SPC MD 1617

MD 1617 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR PORTIONS OF AZ

Mesoscale Discussion 1617
NWS Storm Prediction Center Norman OK
0510 PM CDT Mon Sep 04 2017

Areas affected...Portions of AZ

Concerning...Severe potential...Watch unlikely 

Valid 042210Z - 050045Z

Probability of Watch Issuance...20 percent

SUMMARY...Thunderstorms developing over the higher terrain of mainly
central/southern AZ should move west-southwestward this afternoon
and evening while posing an isolated threat for damaging winds and
marginally severe hail. Watch issuance is unlikely.

DISCUSSION...Visible satellite and radar imagery as of 22Z depict
widely scattered convection that has developed along the Mogollon
Rim of central AZ on the southern extent of a mid-level anti-cyclone
over the Great Basin. 15-25 kt of northeasterly to easterly
mid-level winds are present over much of AZ and western NM per
latest RAP Mesoanalysis, and this modestly enhanced flow will likely
encourage ongoing thunderstorms to develop west-southwestward off
the higher terrain and into the lower deserts of central/southern AZ
over the next few hours. Additional convection may form over the
White Mountains of southeastern AZ and subsequently move westward
towards Tucson.

Strong diurnal heating with generally clear skies has allowed
surface temperatures to warm into the upper 90s to lower 100s across
lower elevations, which is combining with a seasonably moist
low-level airmass (surface dewpoints mostly in the mid 50s to mid
60s) to support 500-1500 J/kg of MLCAPE. A very well-mixed boundary
layer with inverted-v characteristics will encourage efficient
momentum transfer and acceleration of convective downdraft winds to
the surface, and isolated instances of damaging winds should be the
main threat with convection as it moves off the higher terrain. Some
marginally severe hail may also occur given the degree of buoyancy
present, along with steep mid-level lapse rates. Regardless, without
stronger mid-level winds and related effective bulk shear, the
overall severe threat will probably remain too marginal/isolated to
warrant watch issuance.

..Gleason/Dial.. 09/04/2017

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

ATTN...WFO...TWC...FGZ...PSR...VEF...

LAT...LON   31721247 32851309 33871363 34661391 35391402 35831369
            35071200 34111055 33250972 31290958 31301107 31721247 

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