FXUS65 KTWC 192138

Area Forecast Discussion
National Weather Service Tucson AZ
238 PM MST Tue Sep 19 2017

.SYNOPSIS...Dry conditions across much of the area with seasonably
warm temperatures through Wednesday. A strong low pressure trough
will then bring isolated showers and thunderstorms, gusty winds and
a cooling trend Thursday into Friday. Expect dry conditions with
below average temperatures this weekend.


.DISCUSSION...A zonal flow across the region with dry conditions
north of us and relatively deeper moisture still available in
Sonora. We`ll continue to see just enough moisture for isolated
thunderstorms near the far southeast mountains. Otherwise, a
deepening trough will dominate weather through Western states. For
us that will translate into gusty winds and a cooling trend. Yay!

The pattern is becoming stagnant and amplified, with western
states slowly developing an unseasonably deep trough over the next
several days, while eastern states experience a high amplitude
ridge. Temperatures will initially hang out a few degrees above
average through Thursday before dropping several degrees each day
Friday into Sunday. By Sunday afternoon we`ll be around 6 to 8
degrees below average. Overnight lows Sunday morning through
Tuesday morning around 3 to 7 degrees below average, with our
first reading in the 50s expected at Tucson International since
May 21st.

Isolated thunderstorms possible with the trough, but winds and
cooler temperatures will likely be the bigger stories for most
folks. With SE AZ in between major features, expect the gradient
to enhance to windy levels at times, especially near higher
terrain and typical wind prone locations. Strongest winds Friday
or Saturday afternoon, but remaining below advisory levels.

All in all, a nice transition season trough that will cool things
down and bring gusty winds at times. Just remember, cooler is a
relative term.


.AVIATION...Valid thru 21/00Z.
A few storms near the far southeast mountains and international
border this afternoon, otherwise few to scattered clouds above 8k
ft AGL. Surface wind through the early evening hours will be swly
to nwly at 13-20 kts with gusts to near 30 kts. Surface wind
mainly less than 12 kts at other times. Aviation discussion not
updated for TAF amendments.


.FIRE WEATHER...A deepening upper trough over the western United
States will result in gusty southwest winds, especially during the
afternoon and evening hours through Saturday. The strongest winds
are expected on Thursday and Friday, with a cooling trend Friday
through Sunday. A few storms possible near eastern and
southeastern mountains before drying this weekend.






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