Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 252120

Area Forecast Discussion
National Weather Service Phoenix AZ
220 PM MST Sat Mar 25 2017

A weak upper level disturbance will exit the area tonight with
high pressure moving in for Sunday and early Monday. Another
Pacific low pressure system will then affect the region late
Monday through Tuesday bringing chances of showers mainly to the
higher terrain north and east of Phoenix. Dry and warmer weather
will return for Wednesday and Thursday, but followed by yet
another Pacific storm Friday and next Saturday.


A weak shortwave trough continues to track eastward through
Arizona early this afternoon with the main circulation center
moving through southwest Utah and a weaker secondary vort max near
Flagstaff. Skies have mostly cleared across southern Arizona and
southeast California aside from a few high based CU across La Paz
and northern Maricopa counties. Any shower activity remains well
north of our CWA near the vort max and expect this activity to
stay out of our area through the rest of today.

Weak ridging aloft returns starting tonight lasting through
Sunday night, but temperatures will change very little through
Monday. The active weather pattern continues into next week as
another quick moving Pacific low is set to move southeastward into
northern California early Monday and then into northwest Arizona
by Monday afternoon. As with the previous system, this one will
again be fairly moisture starved. However, models agree this
system will be stronger as it deepens and close off over northern
Arizona Monday night into early Tuesday. The latest model forecast
has the low tracking into central Arizona Tuesday morning before
turning eastward into New Mexico Tuesday night. Shower activity
will likely be scattered and mainly confined to higher terrain
areas on Tuesday, but can`t rule out a few showers into the
Phoenix area. QPF amounts will be on the light side with most
areas seeing less than a tenth of an inch. Winds will likely be an
issue starting Monday afternoon across southeast California ahead
of the cold front and again behind the front on Tuesday. Gusts
approaching 40 mph will be possible and a Wind Advisory may be
needed for our western zones.

Some model disagreement exists with the exit timing of the
Tuesday system, but general model consensus shows increasing
subsidence and building heights by Wednesday morning. This should
lead to a quick rebound in temperatures by Wednesday as highs
should easily climb back into the 80s over the lower deserts for
both Wednesday and Thursday.

Friday and Saturday...

All models are in general agreement in developing yet another
Pacific trof over AZ this period. Models however are still
conflicted in the eventual track of this system, which has potential
to be the strongest, coldest, and wettest system in the series.
However big disparities exist with the model guidance, with the
European suggesting a more progressive trof through AZ Friday and
into New Mexico Friday night. The GFS on the other hand forecasts a
deep cold cutoff low to become nearly stationary over central AZ
Friday and Saturday. Forecast confidence is very low this far out,
so precip probabilities will be shaded toward a slight chance in
south central AZ.


South-Central Arizona including KPHX, KIWA, and KSDL:

The area of low pressure that is now tracking eastward across
Northern AZ is expected to move eastward off into NM this evening
and tonight with high pressure ridging beginning to move back into the
region on Sunday. Gusty westerly winds this evening to diminish
later tonight as winds aloft begin to weaken, then revert back to
more typical easterly drainage winds after midnight, as winds aloft
decouple from the surface. Typical diurnal light westerly winds to
return on Sunday afternoon. Scattered mid and high level cloud
layers to become FEW-CLR late tonight and Sunday as drier air moves
back into the region.

Southeast California/Southwest Arizona including KIPL and KBLH:

Gusty westerly winds at both KIPL and KBLH to gradually diminish
later tonight and early Sunday as high pressure building eastward
into the region helps to weaken the winds aloft. Lighter westerly
to northwesterly winds will then prevail through the day on Sunday.
Drier air moving into the region will bring mainly clear skies to
both of the terminals tonight and Sunday.

Aviation discussion not updated for amended TAFs.


Monday through Friday...
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 10-25 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 that may turn into critical fire weather conditions for some
locales. A fair bit of uncertainty remains with the track of the
next few systems to move through the region in the far extended
period that may ramp up or back off concerns for
elevated/critical fire danger.


Spotter reports will not be needed through the weekend.




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