927
FXUS65 KPSR 130938
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
238 AM MST Thu Jun 13 2024

.SYNOPSIS...
Very hot and overall dry conditions will persist through the
coming weekend with an Excessive Heat Warning in effect through
Sunday for the lower deserts of south-central Arizona. A weak
area of low pressure will move over the region later today and
tonight leading to increased cloud cover, breezy conditions, and
perhaps a few light showers focused more across central Arizona.
Temperatures will eventually cool down early next week with
readings closer to normal for the first half of next week.

&&

.DISCUSSION...
The main forecast concern continues to be the near record heat
across portions of the area through the upcoming weekend. For
today, the strong sub-tropical ridge currently centered over
southern New Mexico will continue to shift to the east of the
region while a weak cut-off low approaches southern California.
The heat dome over the region will largely stay in place despite
increasing mid-level moisture and clouds across Arizona as the
cut-off low approaches the region. Forecast highs of 107-111
degrees today may not be realized across south-central Arizona if
the clouds are thick and expansive enough to greatly impede
insolation, but breezier conditions very well could counteract the
clouds with increased mixing.

We also anticipate narrow bands of mostly virga showers
developing as early as sunrise this morning, but more so during
the afternoon and evening hours across western Pinal, Maricopa and
eastern La Paz and Yuma counties. Model soundings continue to
show cloud bases above 12K feet with a very dry sub-cloud layer
evaporating the majority of any rainfall from the shower activity.
However, would not be surprised to see a stationary narrow band
of showers allowing for enough top-down saturation for a hundredth
of an inch or so in a few spots.

As the cut-off low quickly exits to the northeast during the day
Friday, the temporary lower heights over Arizona will drop
temperatures to below 110 degrees across the south-central lower
deserts. However, building heights will quickly be seen across
the western deserts leading to forecast highs between 108-112
degrees across southeast California. The sub-tropical ridge will
build back over the southern part of the Desert Southwest late
Friday into Saturday with H5 heights back to between 590-592dm, or
easily into the 90th percentile of climatology. As a result, NBM
forecast highs Saturday rise to 109-114 degrees reaching Major
HeatRisk again for portions of the area. This renewed heat will
however be temporary as a large Pacific trough is expected to
enter the Pacific Northwest this weekend with the southern extent
of the trough reaching our region starting Sunday. Temperatures
Sunday will still be quite hot over the area, especially across
south-central Arizona where readings are expected to be around
110 degrees. With widespread Moderate HeatRisk and localized Major
HeatRisk over portions of the lower deserts over the next several
days, we decided to extend the Excessive Heat Warning in Arizona
through Sunday while upgrading the Excessive Heat Watch to a
Warning across portions of southeast California on Friday and
Saturday.

Gradually lower heights and temperatures are expected early next
week as the Pacific trough slowly slides by just to our north. By
Monday, highs are likely to fall back closer to seasonal normals
before bottoming out on Tuesday with highs between 100-105
degrees. The relief from the excessive heat will however be
short-lived as the sub-tropical ridge is expected to build back
over the region during the latter half of the week. Eventually it
seems likely highs will reach or exceed 110 degrees again by next
Thursday or Friday as the center of the ridge moves near or even
over the region.

&&

.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...
Hot and overall dry conditions will prevail over the next few
days. A weak weather system moving through later today and tonight
will bring some high based light showers, but much of the rain
will not reach the surface due to the very dry lower levels. Some
of these virga showers may produce locally gusty winds in excess
of 30 mph. Outside of any shower activity, gusts 20-25 mph will be
fairly common this afternoon and evening, resulting in locally
enhanced fire weather conditions. MinRH values will range between
5-10%, while poor overnight recoveries can be expected with MaxRHs
only reaching towards 15-35%. The above normal temperatures will
continue through the upcoming weekend, while winds increase
further with afternoon gusts of 20-30 mph likely on Sunday and
Monday. The combination of the increased winds and low RHs will
continue to bring elevated fire danger across the area into early
next week.

&&

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

     Excessive Heat Warning until 8 PM MST Sunday for AZZ560-562.

CA...Excessive Heat Warning from 10 AM Friday to 8 PM PDT Saturday
     for CAZ562-563-566-567-570.

&&

$$

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