Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 200336

Area Forecast Discussion
National Weather Service Tucson AZ
835 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 quiet evening across southeast Arizona with mostly
clear skies and decreasing southwesterly winds. After high
temperatures reached normal to slightly above normal values this
afternoon, many locations have cooled down into the upper 70s and
80s as of 03Z. We`ll see the gusty southwest winds kick up again
Wednesday afternoon as the pressure gradient remains tight, with the
strongest winds occurring during the second half of the work week.
Otherwise, dry conditions into Thursday with perhaps a shower or two
near the Int`l border Wednesday afternoon. Confidence is pretty low
on this occurrence however, as moisture is lacking, especially above
700 mb. No updates to the forecast this evening. Please see the
remaining sections for additional details.


.AVIATION...Valid thru 21/06Z.
FEW clouds above 8k ft AGL becoming SKC overnight into Wednesday.
FEW-SCT clouds redeveloping above 8k ft AGL Wednesday afternoon. SFC
wind mainly less than 10 kts into Wednesday morning. SWLY SFC wind
increasing late Wednesday morning to 12-16 kts with gusts to 25 kts
continuing through the afternoon hours. 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 will be possible near eastern and
southeastern mountains before drying out this weekend.


.PREV 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.






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