Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 112037
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
135 PM MST Mon Dec 11 2017

.SYNOPSIS...
High pressure parked across the western United States will result in
dry and quiet weather this week. Temperatures will be well above
average for this time of year with highs in the middle and upper 70s
across the lower deserts. Mostly clear skies will be punctuated at
times with varying amounts of high clouds.

&&

.DISCUSSION...
As expected, a stubborn Rex block maintains its hold on the region
this afternoon with the southern stream cutoff low portion of this
pattern providing the most impact locally (and only minimal at
that). Thicker high clouds continue to stream across the forecast
area within an area of notable upper level deformation, though
weakening ascent as the system pulls away from the area should
result in a gradual thinning of this cloud deck. The vast majority
of models indicate a series of shortwaves and jet streak rotating
about the closed low Tuesday re-enhancing the pressure gradient
splayed through central Arizona. While not nearly as influential as
several nights ago, some gusty ridge top/gap LLJ winds should keep
overnight lows locally elevated, then begin a deeper mixing process
Tuesday. Thus despite almost no change in heights/thicknesses aloft,
the combination of better insolation and seasonably deep mixing
depths will yield highs Tuesday near record levels (at least locally
- see Climate section below).

The blocking pattern will persist through the middle of the week
before a fast moving shortwave digs through the Central Rockies into
New Mexico on Thursday. This will push the quasi-stationary low to
our south further southward allowing the persistent ridge axis to
our west to edge closer to the Desert Southwest. All this pattern re-
alignment will change very little in sensible weather across our
region with the exception of clearing skies as much drier air aloft
advects from the north. High temperatures will fluctuate very little
and mostly fall in the middle 70s over the lower elevation deserts.
Overnight lows should dip into the 40s with the coldest desert spots
likely dipping into the 30s on some nights.

Operational models and their respective ensemble means are in
fairly good agreement that a trough axis will move through the
region on Saturday with the bulk of the upper level energy
remaining well to our north and northeast. For now, it would seem
this trough will have minimal effects on our weather as the
preponderance of guidance shows continued well above normal
temperatures and overall dry conditions though the weekend.

&&

.AVIATION...
South-Central Arizona including KPHX, KIWA, and KSDL:
Easterly winds will persist into mid-late afternoon at most area
terminals, with brief periods where speeds may increase to 12-14
kt. Should see general weakening trend after 19Z. West winds will
take hold into the late evening at most sites, but will remain
less than 7 kt. Broken high-level clouds (above 20 thousand feet)
will persist as a closed low remains nearly stationary over
northwest Mexico. May see some thinning of these clouds into
Tuesday morning. Aviation weather concerns will likely remain
minimal.

Southeast California/Southwest Arizona including KIPL and KBLH:
Typical diurnal wind directions at both KIPL and KBLH can be
expected, with winds remaining under 10 kt. Cloud cover should
gradually thin out through tonight, with bases remaining above 20
thousand feet.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Wednesday through Sunday...
With a dry fair weather pattern dominating the region expect
continued above normal maxTs in the mid to upper 70s. Min RH
values in the 7-15 percent range are expected to increase slightly
to the 11-17 percent range by Saturday. Winds will be mainly
light and favor normal diurnal patterns. Otherwise generally fair
to poor overnight recoveries are expected for most of the period.

&&

.CLIMATE...

Record highs for December 12th:

Phoenix: 79 in 2010
Yuma: 85 in 1958 and 1950

&&

.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.

&&

$$

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DISCUSSION...MO/Kuhlman
AVIATION...Rogers
FIRE WEATHER...Sawtelle
CLIMATE...MO


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