Severe Storm Outlook Narrative (AC)
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874
ACUS02 KWNS 270546
SWODY2
SPC AC 270546

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1246 AM CDT Tue Jun 27 2017

Valid 281200Z - 291200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS EASTERN
COLORADO INTO NORTHERN KANSAS AND NORTHEASTWARD ACROSS IOWA INTO
SOUTHERN WISCONSIN...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE CENTRAL
HIGH PLAINS INTO THE UPPER MISSISSIPPI VALLEY...

...SUMMARY...
Scattered severe thunderstorms with large hail and damaging winds
are expected mainly from northern Kansas into Iowa, with more
isolated activity stretching from Wisconsin to Colorado and eastern
Wyoming. A couple tornadoes are also possible mainly northeast of
the Missouri river, including Iowa, far southeast Minnesota and
southern Wisconsin.

...Synopsis...
A belt of relatively strong westerly upper flow for late June will
stretch from the central Rockies into the Northeast, with several
embedded shortwave troughs. One wave will be located over the upper
MS Valley Wed morning, and will move toward Lake Michigan by
afternoon. To the west, another wave will affect WY and CO. At the
surface, a warm front will lift northeast into WI, with front
extending southwest across central IA and into northern KS. Western
parts of this front will lift north late into CO. Both these
shortwave troughs and boundaries will lead to scattered severe
thunderstorms, beginning early in the day across the upper MS
Valley, and by late afternoon farther west.

...Northern KS into southern WI...
Scattered thunderstorms will be ongoing Wed morning from MN
southward into northern MO, aided by strong low-level warm advection
and in association with a shortwave trough. Some of this activity
may contain severe hail, especially from the MO river into IA where
instability will be strongest. This activity should generally weaken
during the day but additional storms are expected from southeast
MN/southwest WI into IA as destabilization occurs. The early storms
may create an outflow boundary in the region, which would serve as a
focus for supercell development with the possibility of a couple
tornadoes as low-level shear will be favorable. Predictability is a
bit low given variance in model output, and this area will
experience rising heights in the wake of the shortwave trough.
Therefore will defer a possible upgrade to later outlooks.

To the southwest, additional activity will form late in the day
along the stalled front across northern KS/southern NE, as areas to
the south experience strong heating which will erode the cap.
Midlevel flow on the order of 40 kt along with MUCAPE in excess of
2000 J/kg will support large hail and damaging winds.

...Eastern WY into CO...
Lee troughing will occur during the day with weak surface upslope
and convergence initiating storms after 21Z. Strong heating will
lead to very steep lapse rates, and substantial mid to high level
flow may support a few supercells capable of large hail. With time,
activity could merge into an MCS, and continue eastward along the
stationary front into western KS with a continued hail and wind
threat.

..Jewell.. 06/27/2017

$$



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