Severe Storm Outlook Narrative (AC)
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000
ACUS48 KWNS 220856
SWOD48
SPC AC 220855

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0355 AM CDT Mon May 22 2017

Valid 251200Z - 301200Z

...DISCUSSION...
As the upper low moves off the Atlantic seaboard Thursday, a
low-amplitude upper pattern will evolve upstream across the Plains.
A series of low-amplitude shortwave troughs will traverse this
region as moisture returns northward, resulting in increasing severe
potential days 4-5 over the central/southern Plains region. However,
predictability remains too low to introduce a categorical risk area
this update.

Day 4 (Thursday) Partially modified Gulf air will begin returning
through the southern and central Plains as a lee trough evolves over
the High Plains. In wake of shortwave ridging, model consensus is
that a low-amplitude shortwave trough will move into the central
high plains by evening and promote the development of high based
storms. These storms will spread east trough the central plains
north of a warm front where they may evolve into an mcs during the
evening and overnight supported by a strengthening low-level jet. At
least a modest threat for hail and isolated damaging wind may
accompany this activity.

Day 5 (Friday) Persistent southerly winds east of a lee-low will
advect richer gulf moisture northward through the southern and
central Plains beneath an eastward-expanding EML, contributing to
moderate to strong instability, but with a capping inversion in
moist warm sector. Progressive, low-amplitude impulses will move
through this region, and at least very isolated strong to severe
storms will be possible along the dryline from northwest TX into OK,
but storms are more likely to initiate in evolving upslope regime
over CO during the afternoon and subsequently spread into KS
supported by warm advection and isentropic ascent north of warm
front. Confidence in timing and amplitude of ejecting impulses
lowers predictability at this time, but a severe risk area will
probably need to be introduced at some point in later updates.

Beyond day 5 ensemble spreads increase substantially resulting in
low predictability.

..Dial.. 05/22/2017



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