Severe Storm Outlook Narrative (AC)
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000
ACUS02 KWNS 251729
SWODY2
SPC AC 251728

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1228 PM CDT Sat Mar 25 2017

Valid 261200Z - 271200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ON SUNDAY
AFTERNOON AND EVENING OVER PARTS OF OKLAHOMA AND NORTH TEXAS...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE
SOUTHERN PLAINS...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
THE SOUTHERN PLAINS AND OZARKS...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE
SOUTHERN APPALACHIANS TO PARTS OF THE OHIO VALLEY...

...SUMMARY...
Severe thunderstorms capable of large hail, damaging winds, and a
couple tornadoes will be possible across parts of the southern
Plains on Sunday. A few strong wind gusts and/or instances of
marginally severe hail may occur over parts of the Appalachians and
Ohio Valley as well.

...Synopsis...
A fairly progressive, but vigorous, shortwave trough (currently
evident in water-vapor imagery near the lower Colorado Valley) will
advance east towards the southern Plains on Sunday. This impulse
will follow closely behind an opening wave initially over the mid
Mississippi Valley Sunday morning. This downstream trough will
continue to lift northeast as it approaches the lower Great Lakes
Sunday night.

...Southern Plains...
In response to the approaching impulse, a surface low will likely
translate east from the Texas Panhandle into western Oklahoma during
the afternoon hours, with a dryline extending south across western
north Texas and the Hill Country. The low-level mass response ahead
of the dryline will support modest northward moisture return over
central/north Texas and Oklahoma. At this time, considerable
uncertainty remains with the quality of low-level moisture that will
spread northward. Water vapor imagery currently depicts considerable
subsidence, associated with shortwave ridging, across far south
Texas and northern Mexico. Furthermore, despite being in the
warm/moist sector, the 12Z Brownsville sounding sampled only a
shallow layer of rich moisture, with a mean mixing ratio around 9
g/kg.

Nonetheless, surface dew points in the mid/upper 50s, with a few
pockets near 60, should stream northward ahead of the dryline
Sunday. A relatively favorable orientation and timing with the
shortwave trough will result in considerable effective shear (around
40-50 kt), with vectors generally perpendicular to the dry line. As
such, with steepening mid-level lapse rates overspreading the
region, a few discrete supercells should organize across portions of
Oklahoma, with convective coverage becoming more isolated over north
Texas. Rotating mid-level updrafts will likely be capable of large
hail, and dry air aloft will combine with low-level mixing to
encourage damaging winds in stronger downdrafts. Considerable
veering of flow with height will likely enhance low/mid-level
mesocyclogenesis potential. However, a lack of greater moisture may
hamper near-surface supercell processes favorable for
tornadogenesis. Despite this, the discrete nature of the convection
may support a couple tornadoes.

Farther east, the slight and marginal risks were adjusted to capture
the potential for small upscale growth overnight across northeast
Oklahoma/northwest Arkansas as convection blossoms near the nose of
the low-level jet.

...Appalachians into the Ohio Valley...
As a negatively tilted trough lifts towards the Great Lakes, a
corridor of marginal instability should organize from the southern
Appalachians northward to southern Ohio. Despite relatively narrow
buoyancy profiles, effective shear of 30-40 kt and cooling
temperatures aloft (especially across northern portions of the
marginal risk) may favor a few instances of marginally severe hail
and gusty winds Sunday afternoon into the early evening.

..Picca.. 03/25/2017

$$


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