Severe Storm Outlook Narrative (AC)
Issued by NWS
ACUS01 KWNS 211628
SPC AC 211627
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1027 AM CST Tue Feb 21 2017
Valid 211630Z - 221200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
The risk for severe thunderstorms appears negligible across the
U.S., today through tonight. Isolated thunderstorms are possible
from the lower Mississippi Valley region eastward along the Gulf
Coastal Plain, and from northern California to parts of Wyoming and
the northern High Plains.
...Lower Mississippi Valley and Eastern Gulf Coast...
Scattered thunderstorms are expected along with and in advance of an
upper low that will move eastward along the Gulf Coast this
afternoon and tonight. Cold temperatures aloft will support some
small hail across portions of southern LA this afternoon as modest
heating/destabilization occurs, though low tropopause heights in the
vicinity of the upper cyclone will limit the depth of convection and
preclude any substantial severe hail risk.
...Northern CA/Southern OR into the Great Basin/Northern Rockies...
As an upper trough approaches the Pacific Coast, generally weak
convection is expected across a broad area from the northern
CA/southern OR coast eastward into the Great Basin and Northern
Rockies, with isolated thunderstorms possible where convection
becomes sufficiently deep. Somewhat greater instability across
portions of the northern CA coast into the northern Sacramento
Valley may support some thunderstorms capable of small hail and
locally gusty winds, though generally weak effective shear
magnitudes should limit storm organization.
...Portions of the Northern High Plains...
A shortwave trough over portions of the Northwest will move quickly
into the northern High Plains this afternoon and evening. Ahead of
this feature, weak but sufficient instability will support
fast-moving clusters of convection later this afternoon and tonight
from central/eastern MT into ND. Relatively strong low/midlevel flow
and effective shear may support locally gusty winds and perhaps some
small hail with the strongest of these clusters.