Severe Storm Outlook Narrative (AC)
Issued by NWS
ACUS02 KWNS 200531
SPC AC 200530
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1130 PM CST Thu Jan 19 2017
Valid 211200Z - 221200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PORTIONS
OF THE LOWER MISSISSIPPI VALLEY TO WESTERN ALABAMA...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE LOWER
SABINE RIVER VALLEY TO WESTERN GEORGIA...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
SLGT RISK FROM EAST TEXAS TO EASTERN GEORGIA...
Severe thunderstorms, some with very large hail and a few tornadoes,
are expected to develop across a broad area of the lower Mississippi
Valley and Southeast States Saturday. Locally damaging winds are
...Lower Mississippi Valley/Southeast States...
Strong southern stream jet will continue at low latitudes across the
contiguous United States through the day2 period. Latest model
guidance continues earlier trends with a 110kt+ 500mb speed max
forecast to translate across south-central TX by 22/00z...increasing
to near 120kt along the central Gulf coast by sunrise Sunday. In
response to this feature, 40kt LLJ will establish itself early
across LA before shifting downstream into AL/GA/FL Panhandle during
the afternoon hours. Warm advection is expected to aid in pre-dawn
thunderstorm clusters over the lower Sabine River Valley which
should expand in areal coverage and shift east as the LLJ is shunted
into the eastern Gulf States region.
In the wake of the strong low-level warm advection, substantial
surface heating is expected to develop from south-central TX,
northeast into the MS delta region of AR. There is some concern
that a weak surface low could evolve near the Arklatex by 18z as
exit region of upper jet spreads over head. Subsequent movement
would allow the low to track into northeast AR during the evening
hours. Very cold mid-level temperatures and steep lapse rates will
spread across this region such that forecast soundings exhibit the
potential for substantial acceleration within the mid-upper portions
of any supercells that evolve. High-level venting will favor mass
evacuation aloft and for this reason it appears very large hail
could develop within a moistening/destabilizing environment. In
addition, a few tornadoes also appear likely, though stronger
low-level shear will be maximized along the northward-lifting warm
front, and much farther east beneath the LLJ. For these reasons
have introduced 30% severe probs with sig hail possible.