Weather Service Report

FXUS65 KPSR 281203

Area Forecast Discussion
National Weather Service Phoenix AZ
503 AM MST SAT MAY 28 2016



A broad area of low pressure will persist over the western United
States through the beginning of next week yielding somewhat cooler
than normal temperatures and dry conditions. Strengthening high
pressure much of next week will bring a warming trend with high
temperatures in the lower deserts pushing near 100 degrees by the
middle of the week. A stretch of well-above normal temperatures is
likely later in the week.


Dry westerly flow predominates across the desert southwest this
morning. Further upstream, latest streamline analysis indicates the
presence of a weak trough off of the CA coast. Continued increase in
thicknesses is expected today ahead of the trough which will equate
to temperature rises generally between 4 and 6 degrees across south-
central AZ. Despite the warming trend, temperatures will still fall
in the below-normal category.

Operational models remain in good agreement through the short-term,
indicating that the aforementioned mid-level trough will briefly
close off Sunday while moving into southern CA. This system is
moisture-starved and its main impact will be on temperatures, which
will be a degree or two cooler on Sunday. The trough will weaken
slightly Monday while continuing to slide eastward into AZ. An
additional degree of cooling is likely across AZ, however much warmer
conditions are expected across CA as a ridge in the eastern Pacific
moves eastward towards the west coast.

Residual moisture in the wake of the compact low pressure system
should be sufficient for isolated showers and thunderstorms
Tuesday/Wednesday. However, latest hi-res guidance suggests that the
activity will mainly be relegated to the higher terrain north and
east of Phoenix. Pops generally remain less than 5 percent in these

Latest guidance continues to indicate that the ridge will build
across the western CONUS, yielding steady height rises and a
continued warming trend during the mid to late week period. Temperatures
were increased for Thursday and Friday and generally represent the
70th percentile of all available guidance, which is well short of
records. Looking ahead to next weekend, operational GFS and ECMWF
diverge markedly, with the GFS depicting an eastern Pacific trough
fracturing and moving into the intermountain west. This solution is
not supported by other ensemble members and was dismissed, with the
expectation that the dry conditions and above normal temperatures
will persist.


South-Central Arizona Including KPHX, KIWA, and KSDL and 
Southeast California/Southwest Arizona Including KIPL and KBLH

A weak upper low near the California coast will lead to strengthening
southerly flow in the lower levels of the troposphere. Over south-
central AZ as mixing develops this morning, surface winds will hold
on to a predominantly southerly component through at least 21Z before
slowly trending to westerly by late afternoon. Expect gusts to be
well below 20kts. Southerly winds will be stronger over southwest AZ
and southeast CA (most noticeably over the Lower Colorado River
Valley with gusts of 15-20kts). Otherwise, clear skies except perhaps
for some very minor cirrus. 



Monday through Friday...
A weak upper low will keep temperatures near normal on Monday. A
ridge of high pressure then begins moving into the Desert Southwest
on Tuesday for the beginning of a warming trend. Expect most lower
elevations to reach 100 by Wednesday. Additional warming will make
for well above normal temperatures by Friday. Minimum humidities
will be in the 10-15% range on the lower elevations (dipping to
single digits east of the Lower Colorado River Valley by Friday).
Overnight recovery will be fair to good. No strong wind events are
expected. Anticipate Wednesday to have the strongest afternoon
breezes and Thursday the lightest. Otherwise, familiar warm season
wind patterns can be expected.


Spotter activation is not expected.




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