Heat in Arizona, September 29, 2023

Area Forecast Discussion
National Weather Service Tucson AZ
153 AM MST Fri Sep 29 2023

.SYNOPSIS...Above normal temperatures continue today as dry
conditions prevail. A weather system will pass to our north bringing
gusty winds this weekend into early next week along with cooler
temperatures.

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.DISCUSSION...Clear skies this morning across our forecast area as
southwesterly flow aloft starts to increase today out ahead of a
trough digging down the west coast. Heights and thicknesses remain
elevated enough in this southwest flow regime to continue resulting
in well above normal temperatures with Tucson once again approaching
triple digit high temperatures. As the gradient starts to tighten,
surface winds will increase just a bit today with some afternoon
breezes peaking in the 15 to 20 mph range.

As the trough continues to dig this weekend, a closed mid/upper low
will form over northern California and slowly move east through the
Great Basin. This regime will result in a transition to cooler
temperatures but will be accompanied by gusty winds both Saturday
and Sunday. The strongest winds will be from Tucson area westward
Saturday, then from Tucson eastward Sunday. South to southwest winds
of 20 to 30 mph with gusts to 40 mph will be possible. Expect winds
to generally stay below wind advisory threshold levels, with
critical fire weather the main concern. A Red Flag Warning has been
hoisted for Saturday for Pima and Pinal Counties and most of the Sky
Islands. Areas of critical fire weather are possible Sunday as well
from Tucson eastward. See fire weather discussion below for
additional information. Otherwise, dry weather with this system
except for right along the New Mexico border where a 10 to 20
percent chance of showers is expected Saturday. By Sunday,
temperatures will have lowered to near normal levels for early
October.

Monday will still see some residual gusty winds mainly for eastern
areas as the trough axis will be slow to push east. The coolest
temperatures are likely Tuesday with highs near to slightly below
normal before heights increase the middle of next week as ridging
aloft builds back in.

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.AVIATION...Valid through 30/12z.
Generally SKC for most of the forecast area through the forecast
period with the exception being eastern areas near the NM border.
This includes KDUG where FEW-SCT clouds AOA 12-20k ft MSL are
expected. SFC winds light and variable early this morning, becoming
SLY/SWLY with speeds ranging btwn 12-18kts aft 29/16Z and occasional
gusts up to 30 kts. Sfc winds taper off to 12 kts or less aft
30/04Z. Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Dry weather will prevail through most of next week
except for Saturday when there will be a 10-20 percent chance of
showers along the New Mexico border. Minimum relative humidity
values through the forecast period will be mainly 10-20 percent from
Tucson west, 15-25 percent in south/eastern valleys and 20-30
percent over the higher elevations. As a weather system impacts the
area, expect south to southwest afternoon breezes to increaese
today, peaking on Saturday and Sunday, then gradually tapering off
early next week. Expect sutained south to southwest winds Saturday
of 20 to 30 mph for much of the area, then for areas from Tucson
eastward Sunday. The combination of these strong winds and low
relative humidity values has led to the issuance of a Red Flag
Warning for Pima and Pinal Counties and most of the Sky Islands
Saturday. Relative humidity values will be slightly higher Sunday
but areas of critical fire weather conditions are possible
Sunday from Tucson eastward.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 11 AM to 7 PM MST Saturday for AZZ150-151-154.

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