Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 311153 AAA
AFDPSR

Area Forecast Discussion...Updated
National Weather Service Phoenix AZ
450 AM MST TUE MAY 31 2016

.UPDATE...updated aviation and fire weather discussions.

&&

.SYNOPSIS...
A slow moving low pressure system across the Desert Southwest will
bring near normal temperatures and dry conditions to the deserts
today, but a slight chance of showers and thunderstorms over the
higher terrain. Thereafter, strong high pressure will build over the
region resulting in a sharp warming trend. By the weekend, excessive
heat will prevail with many lower desert locations reaching the 110
degree mark.

&&

.DISCUSSION...
The main forecast focus over the next week will be the expected
excessive heat (potential record highs) later this week into the
weekend, but first a weak upper low will pass through Arizona today.
This upper low is easily seen on water vapor imagery early this
morning, centered just east of Yuma. For the most part, this upper
low is innocuous, but there is some mid level moisture wrapping
around the upper low. On the back side of the low, scattered mid
level altocu is seen on IR imagery across southeast California along
with some very light returns on radar.

As the upper low slides southeastward into northern Mexico this
afternoon, mid level moisture will wrap around the northern fringe of
the low entering east-central Arizona from New Mexico. This moisture
along with some modest upper level support should allow for some
scattered showers and thunderstorms along the Mogollon Rim and over
the White Mountains this afternoon. Storm bases will be fairly high
(12-15K ft MSL) so not anticipating much in the way of rainfall over
our higher terrain spots, but there will be a gusty wind potential
due to a dry sub-cloud layer. A weak northeasterly steering flow
may bring some of these storms closer to the lower deserts by early
evening, but they stand little chance of surviving off the high
terrain. However, the gusty outflow winds have a better shot at
affecting the Phoenix area along with a small potential for some
blowing dust.

By Wednesday, the upper low moves out of the region giving way to an
impressively strong Pacific ridge. Once this ridge shifts over the
Western United States later this week, an omega block regime sets up
as the ridge continues to build in strength. Currently, 500mb heights
associated with the high center off the West Coast are around 585dm
and should maintain this strength through Wednesday as the ridge axis
shifts eastward into southern California. The ridge will then
strengthen as it moves into the Desert Southwest for later this
week, easily topping 500mb heights of 590dm by early Friday.
Temperatures during this period will quickly climb from the current
slightly below normals to highs above 100 on Wednesday and then
quickly approaching 110 degrees Thursday. Once high temperatures get
to 110 or above, excessive heat watches and warnings come into play,
and this is all but a sure bet starting Friday.

Will be keeping the Excessive Heat Watch for much of our area going
without any changes and anticipate needing to upgrade to a warning
very soon. Model deterministic and ensemble means all point to this
impressive ridge setting up later this week and strengthening into
Saturday, before starting to shift eastward on Sunday. Models over
the past several days continue to bump up heights and temperatures
and the newest 00z model suite followed suite. Highest 500mb heights
now top out around 594dm on Saturday with NAEFS mean values
indicating above 97% of climo. 850mb and 700mb temperatures also peak
at around 99% of climo on Saturday. Given these data, anticipating
widespread highs in a 110-114 range for the Friday through Sunday
period. Readings like this would be near or in record territory,
especially for Phoenix. For Phoenix to hit 110 or above during the
first week of June is actually quite rare as it has only occurred a
handful of times on any given day in early June since records began
in 1895.

The excessive heat may extend another day into next Monday, but
mainly for the south-central Arizona deserts as an upper low is still
advertised to pass through southern California. Ensemble spread is
quite a bit higher for this early next week scenario so confidence
on when and how much of a cool down is still somewhat low.

&&

.AVIATION...
South-Central Arizona Including KPHX, KIWA, and KSDL...A weak upper
low moving south and across Arizona will circulate some mid level
moisture into the higher terrain of eastern Arizona today, leading
to isolated high based thunderstorms across the higher terrain to
the east of Arizona this evening. We do not expect any thunderstorms
reaching into the greater Phoenix area tonight, just scattered to
broken mid level debris cloud decks which should arrive by around
03z this evening. The biggest impact may be gusty east or southeast
outflow winds moving into the terminals after 05-06z and this has
been reflected in the various TAFs. Patchy blowing dust may
accompany the winds but confidence way too low at this time to
mention any visibility restrictions in the morning TAF package.

Southeast California/Southwest Arizona Including KIPL and KBLH... A
weak upper low slowly exiting to the east may result in some mainly
high level cloud decks this morning with skies becoming mostly clear
by the afternoon. Otherwise winds to favor the south next 24 hours
at KBLH with speeds mostly aob 12kt and winds to favor the southeast
at KIPL. No significant aviation concerns for the terminals next 24
hours.

Aviation discussion not updated for amended TAFs.

&&

.CLIMATE...

Record high temperatures later this week:

Date        Phoenix           Yuma
----       ---------         ------
June 2     110 in 2014       115 in 1957
June 3     112 in 2006       113 in 2006
June 4     113 in 1990       114 in 1990
June 5     112 in 1990       115 in 1957
June 6     110 in 2013       114 in 1928

&&

.FIRE WEATHER...
Thursday through Monday...
An unseasonably strong high pressure system will build over the
region this period, bringing some of the warmest afternoon
temperatures of the season. Many hotter desert locations will easily
exceed the 110 degree mark by Friday, with some locations
approaching 115 on Saturday. Slight cooler temperatures are forecast
on Monday. Minimum relative humidities will range from 7 to 10
percent. Typical warm season upslope afternoon winds are expected in
the 10 to 20 mph range each day, with stronger and gusty southwest
winds expected on Monday especially across south central Arizona.
Good overnight recovery is also forecast.

&&

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

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Watch from Friday morning through Sunday evening
     for AZZ020>023-025>028.

CA...Excessive Heat Watch from Friday morning through Sunday evening
     for CAZ031>033.

&&

$$

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DISCUSSION...Kuhlman
AVIATION...CB
CLIMATE...MO
FIRE WEATHER...Vasquez/CB



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