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Day 1 Outlook Convective Tornado
Hail Wind
Categorical Day1 1200Z Outlook
  
Images courtesy of the NWS Storm Prediction Center
 Forecast Discussion

  
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ACUS01 KWNS 220559
SWODY1
SPC AC 220557

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1257 AM CDT Thu Jun 22 2017

Valid 221200Z - 231200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM IOWA
NORTHEASTWARD TO LOWER MICHIGAN...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS EASTERN
COLORADO...WESTERN KANSAS...PORTIONS OF THE OKLAHOMA AND TEXAS
PANHANDLES...AND FAR NORTHEASTERN NEW MEXICO...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE LOWER
MISSISSIPPI VALLEY AND DEEP SOUTH...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE CENTRAL
AND SOUTHERN HIGH PLAINS EASTWARD TO WESTERN NEW YORK AND
VICINITY...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE LOWER
MISSISSIPPI VALLEY NORTHEASTWARD INTO KENTUCKY...

...SUMMARY...
Severe thunderstorms are expected Thursday afternoon into Thursday
night across portions of the southern Great Lakes through Iowa,
Nebraska, northern and western Kansas into portions of the central
and southern High Plains.  Meanwhile, a tornado threat will exist
across the lower Mississippi Valley and Deep South as the remnants
of Tropical Storm Cindy advance inland.

...Synopsis...
A vigorous mid-level system currently centered in Saskatchewan will
migrate southeastward into Manitoba and Ontario throughout the
forecast period.  A trailing, positive-tilt trough extending
southwest from this disturbance will amplify across the northern
Rockies and Plains, spreading broadly cyclonic and increasing
mid-level flow atop downstream areas from the Dakotas to the Great
Lakes.  To the southwest, a persistent mid/upper ridge will remain
anchored over Arizona.

At the surface, a cold front currently observed from northwestern
Minnesota to central South Dakota will migrate southeastward during
the day ahead of a substantial surface ridge.  This front will
extend from central Wisconsin into northwestern Kansas by early
evening and reach central Illinois by the end of the period,
interacting with an unstable airmass just ahead of it and resulting
in areas of scattered to numerous thunderstorms in the central U.S. 
Farther south, Tropical Storm Cindy will make inland progress across
western Louisiana/far east Texas throughout the day. 
Shear/instability profiles east of the circulation will result in an
isolated tornado threat throughout much of the forecast period,
perhaps peaking in the mid-afternoon.

...Iowa/Missouri eastward to Lower Michigan and into western New
York...
Scattered thunderstorms (containing at least a marginal hail/wind
threat) will be ongoing at the beginning of the forecast period
across Lower Michigan and eastern Wisconsin.  These storms should be
mostly elevated atop a shallow, stable boundary layer, although
shear profiles and modest elevated instability will be supportive of
organized convection into the early morning hours.  In the
afternoon, storms will redevelop along and just ahead of the
advancing surface cold front initially in central Wisconsin and
vicinity, with more development southwestward along the front into
Iowa.  Surface temperatures in the 80s F will help boost
surface-based CAPE into the 1500-2000 J/kg range, while mostly
unidirectional wind profiles will favor splitting cells and
eventually lines/bands of convection given the linear forcing along
the front.  Hail and damaging wind gusts will be the primary threats
with this activity, and storms should eventually congeal into one or
two linear convective complexes while migrating southeastward toward
northern Missouri eastward to central Illinois.

Farther east into Pennsylvania and western New York, models
(particularly CAMS) suggest that isolated convection will develop
from noon onward.  This scenario is a bit uncertain given rising
mid-level heights (and likely attendant mid-level subsidence). 
Nevertheless, shear/instability profiles will likely support some
hail and damaging-wind threat if storms do indeed evolve. 
5%/marginal wind/hail probabilities have been extended eastward into
the region for this outlook update, and may need to be extended
further east in later updates if models/observations continue to
suggest convection evolving further east than currently expected.

...Portions of the High Plains from southeastern Wyoming into
eastern New Mexico and the Texas South Plains...
A complicated surface pattern will evolve over the course of the
afternoon as a cold front migrates southward across western Kansas
and a surface low/trough extends southward across eastern New
Mexico.  Very hot surface temperatures will develop out ahead of the
front, with an uncapped, deeply mixed boundary layer and appreciable
instability rooted just above that boundary layer supporting
high-based convection.  Storms should develop around/after 21Z and
propagate southward, with congealing cold pools fostering linear
segments capable of severe wind gusts and large hail.  Farther
northwest into Colorado, a post-frontal upslope regime will foster
isolated to scattered thunderstorms with hail and damaging wind
gusts potential.  A supercell or two cannot be ruled out in this
regime given low-level easterly flow veering to westerly in the
mid-levels.  

...Portions the Lower Mississippi Valley and Deep South extending
northward into Kentucky...
Wind fields will gradually increase across the region as Cindy
migrates northward into western Louisiana.  Surface heating will
occur within the moist and strongly sheared environment, boosting
instability and resulting in scattered bands of convection
throughout the day.  This convection will likely contain transient
mesocyclones, with a few tornadoes possible in cells that can
exhibit strong rotation.  Models consistently depict a north-south
band of convection across Alabama during the day with strong shear
profiles, and 5% tornado probabilities have been extended eastward
into this region to address this potential threat.

..Cook/Broyles.. 06/22/2017

$$