686
FXUS65 KPSR 122132
AFDPSR

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

.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 1705Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No weather issues will exist through Thursday afternoon with clear
skies today giving way to 15-20K AGL cigs Thursday morning. An
extended period of variable wind directions (140v250) should be
common again during the transition to a westerly component early/mid
afternoon. Any gusts late afternoon/early evening should be limited
to around 15-20kt. West winds will have a greater probability of
being retained later into the overnight than usual with KPHX
possibly not flipping direction until closer to sunrise.

Southeast California/Southwest Arizona including KIPL and KBLH:
Only briefly gusty afternoon/evening winds will be an issue through
Thursday afternoon under clear skies. Winds will generally vary from
a S/SE direction during daylight hours, then veering to W/SW during
the evening/overnight. Occasional late afternoon/evening gusts 20-
25kt will be possible with periods of light and variable winds
around sunrise.

&&

.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...18
FIRE WEATHER...Kuhlman