-- Discussion containing changed information from previous version are highlighted. --
363
FXUS65 KPSR 062346
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
446 PM MST Thu Jun 6 2024

.UPDATE...
-- Changed Discussion --
Updated 00Z Aviation Discussion.
-- End Changed Discussion --

&&

.SYNOPSIS...
A strong ridge of high pressure positioned over the region will
promote some of the hottest temperatures so far this year today and
tomorrow. As a result, Excessive Heat Warnings will remain in effect
across much of the lower deserts through Friday evening. A weak
weather system will traverse the Desert Southwest this weekend,
leading to increased cloud cover and a slight cooldown before
another warming trend into the middle of next week.

&&

.DISCUSSION...
Current wv imagery and upper air streamline analysis shows our
region between a cutoff low centered west of the Baja Peninsula and
an anticyclonic circulation over New Mexico, with southeasterly flow
overhead. As is typical with southeasterly flow this time of year,
moisture has begun to move into the region, but mostly at higher
levels (i.e., above 15 kft). Increasing mid and high level clouds
over the lower deserts can be expected as a result. This increase
in moisture has also led to cumulus formation over the high
terrain of the White Mountains and along the Mogollon Rim, which
are expected to continue developing over the afternoon into
isolated to scattered dry thunderstorms. Convective activity will
stay far north/east of Phoenix, but eastern Gila County could
(less than 10% chance) see an isolated dry thunderstorm.

The main sensible weather impact of the current upper level setup
will be excessively hot temperatures. Strong positive 500 mb height
anomalies have set up over much of the Southwestern US, with current
RAP analysis showing a broad area of 592+ dam heights, particularly
east of our CWA (along the upper level ridge axis). With mostly
sunny skies through this afternoon and strong high pressure aloft,
the lower deserts will see their hottest temperatures so far this
year. Sky Harbor has already reached 110 degrees F this afternoon,
and the forecast high remains at 113 degrees, which would be 2
degrees above the daily record for 6 June if it comes to fruition.
The current upper level setup will remain relatively unchanged into
tomorrow, leading to similar highs across the lower deserts ranging
from 107 to 112 degrees, and repeat chances for (mostly) dry
thunderstorms over the high terrain of eastern AZ.

The cut-off low will start to affect our region more starting
Saturday as the low center reaches the northern Gulf of California
later in the day. The increasing proximity of the low should also
bring even more higher level clouds into the region for Saturday,
lasting through Sunday when the weakening low moves through the
area. Some modest cooling will be realized this weekend as NBM
forecast temperatures lower to between 104-110 degrees Saturday and
103-107 degrees Sunday.

Beyond this weekend, WPC cluster analysis reveals good agreement
between global ensembles as to the upper level flow evolution over
the next 7 days. Another cutoff low is expected to form by Monday
and meander off the northern Baja/Southern California coast through
the middle of next week. Discrepancies in the strength of ridging
over the Western CONUS and exact position/proximity of the cutoff
lead to large uncertainty in daily highs (probabilistic NBM inner
quartile spread of 5+ degrees as early as Monday) and moisture
availability for high terrain convective activity. However, another
warming trend into the middle of next week looks likely such that
Excessive Heat could again be a concern.

&&

.AVIATION...
-- Changed Discussion --
Updated at 2345Z.

South-Central Arizona including KPHX, KIWA, KSDL, KDVT; and
Southeast California/Southwest Arizona including KIPL and KBLH:

Winds will follow typical diurnal tendencies at all terminals,
with speeds generally aob 10 kts outside of some occasional gusts
up to 15-20 kts through sunset tonight and then again tomorrow
afternoon and early evening. SCT-BKN high clouds will continue
through the TAF period for the Phoenix Metro. High clouds are
starting to push into SE CA and will become SCT-BKN for those
terminals later this evening and then will continue through the
remainder of the TAF period.
-- End Changed Discussion --

&&

.FIRE WEATHER...
Hot and dry conditions will continue to support high fire danger
across the area. Well above normal temperatures are forecast
through Friday with highs at or just above 110 degrees for a good
portion of the lower deserts. Winds will continue to be fairly
light much of the time, but occasionally gusting upwards of 20
mph during the afternoon hours. MinRH values will hover around
10%, with poor to fair overnight recoveries as MaxRHs range
between 20-40%. A weak weather system is then expected to move
through the region this weekend allowing temperatures to start to
lower, but remaining above normal. Winds will also increase a bit
which could push afternoon gusts up to 25 mph in some locations.

&&

.CLIMATE...

Record high temperatures:

Date        Phoenix         Yuma         El Centro
----        -------         ----         ---------
June 6    111 in 2016    114 in 1928    113 in 2002
June 7    115 in 1985    116 in 1985    113 in 1985

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST Friday for AZZ530>556-
     559>562.

CA...Excessive Heat Warning until 8 PM PDT Friday for CAZ561-563-566-
     567-569-570.

&&

$$

DISCUSSION...Whittock
AVIATION...Berislavich
FIRE WEATHER...Kuhlman
CLIMATE...18