Severe Storm Outlook Narrative (AC)
Issued by NWS
ACUS03 KWNS 230729
SPC AC 230728
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0228 AM CDT Thu Mar 23 2017
Valid 251200Z - 261200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE LOWER MISSISSIPPI VALLEY AND SOUTHEAST...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE LOWER TO MID MISSISSIPPI VALLEY AND SOUTHEAST...
An isolated severe thunderstorm threat may develop across parts of
the lower to mid Mississippi Valley into the Southeast on Saturday.
An upper low over eastern KS/western MO will move east-northeastward
across the mid MS Valley Saturday, likely reaching the IL/IN
vicinity by the end of the period. A surface low initially over MO
should develop only slowly northeastward towards IL while undergoing
further weakening. A narrow warm sector, becoming increasingly
confined with northward extent, will exist across parts of the lower
to mid MS Valley and Southeast ahead of an eastward-moving surface
cold front. A high-pressure area over the western Atlantic will act
to limit greater low-level moisture return from the Gulf across GA
and much of FL.
...Lower/Mid MS Valley and Southeast...
A line of thunderstorms will probably be ongoing across the lower MS
Valley Saturday morning along/ahead of a cold front. The evolution
of this line with eastward extent into AL/TN remains uncertain, but
40-55 kt southwesterly mid-level winds associated with the upper low
should overspread the warm sector through Saturday afternoon. In
concert with some diurnal destabilization, these strengthening winds
aloft may allow for the line of convection to continue/intensify as
it moves eastward across parts of the Southeast. Strong to damaging
winds would probably remain the primary risk given the expected
linear mode. Additional convection may form behind the initial line
along the front, although this remains highly uncertain/conditional.
If this activity did form, it would also pose a damaging-wind
Across western TN into the mid MS Valley, instability will likely
remain limited owing to marginal low-level moisture, but strong
forcing for ascent, cold mid-level temperatures, and strengthening
mid-level winds may allow for some thunderstorm organization ahead
of the upper low across this region. With time, any thunderstorms
that do form/persist will encounter a less-favorable thermodynamic
environment as they move eastward across the mid MS Valley and
Southeast, suggesting a lessening of the overall severe threat with
eastward extent into Saturday evening/night.