000
FXUS65 KPSR 232226
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
326 PM MST Sun Sep 23 2018

.SYNOPSIS...
High temperatures will continue at or just above 100 degrees through
the week with only modest day to day changes anticipated. Expect a
slight to moderate increase in moisture aloft through the early
part of the week followed by drier air again by Wednesday.
Precipitation and storm chances will remain very low and are
generally not expected through the forecast period with the
occasional slight possibility of very isolated, short-lived
pop-up morning showers or afternoon storms.

&&

.DISCUSSION...
A flat high pressure ridge aloft remains in control of south-central
AZ today to bring yet another day of hot, above normal temperatures
across the region. Early afternoon temperatures ranged from the low
to mid 100s out west to the upper 90s to low 100s across the lower
deserts. It`s also drier today with surface dewpoints two days into
a drying trend registering 12 to 19 degrees lower than yesterday
afternoon with readings in the mid 30s to mid 40s. Afternoon
satellite imagery depicted patchy middle clouds drifting
northeastward over southern to southwest AZ with mostly clear skies
across other lower desert areas.

Little change is expected in the sensible weather this week with
high temperatures near or just above 100 degrees into next weekend
amidst very low storm chances. The high pressure aloft is forecast
to flatten and reposition more to the southwest of the region as
broad, saggy cyclonic troughing and stronger westerly flow takes its
place over Arizona. In addition a slight to moderate increase in
moisture parameters is also expected from now through Monday as PW
near 0.75 in. increase to near 1.4 in. due to light to moderate
midlevel and some BL moisture advection from NW Mexico. As a result
several of the high-res models such as the HREF show very isolated
and small pop-up storms and showers over portions of the lower
deserts through Monday, thus the non-zero POPS across the lower
deserts are included in the forecast.

On Tuesday and Wednesday a relatively dry, shallow and weak four-
corners trough axis will move across the region and try to draw up
some moisture from NW Mexico into far SE, E and NE AZ, although
during a simultaneous drying trend further west in the lower
deserts. Models remain in agreement that the isolated storm activity
associated with this feature will likely be confined to far SE, E
and north-central AZ.

For the second half of the week dry northwesterly flow will be in
control followed by a ridge of high pressure moving into the
Intermountain West which will increase H5 heights over south-central
deserts to near 588-590dam by Thursday and Friday. By Saturday the
ridge axis shifts east of the region and is replaced by
southwesterly flow aloft as well as increasing moisture out ahead
of a closed low pressure storm system moving east into northern
CA.

&&

.AVIATION...
South-Central Arizona including KPHX, KIWA, and KSDL:
Only minimal aviation impacts through Monday afternoon with only
some occasional cigs around 10K ft and virga developing overnight.
Gusty southeast winds this afternoon will relax and eventually shift
towards a southwest heading prior to sunset though timing is more
uncertain than usual. A shift back to an easterly direction should
occur after midnight and may be more delayed than usual.

Southeast California/Southwest Arizona including KIPL and KBLH:
Little to no aviation concerns through Monday afternoon with just
some occasional mid/high clouds. Winds will favor a southerly or
southwest direction during afternoon/evening hours, and more
variable or northerly during the morning.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Wednesday through Sunday:
Temperatures will remain several degrees above seasonal normals
through the weekend with dry weather for all districts. Minimum
afternoon humidity levels will range from the teens in lower
elevations to around 25% at higher terrain north and east of
Phoenix. Overnight recovery will be fair to good. Wind speeds should
remain typically light for early autumn with only the usual
afternoon upslope gustiness.

&&

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

&&

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

$$

DISCUSSION...Sawtelle
AVIATION...MO
FIRE WEATHER...MO

NWS PSR Office Area Forecast Discussion