Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 251140
AFDPSR

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

.UPDATE...Updated Aviation and Fire Weather Discussions...

&&

.SYNOPSIS...
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.

&&

.DISCUSSION...

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:
Easterly winds this morning should switch westerly earlier than
normal like yesterday with occasional gusts during the afternoon.
Late afternoon and evening high terrain storms may again bring
outflows into the lower deserts this evening with a remote chance of
an isolated thunderstorm in the Phoenix area. Confidence in outflow
timing and strength is low and not yet included in area TAFs.

Southeast California/Southwest Arizona including KIPL and KBLH:
Winds predominantly to stay out of the south to southeast through the
period. Thicker clouds this morning from decaying Mexican storms will
eventually thin out by noon. Impacts to aviation should be minimal.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
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 Friday 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 this weekend 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 starting Friday.

&&

.SPOTTER INFORMATION STATEMENT...
Spotter activation is not expected.

&&

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

$$

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DISCUSSION...Percha
AVIATION...Kuhlman
FIRE WEATHER...Kuhlman



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