Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 251000

Area Forecast Discussion
National Weather Service Phoenix AZ
300 AM MST MON JUL 25 2016

An increase in moisture and cloud cover over the region is expected
to take some edge off the heat, and provide somewhat better chances
of showers and thunderstorms through the middle part of this week.
The best opportunity for rainfall will occur over the higher terrain
north and east of Phoenix, with lesser chances heading west into
southeast California. A better chance for showers and thunderstorms
is then forecast for the end of the week and into the upcoming
weekend, as deeper moisture begins to move into the region from the
south and southeast.



Today through Tuesday...

A return to more favorable easterly flow aloft has brought
additional moisture back into the region this morning, with pwat
values now up into the 1.50-1.60 inch range across South-Central AZ.
A few showers and thunderstorms have even developed at this hour
across parts of NW Pinal and SE Maricopa Counties, which have likely
brought a bit of rain and gusty winds to a few locations across the
region. The latest HRRR high-res model run is showing these isolated
showers and storms continuing for the next few hours before
dissipating later this morning. Although some debris clouds are
still expected to linger across South-Central AZ through the morning
hours, the latest GFS/NAM model runs are showing a more rapid
clearing of these than what was earlier forecast. The combination of
this earlier clearing along with slowly increasing amounts of
available moisture will likely allow a bit more convective activity
to develop than what was earlier forecast across the region this
afternoon into tonight. Still, the lack of available moisture and
rather warm air aloft (500mb temps in the -5C to -6C range) is
expected to limit the amount and coverage of any showers/storms that
do develop, with the greatest threat for most locations being gusty
winds/blowing dust. The forecast for Tuesday looks to be similar to
today, although convective activity could be reduced somewhat if
significant debris cloudiness from today`s storms lingers very long
into Tuesday morning.

Wednesday and Thursday...

A reduction in convective activity looks likely during this period
as ridging aloft strengthens over the region and some drying of the
airmass occurs. 500mb heights are expected to approach 596dm by
Thursday, with many lower desert locations once again seeing highs
at/above 110F. The euro is the most aggressive model in terms of the
warming, taking the high at Phoenix Sky Harbor all the way up to
116F on Thursday! However, we are currently leaning towards the
somewhat cooler GFS, since lingering moisture/cloudiness is expected
to hold temperatures down somewhat. Convective development during
this period will likely be mainly confined to the higher terrain
north and east of Phoenix, with just a few storms (at most) making
their way into the lower deserts each day.

Friday through Sunday...

Although we are still expecting a uptick in the monsoon activity
during this period, as easterly winds aloft increase and moisture
levels rise further, there now appears to be a drying trends showing
up in the latest model suites, especially on Friday. This is likely
due to the fact that the global models seem to be having a tendency
so far this summer to weaken the upper-level ridging that has
persisted over our region too much, and also pushing the main ridge
axis too far to our north. This results in the airmass ending up
drier and more stable, resulting in less convective activity.


.AVIATION...South-Central Arizona Including KPHX, KIWA, and KSDL:
Mostly westerly winds for the terminals but there seems to only be a
hint of an easterly shift in the winds. This wind shift, if it
occurs, is more likely to be brief before going back to westerly.
However, decaying storms over northern Mexico and SE Arizona may
produce an impressive outflow out of the southeast that may reach
the terminals by early morning. Confidence in extent or speed of
this possible wind shift is lacking. Otherwise, expect debris
cloudiness tomorrow morning and a small possibility of a
stray shower.

KPHX CHANCES: Outflows/Sudden Wind Shifts: 20%
Blowing Dust: 10%
Storms Directly Impacting the Terminal: 10%

Southeast California/Southwest Arizona including KIPL and KBLH:
Winds predominantly to stay out of the south to southeast. The
gustiness at the terminals may subside a bit tonight. The
possibility of another Gulf surge tonight and into the morning
leaves the chance of haze and more gusty conditions tomorrow. Can
expect some thicker clouds in the morning from decaying Mexican
storms but impacts to aviation should be minimal.

Aviation Discussion not updated for amended TAFs.


Wednesday through Sunday...
Monsoon moisture working its way back into the region will bring
chances for afternoon and evening thunderstorms each day. The best
chances for wetting rains will be over the higher terrain east of
Phoenix through the mid week window with lesser chances over the
lower deserts of south- central and southwest Arizona and only slight
chances over southeast California. Some increase in convective
activity is expected on Friday as deeper moisture begins to move into
the region. Temperatures to remain slightly above normal through the
entire forecast period. Minimum humidities should fall in the 15-30
percent range through Thursday and rise into the 20-35 percent range
for Friday and Saturday.


Spotter activation is not expected.




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