Severe Storm Outlook Narrative (AC)
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000
ACUS01 KWNS 270521
SWODY1
SPC AC 270519

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1119 PM CST Sun Feb 26 2017

Valid 271200Z - 281200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE LOWER
MS VALLEY...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM EASTERN OK
TO CENTRAL MO...

...SUMMARY...
A few strong to severe storms will be possible over a portion of the
lower Mississippi Valley on Monday. Primary threats will be damaging
wind gusts and some hail.  Isolated large hail is possible after
dark from eastern Oklahoma into central Missouri.

...Lower MS Valley...

De-amplifying short-wave trough will quickly eject across the TN
Valley into the Middle Atlantic region by early evening.  This
feature will have minimal impact in the development of strong/severe
thunderstorms as heights are expected to rise across most of the
contiguous US east of the Rockies.  This feature will, however, aid
the northward advance of Gulf moisture across the lower MS valley as
veered LLJ is shunted into the central Gulf states early before
weakening.  Latest model guidance suggests a southwest-northeast
oriented corridor of convection will be ongoing at daybreak from
portions of northeast TX into northern MS.  Low-level warm advection
will be the primary driving mechanism for this activity which should
propagate east within deep westerly flow regime.  Along the southern
fringe of this convection near the warm front, boundary-layer
moisture/instability will be somewhat greater and could support a
few strong, to perhaps isolated severe, thunderstorms.  Will
maintain 5% severe probs for both wind and hail as near-surface
based convection will be adequately sheared for sustained updrafts
within an increasingly buoyant air mass.

...Eastern OK to Central MO...

Late in the period LLJ is expected to increase from northeast TX
into central MO.  NAM guidance has 850mb flow in excess of 50kt by
28/06z which will allow substantial moistening to occur above the
boundary layer after dark.  While large-scale height rises will be
noted across this region there is some concern that strong elevated
convection may develop within this warm advection zone.  There is
some question regarding thunderstorm coverage but strong bulk shear
would support storm rotation.  NAM forecast soundings exhibit
substantial CAPE if lifting a parcel near 850mb, and steep mid-level
lapse rates favor hail production.  Will introduce 5% hail probs
across this region for elevated convection during the latter half of
the period.

..Darrow/Picca.. 02/27/2017

$$



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