Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 250347

Area Forecast Discussion
National Weather Service Phoenix AZ
847 PM MST Fri Mar 24 2017

A new Pacific disturbance is expected to move eastward across
northern Arizona on Saturday. This Saturday system is expected to be
a dry one for southeast California and southern Arizona, with just
some increase in cloudiness and winds. This will be followed by
another quick moving high pressure system on Sunday, then another
Pacific disturbance is forecast for later Monday and Tuesday,
particularly over eastern Arizona. Dry and warmer weather will
return next Wednesday and Thursday, followed by another Pacific
storm on Friday.



Mostly clear skies are being reported across our CWA this evening
as most of our area is sitting under a weak transient ridge.
However, the next Pacific trough is already moving inland and is
bringing light rain to portions of central and northern
California. For us, all we are expecting from this trough is an
increase in high level clouds late tonight and stronger winds for
Saturday. Numerical model guidance suggests the strongest winds
should stay out west in SE California where gusts could possibly
approach 30 mph. Unlike the last system, the best dynamics and
moisture should stay to our north so we are not expecting anything
in terms of precipitation. However, the SREF plumes do have one
member that shows a trace of precipitation at Sky Harbor tomorrow
so it is not out of the realm of possibility (<5% chance) to see a
rogue sprinkle for the northern most parts of our CWA. Outside of
the stronger winds, Saturday looks like it is shaping up to be
quite pleasant.



Sunday and Sunday night...

Another transitory upper level ridge will build over the region
Sunday and Sunday night, resulting in mostly clear, dry, and warm
conditions. Light surface wind.

Monday through Tuesday Night...

Another in a series of Pacific weather systems is still forecast to
move into the region late Monday afternoon and night. Global models
continue to come into better agreement on the track of this system.
Both the operational GFS and EURO output (and many of their
respective ensemble members) now deepen the trof over eastern AZ,
then move it quickly into New Mexico on Tuesday. Most dynamics
initially will develop north of Phoenix late Monday and Monday
night, and since this system will have more of a continental track
through the western states, not much moisture will is associated.
However, as cold mid level temperatures settle over the eastern half
of AZ Tuesday afternoon instability showers are a certainty,
particularly over the mountains from Phoenix north through east. As
with the Saturday system, the main impact will be to increase winds
over the region. However, with greater cooling and stronger winds
aloft than the Saturday system, the Tuesday system will likely
produce stronger winds, with some SE CA locations approaching
advisory criteria on wind speeds on Tuesday afternoon. Somewhat more
cooling can also be expected, but still likely no more than a few
degrees from Monday`s highs, pushing lower desert highs across south-
central AZ back down into the mid-high 70s.

Wednesday and Wednesday Night...

Another transitory upper level ridge will build over the forecast
area this period resulting in mostly clear skies and warmer

Thursday and Friday...

All models are in general agreement in developing yet another
Pacific trof over AZ this period. Like yesterday, models are
conflicted in the eventual track of this system through AZ. Like the
previous system, it will have a dry inland track through the western
states before AZ, so any shower activity will be relegated mostly to
the afternoon instability hours. Due to the track uncertainty, a
slight chance of showers are forecast on Friday over a large part of
our south central AZ deserts and mountains.


.AVIATION... South-Central Arizona including KPHX, KIWA, and KSDL:
No aviation weather impacts anticipated through Saturday. Winds will
generally remain diurnal and less than 10 kt.

Southeast California/Southwest Arizona including KIPL and KBLH: An
area of low pressure will bring an increase in wind to southeastern
California Saturday. Westerly winds at KIPL have the potential to
gust to 20-25 kt with weaker winds expected at KBLH.

Aviation discussion not updated for amended TAFs.


Sunday through Thursday...
Active storm pattern will remain over the Intermountain West
at least through the end of the month and possibly into early
April as a series of Pacific storms pass through. Breezy weather
will remain a common feature of most afternoons/early evenings for
the districts with daytime humidity levels ranging 15-25 percent
at their driest. Most of the Pacific storms will travel through
the Great Basin before sweeping into Arizona, allowing for above
normal chances of precipitation for the Arizona districts but near
to below normal chances for precip along and west of the Colorado
River Valley. With an active storm track over the area,
temperatures will trend more towards seasonal averages. Periods of
stronger winds may lead to a locally elevated fire danger at
times, but critical conditions should not be breached.


Spotter reports will not be needed through the weekend.




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