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Forecast Discussion for Phoenix, AZ

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000
FXUS65 KPSR 212020
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
120 PM MST Wed Nov 21 2018

.UPDATE...Updated fire weather discussion.

&&

.SYNOPSIS...
Skies will be mostly clear today before high clouds start to
increase in the afternoon. A series of relatively dry low
pressure systems will move through the region over the next
several days. The main result will be breezy conditions at times,
occasional thick high cloudiness, and a gradual cooling trend
through the weekend. The best chance of precipitation will be
Thursday afternoon and evening.

&&

.DISCUSSION...
Today through Friday...
The upper low that brought high clouds to the forecast area
yesterday has now shifted to the southern Plains. That feature is
within undercutting flow on the southern side of a ridge over the
western CONUS. This will make for mostly clear skies today with
similar high temps as Tuesday. The ridge will be short lived
though due to an upper trough already moving into the West Coast.
In addition to moisture already within the trough, it is helping
to advect some subtropical moisture northeastward toward far
northwest Mexico and the Desert Southwest. Models continue to show
the trough tracking through the western CONUS on Thursday and
Thursday night. However, it weakens quite a bit in the process as
hits the ridge and an upstream system steals its thunder so to
speak. That will mean less robust moisture making it across the
southern California and northern Baja mountains and less moisture
from the subtropics making it north of the Mexico border. This
will hinder precip potential for our forecast area. Another
hindrance is that the dynamical forcing largely misses us just to
the north. That will mean only very slight chances of light rain
limited primarily to higher terrain areas. Too bad since the jet
core with the system peaks at about 140 kts over western AZ.
Otherwise, breezes pick up on Thursday and there will be some
minor cooling followed by some slight additional cooling on
Friday.

Saturday through Tuesday...
Yet another system affects the western CONUS late in the week and
over the weekend. This system will track from northwest to
southeast. The brunt of it goes through the NW CONUS and into the
central Rockies. Though there is some leftover moisture over the
Interior West for this system to work with, it won`t be strong
enough over our area for precip. Instead, we will get some north
and northeasterly breezy to windy conditions later Saturday into
Sunday. There will be some minor cooling as well felt on Sunday.
That will mean highs in the Phoenix area struggling to reach 70
with the warmest deserts such as Yuma and El Centro in the lower
70s. For early next week, models are in fairly good agreement that
there will be narrow high amplitude ridging over western North
America. There is also agreement in the idea of a short wave
moving through the ridge and enhancing split in the Westerlies as
it develops into a weak upper low centered roughly over Baja
Mexico. There are differences in the model solutions on this
feature but for now, it looks to be a non-factor for our forecast
area. However, it will help keep temperatures from rebounding.

&&

.AVIATION...
South-Central Arizona including KPHX, KIWA, and KSDL...
Southeast California/Southwest Arizona including KIPL and KBLH:

Dry and stable conditions can be expected today and tonight.
Wind directions at the surface and within the lowest 5-10kft ASL
will favor east and southeast directions for much of the day.
Surface winds over metro Phoenix will become light and variable in
the afternoon favoring westerly directions. No significant clouds
except for increasing cirrus during the afternoon.

For the Imperial Valley, there will continue to be locally
reduced visibilities in haze this afternoon. The KIPL ASOS has
occasionally observed readings as low as 4SM since midnight. Went
ahead and added HZ into the KIPL TAF.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Saturday through Wednesday:
Conditions are expected to be dry through the weekend and early
next week. A storm system passing mainly through the Rockies will lead
to breezy northerly winds Saturday afternoon into Sunday along
with somewhat cooler temperatures. Winds will continue to favor
north and northeast directions through early next week with high
temperatures remaining a few degrees below normal. Humidities
begin trending down Friday with a sharp decline on Sunday
resulting in minimum humidities in the upper teens to low 20s at
most places. Anticipate little change thereafter with overnight
recovery remaining at least fair to good.

&&

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

&&

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

$$

DISCUSSION...AJ
AVIATION...AJ/Smith
FIRE WEATHER...AJ/Rogers

Previous Forecast Discussions may be found at
NWS Phoenix, AZ (PSR) Office Forecast Discussions.
(Click 'Previous Version' there to view past versions successively.
Some may differ only in time posted.)

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