Severe Storm Outlook Narrative (AC)
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000
ACUS02 KWNS 231749
SWODY2
SPC AC 231748

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1248 PM CDT Thu Mar 23 2017

Valid 241200Z - 251200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS EASTERN
PORTIONS OF THE SOUTHERN PLAINS AND SOUTHEAST TEXAS TO THE LOWER
MISSISSIPPI VALLEY...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
SLIGHT RISK AREA FROM EASTERN KANSAS AND MISSOURI TO SOUTHEAST
LOUISIANA AND SOUTH TEXAS...

...SUMMARY...
Wind damage, large hail, and a tornado threat are forecast Friday
and Friday night across eastern portions of the southern and central
Plains, Arklatex, and lower to mid Mississippi Valley.

...Synopsis...
An upper trough located over western portions of the central and
southern Plains at 12Z Friday will advance east toward the lower and
mid MS Valley this forecast period.  An embedded low centered near
southwest KS is expected to remain closed Friday, though should
weaken as it moves east reaching southwest MO/northwest AR area by
12Z Saturday.  Meanwhile, a couple of midlevel impulses are expected
to track through the base of the synoptic trough across
south-central to southeast TX and the northwest Gulf of Mexico.  An
embedded and cyclonically curved 80-100 kt 500-mb jet moving across
parts of the central and southern Plains at 12Z Friday is expected
to weaken some as the synoptic trough maintains a neutral
orientation with eastward translation.  At the surface, a low should
move east from southwest KS along the KS/OK border region into
southwest MO by the end of the forecast period.  A dry line
extending from the low into central OK and central TX will mix
eastward and should be the primary focus for new thunderstorm
development from eastern OK into east TX by late Friday morning and
early afternoon.  Meanwhile, a cold front will advance east across
the central and southern Plains Friday afternoon and overtake the
dryline near the OK/AR border into northeast TX near or after
25/00Z.  The cold front should then maintain an eastward movement
toward the mid MS Valley to near the TX coast Friday night.

...Southern and Central Plains/Arklatex/Lower to Mid MS Valley...
Southerly low-level flow across the warm sector will maintain
boundary layer moistening with surface dew points in the mid-upper
50s reaching northeast OK to MO and the mid MS Valley, while values
in the lower 60s spread into southeast OK and AR, and mid-upper 60s
should remain from the TX coast to southern LA.  Showers and
embedded thunderstorms located near and east of the dry line at 12Z
Friday will spread east with associated cloudiness tending to limit
greater destabilization until late morning or early afternoon.  At
that time, steeper midlevel lapse rates spreading east atop the
moisture return will result in MLCAPE of 1000-1500 J/kg from eastern
OK into AR and south through LA to the middle and upper TX coast.
MLCAPE of 500-1000 J/kg are expected with northward extent into
eastern KS and western MO.

The leading extent of stronger forcing for ascent with the upper
trough/closed low and attendant 60-90 meter 12-hr height falls are
expected to reach the dryline in eastern OK to parts of east TX by
late morning or early afternoon, supporting an increase in
thunderstorm development from eastern OK through east TX to near
KAUS as the air mass destabilizes.  Strong bulk shear suggests all
severe hazards will be possible with the initial storms along the
dryline, though vectors oriented nearly parallel to the dry line
suggests more of a linear storm mode.  A linear storm mode may be
maintained with eastward extent, given surface dew points in the
lower 60s that could limit destabilization across northern and
eastern AR.  While these factors could limit the development of
storm modes other than linear, a strengthening south-southwesterly
low-level jet of 50-60 kt from the Arklatex into AR and northern LA
could increase the damaging wind threat, and a greater tornado
threat.  However, mixed messages in the model data results in lower
forecast confidence that would warrant an enhanced severe risk.
Moderate instability persisting through Friday night from east TX
through LA and perhaps southern AR suggests a continued threat for
damaging winds as the cold front spreads east.

Farther north, thunderstorms will be possible across eastern KS into
western MO Friday afternoon/evening, where the likelihood for early
day thunderstorms is less probable, and the air mass should become
sufficiently unstable (MLCAPE 500-1000 J/kg).  Strong wind gusts and
hail should be the primary threats across this portion of the
marginal risk area.

..Peters.. 03/23/2017

$$


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