Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 220341

Area Forecast Discussion
National Weather Service Phoenix AZ
840 PM MST Sat Oct 21 2017

Near-normal temperatures will make a brief return this weekend,
before a strong area of high pressure builds over the Western U.S.
This will result in another warming trend with dry conditions and
well above normal temperatures throughout much of next week.


Strong high pressure aloft was building into the desert southwest
behind an exiting upper level open wave trof; as seen in the 00z
500mb plot data 60-90m height rises were present across Arizona as
well as far southern Nevada and California. Dry northwest flow aloft
has moved into the area and 8 pm IR imagery showed generally clear
skies area wide. Low/mid level gradients continue to relax and winds
this evening have tapered off; for the rest of tonight expect clear
skies, mostly light winds and mild overnight low temperatures.
Current forecasts look to be in great shape and no updates are

Rest of Today through Tuesday.
Very hazy looking skies today over some of the lower deserts today
including metro Phoenix. It`s due to the dust that got kicked up
yesterday over the deserts of far southeast California and
southwest AZ (mainly Imperial County where winds were VERY
strong). Much of what is visible is above the surface but without
more distinct winds to push it along, it will be with us the rest
of the day. Expect that skies will be much clearer by Sunday
afternoon (if not a little sooner) as northeasterly winds develop
with surface high pressure centered over Colorado.

Meanwhile, a subtropical high (currently centered west of Baja
Mexico) will strengthen and expand into the western CONUS leading
to a considerable warming trend Sunday through Tuesday. There
will be periods of breezy conditions (especially Tuesday) favoring
northerly directions over SE CA and SW AZ with easterly
directions favored over south-central AZ (incl. metro Phoenix).
With 500mb heights exceeding 590dm and enhanced mixing, highs
Monday and Tuesday will be a good 10 degrees above normal. Tuesday
looks to be the warmest day with a number of lower desert
locations getting very close to 100 degrees.

Wednesday through Saturday.
The high amplitude flow pattern in place over North America and
the northeast Pacific will retrograde on Wednesday with the ridge
axis shifting offshore. Then, a short wave riding over the ridge
tracks southeastward through Rockies. This enables a cooling trend
during the latter half of the workweek. However, most lower desert
locations will still reach at least 90.



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

Dry northwest flow aloft has settled into the greater Phoenix area
behind an exiting trof; this will result in generally clear skies at
the terminals for the next 24 hours at least. Low level gradients
continue to relax and we can expect relatively light winds following
mostly typical diurnal trends tonight through Sunday afternoon.
There will be a bit of a tightening of the NE to SW oriented surface
gradient overnight supporting modest low level northeast winds; this
may lead to a period of light variable or even light southwest
surface winds at KPHX starting after 10z and running through mid
morning before better mixing allows northeast surface winds to set
in at the airport. Otherwise, suspended dust in the air may lead to
restricted slant-wise visibility at the airports, including KPHX,
tonight into Sunday but do not expect normal visibility values to be
affected - they should stay well above 6SM.

Southeast California/Southwest Arizona including KIPL and KBLH:

Dry northwest flow aloft will lead to generally clear skies across
the western deserts including KIPL and KBLH through Sunday
afternoon. Low level gradients will continue to relax and winds will
be mostly below 10kt at the TAF sites next 24 hours. Winds to favor
the north at KBLH and at KIPL will favor the west tonight, turning
to the north later in the morning on Sunday. No aviation concerns at
the TAF sites for at least the next 24 hours.


Tuesday through Saturday: The warmest temperatures of the week
will be Tuesday (close to 100 degrees lower deserts). Thereafter,
high pressure over the area slowly weakens (aided by a weather
disturbance tracking through the Rockies). In turn, temperatures
trend downward. However, highs will still be above normal. There
will be continued breeziness at times - especially Tuesday with
northerly directions favored near the Lower Colorado River Valley
and westward and easterly directions favored elsewhere in the
forecast area. Winds favor southwesterly directions Thursday and
Friday before trending back to more of a north and east pattern
Saturday. Minimum humidities will be very low - below 20% for all
but the highest elevations. Overnight recovery will be modest.


Spotters should follow standard reporting procedures.




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