Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 240304

Area Forecast Discussion
National Weather Service Phoenix AZ
805 PM MST SAT JUL 23 2016

Moisture and cloud cover will gradually increase over the area
through the beginning of the week taking some edge off the heat,
and providing better chances of showers and thunderstorms. The best
opportunity for rainfall will occur over the higher terrain north
and east of Phoenix with lesser chances heading west into southeast
California. Outside of thunderstorms, gusty winds and blowing dust
will be possible throughout the week as well.


A well defined MCV continue to churn westwards across the Baja
peninsula while a subtropical anti-cyclone remains centered over
cntrl/ern New Mexico. This synoptic configuration has placed much of
east/northeast Arizona within a favorable difluent jet region, and
an embedded weak H5 shortwave has supported semi-organized
convection over the White Mountains and Mogollon Rim. However,
despite a shallow morning Gulf moisture surge, 00Z KPSR and KTWC
sounding data indicated this layer has already been scoured away
leaving sfc-750mb mixing ratios only in a 8-9 g/kg range (and even
drier towards the more critical 700 mb layer). This has yielded
minimal MLCape below 500 J/kg and a more pronounced Cinh measure at
lower elevations.

As a result, outflow boundaries have been largely insufficient to
initiate additional convective complexes; and only a few boundaries
combined with synoptic scale ascent have kept storms persisting
through eastern Arizona. This activity should gradually wane
through the remainder of the evening as inhibition grows more
substantial. Otherwise with temperatures falling this evening, have
cancelled the excessive heat warning. Modest adjustments were also
made to cloud cover forecasts given recent satellite trends.


/211 PM MST SAT JUL 23 2016/
Sunday and Monday...
On Sunday, the pattern gets a little more interesting especially for
the evening and nighttime hours. An inverted trof, weakly seen in
south Texas this morning, is modeled to move northwestward an
approach southeast AZ later Sunday evening. The 12z GFS model
(current run) is now a little slower with moving this feature into
southeast AZ, and any forcing in our forecast area in south central
AZ including Phoenix comes overnight. Therefore, a slight chance of
showers and thunderstorms are forecast for a large portion of south
central AZ, including Phoenix Sunday night into early Monday morning.

Tuesday through Saturday...
This period contains a lot of uncertainty as the 300/250 mb flow
pattern transitions from southeasterly (and containing a few
disturbances from Mexico), to north and northeasterly Thursday
through Saturday. With continued elevated boundary layer moisture,
afternoon thermodynamics, and small hard to time perturbations in
the upper flow, its best to go with a broad brush forecast of slight
chance showers/thunderstorms this period just about everywhere in
our forecast area.


South-Central Arizona Including KPHX, KIWA, and KSDL:
Moderate confidence exists regarding limited aviation impacts
through Sunday afternoon before potential stronger outflow
boundaries affect aerodromes tomorrow evening. Some increase in
mid/high clouds will be likely from decaying storms over eastern AZ
tonight. Solid westerly winds will weaken later in the evening with
some uncertainty if/when a true shift to an easterly direction will
occur. Weak outflow boundaries from distant storms to the east may
eventually be the impetus for a wind shift overnight, though a quick
return to west winds would be common late Sunday morning.

Southeast California/Southwest Arizona including KIPL and KBLH:
Strong south to southeast prevailing winds will be the most likely
outcome through Sunday afternoon with lofted dust/haze impacting
slantwise visibilities tonight. After some weakening of speeds
overnight, occasional gustiness will once again be possible Sunday.
Some mid/high clouds will be possible along with dust trapped in the
lower atmosphere.

Aviation Discussion not updated for amended TAFs.


Tuesday through Saturday...
Monsoon moisture working its way back into the region will bring
chances for afternoon and evening thunderstorms each day through
Thursday. The best chances for wetting rains will be over the higher
terrain east of Phoenix, will 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 in the 15-30 percent range
Monday-Thursday to rise into the 20-35 percent range on Friday.


Spotter activation is not expected.





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