Forecast-Discussion

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FXUS65 KPSR 231214
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
514 AM MST Thu Mar 23 2017

.UPDATE...To Aviation and Fire Weather Discussions...

&&

.SYNOPSIS...
A strong low pressure system will continue to move through the
region today, exiting Arizona later tonight. Shower activity today
will develop mainly from Phoenix eastward. High pressure will build
back into the region Friday, however another Pacific disturbance
will move into the region Saturday. The Saturday system will remain
dry, but a larger and colder weather system next Tuesday and
Wednesday may bring another period of showers.

&&

.DISCUSSION...

Today and Tonight...

A large Pacific storm was moving into the region this morning.
Actually this system is coming through in two parts. The cold front
moved through last evening developing gusty winds area-wide,
followed by a line of showers and isolated thunderstorms generally
along the leading edge of the 500 mb cold pool. Additionally, shower
and thunderstorm cells at 9 pm had moved toward the northeast at 50
knots, fast enough to develop strong downburst winds. One cell moved
through the Wickenburg area at 9 pm and subsequently produced a 62
mph wind at a RAWS observation site not to far away in Yavapai
county.

The second disturbance was moving through southwest AZ at 2 am, with
the strongest h5/h3 height falls forecast between Phoenix and Tucson
around 12z Thu or 5am. At 3 am the line of showers had refocused
from Gila Bend to Phoenix. Shower elements were still tracking
toward the northeast at 48 knots, fast enough for potentially strong
gusty winds in the 35 to 45 mph.

Later this afternoon instability showers and isolated thunderstorms
will be mainly confined to Phoenix north through southeast,
especially in the mountains. Clearing overnight.

Friday and Friday night...

A transitory high pressure system will build into the region Friday
and Friday night. Clear skies are forecast Friday with temperatures
rebounding somewhat, i.e. desert temperatures back into the lower
80s.  High clouds will likely spread into the region Friday night
ahead of another Pacific disturbance expected into the region
Saturday.

Saturday and Saturday night...

Another fast moving Pacific disturbance will move through the region
Saturday. The airmass will be relatively dry in the aftermath of
Thursdays system, so any shower activity will be relegated to
northern AZ. Desert temperatures will remain in the low to mid 80s
Saturday.

Sunday and Sunday night...

Another transitory high pressure system will build into the region
Sunday and Sunday night, ahead of another Pacific disturbance
expected in the region Monday night.

Monday through Wednesday...

A stronger and colder Pacific weather system is forecast to move
into the region Monday night through Wednesday. Some afternoon
cooling is expected across southeast CA and southwest AZ, with
relatively warm conditions remaining in Phoenix. Also, very strong
afternoon west winds will develop over southeast CA and the Colorado
River area ahead of the cold front.

Any shower activity will likely wait until Tuesday and Wednesday
afternoons, mostly a threat of instability showers with a developing
cutoff low over the region. Shower threat locations will be a
function of where the cutoff low settles Tuesday and Wednesday. The
Gfs model parks it over Phoenix, while other models suggest eastern
AZ.  This far out in time we will settle on a slight chance of
showers across most of the forecast area, i.e. southeast CA to south
central AZ.

Thursday...

Dry and slightly warmer, however there is a hint in the long range
models that another Pacific trof is in the offing for Friday,
outside this forecast period.

&&

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

Light to moderate scattered showers and west winds to persist for
the Phoenix area terminals for the morning hours. Shower activity
will continue to track from SW to NE and diminish in coverage
through midday. Low level/just-off-surface wind profile will be
dominated by west-northwest winds, while surface winds may veer
off of westerly headings and be more erratic at times due to the
passing shower activity. Morning BKN-OVC CIGs 3-5kft will slowly
lift and thin later into the day but anticipate afternoon
congested CU fields SCT to BKN in coverage 6-8kft to fill back in
from Phoenix eastward by the afternoon. West winds to continue
into the evening with skies clearing rapidly after sunset.

Southeast California/Southwest Arizona Including KIPL and KBLH:

Conditions will continue to dry in the wake a strong cold front,
but winds will remain elevated throughout the day. SCT to BKN mid
level clouds will begin to dissipate and thin into the day. West
winds will continue to dominate with sustained speeds 10-15kts and
gusts nearing 30kts again today. Lighter winds, speeds less than
10kts, will develop into the terminals in the late evening.

Aviation discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Saturday through Wednesday...
Temperatures will moderate back towards the seasonal normal over
the weekend as high pressure and dry weather build back into the
region. Breezy weather will be common through most of the
districts, especially Saturday and Monday afternoon. Despite the
stronger winds and drying trend, humidity levels will be
manageable only falling into a 15-30 percent range. Overnight
recovery will be good to excellent. Periods of stronger winds may
lead to a locally elevated fire danger at times, but critical
conditions should not be breached. An active storm pattern will
remain over the Southwest states, leading to periods of cooler and
windy weather through the end of the month.

&&

.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...Vasquez
AVIATION...Nolte
FIRE WEATHER...MO/Nolte

NWS PSR Office Area Forecast Discussion