Severe Storm Outlook Narrative (AC)
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000
ACUS02 KWNS 221723
SWODY2
SPC AC 221722

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1122 AM CST Wed Feb 22 2017

Valid 231200Z - 241200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
FAR NORTHERN MISSOURI...SOUTHERN IOWA AND FAR NORTHWESTERN
ILLINOIS...

...SUMMARY...
Isolated thunderstorms with hail are forecast across portions of the
Midwest primarily after sunset on Thursday through early Friday
morning.  A few storms may also occur across the southern Great
Lakes region and upper Ohio Valley. Isolated thunderstorms will also
be possible along the east coast of Florida.

...Iowa/Northern Missouri/Far Northwest Illinois...
A negatively-tilted upper-level trough will move eastward across the
Rockies on Thursday and into the southern and central Plains
Thursday night as an upper-level low develops across Nebraska.
Southwest mid-level flow will be in place ahead of the system in the
mid to upper Mississippi Valley as a strong surface low develops in
the central Plains. The surface low will move into the mid Missouri
Valley during the evening with moisture advection taking place from
the Arklatex northward into the Ozarks. To the east of the surface
low, a warm front is forecast to move northward into the mid
Missouri Valley extending eastward into the Mississippi Valley. The
models suggest convective development will be possible along and to
the north of the warm front from northern Missouri into southern
Iowa during the mid to late evening.

NAM forecast soundings from 03Z to 06Z/Friday to the north of the
warm front in northern Missouri and southern Iowa show a low-level
temperature inversion with a stable boundary layer. Instability is
located primary above 700 mb with MUCAPE values forecast to be in
the 1000 to 1500 J/kg range just to the north of the warm front. In
addition, 500 mb temperatures are forecast to be in the -18 to -20C
range with 700 to 500 mb lapse rates around 7.5 C/km. This
thermodynamic environment along with 50 kt of effective shear should
support hail formation within the stronger elevated updrafts.  A 5
percent probability has been added for this outlook across far
northern Missouri, southern Iowa into far northwestern Illinois
where it appears a hail threat may develop during the mid to late
evening on Thursday.

..Broyles.. 02/22/2017

$$


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