Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 281540
AFDPSR

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

.SYNOPSIS...
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.

&&

.DISCUSSION...
A flattened ridge was prevalent over the SW Conus earlier this
morning, however weak cyclonic flow and a vorticity center was
already evident along the central California coast dropping south
per WV imagery. This wave will propagate into srn CA through the
afternoon acting to increase heights/thicknesses downstream over
Arizona. As such, afternoon highs will edge some 1F-5F warmer than
Friday. Given the stable and tranquil pattern, current forecast
parameters are tracking extremely close to observations and little
to no morning adjustments were necessary.

&&

.PREVIOUS DISCUSSION...
/503 AM MST SAT MAY 28 2016/
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
areas.

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.

&&

.AVIATION...
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.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
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 INFORMATION STATEMENT...
Spotter activation is not expected.

&&

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

&&

$$

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DISCUSSION...MO/Hirsch
AVIATION...AJ
FIRE WEATHER...AJ



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