National Weather Service
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Severe Storm Outlook Narrative (AC)
acus03 kwns 180733
spc ac 180731
day 3 convective outlook
nws storm prediction center norman ok
0231 am cdt sat may 18 2013
valid 201200z - 211200z
... there is a slgt risk of svr tstms across parts of the srn
plains ... cntrl plains ... mid ms valley ... upper ms valley and great
... regional severe weather episode possible across parts of the srn
and cntrl plains into the ozarks monday afternoon and evening...
... srn and cntrl plains/ozark plateau...
an upper - level low will remain in place across the nrn and cntrl
plains on monday with southwest flow located from the srn plains
into the mid ms valley. at the sfc ... a low is forecast to move newd
across the srn plains with dewpoints south and east of the low in
the mid to upper 60s f. a capping inversion in place for much of the
day ... should weaken by late afternoon allowing for robust convective
initiation. model forecasts develop several clusters of
thunderstorms late monday afternoon from the sfc low near the red
river newd into cntrl and ern ok. the models appear to organize an
mcs across the srn plains and move this convective system newd into
the ozarks during the evening.
forecast soundings in srn ok and near the red river in north tx at
00z/tue show impressive thermodynamic and shear profiles with mlcape
values of 2500 to 3500 j/kg and 0 - 6 km shear values of 45 to 55 kt.
this environment should be favorable for supercells with large hail.
hailstones of greater than 2 inches in diameter will be possible
with the more dominant supercells. in addition ... low - level
hodographs also look impressive with 0 - 3 km storm relative
helicities in the 400 to 50o m2/s2 range by early monday evening.
this suggests tornadic supercells will be possible with a potential
for strong tornadoes. if mesoscale conditions come together as the
models suggest ... then a cluster of tornadoes could occur across
parts of the srn plains late monday afternoon into the evening. wind
damage will also be possible with supercells and bowing
line - segments. the main concern about forecasting a significant
event this far out ... is that multiple days of thunderstorms between
now and monday will likely alter the outcome and that the scenario
will be different than what is currently presented by the models.
... mid to upper ms valley/great lakes...
an upper - level low is forecast to remain in place across the nrn and
cntrl plains on monday as a shortwave trough rotates around the ern
side of the upper - level low. the shortwave trough and an associated
mid - level jet will help focus convective development across the mid
to upper ms valley and great lakes region monday afternoon. sfc
dewpoints are forecast to be in the lower to mid 60s f across a
broad corridor from the mid ms valley extending newd into the lower
oh valley where the models develop moderate instability by
afternoon. this combined with moderate deep layer shear
profiles ... enhanced by the mid - level jet ... should support severe
thunderstorm development. the severe threat should develop across a
broad area where mesoscale features and the magnitude of instability
will become important for severe threat coverage. wind damage and
large hail appear to be the greatest threats at this time but much
uncertainty exists concerning how the event will play out.
.. broyles.. 05/18/2013