Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 202159

Area Forecast Discussion
National Weather Service Phoenix AZ
259 PM MST Mon Feb 20 2017

Drier and more stable conditions will develop through Wednesday
as a ridge of high pressure system builds over the region. This
will result in a significant warming trend. A mostly dry cold
front will move through the region Wednesday night and Thursday,
with temperatures dipping a bit below normal. Another system will
affect the region over the weekend.



Today through Wednesday: Plenty of lingering low level moisture
remains over the region and latest satellite imagery is showing
scattered to broken cumulus/stratocumulus clouds over much of the
south-central deserts. Cloud ceilings right now range primarily
between 4 and 7 kft with these ceilings expected to gradually rise
this afternoon as more day time mixing occurs. More significant
clearing will occur near sunset, with mostly clear skies expected

Tomorrow morning across the lower deserts of south-central
Arizona, dewpoints will be in the upper 40s to low 50s and low
temperatures are expected to dip down into this range as well.
This small temperature/dewpoint spread, along with clear skies and
calm winds could result in some redevelopment of patchy fog/ mist
in this area. NAM BUFKIT PHX sounding is backing up this thinking,
indicating that the best window for possible fog development will
be between 5AM and 10AM.

Ridging will continue to strengthen and build into the region
bringing warmer and more stable conditions. High temperatures
will be climbing well above normal (normal for Phoenix is 72
degrees both tomorrow and Wednesday) and will be reaching the mid-
to upper- 70s each day.

Wednesday night through Thursday:

The ridge will start to break down as a cold front starts to make
its way across the desert southwest Wednesday night into
Thursday. This system will remain relatively dry with NAEFS
probabilities of QPF only showing less than a 10 percent chance
of rain in our region, with slight chances across the higher
terrain north and east of Phoenix. The main impact with this
system will be slightly elevated winds along and west of the
Colorado River valley Wednesday night into Thursday morning and
primarily east of the Colorado River valley Thursday morning into
Thursday evening. Sustained westerly winds will be near 10-15
kts, gusting up to 20-25 kts as this front sweeps across the

Friday through Sunday...
Temps warm slightly Friday and Saturday before another trough
moves through the region Saturday night and Sunday. The 00Z ECMWF
is a bit faster than previous runs and thus is faster than the
00Z GFS (even more so for the 06Z GFS). The 00Z CMC is in
between. NAEFS output and calibrated GEFS develop depict slight
chance PoPs with this system (mainly for our Arizona zones) and
that is reflected in the forecast. Temps drop on Sunday as well
but not dramatically.


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

Despite the upper low exiting well to our east, considerable amounts
of low level moisture remained trapped in the boundary layer. As
such we can expect a significant development of lower-based CU/SC
during the afternoon today. Current visible satellite imagery show
this already occurring. At the TAF sites we should see scattered
decks between 4 and 6k feet with CIGS possible at times. KPHX could
easily see a ceiling at 5k feet this afternoon, although currently
the TAF only mentions SCT decks. Expect these lower clouds to
dissipate later this afternoon or shortly after sunset. Otherwise
winds will be very light and variable with only weak diurnal
tendencies for the next 24 hours.

There is an outside chance for fog to develop in the greater Phoenix
area after about 3am Tuesday morning; some forecast soundings show
favorable fog profiles as boundary layer stays humid with mostly
clear skies and light winds. Confidence too low at the moment to put
fog in the TAFs; should it develop visibilities would likely stay aoa

Southeast California/Southwest Arizona including KIPL and KBLH:

We don`t expect the same amount of low level CU/SC development today
as compared to the central AZ deserts, but FEW-SCT decks are
possible through the afternoon with bases genly 4-6k feet. The low
clouds at KIPL have already dissipated and we don`t expect clouds
below 2k feet to occur for the rest of the day. Winds to be very
light and variable next 24 hours at KIPL. Slightly stronger winds at
KBLH favoring the south this afternoon and evening.

Aviation Discussion not updated for amended TAFs.


Wednesday through Sunday...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. Slight chances for
rain 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. Another storm system will affect the
region this weekend. The main effect will be breezy west winds on
both Saturday and Sunday. A slight chance for rain is also
forecast on Sunday for south-central Arizona.


Spotters should follow standard reporting procedures.




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