Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 220415
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
915 PM MST Thu Sep 21 2017

.SYNOPSIS...A low pressure system will bring strong and gusty
winds each afternoon through Saturday with predominantly dry
weather. Cooler temperatures arrive Friday, with readings holding
below average through at least the middle of next week.

&&

.DISCUSSION...Another breezy to windy afternoon across southeastern
Arizona due to a well amplified trough that continues to deepen over
the Intermountain West. Most of the area experienced peak gusts of
25-35 mph before winds quickly decreased after sunset. Satellite
imagery currently shows a dissipating cu field with some orographic
cirrus streaming in from the northern Baja Peninsula due to a strong
west-southwesterly jet. The stable 22/00Z sounding measured
precipitable water at 0.8", which is right on average for the waning
days of the monsoon. No reason to expect deviation from a dry and
mostly clear night with near seasonal temperatures. Please see the
previous discussion below for further details on the days to come.

&&

.AVIATION...Valid thru 23/06Z.
Mainly SKC through tonight with variable SFC winds below 10 kts.
Winds increase Friday afternoon SWLY 15-20 kts with gusts to 30 kts,
quickly decreasing after 23/02Z. 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 early evening hours through Saturday. Temperatures
will be decreasing below normal Friday and this trend continues into
next week. Dewpoints also drop on Sunday as the trough slowly pushes
through the region.

&&

.PREV DISCUSSION...Winds have picked up about as expected this
afternoon as a trough digs into the region from the northwest.
Most of our area will be a little stronger tomorrow, but still under
wind advisory levels (sustained 30 mph winds are needed). On
Saturday the focus will be ahead of the front with mainly eastern
areas emphasized. Wind prone locations in Cochise county may reach
advisory levels Saturday afternoon, but it shouldn`t be very
widespread.

Temperatures today have been similar to yesterday,ahead of height
falls bringing few degrees of cooling tomorrow. Some cool air
advection associated with the trough will drop temperatures several
degrees below average for late September over the weekend.
That means widespread 80s for daytime highs. Overnight lows Sunday
morning and Monday morning generally in the 50s from Tucson into the
lower deserts, and 40s in cooler eastern valleys. One or two coldest
valley spots could see upper 30s Monday morning with freezes
possible in a few higher mountain locations.

Medium range operational models and ensembles are pretty consistent
in leaving modest low pressure behind over the desert southwest as
higher latitude support lifts into the northern plains early next
week. That would tend to retard any warming trend next week while
also tapping into a little moisture from the southeast and east
around the middle of the week. Any shower activity that we might
manage would be closer to the New Mexico border.

Even with the residual troughiness delaying things, we should see
high pressure build in from the west by later next week. An
amplified flow at day 10 hints at a chance of relatively hotter
temperatures to start October.

&&

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

&&

$$

Howlett

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