Severe Storm Outlook Narrative (AC)
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000
ACUS03 KWNS 280728
SWODY3
SPC AC 280727

Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0227 AM CDT Wed Jun 28 2017

Valid 301200Z - 011200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS LOWER
MICHIGAN...INCLUDING LAKE MICHIGAN...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM MICHIGAN
SOUTHWESTWARD TO THE RED RIVER...

...SUMMARY...
Isolated severe thunderstorms capable of hail or damaging wind are
possible on Friday from Lower Michigan to Oklahoma. The greatest
severe risk will be over Lower Michigan, where a few tornadoes will
be possible.

...Synopsis...
A shortwave trough will exist over the northern Plains on Fri, with
an embedded lead wave affecting the upper Great Lakes during the
day. A surface low is forecast to move from WI across northern MI,
with a cold front extending southwest into OK. Ahead of this front,
substantial moisture will exist with dewpoints generally in the
65-70 F range. Increased southwesterly flow aloft with the upper
trough, combined with relatively cool temperatures aloft will result
in a broad area of thunderstorm potential from lower MI to OK.

...Lower Michigan and surrounding Great Lakes...
Areas of thunderstorms are likely to be ongoing across IA, northern
IL or WI early on Friday, but predictability is currently low as
possible MCS`s are involved. Still, a focused area of afternoon
severe thunderstorm development appears likely ahead of the surface
low, mainly over Lower Michigan. Here, southerly low-level flow will
help bring upper 60s F dewpoints northward, while also enhancing
shear. A few supercells are possible given the forecast hodographs
which depict effective SRH around 200 m2/s2, with the greatest
tornado threat near the surface low track.

While Lower Michigan appears to have the greatest probability of
severe storms on Friday, greater severe probabilities could be
expanded south or west to include parts of WI, IL, and IN in later
outlooks once predictability increases.

...OK into MO...
A slow-moving cold front/outflow boundary will stretch from southern
MO across central OK Friday afternoon, with a very moist and
unstable air mass in place. Elevated instability is likely to exist
north of the wind shift as well as 850 mb winds remain southerly.
Lapse rates aloft will be steep, with 500 mb temperatures around -10
C. Further, westerly flow aloft will elongate hodographs and
conditionally support severe storms. Storms would probably form
close to 00Z, as forecast soundings show a small capping inversion.
Once initiation occurs, a slow southeastward movement is expected,
with wind and hail threat. If model trends hold, a Slight Risk will
be introduced in the day 2 outlook.

..Jewell.. 06/28/2017

$$



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