Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 200315

Area Forecast Discussion
National Weather Service Phoenix AZ
815 PM MST Sun Feb 19 2017

Drier and more stable conditions will develop over the region Sunday
night. A high pressure system will build over the region Monday
through Wednesday, resulting in a significant warming trend. A
mainly dry cold front will move through the region Thursday, with
temperatures returning to near normal. A more potent storm system
may affect the region next Sunday.



Copious amounts of boundary layer moisture across portions of
southwest and south central AZ, from nearly 15 hours of continuous
light rain Saturday and Saturday night, produced cloudy skies and
scattered instability showers throughout Sunday. Interesting that
afternoon cloud tops were no higher than 15 thsd feet, though a
couple of cold air funnel clouds were photographed over portions of
the Phoenix east valley late afternoon. The mid level cold pool, or
coldest temperatures aloft over the area were slowly exiting to the
east with clouds dissipating and showers ending at 8 pm mst.

A building high pressure system is forecast to follow on Monday, and
although boundary layer moisture remains nearly the same, modeled
soundings forecast strong mid level subsidence warming to work down
toward the surface by late in the day. In other words, only a few
clouds will remain over the forecast area by Monday afternoon and
evening. Patchy fog also remains in the forecast over the southwest
quarter of AZ for Monday morning.

The high pressure system will result in substantial warming Tuesday
and Wednesday as afternoon temps approach the 80 degree mark.

Current forecasts which have showers ending this evening along with
drier and warmer conditions through Wednesday look ok. Our only
short term update will be to remove the slight chance of shower
wording for portions of south central AZ generally from Phoenix
eastward after 06z or after 11 pm mst.


Scattered instability type showers across south-central and
eastern Arizona will gradually diminish starting late this
afternoon with most of the activity coming to an end early this
evening. Soggy conditions in the wake of the exiting Pacific low
will persist into tonight with low stratus likely continuing
across much of south-central and eastern Arizona. Areas west of
Phoenix through the Lower Colorado River Valley should mostly
clear out by midnight leaving a brief window before high clouds
stream in from the west. Fog formation is possible tonight with
the clearing skies, lingering boundary layer moisture, and light
winds, but thinking it will mostly be localized and situated
across southern Maricopa and Yuma counties. Have added patchy fog
mention to these areas late tonight through early Monday morning.

A substantial warming trend begins on Monday and especially
Tuesday, as midlevel ridging builds over the Southwest. High
temperatures are expected to be just shy of 80 degrees across many
lower desert locations on both Tuesday and Wednesday. A
significant, but mostly dry, cold front will move through the area
on Thursday, bringing high temperatures back into the upper 60s
to lower 70s for the remainder of the week. This will be
associated with a fast moving storm system that will glance
central Arizona.

Model guidance continues to advertise a more significant upper
trough developing next weekend near the Pacific coast, but with
significant timing/evolution differences still remaining. The
most probable solution at this point reflects the storm system
affecting southeast California as early as late Saturday evening,
and the remainder of western/central Arizona on Sunday. This storm
system does not appear to be as moisture-rich as more recent
events, but still could see an uptick in precipitation chances for
Sunday/Monday. However, given the uncertainty, only slight chance
PoPs are currently forecast. Below-normal temperatures are also
possible by Sunday, with high temperatures forecast to be in the
mid-upper 60s.


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

An upper level low pressure system will move out of the region
Sunday night. Lingering boundary layer moisture from recent rainfall
will continue cigs between 6-7 thsd agl over the area through 16z
Mon. Light east wind under 5 knots is also forecast through 16z Mon.
Btwn 16z-19z Mon cigs lifting to 8 thsd agl, then becoming sct 8
thsd agl by 22z Mon. Light and variable wind.

Southeast California/Southwest Arizona including KIPL and KBLH:

Through 19z Mon, sct clds between 6-8 thsd agl. Light south to
southwest winds under 7 knots.

Aviation Discussion not updated for amended TAFs.


Tuesday through Saturday...Dry conditions are expected for most
areas through Saturday. Above normal temperatures can be expected
Tuesday and Wednesday. A low pressure system passing mainly to
the north Wednesday night and Thursday will lead to cooler
temperatures and locally breezy conditions. Rain chances with the
midweek system will be limited to the higher terrain of south-
central AZ. Anticipate slight warming Friday and Saturday. Minimum
humidities will trend downward through the workweek (especially on
Thursday) with most lower elevations in the 15-20% range by Friday.
Overnight recovery though will remain good.


Spotters should follow standard reporting procedures.




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