Severe Storm Outlook Narrative (AC)
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000
ACUS02 KWNS 250601
SWODY2
SPC AC 250600

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
0100 AM CDT Tue Jul 25 2017

Valid 261200Z - 271200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE MID
MISSOURI VALLEY VICINITY EAST/NORTHEAST TO PORTIONS OF THE UPPER
GREAT LAKES AREA...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
SLIGHT RISK AREA...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF THE INTERMOUNTAIN WEST INCLUDING PARTS OF THE GREAT BASIN...

...SUMMARY...
Scattered strong/severe storms will be possible across portions of
the upper Great Lakes and Midwest regions Wednesday.  A few severe
storms may also occur across a portion of the Intermountain West
including parts of the Great Basin.

...Synopsis...
Short-wave troughing aloft is forecast to cross the northwestern
U.S. Wednesday, being shunted northeastward by a strengthening ridge
over the Interior West.  Farther east, short-wave troughing is
forecast to cross the Great Lakes/Midwest region through the period.

At the surface, a cold front will shift east/southeast across the
Great Lakes/Midwest and central Plains area, focusing a zone of
strong/locally severe storms through much of the period.

...Upper Great Lakes/Midwest into the mid Missouri Valley...
Showers and thunderstorms will likely be ongoing at the start of the
period across northern and western portions of the risk area.  As
upper troughing continues advancing east/southeast into/across the
risk area in conjunction with weak upper troughing, daytime
heating/destabilization south and east of ongoing convection will
combine with favorable large-scale ascent to support a diurnal
increase in storm coverage/intensity.  With a consistent model
signal of weak low pressure shifting northeast along the front
across northern Kansas and -- later -- northern Missouri,
backed/southerly low-level flow is expected across the slight risk
area beneath moderately strong mid-level westerlies.  Resulting
shear will support organized/rotating storms, though predominant
mode should trend toward clusters/linear segments near the front as
well as prior outflow.  While some tornado risk will exist, mainly
during the afternoon earlier in the convective cycle, large hail and
damaging winds will be the prevalent risks.  Storms will spread
east-southeast with time into the Midwest, with severe potential
likely lingering well into the overnight hours.

...Portions of the Intermountain West...
Gradual northeastward advance of a short-wave trough across the
Pacific Northwest and Great Basin region will provide a rather broad
area of modestly enhanced mid-level southwesterlies, as well as a
similarly extensive zone of favorable large-scale ascent.  In
conjunction with diurnal heating/destabilization, this will support
isolated afternoon thunderstorm development, spreading northeast
with time across the Great Basin vicinity toward WY/MT.  Along with
risk for hail with stronger cells, evaporatively enhanced downdrafts
-- owing to the deep mixed layer -- may produce locally damaging
wind gusts.  Risk should diminish later in the evening with the
onset of a diurnal decrease in storm intensity.

..Goss.. 07/25/2017

$$


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