Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 172016

Area Forecast Discussion
National Weather Service Phoenix AZ
116 PM MST Sun Dec 17 2017

.UPDATE...Updated Aviation Discussion...


Cool weather will linger into Monday and skies will continue to
clear up as a weather system slowly moves off to the east. Quiet
and warm weather will hold Tuesday and Wednesday before another
system ushers in windy and cool, but still dry, conditions
Thursday. The cool weather will remain in place Friday and only
show modest warming into next weekend.


After a loud morning across southern Arizona, a more tranquil
afternoon is unfolding across the region. The upper level low is
currently around Ajo and moving rather slowly to the
east/northeast. Shower activity continues to decrease as the low
loses its punch. Rainfall amounts were fairly light, around a 1/4"
or less (one FCD gage in Apache Junction did hit 1/2").
Temperatures remain rather cool and will come in below normal once
the day closes.

Short wave ridging will nudge into the Southwest the next few
days, which will brush this low off to the east. End result will
be gradually warming weather with clearing skies.

Next system will approach Wednesday and swing through Thursday.
Trend continues that this will be a dry system but it`ll bring
about an increase in winds and a drop in temperatures. Northerly
winds will be strongest Thursday and we may end up exceeding
advisory level winds. Added patchy blowing dust to the forecast
Thursday for our western CWA where winds are expected to be

The cold air will (H7 temps near -10C) will push afternoon
temperatures down into the 40s and 50s Thu/Fri with morning lows
in the 30s and 40s. We may see sub-freezing temperatures across
the lower elevation valleys of southern Gila County, including the
Globe area. We`ll monitor for a potential Freeze Watch.

Broadly looking toward next weekend, the long wave pattern across
North America will feature a pronounced/anomalous ridge over
Alaska which will promote troughing across the western CONUS (and
another ridge over the East Coast). We would expect this pattern
to yield below normal temperatures and a potential for traversing
short waves/precipitation chances. Details will come into focus as
we get closer.


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

Isolated showers, somewhat variable shower-driven winds and
lowered cigs will continue to be the primary aviation weather
concern through this afternoon. Southeast winds will generally
prevail, however more variable winds may result from any passing
showers. Shower activity has already diminished considerably, but
the threat for isolated showers will remain into this evening.
CIGs of around 6-7K ft should persist into the evening with peaks
of sun at times, especially from Phoenix west and northwest.
Clouds will scatter out sometime after midnight with light
easterly winds prevailing.

Southeast California/Southwest Arizona including KIPL and KBLH:

Gusty north winds to continue this afternoon and early evening as
an upper low moves through Arizona, wrapping northerly flow on
the back side of the system. Gusts to around 20-25kts will occur
at KBLH with periodic gusts to 20kts at KIPL. Will see a few
patches of mid clouds this afternoon, but skies should clear

Aviation Discussion not updated for amended TAFs.


Tuesday through Saturday...
Winds will be light and variable with subtle trends toward
drainage slopes and diurnal patterns. Dry northwest flow will
linger for Tuesday and Wednesday before another colder and more
potent storm system sweeps in from the northwest. Breezy west-
northwest winds will develop overnight Wednesday and into
Thursday, impacting area ridgetops first then mixing into the
lower desert elevations during the daytime. Model forecasts have
backed off any precipitation chances with this system, so
conditions will stay mostly dry over the Districts. Daytime
humidities will be range higher than the last few weeks, 15 to 20
percent for the lower elevations and 30 percent or greater for the
higher terrain. After temperatures rebound in the early week to
slightly above normal readings, they will drop to near normal
readings (60s for the deserts and 40s/50s for the foothills/higher
terrain) by Thursday into the coming weekend.


Spotters should follow standard reporting procedures.




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