SPC Mar 22, 2017 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0751 AM CDT Wed Mar 22 2017

Valid 221300Z - 231200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
THE GREAT BASIN REGION...

...SUMMARY...
Isolated damaging thunderstorm gusts may occur over parts of the
Great Basin.

...Synopsis...
In mid/upper levels, a progressive and fairly highly amplified
synoptic pattern will characterize the day-1 period.  Troughing now
over QC and the northern/central Appalachians region will cross the
Northeast today and exit New England overnight.  Upstream, a
full-latitude synoptic ridge currently extends from central MX up
the U.S. High Plains and northwestward to the Mackenzie River Valley
of northwest Canada.  By 12Z, this ridge will shift eastward to the
western Gulf and the tier of states from LA-MN.  Meanwhile, split
flow will develop out of a major northeastern Pacific trough -- now
evident in moisture-channel imagery extending southeastward from a
low west of the BC coast.  That process will happen as the northern
portion (the cyclone) devolves into an open wave and pivots
northeastward across the AK Panhandle and northern BC, while its
southern-stream component shifts almost due eastward across CA.  By
the end of the period, the latter trough should extend at 500 mb
from eastern NV southward through a primary vorticity lobe over
northern Baja, to the Pacific offshore central/southern Baja.

At the surface, 11Z analysis showed a wavy frontal zone from a low
offshore NC through south-central GA, central MS, then roughly along
I-20 from JAN-SHV-DAL-ABI-MAF.  A dryline intersected the front
along with a weak surface low between FST-INK.  As a major
continental/polar anticyclone spreads southeastward out of the upper
Great Lakes region today, the cold front will move southward down
the FL peninsula, preceded by veering and difluent surface flow. 
The front should remain quasistationary from the Delta region to the
Arklatex, with some northward motion as a warm front likely
overnight across northwest TX and the southern High Plains. 

...Great Basin...
Scattered to widely scattered thunderstorms are forecast to develop
this afternoon across this region, primarily over areas of
well-heated higher terrain where CINH is minimized, then move
rapidly northeastward across the outlook area.  Some of this
activity may organize into small clusters yielding aggregated cold
pools.  Isolated damaging gusts are the main threat.  Supportive
large-scale ascent/destabilization should arise from low-level warm
advection, the left-exit region of a cyclonically curved/100-kt
250-mb jet, and shots of DCVA immediately preceding embedded
vorticity lobes ejecting through strengthening mid/upper-level
southwesterlies.  Strengthening flow with height will yield
effective-shear magnitudes in the 40-55-kt range across much of the
region.  Forecast soundings suggest well-mixed subcloud/boundary
layers where slots of sustained diabatic surface heating develop,
beneath 300-700 J/kg MLCAPE.  This will support maintenance of
strong-severe gusts generated aloft to the surface in a few locales.

..Edwards/Gleason.. 03/22/2017

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