Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 222126

Area Forecast Discussion
National Weather Service Tucson AZ
226 PM MST Fri Sep 22 2017

.SYNOPSIS...A strong low pressure system over the western United
States will continue to result in gusty winds across southeast
Arizona through Saturday, as well as a slight chance of showers and
thunderstorms mainly in the White Mountains. This system will also
usher in cooler temperatures, with readings expected to be below
normal through the early part of next week.


.DISCUSSION...A strong west coast trough and associated low pressure
system centered over northern Nevada will move slowly east/southeast
through Sunday when the low will be centered over southeast Utah.
Gusty southwest winds will occur across southeast Arizona ahead of
the trough axis, which is expected to push across the area late
Saturday afternoon into Saturday evening with a change in wind
direction from south/southwest ahead of the trough to west/northwest
behind the trough axis. Satellite imagery indicates some mid-level
moisture pooling ahead of this system over the eastern half the
forecast area, with a cloud band extending northeast-to-southwest
from near Springerville to Tucson to west of Nogales. There may be
just enough moisture to eke out a few sprinkles in the valleys, with
a slight chance of showers over the higher terrain and even the
possibility of some thunder in the White Mountains through Saturday
afternoon, or trough axis passage. Otherwise, falling heights and
thickness values will result in cooler temperatures across southeast
Arizona, starting in earnest on Saturday as drier air and dewpoints
in the 30s move in on the back side of this system. By Saturday
night/Sunday morning, clear skies and dewpoints falling into the 20s
will lead to morning lows in the mid 40s to mid 50s across the
forecast area, or the coolest readings since mid May. Below normal
temperatures will then continue through early next week.

In the Tuesday through Friday time frame next week, not many changes
from the previous forecast as there is still a high degree of
uncertainty pertaining to the models/ensembles in regards to
developing a closed low across the southwestern United States. Where
this low develops and how long it sits before ejecting northeast
play a big factor in how much moisture gets pulled back into the
region and where. Overall, with upper level troughiness across the
region have kept temperatures right around seasonal normals and gone
with a slight chance of showers and thunderstorms across the eastern
half of the forecast area.


.AVIATION...Valid thru 23/23Z.
There will be a slight chance of -TSRA/-SHRA mainly across the White
Mountains northeast of KSAD thru the forecast period. Otherwise, VFR
conditions are expected. SFC wind SWLY at 14-22 kts with gusts
around 30 kts thru 23/02Z, then diminishing SFC wind. SFC wind less
than 12 kts between 23/05Z and 23/16Z. Increasing SFC wind expected
again aft 23/16Z, with SWLY SFC wind at 12-20 kts and gusts to near
30 kts aft 23/19Z. The strongest winds Saturday will be east of KTUS
in the vicinity of KDUG and KALK. Aviation discussion not updated
for TAF amendments.


.FIRE WEATHER...There is a slight chance of thunderstorms mainly
across the White Mountains through Saturday. Dry conditions will
prevail area-wide Sunday through Tuesday morning. A slight chance of
thunderstorms returns to the White Mountains Tuesday afternoon, then
a slight chance of thunderstorms exists east of Tucson Wednesday and
Thursday. Expect gusty southwest 20-foot winds through early this
evening and then again Saturday afternoon. 20-foot winds will then
be terrain driven less than 15 mph Sunday into next Thursday.






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