Weather Service Report


787 
FXUS65 KPSR 260420
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
920 PM MST Sat Mar 25 2017

.SYNOPSIS... 
A weak upper level disturbance will exit the area tonight with 
high pressure moving in for Sunday and early Monday. Another 
Pacific low pressure system will then affect the region late 
Monday through Tuesday bringing chances of showers mainly to the
higher terrain north and east of Phoenix. Dry and warmer weather 
will return for Wednesday and Thursday, but followed by yet 
another Pacific storm Friday and next Saturday.

&&

.DISCUSSION...
Upper level open wave trof continued to push east/southeast across 
the desert southwest this evening; 500mb plot data depicted some of 
the most significant height falls across far northern AZ with 110m 
seen at Flagstaff. Coldest temps aloft - minus 20c or lower - were 
also well to the north of the Phoenix area and this proved to be a 
dry system for southern Arizona. For the most part skies were sunny 
today with just a bit of high based cumulus developing over nrn 
Maricopa and southern Gila county and after sunset the lower clouds 
quickly dissipated. As the system quickly pushes off to the east 
tonight, skies will continue to clear as stronger DVV/subsidence/Q 
divergence moves in behind the exiting system. At 9 pm IR imagery 
showed genly clear skies from Phoenix westward. Main impact of the 
passing system today was increased wind; a few locations over the 
central deserts reported peak gusts over 30 mph including Phoenix 
and Imperial saw similar gusts earlier in the evening but for the 
most part winds have tapered off following sunset and lack of 
mixing. Forecasts look to be in decent shape and no updates are 
needed at this time.

.PREVIOUS DISCUSSION...
A weak shortwave trough continues to track eastward through
Arizona early this afternoon with the main circulation center
moving through southwest Utah and a weaker secondary vort max near
Flagstaff. Skies have mostly cleared across southern Arizona and
southeast California aside from a few high based CU across La Paz
and northern Maricopa counties. Any shower activity remains well
north of our CWA near the vort max and expect this activity to
stay out of our area through the rest of today. 

Weak ridging aloft returns starting tonight lasting through 
Sunday night, but temperatures will change very little through
Monday. The active weather pattern continues into next week as
another quick moving Pacific low is set to move southeastward into
northern California early Monday and then into northwest Arizona
by Monday afternoon. As with the previous system, this one will
again be fairly moisture starved. However, models agree this 
system will be stronger as it deepens and close off over northern 
Arizona Monday night into early Tuesday. The latest model forecast
has the low tracking into central Arizona Tuesday morning before 
turning eastward into New Mexico Tuesday night. Shower activity 
will likely be scattered and mainly confined to higher terrain 
areas on Tuesday, but can't rule out a few showers into the 
Phoenix area. QPF amounts will be on the light side with most 
areas seeing less than a tenth of an inch. Winds will likely be an
issue starting Monday afternoon across southeast California ahead
of the cold front and again behind the front on Tuesday. Gusts 
approaching 40 mph will be possible and a Wind Advisory may be 
needed for our western zones.

Some model disagreement exists with the exit timing of the 
Tuesday system, but general model consensus shows increasing
subsidence and building heights by Wednesday morning. This should
lead to a quick rebound in temperatures by Wednesday as highs 
should easily climb back into the 80s over the lower deserts for
both Wednesday and Thursday.

Friday and Saturday...

All models are in general agreement in developing yet another 
Pacific trof over AZ this period. Models however are still 
conflicted in the eventual track of this system, which has potential 
to be the strongest, coldest, and wettest system in the series. 
However big disparities exist with the model guidance, with the 
European suggesting a more progressive trof through AZ Friday and 
into New Mexico Friday night. The GFS on the other hand forecasts a 
deep cold cutoff low to become nearly stationary over central AZ 
Friday and Saturday. Forecast confidence is very low this far out, 
so precip probabilities will be shaded toward a slight chance in 
south central AZ.

&&

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

Weather system continues to push off to the east and following 
sunset skies have cleared nicely. Expect genly clear skies into 
Sunday morning with some high cirrus moving in during the day 
tomorrow. Winds will remain from the west past midnight but should 
eventually turn east after 08z and remain there into the early 
afternoon on Monday. Since the gustiness has pretty much ended we do 
not expect any aviation concerns for the next 24 hours at least.

Southeast California/Southwest Arizona including KIPL and KBLH: 

Weather system continues to push off well to the east and gradients 
have relaxed, as such winds have tapered off and the gustiness at 
KIPL has subsided. Expect west winds to continue into mid morning 
Monday but stay mostly below 15kt. Winds have been less at KBLH and 
should continue to favor the northwest through north into Monday 
morning with speeds less than 12kt. Skies to be clear for the most 
part with possibly some thin high clouds moving into the area during 
the day on Monday. Now that the winds have died off there are no 
aviation concerns for the next 24 hours at least.

Aviation discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Monday through Friday...
Active storm pattern will remain over the Intermountain West at 
least through the end of the month and possibly into early April 
as a series of Pacific storms pass through. Breezy weather will 
remain a common feature of most afternoons/early evenings for the 
districts with daytime humidity levels ranging 10-25 percent at 
their driest. Most of the Pacific storms will travel through the 
Great Basin before sweeping into Arizona, allowing for above 
normal chances of precipitation for the Arizona districts but near
to below normal chances for precip along and west of the Colorado
River Valley. With an active storm track over the area, 
temperatures will trend more towards seasonal averages. Periods of
stronger winds may lead to a locally elevated fire danger at 
times that may turn into critical fire weather conditions for some
locales. A fair bit of uncertainty remains with the track of the
next few systems to move through the region in the far extended 
period that may ramp up or back off concerns for 
elevated/critical fire danger.

&&

.SPOTTER INFORMATION STATEMENT... 
Spotter reports will not be needed through the weekend.

&&

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

$$

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DISCUSSION...CB
PREVIOUS DISCUSSION...Kuhlman/Vasquez
AVIATION...CB
FIRE WEATHER...Nolte

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Western Regional Climate Center, wrcc@dri.edu