Severe Storm Outlook Narrative (AC)
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303
ACUS01 KWNS 260540
SWODY1
SPC AC 260538

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1138 PM CST Sat Feb 25 2017

Valid 261200Z - 271200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS CENTRAL
AND NORTHEAST TEXAS...

...SUMMARY...
Thunderstorms are expected to develop from central into northeast
Texas Sunday evening.  Large hail is possible with the strongest
activity.

...Texas...

Late evening model guidance suggests a digging short-wave trough
along the CA coast will deamplify and eject east across the southern
Rockies Sunday as a strong 500mb speed max translates into the
southern High Plains after dark.  While this feature is expected to
weaken with time, a small pocket of height falls will overspread TX
during the evening hours and a notable LLJ should establish itself
over east TX enhancing warm advection across this region.

Latest diagnostic data suggests boundary-layer air mass over the
western Gulf basin is beginning to advance northward toward deep
south TX.  As a result, a surface warm front will move inland across
the coastal plain...extending from near Houston to north of Austin
by 27/00z.  Timing of the low-amplitude short wave and expected
destabilization north of the warm front favor thunderstorm
initiation near or just after 00z.  Mid-level lapse rates should
steepen during the evening as a pronounced thermal trough approaches
the I-35 corridor late evening.  Forecast soundings suggest MUCAPE
in excess of 1000 J/kg with strong bulk shear through the cloud
bearing layer.  Given the expected large-scale ascent, due to warm
advection, and thermodynamic environment, have introduced 5% severe
probs for hail with the strongest updrafts.  Thunderstorms will
spread/develop into northeast TX as the warm front lifts into this
region of the state.

...Pacific Northwest...

Strong mid-level short-wave trough will dig southeast across western
WA/OR during the day1 period and very cold air aloft will overspread
the Pacific Northwest.  500mb temperatures should cool below -30C
beneath the trough and lapse rates will steepen accordingly.  While
instability will be weak, shallow convection could attain heights
necessary for lightning discharge given the cold profiles.  Greatest
risk for isolated thunderstorms will be during the first half of the
period.

..Darrow/Picca.. 02/26/2017

$$



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