Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 241204

Area Forecast Discussion
National Weather Service Phoenix AZ
504 AM MST Tue Jan 24 2017

.UPDATE...To remove Winter Weather headline from
Watch/Warning/Advisory section...


Troughing will remain stretched over the Interior West through the
end of the week, loosing access to the Pacific moisture feed. Enough
moisture will linger over the higher terrain for showers to linger
into today. Skies will return to more clear conditions as a drier,
colder airmass settles over the region midweek. Some of the coldest
low temperatures of this winter season are forecast for Wednesday and
Thursday mornings. Clear skies, a slow temperature warming trend and
breezy conditions will develop by the coming weekend.


Surface cold front that passed through the forecast area Monday is
now working eastward just into New Mexico this overnight. Shower
activity lingers loosely in a line from Williams down through
northeastern Maricopa County and down south to Tucson this hour.
Very stark boundary on overnight IR imagery and sfc obs w/ pressure
rises also place the front now to our east, with mostly clear skies
spanning westward from central Phoenix across the southwest AZ
deserts and out towards Imperial/JTNP near and along the leeward side
of the Peninsular Ranges. Rain shower activity has mostly wrapped
for the lower desert locales in the wake of the surface front and
lower valley rain/mountain snow showers will persist over the higher
terrain of Southern Gila County and on and off through the day.
Winter Weather Advisory remains out through this morning for
elevations above 6000ft where the greatest snow accumulations are
expected and while snow levels continue to fall, a few flurries and
flakes are possible down as low as 4000ft or so as the main trough
axis cuts a slow path across northern AZ, fully exiting the Four
Corners by Wednesday.

Cold airmass will settle into the area, with afternoon 850mb
temperatures progged only to peak around 0C this and Wednesday
afternoons. Values this cool are near daily climo mins per SPC
Sounding Climatology (using KTWC as a proxy). Below normal high
temperatures will result, with many lower desert locales holding in
the 50s and low 60s for the western forecast zones. This incoming
airmass is the coldest so far this winter season and will be enough
to drop minimum temperatures on the lower deserts into the low to mid
30s, possibly 28 degrees both Wednesday and Thursday mornings.

By the late week and coming weekend, temperatures will slowly recover
to forecast values closer to seasonal averages if not just a little
below average. Another low pressure trough will make a trip through
the Four Corners and Colorado River Valley regions from the north
Friday. Given the overland trajectory of the system and little by way
of moisture advection into the area ahead of it, PoP chances remain
at or close to zero for the weekend. Sensible weather impacts from
this dry trough passage will likely be a prolonged period of
northerly to northeasterly breeziness, with gap/pass winds filtering
through the mountains northeast of Phoenix as well persistent gusty
conditions along and west of the Colorado River Valley. High pressure
will begins to build off the CA coast and could gradually expand into
SE CA and Arizona by early next week. Temperatures trending closer to
late January normals are probable with dry conditions continuing.


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

The cold front that brought the rain to the greater Phoenix
area today is now beginning to move off to the east, with its
associated rain beginning to shift out of the area. Shower activity
and lowered cigs that are now affecting the PHX area terminals at
this hour should begin to move off to the east over the next few
hours, with clearing skies towards morning. Tuesday will feature
partly cloudy skies with sct-bkn stratocu in the 6-8k foot range
developing for a time during the afternoon/early evening hours.
Westerly winds at this hour to become easterly towards morning
before returning to more typical light westerly winds on Tuesday

Southeast California/Southwest Arizona including KIPL and KBLH:

Mainly clear skies to overspread the region tonight and Tuesday
as drier air moves in from the west, with just a few high
clouds remaining on Tuesday afternoon. Westerly to southwesterly
winds at both terminals to gradually diminish through the taf period.

Aviation discussion not updated for amended TAFs.


Wednesday through Sunday: Weakened but broad and dry troughing will
settle over the west Wednesday keeping flow aloft westerly with low
level winds north to northwesterly but rather light. Quasi-zonal
flow will develop into the region as high pressure attempts to build
into the west and various shortwave systems ride over the ridge
flow. Temperatures initially will be well below normal but will
gradually warm during the five day period, becoming near seasonal
seasonal normal by Sunday. Humidity values will start highly
elevated with minimum RH values 30-45 percent, gradually drying
during the week and lowering into the mid to upper teens by the
weekend. One stronger storm system passing through the Four Corners
during the late week/early weekend will produce enhanced easterly
surface flow over the Mogollon Rim and northerly flow down the
Colorado River Valley, introducing breeziness and periodic gustiness
from the north and northeast for the districts.


Spotters should follow standard reporting procedures.




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