Area Forecast Discussion
Issued by NWS Phoenix, AZ

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365
FXUS65 KPSR 230442
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
942 PM MST Wed Mar 22 2017

.SYNOPSIS...
A strong low pressure system moving through during the late day
into the overnight hours today will bring rainfall chances
producing light rainfall amounts as well as significantly cooler
daytime temperatures. Isolated thunderstorms are possible mainly
west of Phoenix this afternoon the associated cold front moves
across the area. Dry conditions and near normal temperatures will
return across the Lower Desert elevations for the late week and
weekend periods while an active storm track remains over the West.

&&

.DISCUSSION...

A large upper level trough is currently moving into our area and is
clearly evident in water vapor imagery this evening. Thunderstorms
developed earlier this afternoon on the leading edge of this
trough in SE California & SW Arizona which brought blowing dust
and gusty winds. Yuma briefly reported a 2.5 mile visibility with
gusts to 37 mph; however, a couple locations just to the north
and east of Yuma had a brief period of gusts to 45-50 mph. These
strong winds were a combination of the outflow boundary of a
nearby thunderstorm and a cold front racing across the state.

Since then, the cold front has moved across Central Arizona and into
the Phoenix metro around 8:00pm.  Winds of 40 mph were observed
throughout the valley with blowing dust and reduced visibility (2SM
at KPHX).  Behind the front, winds have weakened but will continue
to stay westerly throughout the night. Showers are expected
to continue tonight and early tomorrow AM although progressively
dryer air will be working its way into our CWA. Precipitable water
values over Phoenix are forecast to drop from around 1.00 inch
this afternoon to less than 0.5 inches by mid-morning on
Thursday. So while the cold upper level low will move directly
overhead tomorrow morning, a relatively moisture starved
atmosphere should limit shower activity to mainly the higher
elevations north and east of Phoenix tomorrow.

&&

.PREVIOUS DISCUSSION...

The other short-term forecast impact will breezy westerly winds,
which will persist into Thursday across the entire forecast area.
Currently not expecting widespread advisory-level winds, with wind
gusts of 20-25 mph forecast for tomorrow, but locally stronger
winds are possible especially across parts of southeast
California. Precipitation chances will continue into tomorrow
mainly north and east of Phoenix as the storm system quickly
shifts eastward, but only spotty light showers are expected.

Drier air will overspread the region as the upper trough shifts
into the Great Plains, but only modest warming will occur through
Friday as midlevel ridging will remain transient ahead of another
upper trough. However, with the progressive pattern, moisture
return associated with this system will be quite limited, with the
highest precipitation chances remaining across the higher terrain
of central and northern Arizona, with only light showers at best
across the lower deserts.

&&

.AVIATION...
South-Central Arizona Including KPHX, KIWA, and KSDL:

Winds will be the primary aviation concern this afternoon and
evening with westerly gusts between 20 to 30 kts. The winds will
stay primarily out of the west although there may be some temporary
variability in wind direction due to passing showers late tonight
and early Thursday. However, there is no tempo group for these
changes due to uncertainty regarding the timing and duration of any
variable winds. The aforementioned showers will likely move through
the terminal between 8z and 14z. Decided to leave as VCSH in the
TAFs at this time although any showers late tonight should be brief
and light. There is the potential for cigs around 6K ft (and
mountain obscuration) to impact the terminals as showers pass
through.

Southeast California/Southwest Arizona Including KIPL and KBLH:

Strong and gusty winds will prevail through the area for much of the
day with gusts approaching 30 kts. The stronger winds near Imperial
may cause blowing dust that could also reduce visibility. In
addition, there is potential for showers, a thunderstorm, and
ceilings to drop below 6K ft during the afternoon and early evening.

Aviation discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Friday through Tuesday...
Temperatures will moderate back towards the seasonal normal over the
weekend as high pressure and dry weather build back into the region.
Breezy weather will be common through most of the districts,
especially Saturday and Monday afternoon. Despite the stronger
winds and drying trend, humidity levels will be manageable only
falling into a 15-30 percent range. Overnight recovery will be good
to excellent. Periods of stronger winds may lead to a locally
elevated fire danger at times, but critical conditions should not be
breached.

&&

.SPOTTER INFORMATION STATEMENT...
Spotter reports will not be needed through the weekend.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

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DISCUSSION...Wilson
PREVIOUS DISCUSSION...Rogers
AVIATION...Deemer
FIRE WEATHER...MO



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