Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 151635
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
935 AM MST Sun Oct 15 2017

.SYNOPSIS...Dry conditions with above normal daytime temperatures
will continue this week. Gusty east to southeast winds will also
occur at times this afternoon into early Tuesday. Expect cooler
temperatures Saturday, and a few showers and thunderstorms may occur
mainly near the White Mountains.

&&

.DISCUSSION...IR/visible satellite imagery and surface observations
indicate clear skies to scattered cirriform clouds across southeast
Arizona at this time. Dew points at lower elevations valid 9 am MST
ranged from the mid teens across northeastern sections (e.g. KSAD)
to the mid 20s-mid 30s elsewhere. These temps were 15-25 degrees
lower versus 24 hours ago across eastern sections, and were about 2-
5 degrees lower elsewhere versus this time Saturday. Surface temps
valid 9 am MST were within a degree-or-two (plus or minus depending
upon location) of temps from 24 hours ago.

15/12Z KTWC sounding total precip water value of 0.49 inch was down
nearly 0.20 inch versus Saturday morning. 15/12Z upper air plots
depicted a ridge axis extending from northern California
southeastward across southern Arizona and into Chihuahua Mexico.
Meanwhile, a 500 mb trough axis extended from west Texas
northeastward into the Great Lakes region. Light to moderately
swly/wly flow aloft prevailed across southeast Arizona.

Surface pressure gradient continues to tighten across eastern
sections in response to high pressure building across west Texas.
Gusty east to northeast surface winds have occurred earlier this
morning across southwest New Mexico, and easterly winds are expected
to increase in speed east of Tucson later today. High temperatures
today across eastern sections will be about 5-10 degrees cooler
versus Saturday, but a few degrees of warming will likely occur
today from Tucson westward into the western deserts due to the
general downslope near-surface wind regime.

Surface winds are expected to strengthen elsewhere tonight and into
Monday. Favored east wind prone locales including KTUS should
experience gusty east to southeast winds especially late tonight and
Monday morning, then winds are expected to diminish somewhat Monday
afternoon. Some locally gusty winds will continue Monday night into
Tuesday morning, then winds will abate by Tuesday afternoon as the
surface pressure gradient loosens. A few degrees of warming will
occur across eastern sections by Tuesday, but virtually no change in
daytime high temperatures from Tucson westward Monday into Tuesday.
Otherwise, clear skies to mostly clear skies will prevail into
Tuesday.

There are no updates planned at this time. Please refer to the
additional sections for further detail.

&&

.AVIATION...Valid thru 16/18Z.
Expect clear skies to scattered clouds above 20k ft AGL into Monday
morning. Surface wind generally becoming ely/sely 5-15 kts with
gusts to 20 kts this afternoon. The strongest speeds this afternoon
should occur east of KTUS. Surface wind this evening into Monday
morning ely/sely 8-18 kts with gusts to 30 kts. The strongest speeds
late tonight and Monday are expected to occur vicinity of KTUS.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Dry conditions will continue through Friday followed
by a slight chance of showers and thunderstorms mainly near the New
Mexico border Saturday. Gusty east to southeast winds will occur at
times this afternoon into early Tuesday. Normal diurnal wind trends
with occasional afternoon west to southwest gusts will then prevail
during the latter part of this week.

&&

.PREV DISCUSSION /204 AM MST/...Quiet weather remains in place
across the region once again this morning as only a few high clouds
are noted on IR satellite as of 09Z. Longwave ridging is evident
across the area per water vapor imagery with a cold front clearly
visible from the Great Lakes through Oklahoma and into New Mexico.
Quite an impressive front as the mid level GOES-16 water vapor
channel is picking up some of the near surface features associated
with it as it makes its way through the TX panhandle.

This cold front will bring increased easterly winds to the area
later today along with slightly cooler temperatures to areas east of
Tucson. Points from Tucson westward will likely see similar
temperatures to those we`ve seen for much of the past week with
highs in the low/mid 90s. Similar story expected for Monday with
another round of persistent easterly winds (albeit with slightly
lower speeds) with desert temps in the low/mid 90s. Easterly winds
will relax across the area on Tuesday through Thursday although
temps will remain virtually unchanged from day to day.

Finally - a change from the norm late in the week as deterministic
and probabilistic guidance continue to point to a trough moving
through the Great Basin and into the Four Corners late in the
week/into the weekend. Nearly all guidance is suggesting an increase
in clouds/moisture ahead of the trough, but are less than
enthusiastic about precip chances (especially in the lower
elevations). There could be a few terrain driven sprinkles or a
brief shower that occurs in the White Mountains this coming weekend,
otherwise it appears precip chances are slim given the trajectory of
the trough. Maintained the idea of a mention of precip in the
northern parts of Graham/Greenlee Co`s on Saturday but this should
be short lived. If nothing else it will knock lower elevation
temperatures back a few degrees into the mid/upper 80s late in the
week/early next weekend.  Some of the more protected high elevation
valleys could see readings fall into the upper 30s Sunday morning if
clouds manage to clear out fast enough. Following the trough - more
sunny/dry weather in the cards to close out next weekend.

&&

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

&&

$$

Francis
PREVIOUS DISCUSSION...Leins

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