663
FXUS65 KPSR 130600
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1100 PM MST Wed Jun 12 2024

.UPDATE...Updated 06Z Aviation Discussion.

&&

.SYNOPSIS...
Very hot and dry conditions will persist over the next few days with
an Excessive Heat Warning in effect through Thursday for the lower
deserts of south-central Arizona. A weak area of low pressure will
move over the region Thursday into early Friday, leading to
increasing cloud cover, breezy conditions, and perhaps a few
showers, primarily east of the Colorado River. Temperatures will
continue to run well-above normal through this weekend as high
pressure builds in once again.

&&

.DISCUSSION...
Atmospheric analysis reveals our forecast area flanked by an area of
building high-pressure to our east, while a cut-off low continues to
spin just off the coast of the Baja Peninsula. This setup will
remain relatively unchanged over the next 24 hours or so and will
help to keep very hot conditions over the region for today and
Thursday, with lower desert highs ranging between 108-112
degrees. Phoenix will continue to flirt with record high
temperatures during this timeframe, with 113 (2022) and 114 (1936)
being the records for today and Thursday respectively. Widespread
Moderate, to areas of Major HeatRisk will result from these
unseasonably hot conditions. Extra caution should be exercised if
you work outdoors or have plans to be outside during the hottest
period of the day. Take frequent breaks and be sure to hydrate
accordingly. In response to this elevated HeatRisk, and Excessive
Heat Warning remains in effect for Maricopa and parts of Pinal
Counties through Thursday evening.

Model guidance shows the cut-off low starting to progress eastward
by late Thursday morning, reaching southern California by
Thursday evening. Southerly flow will increase as this disturbance
advances toward our forecast area, resulting in enhanced moisture
flux, with PWATs forecasted to increase to the tune of 0.8-1.0
in. The associated dynamic ascent with the cyclonic circulation,
combined with increase in moisture may lead to some shower
activity across the region Thursday afternoon through early
Friday, with the best chances (20-30%) focused over the high
terrain areas of Maricopa and Gila Counties. Chances across the
lower elevations of south-central and SW Arizona are only around
10-20%, which is likely due to the dry sub-cloud layer that will
be in place, limiting the likelihood of seeing measurable rainfall
over the lower deserts. Most of the shower activity over these
areas is likely to be virga, but a few sprinkles or light showers
reaching the ground cannot be completely ruled out. Hi-res
guidance keeps the majority of rainfall east of the Colorado
River, but it would not be surprising to see a stray shower or two
over parts of SE California. Locally gusty winds associated with
these virga showers will also be possible (10-30% chance of gusts
exceeding 35 mph), primarily over southwestern Arizona. This low
will also tighten up the regional pressure gradient resulting in
afternoon and evening breeziness across the region regardless of
precipitation activity.

Models have been trending toward a weaker and more progressive
low over the past several runs, with the most recent runs now
indicating the center of circulation over the Arizona-Utah border
by mid-day on Friday. Heights aloft over south-central Arizona
will fall slightly with the passage of this system, promoting a
slight cool down in day-to-day temperatures, but MaxT forecasts
have been trending upwards over the past few days as a result of
the weaker system projections. Daytime highs for Friday are now
forecasted between 106-109 for the Phoenix metro, with hotter
temperatures expected further west as ridging quickly develops in
the wake of the low, with daytime highs there expected to be
around, and for some areas in excess of 110 degrees. Positive
height anomalies then spread over the remainder of the region by
Saturday, with widespread highs above 110 degrees expected across
the lower deserts. These temperatures will once again lead to
Major HeatRisk for some areas heading into the weekend. In turn,
an Excessive Heat Watch has been posted for the Imperial Valley
and eastern Riverside County for Friday and Saturday.

Clusters remain in great agreement regarding a deep trough moving
over much of the western CONUS during the start of next week, with
the southern fringes extending as far south as the Desert Southwest.
The main uncertainty that remains is how deep this trough
becomes, though most of the models favor the greatest height
falls/coolest air remaining well off to our north. Nonetheless,
some cooling is expected next week, with NBM MaxT forecasts
showing a gradual decrease in temperatures starting Sunday, with
daytime highs by Tuesday falling toward near and slightly above
normal levels.

&&

.AVIATION...Updated at 0555Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Winds will tend to follow their typical diurnal pattern, with
speeds generally aob 10 kt outside of tomorrow afternoon and early
evening. A slightly later switch back to the east is expected in
the morning, with the easterly component not expected to develop
until 11-12Z. Another extended period of variable wind directions
(140v250) should be common again tomorrow during the transition to
westerly winds during the late morning and early afternoon hours.
Winds will gust 15-20 kt tomorrow afternoon through sunset. Clear
skies will continue overnight with SCT-BKN mid-level clouds moving
into the region around sunrise. Some virga showers are possible
late tomorrow morning through the evening. Best time for any
activity/sprinkles to reach the ground would be tomorrow evening.
Any virga showers could cause some erratic wind directions with
some occasional gusts up around 30 kt.

Southeast California/Southwest Arizona including KIPL and KBLH:
At KIPL, current NW`rly winds will become light and variable
around sunrise and then become SE`rly tomorrow afternoon. Then,
around 00Z sundowner winds will cause winds to gust 25-30 kt
tomorrow evening. At KBLH, current westerly winds will go S/SW`rly
around 08Z. Wind speeds tomorrow afternoon will gust 20-25 kt
through sunset. At both terminals, FEW mid-level clouds will move
into the region tomorrow afternoon, but quickly clear out in the
evening. Any rain or storms that develop tomorrow afternoon are
expected to stay east of the Colorado River.

&&

.FIRE WEATHER...
Well above normal temperatures along with dry conditions will
prevail over the next couple days. Lower desert high temperatures
will top out between 107-112 degrees through Thursday. Winds will
continue to favor diurnal tendencies with occasional afternoon gusts
up to 20 mph today and to around 25 mph on Thursday when some high
based virga shower activity could bring a brief enhancement of the
winds. MinRH values will range between 5-10%, while poor overnight
recoveries can be expected with MaxRHs only reaching towards 15-35%.
Above normal temperatures will continue through the upcoming
weekend, while winds increase further with afternoon gusts of 20-30
mph likely. The combination of the increased winds and continued low
RHs will create even higher fire danger across the area this
weekend.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST Thursday for AZZ534-
     537>555-559-560-562.

CA...Excessive Heat Watch from Friday morning through Saturday
     evening for CAZ562-563-566-567-570.

&&

$$

DISCUSSION...Kuhlman
AVIATION...Berislavich
FIRE WEATHER...Kuhlman