Severe Storm Outlook Narrative (AC)
Issued by NWS
ACUS11 KWNS 270003
SPC MCD 270002
Mesoscale Discussion 0566
NWS Storm Prediction Center Norman OK
0702 PM CDT Wed Apr 26 2017
Areas affected...Parts of central/northeastern
Concerning...Tornado Watch 164...
Valid 270002Z - 270130Z
The severe weather threat for Tornado Watch 164 continues.
SUMMARY...The risk for a couple of tornadoes and potentially
damaging wind gusts with storms overspreading the region will
continue at least into the 9-10 pm CDT time frame. It is not
certain that an additional watch will be needed to the east of watch
164, but trends will continue to be monitored for this possibility.
DISCUSSION...Sustained vigorous thunderstorms within a pre-frontal
squall line continue to advance eastward into/through the lower
Mississippi Valley, as a supporting short wave trough pivots into an
increasing negative tilt orientation as it approaches the region.
New convective development is ongoing ahead of the line, but is
generally confined to a narrow corridor ahead of it, before merging
into or being overtaken by the line, as the leading edge of
mid-level cooling contributes to a gradual west to east erosion of
the plume of capping elevated mixed layer air.
The leading edge of an inland returning plume of seasonably moist
boundary layer air (characterized by surface dew points in the upper
60s/lower 70s) remains stalled over southern/eastern Louisiana and
southwestern Mississippi, and the squall line appears likely to
increasingly cut-off inland return of higher boundary layer moisture
from the Gulf of Mexico. As it does, easterly inflow of less
unstable air into the storms may tend to contribute to weakening of
updrafts as early as 02-03Z, although it is possible that this may
be counter balanced somewhat by at least some strengthening of
southerly 850 mb flow (and low-level shear). Until convection
begins to wane, a period of increasing risk for strong surface gusts
remains possible into early evening, along with continued potential
for a couple of tornadoes.
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 33469078 33969011 33888938 32978950 31949013 30499167
30179265 30449347 32549152 33469078