NM through west TX and southwest KS. Downburst winds and
hail will remain possible with the stronger storms through about
02-03Z, followed by weakening as the boundary layer stabilizes.

..Dial.. 09/23/2017

$$


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