Severe Storm Outlook Narrative (AC)
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000
ACUS03 KWNS 250732
SWODY3
SPC AC 250731

Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0231 AM CDT Tue Jul 25 2017

Valid 271200Z - 281200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE MID AND
UPPER OHIO VALLEY EAST THE MID ATLANTIC COAST...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
SLIGHT RISK AREA...AND EXTENDING INTO THE SOUTHEAST U.S....

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF THE NORTHERN INTERMOUNTAIN REGION...

...SUMMARY...
Strong/locally severe storms are forecast to spread across the
central Appalachians and mid Atlantic region and vicinity Thursday
afternoon and evening.  Isolated severe risk may also evolve across
the northern Intermountain region Thursday afternoon/evening.

...Synopsis...
Larger-scale mid-level troughing is forecast to expand across the
eastern U.S. this period, as a short-wave trough digs southeast
across the Great Lakes area into the mid and upper Ohio Valley
through the period.  Meanwhile to the west, ridging will prevail,
though a short-wave trough moving eastward out of the Pacific
Northwest will suppress ridging to some degree as it moves through
the northern Intermountain region.

At the surface, a cold front will shift southeast across eastern and
southern portions of the country through the period, while high
pressure prevails across the central and northern portions of the
country.

...Mid and upper Ohio Valley east to the mid Atlantic coast...
Widespread precipitation is forecast to be ongoing across western
and northern portions of the risk area, which -- along with clouds
streaming east ahead of the convection -- should hinder diurnal
destabilization across a large portion of the risk area.  Still,
with a belt of strong flow aloft expected to spread east across the
region in conjunction with a lead short-wave trough ahead of the
main system crossing the Great Lakes, any storms which can
form/organize would likely evolve into fast-moving bands, posing a
damaging wind risk.  Therefore, while uncertainty remains relatively
high, will introduce slight risk across a broad zone from the mid
and upper Ohio Valley east the mid Atlantic area to cover this
potential risk -- which could extend through the evening and into
the overnight hours.

Lesser risk -- due to weaker shear -- is expected along the trailing
cold front as it shifts southeast across the mid South region during
the day, aided by greater CAPE.  Local severe risk may linger
through the evening, spreading south into the Southeast states
before weakening overnight.

...Northern Intermountain region...
As the weakening upper short-wave trough shifts east-northeast
across the area, modestly enhanced mid-level southwesterlies along
with ample large-scale ascent will favor afternoon thunderstorm
development, as modest CAPE develops through peak diurnal heating.
Though modest instability in most areas should limit hail potential,
damaging wind gusts -- aided by sub-cloud evaporation -- may occur
locally with stronger storms through the evening.

..Goss.. 07/25/2017

$$



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