Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 271623
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
920 AM MST Mon Mar 27 2017

.SYNOPSIS...
A Pacific cold front will affect the region this evening through
Tuesday with gusty winds and patchy blowing dust. The strongest
winds will develop over portions of southwest Arizona and Southeast
California. A few light showers are also possible across high
terrain areas of central Arizona. High pressure will then redevelop
across the region Wednesday and Thursday ahead of another weather
system moving into the Desert Southwest on Friday and Saturday.

&&

.DISCUSSION...
A sharp midlevel trough was bisecting California and Nevada this
morning with the leading edge of height falls edging into the
forecast area per 12Z sounding data. More pronounced height falls
were still situated closer to the deepening vorticity center which
will translate into northern Arizona tonight. Early look at 12Z
model data still suggests frontal passage and a steeply tightening
pressure gradient this evening yielding gusty winds and localized
blowing dust. Will be looking at refining details this afternoon,
but in the interim only minor changes to account for current trends
were necessary.

&&

.PREVIOUS DISCUSSION...
/541 AM MST Mon Mar 27 2017/
A very slight chance is possible for elevated portions of Gila
county late this afternoon where the system`s dynamics combined with
the westerly orographic flow could squeeze out a few drops. However,
the main impact with this system will be winds. Surface westerly
winds will gradually increase across our area this afternoon with
the strongest winds focused in SE California. Additionally as the
winds strengthen across SE California, isolated pockets of blowing
dust and sand are possible.

Early Tuesday, the system gradually moves eastward and digs
deeper across our area. This will position us under the dryer
backside of the trough which will gradually turn winds from
westerly to more northerly. During this period, winds are expected
to gust up to 50 mph across Joshua Tree National Park, especially
across the wind prone locations and up to 40 mph across the lower
portions of the Colorado River Valley. This will very likely kick up
dust and sand and cause reduced visibilities on the roadway, not to
mention the strong cross wind creating difficult driving conditions
across I-10.

The system slowly moves eastward Tuesday night and winds
diminish. Models are in fairly good agreement of a transient
ridge building over the area Wednesday into Thursday which is
forecast to push our temperatures back into the upper 80s across
the Phoenix area. However, models show yet another trough diving
down from the Pacific Northwest and into our are on Friday. This
will cause a rather sharp cooling trend into Friday with highs at
least 10 degrees cooler than Thursday. While the details are still
uncertain, the system does look cooler than the one expected
Monday/Tuesday and precipitation amounts do look rather slim again.
As with all these passing upper level troughs, this one looks to
kick up surface winds again.

&&

.AVIATION...
South-Central Arizona including KPHX, KIWA, and KSDL:
Main aviation weather impact through Tuesday will be an increase
in wind. Easterly winds this morning will shift to the west early
this afternoon. Breezy conditions are then expected with gusts
occasionally reaching as high as 20-25 kt late this afternoon.
Winds will subside somewhat overnight, though a return to
easterly is not anticipated. Otherwise, scattered mid clouds will
lower through the afternoon, perhaps as low as 7k ft by this
evening, though ceilings are not anticipated.

Southeast California/Southwest Arizona including KIPL and KBLH:
Breezy conditions will develop this afternoon across southeastern
Arizona with gusts likely reaching 25 kt. There is also a slight
chance of blowing dust and blowing sand, particularly near KIPL
late this afternoon and this evening. Another period of blowing
dust is possible further norther near KBLH Tuesday. Any blowing
dust or sand that develops also has the potential to briefly
reduce visibilities.

Aviation discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Wednesday through Sunday:
The weather pattern will remain quite active across the Desert
Southwest through early next week, though in general precipitation
is not expected, except in the higher terrain well north and east
of Phoenix. Main weather impact will be breezy conditions, which
are expected to redevelop Thursday and Friday associated with the
next low pressure system. With RHs generally remaining below 15
percent, elevated fire danger will again be a possibility across
southeastern California, particularly Friday afternoon.
Thereafter, the low pressure system will likely move through
Arizona during the weekend, bringing below normal temperatures
along with a general decrease in wind and an increase in
moisture.

&&

.SPOTTER INFORMATION STATEMENT...
Spotters are encouraged to follow reporting procedures with
criteria reports this week.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Fire Weather Watch Tuesday afternoon for AZZ131-132.

     Wind Advisory from 3 AM to 4 PM MST Tuesday for AZZ020-021-026.

CA...Fire Weather Watch Tuesday afternoon for CAZ231.

     Wind Advisory from 7 PM this evening to 4 PM PDT Tuesday for
     CAZ030>033.

&&

$$

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DISCUSSION...MO/Wilson
AVIATION...Hirsch
FIRE WEATHER...Hirsch


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