134
FXUS65 KTWC 201548
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
848 AM MST Fri Sep 20 2024

.SYNOPSIS...Breezy and dry conditions with temperatures near
seasonal normal through the start of the weekend. Temperatures will
warm to above normal on Sunday and into the new week.

&&

.UPDATE...Water vapor imagery shows a closed low moving through
southern California with high pressure centered over Texas. The
low will progress eastward today into Arizona and will help
produce gusty southwest winds with speeds 15-25 mph and gusts
25-35 mph. High temperatures will be right around normal with
Tucson likely seeing its 127th straight 90 degree or higher day.
It`s possible this streak is broken tomorrow thanks to cooler air
in the wake of the trough. Please see the previous discussion for
longer term details.

&&

.PREV DISCUSSION... /issued 220 AM MST Fri Sep 20 2024/
A dry weather system will be moving into the region today to
bring breezy conditions. As of the 0840Z water vapor imagery, a
low pressure center is along the Los Angeles coast and moving
southeast into the deserts of southern California. The low
pressure center axis will push into central Arizona and the
resulting pressure gradient will bring those breezy conditions. M
The 00Z HREF wind probabilities show at least 20% to 30% chance of
exceeding 20 mph and higher chances in the more wind prone or
exposed areas that are susceptible to southwest winds. Chances for
exceeding 25 mph is less than 10 percent and mainly confined to
the west facing slopes of the Sky Islands. Therefore, majority of
Southeast Arizona will likely experience at least 15 mph with
several locations can experience closer to 20 mph and up to around
25 mph. Also, with the tightening of the pressure gradient, it
will be enough to squeeze some moisture to form of clouds later
this evening. Cloud coverage will generally be low across the
region, but enough to block a few stars.

The system will exit our area by late Friday and into Saturday
which will keep temperatures near to slightly below normal.
Saturday morning lows is forecasted to be one of the coolest
mornings that most locations haven`t experience for a long time.
Winds will lessen but can be breezy at times on Saturday.

Next change in the pattern starts on Sunday. A ridge of high
pressure will build over the region. Ensemble models have been
consistently showing this ridge building across the region and
lasting through all week and possibly into the new weekend. This
means temperatures are back on the rise to remind us that summer
hasn`t quite finish. (We got a taste of fall today and tomorrow.)
100 degrees temperatures will start to move from the west to the
east, starting in Ajo and reaching to Tucson by midweek. Tucson
has a 25 percent chance of hitting 100 on Thursday and those
chances will increase to 50% through weekend. This broad ridge
appears to stick around for a little over a week. A small wrinkle
to the forecast is the 15 to 25 percent chances for thunderstorms
in the White Mountains and down into Greenlee County. These are
low chances due to the fact not all of the ensemble models agree
on the placement of the high pressure center, but it is a non-
zero chance for a thunderstorm to form over the higher terrain in
the late Wednesday. Something to keep an eye out over the next
several days. Any way, the main story next week is the hot
temperatures across the region.

&&

.AVIATION...Valid through 21/12Z.
SKC through majority of the forecast period with FEW low level
clouds at or around 10-12k ft AGL developing after 21/03 to the
end of the forecast period. Light SFC winds this morning and
becoming southwesterly by 20/16z at speeds 12-18 kts and gusts to
around 30 kts. After 21/04z, SFC winds return to variable and less
than 10 kts to the end of the period. Aviation discussion not
updated for TAF amendments.

&&

.FIRE WEATHER...Dry conditions with temperatures within a few
degrees of normal through Saturday. Today, breezy 20-foot south-
southwesterly winds at speeds of 15 to 20 mph with gusts up to
around 25 mph and locally higher in wind prone areas. Tomorrow`s winds
will lessen down to 10 to 15 mph. Min RHs will generally be 15 to
20 percent in the lower locations and 20 to 30 percent in the
higher locations. Starting Sunday, high pressure ridge will bring
warmer temperatures and lighter winds through the new week.

&&

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

$$

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