Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 241016

Area Forecast Discussion
National Weather Service Phoenix AZ
316 AM MST Wed Jan 24 2018

.UPDATE...Updated aviation and fire weather discussions


There will be some additional warming today at most locations
along with locally breezy conditions. A weak and dry cold front
moves across the region later Thursday and into Friday. This will
result in some modest cooling by Friday. There will also be some
breezy to locally windy conditions for portions of southeast
California Thursday afternoon and evening. A warming trend takes
place Saturday through Monday with little change Tuesday.
Anticipate highs reaching into the low 80s at a number of lower
desert locations by early next week.


A transient ridge tracks across Arizona and southern California
today. This will aid in the warming trend. Close by is a weak and
dry upper low over northwest Mexico which will lead to an enhanced
easterly oriented gradient. In turn, this will produce breezy
conditions over much of southern Arizona. The winds will aid in
mixing as well which in turn helps the warming today. Winds will
be lighter near and east of the Lower Colorado River Valley (LCRV).

Thursday and Friday...
The transient ridge is giving way to a large low pressure system
that moves through the western CONUS Thursday and Friday. The
brunt of the system tracks well north of our forecast area so we
stay dry. The southern end of the associated cold front moves
through southern California and across Arizona during that same
time frame but largely fizzles out over AZ Thursday night and
Friday morning. As far as sensible weather goes, there will be
some cooling but not a lot. There will also be some breezy to
locally windy conditions for portions of SE CA Thursday afternoon
and evening with less wind elsewhere. Friday will see some minor
northerly breeziness over portions of SE CA and SW AZ (mainly

Saturday through Tuesday...
Ridging returns over the weekend for a warming trend along with
some local breeziness from time to time. Monday looks to be the
warmest day of the forecast period for most locations with highs
getting into the lower 80s for a number of lower desert locations.
This is supported by NAEFS guidance showing 850 mb temperatures
peaking on Monday with standardized anomalies of 1-2 SD. The ESRL
calibrated GEFS shows surface temperatures reaching the 90-95th
percentile for a good portion of our area and even a pocket of
95+. It shows even more coverage of the 90+ percentile for
Monday. A potential limiting factor on the temps will be cirrus
clouds. If they are just thick enough and last long enough, we
won`t reach the full warming potential. The ridge weakens Tuesday
in response to a system moving primarily through western Canada
and the NW CONUS. However, surface level warmth will still be in
place and thus anticipate little change in temps. Otherwise, there
will be some continued minor daytime breeziness with a lingering
north and northeast oriented pressure gradient.


South-Central Arizona including KPHX, KIWA, KSDL:
Easterly flow will persist at all TAF sites through at least
Thursday morning. Daytime heating will allow higher momentum air
to mix down to the surface later this morning bringing gusts 15-20
kts. Otherwise, skies will remain clear this afternoon with a FEW
high clouds moving in tonight.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation concerns through the TAF period as winds remain light
and follow typical diurnal tendencies. Only a FEW/SCT high clouds
are expected today.

Aviation Discussion not updated for amended TAFs.


Friday through Tuesday: A weak cold front passing through on
Thursday/Friday will bring temperatures down to near normal on
Friday afternoon. However, this will be short lived as a ridge of
high pressure quickly rebuilds and warms temperatures through the
weekend. By early next week, highs in the upper 70s and low 80s
will be common across the lower deserts. Throughout our extended
forecast, winds will be light while daytime minimum relative
humidity remains low (10-25%). Dry weather is forecast through
the foreseeable future.


Spotters should follow standard reporting procedures.




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