Severe Storm Outlook Narrative (AC)
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000
ACUS02 KWNS 221725
SWODY2
SPC AC 221724

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1224 PM CDT Fri Sep 22 2017

Valid 231200Z - 241200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS CENTRAL NEBRASKA
TO CENTRAL MINNESOTA...

...SUMMARY...
Isolated damaging wind gusts are possible from central Nebraska
northeastward to central Minnesota Saturday afternoon and evening.

...Synopsis...
A large-scale trough will encompass the western U.S. on Saturday,
with the eastern extent advancing slowly into the central and
northern Plains.  Meanwhile, a strong mid- to upper-level ridge will
persist east of the Great Plains.  Between these two systems,
strong,meridionally oriented mid-level flow will extend from the
southern Rockies/High Plains northward to the Dakotas and northern
MN.

At the surface, an expansive surface anticyclone, generally anchored
over the central and southern Appalachians, will persist from the
East Coast and Great Lakes to the southern Plains and Gulf of
Mexico.  A weak low located in vicinity of the CO/KS border should
move little this forecast period, while a stationary front extends
through central NE to central MN.  A weak lee trough/dryline will
extend southward across eastern NM.  A broad area of southerly winds
across the warm sector will maintain an unseasonably moist
environment from NE into the Upper Midwest, with surface dew points
in the lower 60s in NE and around 70 F in MN.

...Central Nebraska northeastward to central Minnesota...
The strongest flow aloft and deep-layer shear are expected to
generally lag the stationary front this forecast period.  The
presence of a moisture rich environment (including precipitable
water values up to 1.5 inches) in vicinity of the stationary
boundary and surface heating in the warm sector should result in
moderate buoyancy.  However, modest mid-level lapse rates (near 7
C/km) and the lack of better forcing for ascent during peak heating
suggest the strength of updrafts should be tempered.  These factors
preclude an increase in severe probabilities with this outlook
issuance.

Deep-layer shear of 20-30 kt near the front should support loosely
organized storm clusters and linear segments capable of producing
isolated damaging wind gusts, especially where storms can move
through a boundary layer with steep low-level lapse rates and
greater DCAPE.  Isolated hail cannot be ruled out with any of the
stronger storms.  The Marginal severe threat should wane after
sunset, given the loss of surface heating.

..Peters.. 09/22/2017

$$



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