Severe Storm Outlook Narrative (AC)
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ACUS11 KWNS 141944
SPC MCD 141944

Mesoscale Discussion 1645
NWS Storm Prediction Center Norman OK
0244 PM CDT Thu Sep 14 2017

Areas affected...Southern Utah...Northern Arizona

Concerning...Severe potential...Watch possible

Valid 141944Z - 142215Z

Probability of Watch Issuance...40 percent

SUMMARY...A severe threat will continue across parts of northern
Arizona and southern Utah this afternoon. Isolated large hail and a
few damaging wind gusts may occur with the stronger storms. The
threat eventually may affect far southwest Colorado and northwest
New Mexico later this afternoon. Weather watch issuance can not be
ruled out.

DISCUSSION...The latest surface analysis shows a broad area of low
pressure from southern Nevada extending southeastward into western
Arizona. Surface winds to the east of this feature are mostly from
the south and south-southwest. This is helping to maintain low-level
moisture from the Mogollon Rim northward into southern Utah where
surface dewpoints are generally in the lower 50s F. Surface heating
this morning into the early afternoon has allowed the airmass to
destabilize with the RAP showing MLCAPE values in the 500 to 1000
J/kg range.

At mid-levels, water vapor imagery shows an upper-level low over far
southern Nevada. Large-scale ascent ahead of this feature is
supporting convective development across north-central Arizona and
southern Utah. This convection is forecast to spread eastward across
northeast Arizona and southeast Utah over the next 2 to 4 hours. The
instability combined with 40 to 50 kt of 0-6 km shear evident on
regional WSR-88D VWPs should be sufficient for a severe threat.
Thunderstorms that form closer to the upper-level low where a cold
pocket is located may have a potential for isolated large hail. A
few damaging wind gusts may also occur especially if a cold pool can
organize as convection moves further east late this afternoon.

..Broyles/Karstens.. 09/14/2017

...Please see for graphic product...


LAT...LON   37471288 36601297 35881252 35611176 35570866 36170809
            37310859 38031145 37471288 is the U.S. government's official web portal to all federal, state and local government web resources and services.