Severe Storm Outlook Narrative (AC)
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ACUS11 KWNS 220435
SPC MCD 220434

Mesoscale Discussion 1663
NWS Storm Prediction Center Norman OK
1134 PM CDT Thu Sep 21 2017

Areas affected...Northeast SD...Central MN

Concerning...Severe potential...Watch unlikely

Valid 220434Z - 220630Z

Probability of Watch Issuance...20 percent

SUMMARY...Scattered thunderstorms are expected to develop across
central MN extending into northeast SD. Hail may accompany the
strongest updrafts; however, severe activity may prove too sparse to
warrant a watch.

DISCUSSION...LLJ is beginning to increase across the central Plains
late this evening and should strengthen into the morning hours as it
focuses into southeast SD ahead of a weak surface low. As a result,
significant boundary-layer moistening is occurring across southeast
SD into southern MN, where surface dew points have risen into the
lower 70s, while elevated buoyancy is increasing north of a warm
front draped from southeast ND to near STC. HRRR model guidance has
been consistent over the last 5-6 runs regarding the evolution of
elevated convection north of the boundary over the next few hours.
Latest radar data supports this with showers now developing from
Douglas County MN into Sherburne County MN. This activity is
expected to gradually mature within a moistening environment
favorable for deep convection. 00z ABR sounding exhibited modest
lapse rate-environment with adequate shear for sustaining some
organization with elevated storms. Hail is the greatest risk with
thunderstorms that evolve along a corridor from northeast SD toward
the western portions of Lake Superior. At this time severe-hail
coverage may prove too sparse to warrant a watch but will continue
to monitor.

..Darrow/Edwards.. 09/22/2017

...Please see for graphic product...


LAT...LON   45119837 46509533 46749339 45469281 45179592 44469785
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