Severe Storm Outlook Narrative (AC)
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ACUS11 KWNS 221521
SPC MCD 221520

Mesoscale Discussion 1665
NWS Storm Prediction Center Norman OK
1020 AM CDT Fri Sep 22 2017

Areas affected...Northern Wisconsin and the Upper-Peninsula of

Concerning...Severe potential...Watch unlikely

Valid 221520Z - 221645Z

Probability of Watch Issuance...20 percent

SUMMARY...Ongoing thunderstorms will continue through the morning.
These thunderstorms will have the potential to produce hail and
gusty thunderstorm winds.

DISCUSSION...Thunderstorms will continue this morning within the
warm-air advection regime of weak mid-level wave moving northeast
within the larger-scale long-wave trough across the West.
Mid-level-lapse rates greater than 7 and surface dewpoint
temperatures in the upper-60s to lower-70s are supporting
surface-based CAPE values in excess of 2000 J/kg (and most-unstable
CAPE in excess of 3000 J/kg) along and ahead of the ongoing
thunderstorms, despite surface temperatures only being in the
mid-70s. Additionally, deep-layer shear is being augmented by the
mid-level wave resulting in values around 40 knots. Although the
thunderstorms appear to be outrunning the better shear, the result
is still an environment supportive of ongoing convection and a
hail/wind threat. As the thunderstorms move east and deep-layer
shear weakens, a transition to outflow dominant/bowing segments will
be possible.

Although the initial development appeared to be elevated, recent
radar trends depict new new thunderstorm development to the south of
the longer-lived thunderstorm cluster. This new development is being
watched for potential transition from elevated to
surface/near-surface based convection which would increase the
likelihood of strong/gusty winds being realized at the surface.

Despite the ongoing thunderstorms, current thinking is that the
limited spatio-temporal nature of the severe threat will not require
a watch. This will be monitored.

..Marsh/Hart.. 09/22/2017

...Please see for graphic product...


LAT...LON   45379186 45809153 46549040 47228850 47068639 45598631
            45258816 45089029 45379186 is the U.S. government's official web portal to all federal, state and local government web resources and services.