Severe Storm Outlook Narrative (AC)
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ACUS01 KWNS 241954
SWODY1
SPC AC 241953

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0153 PM CST Sat Feb 24 2018

Valid 242000Z - 251200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM THE
ARKLATEX TO THE LOWER OHIO VALLEY...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM NORTHEAST
TEXAS TO PARTS OF THE OHIO VALLEY...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM CENTRAL
TEXAS TO CENTRAL OHIO...

...SUMMARY...
Severe thunderstorms capable of damaging winds and tornadoes will
continue through tonight from the Arklatex east/northeastward
through the lower Mississippi and lower/middle Ohio Valleys.
Isolated strong tornadoes are possible.

...Discussion...
No major changes have been made to the ongoing outlook, other than
removing probabilities behind the eastward-advancing cold front. As
a strongly forced band of thunderstorms progresses across Arkansas,
it will encounter a thermodynamic environment increasingly favorable
for damaging winds and tornadoes. Furthermore, recent KLZK VWP data
sampled 0-1km SRH upwards of 500 m2/s2. In turn, bowing segments and
related embedded circulations are likely to evolve within this line
of storms, especially as they move through central Arkansas and
approach the Mississippi Valley through this evening.

..Picca.. 02/24/2018

.PREV DISCUSSION... /ISSUED 0959 AM CST Sat Feb 24 2018/

Only minor changes have been made to the ongoing forecast.  Morning
surface analysis shows that the primary surface boundary currently
extends from northeast TX to the MO Bootheel, then eastward into KY.
 A moist and increasingly unstable air mass is in place to the south
of the boundary with dewpoints in the mid-upper 60s.  The corridor
along and just south of the boundary is expected to be the focus for
severe storm activity this afternoon.

12z CAM solutions agree on development of intense storms around
17-18z over northeast TX/southwest AR, as strong large scale forcing
overspreads the moist air mass.  Considerable cloud cover will limit
the degree of heating and destabilization today.  However, forecast
soundings in this area show substantial low-level helicity of
300-500 m2/s2 and sufficient CAPE for robust convection.  Storm mode
will likely be complex with discrete supercells transitioning to
multiple bow/LEWP structures through the afternoon.  CAPE/shear
parameter ranges suggest the potential for a few strong tornadoes
this afternoon across parts of AR and west TN.  The risk of
widespread damaging winds will also likely increase through the day
as storm structures become more linear.  The line of fast-moving
severe storms is expected to sweep into parts of southern IN/central
KY/middle TN after dark with a continued damaging wind and isolated
tornado threat.

$$



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