Damaging Wind in Arizona, September 5, 2017

Area Forecast Discussion
National Weather Service Tucson AZ
136 PM MST Tue Sep 5 2017

.SYNOPSIS...Isolated to scattered showers and thunderstorms
west of Tucson into this evening. Mostly dry Wednesday with the
exception of the White Mountains where a few thunderstorms are
possible. Additional moisture will move in starting Thursday and
continuing into Saturday resulting in increased thunderstorm
coverage. Temperatures will run several degrees above average
through Thursday, then cool off to seasonal normals Friday through
Sunday.

&&

.DISCUSSION...East to northeasterly flow aloft continues across
southeast Arizona as high pressure aloft is centered across the
Great Basin. Drier air is making its way westward this afternoon
with dewpoints now in the 40s from Tucson, though 50s to low 60s
remain prevalent for Central/Western Pima County. Latest visible
satellite imagery shows a Cu field has developed across much of the
area. The convective initiation is just starting now with a weak
storm over South Central Pinal County. Otherwise, convective
initiation is expected to continue to the west of Tucson in the
vicinity of the lower level convergence from the drier easterly flow
and the more moist atmosphere over the western deserts. Very gusty
outflow winds will continue to be the main concern this afternoon
into early evening which may produce areas of blowing dust reducing
visibility as the storms propagate to the west.

The mid/upper level pattern will gradually transition over the next
few days as the high center shifts more towards the southeast into
New Mexico. Meanwhile, an upper low will continue to meander about
in the eastern Pacific off the California coast. We'll be in a
somewhat dry airmass Wednesday, thus shower and thunderstorm
activity will remain rather limited with the exception of the White
Mountains where a few thunderstorms remain possible. As the flow
gradually becomes more southerly, increased moisture starting
Thursday, but especially on Friday will result in a ramp up of
showers and thunderstorms. This could persist on Saturday as well
but that will much depend on how active Friday is. By Sunday, the
ridge axis will begin to shift west with the atmosphere likely
drying out reducing convective activity into early next week.

Temperatures will remain about 3 to 5 degrees above normal today,
then gradual cooling will commence Thursday, with temperatures
returning to seasonal normals Friday and Saturday before warming up
again Sunday into early next week.

&&

.AVIATION...Valid thru 07/00Z.
VFR conditions. Isolated thunderstorms possible this afternoon and
early evening, mainly near west of KTUS. Surface wind out of the
east at 5 to 15 mph, except gusts to 40 kts near stronger TSRA.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Isolated to scattered afternoon and evening
thunderstorms into Saturday, then isolated thunderstorms mainly near
the mountains northeast of Tucson to the White Mountains Sunday
through Tuesday. 20-foot winds through Friday will generally be from
the east to southeast at 5-15 mph with occasional gusts to 25 mph.
Expect terrain driven surface winds next weekend.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...None.

&&

GL

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Special Weather Statement
National Weather Service Tucson AZ
251 PM MST TUE SEP 5 2017

AZZ502-052215-
Tohono O'odham Nation including Sells-
251 PM MST TUE SEP 5 2017

...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL PIMA COUNTY UNTIL 315 PM
MST...

At 250 PM MST, Doppler radar was tracking a strong thunderstorm over
Sells, moving west at 20 mph.

Half inch hail and wind gusts of 50 mph and blowing dust will be
possible with this storm.

Locations impacted include...
Sells, Topawa, Big Fields, Cowlic, Little Tucson and Artesa.

LAT...LON 3200 11176 3182 11175 3177 11213 3204 11214
TIME...MOT...LOC 2150Z 088DEG 18KT 3191 11185

Francis