Severe Storm Outlook Narrative (AC)
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ACUS11 KWNS 221812
SPC MCD 221812

Mesoscale Discussion 1123
NWS Storm Prediction Center Norman OK
0112 PM CDT Thu Jun 22 2017

Areas affected...Portions of eastern CO

Concerning...Severe potential...Watch possible

Valid 221812Z - 222015Z

Probability of Watch Issuance...40 percent

SUMMARY...Some increase in the threat for large hail and strong to
damaging winds should occur with thunderstorms developing this
afternoon. Watch issuance is possible.

DISCUSSION...Recent visible satellite imagery shows towering cumulus
building along the Front Range of eastern CO near Boulder as a
surface cold front provides the low-level convergence needed to
support convective initiation. Even though low-level moisture
remains quite limited at the moment along/north of the front,
continued diurnal heating and a gradual increase in low-level
moisture (even with northerly trajectories) is expected through the
remainder of the afternoon across much of eastern CO per surface
observations. Steep mid-level lapse rates are also present across
much of this region per 12Z sounding from DNR. As this gradual
increase in low-level moisture occurs, a corresponding increase in
instability is expected, with MLCAPE of generally 500-1500 J/kg
expected by peak heating around 22-00Z. Although low-level flow
should remain weak, mid-level winds around 20-40 kt and a strongly
veering profile with height should support about 35-45 kt of
effective bulk shear, stronger across northeastern CO. A mix of
supercells and short line segments may develop both along the Front
Range and the surface cold front. Isolated large hail and strong to
locally damaging winds appear possible with these thunderstorms, and
a watch may be needed in the next several hours across parts of
eastern CO depending on short-term radar and observational trends.

..Gleason/Guyer.. 06/22/2017

...Please see for graphic product...


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