Severe Storm Outlook Narrative (AC)
Issued by NWS
ACUS01 KWNS 290558
SPC AC 290557
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1257 AM CDT Wed Mar 29 2017
Valid 291200Z - 301200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHERN
MISSOURI...MUCH OF ARKANSAS...EAST TEXAS...NORTHERN AND WESTERN
LOUISIANA...AND SMALL PORTIONS OF SURROUNDING STATES...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM SOUTHEAST
KANSAS...EASTERN OKLAHOMA...AND EAST TEXAS EASTWARD TO THE MID AND
LOWER MISSISSIPPI VALLEY...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
SLIGHT AND ENHANCED RISK AREAS...
Severe thunderstorms are expected on Wednesday into Wednesday night
from parts of east Texas, eastern Oklahoma, and southeast Kansas
into the lower and middle Mississippi Valley.
A deepening closed low aloft crossing the Texas Panhandle/South
Plains vicinity early will shift slowly northeastward through the
period, reaching the northern Oklahoma/southeast Kansas area late.
Strong flow aloft surrounding this system will encompass much of the
central and south-central portions of the country.
At the surface, an associated low is forecast to move across
Oklahoma during the day, reaching the northeast Oklahoma vicinity by
late afternoon and then the southwest Missouri area by 30/12z
(Thursday morning). Ahead of the low, a warm front at the leading
edge of an expanding warm sector will shift northward across
Arkansas and southern Missouri through the afternoon and early
evening, while a trailing cold front crosses Texas and eastern
Oklahoma through the day. By the end of the period, the front
should reach a position from southwest Missouri southward across
western Arkansas and the Sabine River Valley and into the far
western Gulf of Mexico.
...Parts of southeast Kansas/Missouri/southern Illinois south to the
A band of thunderstorms should be advancing east across parts of
western Missouri, eastern Oklahoma, and east Texas at the beginning
of the period, with the convection likely to diminish gradually
through the morning hours. By early to mid afternoon, with remnants
of the prior convection possibly lingering across east/southeast
Texas, storm redevelopment is forecast to occur from southeast
Kansas/southwest Missouri southward across eastern Oklahoma/western
Arkansas into the East Texas/western Louisiana area. Assessment of
a collection of high-res CAM guidance shows differences with respect
to areas of greater convective coverage -- likely tied to differing
evolution of the environment as affected by prior/diminishing
convection. Cloud cover and lingering convection through the
morning will likely hinder destabilization to varying degrees across
the area, which casts some uncertainty with respect to areas of
greatest severe risk. As such, areal uncertainty precludes any
upgrade to prior forecast probability/risk at this time.
With that said, at least pockets of greater destabilization are
expected, and very strong flow aloft is expected to spread across
the warm sector during the day. By late afternoon/early evening,
south-southwesterly flow of 40-50 kt at 850 mb will increase to 60
to 80 kt at 500 mb, from the Arklatex region to the Ozarks, all atop
low-level flow from the south. Resulting shear will be supportive
of strong/rotating storms -- particularly where thermodynamic
support for vigorous updrafts exists.
The most favorable wind profiles will reside near and just north of
the warm front, where an easterly component to the surface flow will
provide greater low-level shear/hodograph curvature. As a result, a
northward expansion of the ENH risk area -- including 10% tornado
probabilities -- into the Ozarks region is being included this
forecast. While generally northeast storm motion suggests storms
crossing -- as opposed to traveling along -- the warm front, a few
supercells capable of producing tornadoes will be possible. Farther
south, lesser tornado risk is indicated, though a broad area of risk
for damaging winds and large hail will exist through the afternoon
and evening. Overnight, clusters of strong/severe storms should
continue advancing eastward across Missouri/Arkansas/Louisiana, with
some severe risk spreading into southern Illinois/western
Tennessee/Mississippi through the end of the period.