Severe Storm Outlook Narrative (AC)
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000
ACUS02 KWNS 261722
SWODY2
SPC AC 261722

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1222 PM CDT Wed Jul 26 2017

Valid 271200Z - 281200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM NEW ENGLAND
TO OK...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
NORTHERN/CENTRAL HIGH PLAINS...

...SUMMARY...
Scattered thunderstorms will develop across a large portion of the
US Thursday. A few storms may produce gusty winds across the
central/northern High Plains and from Oklahoma to southern New
England.

...Frontal Zone from OK to NY...

High-PW plume will be gradually shunted southeast across the
contiguous US during the day2 period as a frontal zone progresses to
a position from Lake ON, southwest across IN into northern OK by
18z. This high PW plume will be characterized by poor lapse rates
with embedded left over convective MCVs. Each of these features will
be difficult to predict with any certainty beyond a few hours and
12z model guidance is not particularly useful identifying any
notable feature that could aid organized strong convection. Even so,
short-wave troughing will shift across ON into QC with the southern
extent of this feature expected to extend to a latitude of southern
New England. Deep-layer shear will be notably stronger across the
northeastern US ahead of this feature but forecast instability
appears inadequate for more than marginal severe at this time. Gusty
winds are the primary threat with convection across this region.

Farther southwest from the TN Valley into the southern Plains,
strong boundary-layer heating will be focused along this corridor
with the steepest lapse rates occurring over the southern Plains
where surface temperatures should soar to near 100F. With PW values
expected to be near 2" across this region a few damaging downbursts
seem possible.

...Northern/Central High Plains...

Modest deep-layer shear will develop across the high Plains from
eastern MT into northeast CO as upper ridging remains anchored over
the Rockies. Afternoon convection that evolves across this region
will do so within an environment favorable for deep rotation and a
few slow-moving supercells could develop during the late
afternoon/early evening, though forecast lapse rates are not
particularly steep for this region and buoyancy modest at best. For
these reasons it appears any supercells that evolve should prove
marginally severe with hail/wind possible.

..Darrow.. 07/26/2017

$$



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