SPC MD 2018

SPC MD 2018


Mesoscale Discussion 2018
NWS Storm Prediction Center Norman OK
0216 PM CDT Sun Aug 20 2023

Areas affected…Central Arizona to far southwest Utah

Concerning…Severe potential…Watch unlikely

Valid 201916Z – 202115Z

Probability of Watch Issuance…5 percent

SUMMARY…Thunderstorms developing through the late afternoon may
pose a risk for sporadic severe gusts. Poor buoyancy will modulate
the overall threat; watch issuance is not expected.

DISCUSSION…Latest GOES visible imagery depicts clusters of
building cumulus across central AZ. This trend is likely
attributable to a combination of filtered heating of the terrain
(with temperatures rising into the 80-90s across central AZ) and
increasing ascent implied by gradually strengthening convergence
between 850-700 mb (per recent objective analysis). Lingering cloud
cover has muted diurnal destabilization downstream into northern AZ
and southern UT, but most forecast guidance continues to suggest
that destabilization will be adequate (MUCAPE generally around 500
J/kg) across the region for convective initiation/maintenance
between 20-23 UTC. Additionally, strong mid-level flow on the
periphery of TC Hilary will promote deep-layer shear values on the
order of 35-45 knots, which may compensate for the meager buoyancy
to some degree.

Regardless, a severe wind risk may emerge as thunderstorms migrate
into areas that can achieve sufficient boundary-layer mixing to
support downdraft accelerations driven by evaporative cooling. Based
on forecast soundings, dewpoint depressions on the order of 30+ F
may be required for such accelerations to occur. A few locations
across central AZ area already reaching this criteria, and areas to
the north/northwest are showing a delayed warming trend as cloud
cover diminishes. These observations hint that this scenario is at
least plausible; however, confidence in the spatial coverage of
favorable thermodynamic profiles (and by extension, the overall
severe threat) remains low.

..Moore/Grams.. 08/20/2023

…Please see www.spc.noaa.gov for graphic product…


LAT…LON 32510941 32000942 31961014 32281105 33161191 35201312
36331369 37061365 37461332 37621291 37671254 37581207

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