Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 270345

Area Forecast Discussion
National Weather Service Phoenix AZ
845 PM MST Sun Mar 26 2017

Another Pacific cold front is expected to affect the region from
Monday afternoon into Tuesday. This system will bring shower chances
to the higher terrain of South-Central AZ, along with gusty winds
across the entire region. The strongest winds, along with areas
of blowing dust are forecast to develop over portions of southwest
AZ and Southeast CA. High pressure will then redevelop across the
region Wednesday and most of Thursday, ahead of another stronger
and colder weather system than is expected to move into the Desert
Southwest on Friday and Saturday.


Early this evening, a flat short wave ridge was in place across far
SE CA and Arizona and this could be clearly seen in the 00z plot
data. 500mb heights were up around 60m and high temps today over the
central deserts were mostly in the lower 80s - slightly above
seasonal normals. The ridge will gradually shift eastward overnight;
current IR imagery showed mostly clear skies across the area but as
the ridge moves off we should see some increase in mainly high
clouds spreading in from the west ahead of the next Pacific upper
level low pressure system. Winds tonight will stay relatively light
and follow typical diurnal patterns. No updates are needed to the


A transitory upper level ridge that will be moving across the region
tonight will keep skies mostly clear, surface winds on the light
side, and overnight lows near or slightly above normal.

Monday through Tuesday Night...

Global models continue to remain in agreement on the timing and
impacts of the next Pacific low pressure system that is expected to
move into and across our cwa from the northwest during this time
period. All of the models continue to move the main upper-level
low center from east-central NV into south-central UT on Monday
and Monday night, then across the 4-corners region into north-
central NM during the day on Tuesday. Given the inland track of
this system, the available moisture levels will be quite limited,
but rather strong frontal lift/cooling aloft (500mb temps as low
as -25C) will be rather efficient in squeezing out what moisture
that is around. Measurable QPF looks quite likely across much of
northern and extreme eastern AZ, with decent chances for
measurable QPF extending southwestward into the higher terrain
north and east of Phoenix, but with only slight chances over the
lower elevations of south-central AZ. As far as QPF amounts are
concerned, they look like they will remain quite low, with the
NCEP SREF plume mean showing only 0.03 inch at Globe.

The main impact from this system will likely be gusty winds,
especially across SE CA and SW AZ from Monday afternoon into
Tuesday. The latest GFS model output develops 30-40 kt northerly
winds at 850mb across the region from Monday afternoon into
Tuesday behind the main upper-level low center as it moves across
northern AZ. Good CAA behind the low center will allow for rather
efficient mixing down of these winds to the sfc. Sustained winds
as high as 35 mph, with gusts to 45 mph look like a good bet in
the most exposed spots across Joshua Tree NP and across Riverside
County in CA. through the entire period, with winds nearly that
strong moving into SW AZ (La Paz and northern Yuma Counties) on
Tuesday. Areas of blowing dust are likely to be generated by these
strong winds, which could reduce visibilities at some locations.

The Tuesday weather system is expected to exit east into New
Mexico Tuesday night, with winds and showers quickly diminishing
as well.


Wednesday, Wednesday Night, and most of Thursday...

It now appears these incoming weather systems will be a little more
progressive than earlier thought, therefore another transitory upper
level ridge will move through the region Wednesday through most of
Thursday. And except for a few high clouds, mostly clear skies,
light wind, and slightly above normal afternoon temperatures are
forecast.  The only caveat Thursday will gusty afternoon evening
west winds over southeast CA and Colorado River with another
approaching cold front for Friday.

Friday and Saturday...

All models are in general agreement in developing yet another
Pacific trof over AZ this period. Models however are still
conflicted in the eventual track of this system, which has potential
to be the strongest, coldest, and wettest system in the series.
However big disparities still exist between the models, which are
flip flopping with the storm track through AZ. Forecast confidence
is very low this far out, so precip probabilities will be shaded
toward slight chances across south central AZ, with better potential
in the mountains of southern Gila County zone 24.


The upper level trof over AZ Saturday could possibly move east into
New Mexico Sunday, however confidence is low at this point. We will
keep it dry across the forecast area this period.


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

Weak short wave ridge to move east across the area tonight into
Monday allowing increasing mid/high clouds to spread into the
greater Phoenix area. Expect SCt-BKN decks aoa 20k feet after
midnight with some mid cloud decks down to around 10-12k feet by
Monday morning. Winds next 24 hours should be mostly below 12kt
following typical diurnal trends with potential for some
afternoon/evening gusts Monday to 18kt or so ahead of an approaching
upper low.

Southeast California/Southwest Arizona including KIPL and KBLH:

As an upper low approaches tonight into Monday, an increase in
mainly high cloud is expected with SCT to BKN decks aoa 20k feet
along with some mid decks down to 10-12k feet. After 18z or so
Monday skies should become genly clear. Wind will become an issue
later Monday especially at KIPL as gradients tighten; mostly west
winds less than 12 kt at KIPL thru Monday morning then increasing
quite a bit during the afternoon with peak gusts over 25kt possible
by 20z. A bit less wind at KBLH but similar trends/tendencies. Gusts
in the afternoon/evening could generate some blowing dust/sand but
vsbys should stay above 6 SM for the most part; confidence rather low
that restricted vsbys will be seen at the TAF sites.

Aviation discussion not updated for amended TAFs.


Tuesday through Saturday...
Active storm pattern will remain over the Intermountain West at
least through the end of the month and possibly into early April
as a series of Pacific storms pass through. Breezy weather will
remain a common feature of most afternoons/early evenings for the
districts with daytime humidity levels ranging 10-25 percent at
their driest. With an active storm track over the area,
temperatures will trend more towards seasonal averages. Periods of
stronger winds in combination with drier air working into portions
of the area may lead to a locally elevated fire danger/critical
fire weather conditions for some locales Tuesday and again on
Friday as another storm transitions in. A fair bit of uncertainty
remains with the track of the next few systems to move through
the region in the far extended period that may ramp up or back off
concerns for elevated/critical fire danger.


Spotters are encouraged to follow reporting procedures with
criteria reports this week.


AZ...Wind Advisory from 3 AM to 4 PM MST Tuesday for AZZ020-021-026.

CA...Wind Advisory from 7 PM Monday to 4 PM PDT Tuesday for



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