Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 220419

Area Forecast Discussion
National Weather Service Phoenix AZ
919 PM MST Sat Jan 21 2017

A break in the weather is expected tonight and early Sunday, however
another Pacific storm will approach the area later Sunday afternoon.
Increasing clouds are expected Sunday afternoon, with a slight
chance of showers developing over portions of southeast California,
spreading east across the remainder of southern Arizona later Sunday
night and Monday. Snow levels Monday afternoon and night will be
between 5 and 6 thousand feet. A drier and much colder airmass will
settle over the region Tuesday through Thursday, resulting in some
of the coldest low temperatures of the year.


The upper trough that was associated with widespread rainfall over
the region has quickly advanced eastward into the southern Plains,
leaving our area in between storm systems this evening. Winds have
weakened and most cloud cover has vacated the region tonight, with
mostly tranquil weather observed. However, high clouds are entering
southern California ahead of the next Pacific storm system, and
should reach central Arizona by Sunday morning. Precipitation chances
still appear on track to begin increasing across southeast California
throughout the day Sunday, spreading eastward into central Arizona
overnight Sunday into Monday morning. Only minor changes were made to
the gridded forecast to reflect observed trends in sky and

The low amplitude ridge tonight and Sunday will be dirty, a term
used for lots of clouds expected to move through at times. Clouds are
from the next Pacific storm forecast to approach the southern CA
coast Sunday afternoon, spreading a slight chance of showers over
portions of our southeast CA zones by Sunday evening. This Pacific
storm will begin to move into AZ late Sunday night through Monday
evening. Models forecast another plume of deep boundary layer
moisture to spread west to east across the forecast area. With 850 mb
southwest winds in the 20-30 knot range, moderate amounts of upslope
mountain precipitation are expected over the south central AZ
mountains north through east of Phoenix. Although precip amounts with
this next system will be on the light side, amounts ranging from 0.25
in Phoenix to around 0.80 inches over the mountains northeast through
east of Phoenix are estimated. Snow levels will be around 5000-6000

Precipitation will diminish from west to east Monday night, however
the coldest airmass of the year is expected to settle over southeast
CA and southern AZ on Tuesday.

Tuesday through Thursday...

The coldest airmass of the year, and perhaps of the season, is
forecast to settle over southern AZ this period. Clearing skies are
forecast with low temperatures approaching the freezing mark at many
lower desert locations maybe Tuesday morning (still some cloudiness
around though), but mainly Wednesday and Thursday mornings. Social
media posts reflecting this forecast will be issued first, followed
by the possibility of Freeze Watches or Warnings as we get closer to
the event.

Thursday through Saturday...

A dry and warmer airmass is forecast to spread into the region from
the west this period, along with mostly clear skies. Temperatures
however will remain several degrees below normal.


South-Central Arizona including KPHX, KIWA,and KSDL:
Observations show easterly winds have developed at KPHX and KIWA as
of 04Z, and these are forecast to persist through Sunday afternoon
while generally remaining AOB 5 kt. Mostly clear skies are expected
overnight before mid-level cloud cover begins to increase from the
west, with bases AOA FL100 currently forecast to occur around 12Z.

Southeast California/Southwest Arizona including KIPL and KBLH:
Winds have weakened in magnitude and will remain less than 10 kt
overnight. An eventual shift towards the south/southeast is
anticipated at KIPL, and has already occurred at KBLH. This should
persist into the day with some strengthening of winds to 10-15 kts
forecast to occur. Mid-level clouds, with bases AOA FL100, will also
approach the area after 06Z. Low-level moisture will enter southeast
California after 23/00Z, and could result in cloud bases approaching
FL050, especially at KBLH.

Aviation discussion not updated for amended TAFs.


Monday through Friday: Unsettled conditions with another round of
precipitation will continue Monday ahead of high pressure building
into the region. Rainfall amounts will be less than those from the
weekend and chances for wetting rains are not as widespread. High
pressure will gradually rebuild across the area Tuesday and
Wednesday, resulting in a drying trend though temperatures will
remain below normal. Fire danger will remain low through the period
due to the persistent and anomalously moist conditions.


Spotters should follow standard reporting procedures.




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