Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 121112

Area Forecast Discussion
National Weather Service Phoenix AZ
412 AM MST Tue Dec 12 2017

.UPDATE...Updated Aviation and Fire Weather Discussions.


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


A bit drier conditions over the region have allowed for skies to
become clear in all areas except for the southeast quarter of
Arizona. The broad cyclonic circulation to our south remains in
place as part of the persistent Rex Block, but the feed of mid
and upper level moisture has diminished quite a bit leaving only
patchy areas of clouds. Height packing aloft will increase today
across southern Arizona allowing an increase in easterly flow with
850mb winds increasing to around 20-25kts by 18Z. This easterly
flow will keep at least some moisture in the mid levels through
the rest of today allowing for at least partly cloudy skies across
southern Arizona. The stronger winds above the boundary layer
will partly mix down to the surface creating a bit of breezy
afternoon and giving a bit of a boost to our temperatures. Highs
today should easily top out in the middle and upper 70s, possibly
reaching the current record high of 79 degrees in Phoenix.

Starting Wednesday, the broad low to the south will begin to sink
farther south as a fast moving shortwave trough slides down
through the Four Corners area. The passage of this shortwave will
have little affect on our weather, but we will see drier air
temporarily filter in from the north and a couple degree drop in

The long lasting high amplitude ridge over the Western U.S. will
weaken somewhat late this week into the early part of the weekend
as a fast moving Northern Pacific trough passes through the
Pacific Northwest Friday and then through the Great Basin and
Desert Southwest on Saturday. So far models indicate nearly all of
the upper level dynamics will slide by to our northeast and then
east. Very little system moisture is advertised and any
precipitation will miss us well to the north and east. It does
seem more likely that a bit of a cool down is in store with the
trough passage, but temperatures are still forecast to remain a
good five degrees above normal for Saturday and Sunday.

Above normal temperatures is a good bet for at least the first
part of next week as the Pacific ridge to our west rebuilds a bit
and heights aloft across our region remain above climo normals
for the period. Though it is pretty far in the extended, both the
GFS and European are depicting a significant Pacific low pressure
trough moving into the Western U.S. sometime late next week. If
this comes to fruition, precipitation chances are likely to return
and much cooler temperatures are a good bet.


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

As an upper level low deepens over northwest Mexico a tightening
gradient over the region will support very breezy to windy
easterly winds beginning by late morning with occasional gusts up
to 22-25kt from around 19-23Z. In addition, BUFKIT model sounding
guidance is in good agreement on LLWS over the area until mid to
late morning and then resuming again this evening, with easterly
winds near 20hft at 28kt this morning, and easterly winds near
19hft at 35kt this evening. Otherwise expect mostly clear to
partly cloudy skies with occasional high clouds passing through.

Southeast California/Southwest Arizona including KIPL and KBLH:

Expect light and variable to westerly winds this morning to become
mostly northerly by mid to late morning at 7-10kt. Otherwise, expect
mostly clear skies with FEW-SCT high clouds passing overhead.

Aviation Discussion not updated for amended TAFs.


Thursday through Monday...

With a high pressure system moving across the region from the
northwest and a dry low pressure system moving through over the
weekend expect dry conditions to continue with above normal
temperatures. MaxTs will remain in the mid 70s until the weekend
when they will fall to the lower 70s. As the dry low pressure system
moves through expect breezy northerly winds to develop from
southeast CA to the lower Colorado river valley and southwest AZ
from Saturday evening through Sunday with gusts reaching 18-25kt.
MinRH`s will generally range from 10-18% during the period along
with overnight recoveries improving a bit to mostly fair by Friday



Record highs for December 12th:

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


Spotters should follow standard reporting procedures.




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