Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 261150

Area Forecast Discussion
National Weather Service Phoenix AZ
450 AM MST Sun Jan 26 2020

Updated 12Z aviation discussion.


Slightly above normal temperatures will continue today as high
pressure predominates across the western states. A series of weak
low pressure systems will move through the Four Corners next week.
However, only light precipitation is expected across the higher
terrain north and east of Phoenix. Another warming trend is expected
for later in the week with warmer deserts climbing into the middle
to upper 70s by the weekend.


As shown in the most recent plot data, a modest upper level high
pressure ridge was situated over the desert southwest; 500mb heights
had climbed 10-20m and typically ranged from 575 to 578dm over the
lower deserts. The high in Phoenix yesterday was 73 degrees. Little
change is expected today and although heights begin to fall off
later in the day as a fast moving short wave approaches from the
northwest, high temperatures will remain several degrees above
normal with lower deserts in the low to mid 70s. IR imagery at 2 am
showed a bit of thin high clouds over the area and some high cloud
will linger today but overall we can expect mostly sunny skies.

There are really no significant changes in the forecast for this
upcoming week as generally dry conditions will persist each day,
especially for the greater Phoenix metropolitan area. As has been
forecast for several days, the aforementioned fast moving wave will
dive southeast across Arizona tonight into Monday, bringing a few
light showers to the higher terrain east of Phoenix. This will be a
dry system for our area and once again, virtually all of the GEFS
ensemble members keep any measurable rain just northeast of our
southern Gila County zones. NAEFS POPs have climbed a bit, but we
will still keep POPs mainly in the 10 to 15 percent range on Monday
over the high terrain zones. Best rain threat will be east of Globe.
In addition to the system being dry it will not even usher in much
cooling; a few degrees of cooling are likely east of Phoenix but the
lower deserts will stay above normal and mostly in the low to mid

Neither the Monday wave nor the upper low moving though the area
Wednesday will be very wet; there is no evidence of any IVT into the
area with either system and current GEFS plumes for Phoenix keeps
nearly a flat line at 0.00 for the entire week. Guidance, including
ensemble output from NAEFS and GEFS, continue to call for flow to
amplify along the west coast mid-week allowing another fast moving
wave to drop south out of Nevada and Utah and move quickly though
Arizona. This fast moving low (which becomes closed off as it
traverses the state) has a dry overland trajectory and is now
forecast to track a bit further to the east with the low center
moving through far eastern Arizona and near the New Mexico border.
This will only bring a few light showers to high terrain areas east
of Phoenix mainly Wednesday afternoon and evening. GEFS ensemble
guidance actually does have a few members bringing around 0.01 inch
contours into south central Arizona with the low, but overall it
will be pretty dry. POPs remain low, with slight chances called for
east of Phoenix but virtually no rain chances in the greater Phoenix
area. The low will not even usher in appreciable cool air as
forecast highs on Wednesday generally stay near 70 or in the low 70s
over the lower deserts. Would not be surprised to see highs reach
into the upper 60s over portions of south central Arizona however.

The main impact of this system will be the breezy to windy
conditions that will set up mainly to the west of Phoenix. Gusty
winds over 30 mph are likely over the western deserts during
afternoon hours and we may need a wind advisory for zones including
along the lower Colorado River valley as we move further into the
week. Expect some amount of blowing dust and sand due to the strong
gradient winds.

Later Thursday into the weekend, strong high pressure aloft
gradually builds east and into the desert southwest with 500mb
heights climbing above 584dm over the western deserts with warmest
conditions into the far southeast California deserts. We will likely
see a nice warming trend over the weekend with highs reaching into
the mid to upper 70s. Warmest deserts could see highs approach 80
degrees by next Sunday and that would represent readings nearly 10
degrees above seasonal normal levels.


.AVIATION...Updated at 1150Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT...
Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation concerns are expected through Monday morning as VFR
conditions persist under increasing cirrus and mid-level clouds.
Diurnal 4-8 knot winds are generally expected across the region,
with easterly winds at the Phoenix terminals becoming westerly
early to mid-afternoon. Winds in southeast California will
generally be southerly or variable, with downsloping southwest
5-10 knot winds possible at KIPL by mid-evening. A weak shortwave
trough will move through the region overnight to cause SCT-BKN
ceilings as low as 10-12 kft at the Phoenix terminals, but
easterly winds after 04-06Z should remain below 10 knots.


Saturday through Wednesday: Temperatures will warm to above seasonal
normal levels during the period with warmer deserts generally low to
middle 70s each day. Conditions will be mostly dry with minimum
humidity values dropping into the 20-30% range across the lower
desert and 30-40% range for the higher terrain. It will be slightly
drier next Tuesday and Wednesday as desert humidity levels fall into
the upper teens in many areas. Winds will remain fairly light
although the Lower Colorado River Valley may see some gusts up to 20
mph Thursday and Friday. There are indications that another weather
system could bring a slight chance for rain early next week mainly
over high terrain areas to the east of Phoenix.


Spotters should follow standard reporting procedures.




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