000
FXUS65 KPSR 192148 CCA
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
250 PM MST Sat Aug 19 2017

...updated aviation discussion...

.SYNOPSIS...
An increase in monsoon moisture over the next couple days will
lead to rain chances moving back into the area, especially across
southeast and south-central Arizona. Rain chances will last into
the middle of the week before another drying trend lowers chances
by Thursday or Friday. Temperatures over the next week will
remain near normal.

&&

.DISCUSSION...
Modest mid level moisture advection occurred during the overnight
hours across south-central and southeast Arizona as southerly
flow increased east of a developing cut-off low just off the
California coast. This led to the 12Z Phoenix sounding showing a
PWAT of 0.96", a decent improvement over the past couple days. A
Gulf surge also moved into southwest Arizona near sunrise this
morning raising surface dew points into the 70s in Yuma. Even with
this moisture advection into the area, we are only expecting
showers and thunderstorms across far eastern Gila county this
afternoon.

Water vapor imagery currently shows a modest shortwave trough
across Sonora Mexico which is very slowly moving to the north
northeast. Models are forecasting this trough to move into
southeast Arizona during the overnight hours tonight as well as a
decaying MCS. Moisture will continue to spread north and west into
the area tonight as PWATS inch closer to 1.25". At least a couple
Hi-Res CAMs show some light shower/sprinkle activity move into
the Phoenix area late tonight, likely influenced by the decaying
MCS.

The cut-off low will continue to sit just off the southern
California coast into early next week allowing for at least some
sort of southerly wind component and moisture feed. Upper level
support for storm activity will mostly stay west of our area and a
south to southwesterly steering flow is not favorable for
widespread storm activity across southwest and south-central
Arizona. PoPs for Sunday through Wednesday remain mainly in the
slight chance category as PWATS hover around low grade monsoon
levels. Temperatures through the period should end up near or
slightly below normal due to the influence of the low to our west.

By the middle part of this week, the low will start to spread
drier air into southeast California and far southwest Arizona as
flow aloft turns slightly southwesterly and this will serve to
confine storm development to areas east of the lower Colorado
River valley. On Thursday the low is forecast to open up and move
inland, bringing more dry air further east across the lower
deserts and as this occurs, storm chances from Phoenix west fall
with POPs to be in the single digits. Slight chances for storms
will continue over the higher terrain of southern Gila County into
the end of the work week. High temps Tuesday into Thursday will
stay a bit below normal, especially over south- central Arizona,
under the influence of the low and its slightly cooler airmass.
Temperatures should climb slightly Friday as low continues to
weaken and high pressure aloft becomes slightly stronger.

&&

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

Westerly winds to persist at the Phoenix area taf sites later than
usual, well into tonight, with stronger gusts possible during the
late afternoon/early evening hours, with the switch to easterly not
likely to occur until sometime after midnight as well. A similar
wind pattern is expected to occur on Sunday as well. Monsoon
moisture returning back to the region will likely produce isolated
showers and thunderstorms Sunday afternoon/evening, but confidence
is far too low to include anything more than an increase in mid/high
cloudiness inn the tafs at this time.

Southeast California/Southwest Arizona including KIPL and KBLH:

Winds to remain mainly southerly at KBLH through the taf period,
under mainly clear skies. Westerly Sundowner winds at KIPL to
persist through Sunday morning, then becoming light/variable for a
time during the mid/late morning hours. Westerly to southwesterly
winds will then return to KIPL on Sunday afternoon.

Aviation discussion not updated for amended TAFs.

&&

.FIRE WEATHER...

Monday through Friday: A moderate amount of monsoon moisture will
persist through at least mid week bringing a chance of storms (20-
30%) to the higher elevations each day and a slight chance (~10%) for
the lower elevations of south-central Arizona. Slightly drier air
moving in late week will likely confine storms to the high
elevations on Thursday and Friday while all areas will see near
seasonal temps. Minimum humidities will hover around 20% for the
lower elevations while the higher elevations of Gila County will be
much more favorable, around 30-40%.

&&

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

&&

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

$$

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DISCUSSION...Kuhlman
PREVIOUS DISCUSSION...CB
AVIATION...Percha
FIRE WEATHER...Wilson

NWS PSR Office Area Forecast Discussion