Severe Storm Outlook Narrative (AC)
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ACUS03 KWNS 210735
SWODY3
SPC AC 210735

Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0235 AM CDT Fri Jul 21 2017

Valid 231200Z - 241200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE CENTRAL
APPALACHIANS VICINITY AND EAST TO THE SOUTHERN NEW ENGLAND AND MID
ATLANTIC COASTS...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE UPPER
GREAT LAKES AREA EASTWARD...SURROUNDING THE SLIGHT RISK AREA...

...SUMMARY...
A broad zone of risk for isolated severe storms will reside over
portions of Great Lakes/mid Atlantic/central Appalachians area Day
3/Sunday.

...Synopsis...
Advance of a slowly expanding mid-level trough across the Great
Lakes region will support the main area of severe potential Day 3,
while ridging prevails over the western states through the period.

...Lower Great Lakes/central Appalachians/mid Atlantic region...
After widespread overnight convection lingering into the start of
the Day 3 period, uncertainty prevails with respect to areas where
afternoon destabilization will become sufficient for new/vigorous
convection.  Still, expect convection to redevelop/reintensify
during the afternoon across the region, aided by large-scale ascent
ahead of the advancing upper short-wave trough.  Moderate westerly
flow aloft progged across the region will likely be sufficient for
clusters/bands of stronger storms -- and thus a broad risk area for
locally damaging winds and hail will be highlighted.  Details remain
uncertain at this time, but risk may linger into the overnight
hours.

...Parts of the upper Great Lakes and vicinity...
In the wake of earlier convection spreading away from the region,
sufficient destabilization may occur near the trough as it crosses
the upper Great Lakes area during the afternoon to support a
secondary area of development of strong/locally severe storms.  The
NAM is most bullish with this scenario, while the GFS and ECMWF
depicting much less pronounced CAPE development.  Still, ample
potential for development of a few stronger cells seems apparent --
along with locally damaging wind and hail risk -- to support a
MRGL/5% probability area across the region.  Any risk should
diminish through late evening.

..Goss.. 07/21/2017

$$



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