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Office: PSR

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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Office: TWC FXUS65 KTWC 120915 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 215 AM MST Tue Dec 12 2017 .SYNOPSIS...Considerable cloudiness will continue across southeast Arizona into this evening due to an area of low pressure centered over the Gulf of California. This low will remain to our south through Wednesday with variable amounts of clouds and potentially even a few sprinkles near the Mexico border. The low will also result in breezy east to southeast winds today. From Thursday into early next week, expect mostly clear skies, dry conditions and less wind as high pressure aloft builds back overhead. Above average temperatures will continue the next seven days. && .DISCUSSION...A Rex block pattern continues across the western United States, with high pressure aloft centered over the Great Basin and a closed low over the northern Gulf of California. Both of these features slowly retrograde west-southwest into Saturday, when the high will be over eastern Pacific Ocean and the upper low west of Cabo. A stronger system then dives southeast out of Canada and into the front range of Colorado by late in the upcoming weekend, with high pressure aloft again nosing eastward into the southwestern United States from the eastern Pacific. Variable amounts of mid/high clouds are expected into Wednesday as southeast Arizona remains in close proximity to the upper low. There may even be a sprinkle or two, although more than likely just some "virga-ish" looking clouds. Main impact of this feature will be to continue the elevated easterly flow across the area today. Breezy east-southeast winds are expected this morning and afternoon at 15 to 22 mph and some gusts to around 30 mph, before diminishing this evening. As the upper low slowly tracks southwest on Wednesday, the forecast area should see greatly reduced wind speeds and more typical diurnal patterns. Otherwise, expect above average temperatures the next 7 days with afternoon highs topping out at 7-10 degrees above normal. Clear skies will return late Wednesday and continue into early next week, with just the possibility of some high clouds over the upcoming weekend. No sign of winter yet. && .AVIATION...Valid thru 13/12Z. SCT-BKN clouds above 15k ft AGL through the period. SFC winds this morning will remain ELY/SELY at less than 12 kts before increasing to 15-20 kts after 12/16Z. Winds will then diminish to less than 12 kts this evening. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Dry air will remain in place over the region through the forecast period. Sustained 20-foot winds will be east-southeast and at 15-22 mph and some gusts to around 30 mph this morning and afternoon before diminishing this evening. A few locations may briefly approach critical fire weather thresholds today, but conditions are not expected to be widespread, nor long-lived. Otherwise, for the rest of the forecast period, expect 20-foot winds to be less than 15 mph and follow typical diurnal trends across the area. && .TWC WATCHES/WARNINGS/ADVISORIES...None. && $$ Discussion...Zell Aviation/Fire Weather...Pegram Visit us on Facebook...Twitter...YouTube...and at
Office: FGZ FXUS65 KFGZ 121122 AFDFGZ Area Forecast Discussion National Weather Service Flagstaff AZ 422 AM MST Tue Dec 12 2017 .SYNOPSIS...High pressure will continue to bring above normal daytime temperatures, cold nights, relatively light winds, and dry conditions through much of this week. && .DISCUSSION... A rather stagnant pattern continues with above normal daytime temperatures and dry conditions for at least the next several days. A trough may brush the region this coming weekend, with an uptick in winds and a cool-down in temps expected. && .AVIATION...For the 12Z package...Expect VFR conditions through the 24 hour period. Sfc winds light and variable or easterly at 5-10kts. Aviation discussion not updated for TAF amendments && .FIRE WEATHER...Expect similar conditions today and Wednesday as the upper air pattern remains unchanged. Daytime temperatures will be 8 to 15 degrees above normal. A stable airmass and light easterly mixing layer winds will combine to to produce extended periods of poor to marginal ventilation. Thursday through Saturday...Above normal temperatures and very dry conditions persist through the period. Some cooling and marginally increased northeast flow may develop Friday or Saturday. && .FGZ WATCHES/WARNINGS/ADVISORIES...NONE. && $$ PUBLIC...KD AVIATION...Peterson FIRE WEATHER...Peterson For Northern Arizona weather information visit