463
FXUS65 KPSR 140029
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
529 PM MST Thu Jun 13 2024

.UPDATE...Updated 00Z Aviation Discussion.

&&

.SYNOPSIS...
Very hot and mostly dry conditions will persist through the
weekend, with Excessive Heat Warnings in effect for various parts
of the region through Sunday. Weak low-pressure will move over
the region later today through early Friday, providing increased
cloud cover, breezy conditions, and perhaps a few sprinkles or
light showers for areas primarily east of the Colorado River.
Temperatures eventually cool towards normal levels during by the
start of next week.

&&

.DISCUSSION...
The pattern over the past 24 hours has not changed much as high
pressure continues build to our east, while the cut-off low
mentioned in previous discussion continues to spin of the coast of
northern Baja, though the latter feature has begun to advance
closer towards the Desert Southwest. This setup has provided our
forecast area with enhanced southerly flow aloft, providing us
with increased moisture flux which can be observed on WV imagery.
This increase in mid-level moisture helped provide increasing
cloud cover over south-central Arizona this morning and early
afternoon, with a few light virga showers being observed over
eastern Maricopa and southwestern Gila Counties. Another plume of
moisture will work its way over southwestern and south-central
Arizona this afternoon and evening, helping to spark more virga
activity. A few sprinkles or light showers reaching the ground
cannot be ruled out, but low-level dry air should inhibit chances
of seeing measurable rainfall. Hi-res data is also hinting at the
the potential (10-30%) of seeing locally gusty winds (>35 mph)
associated with this rainfall activity, primarily over La Paz and
Yuma Counties. Current mesoanalysis does reveal a narrow area of
instability over parts of southwestern Arizona (MUCAPE between
100-250 J/kg), which has led to a few lightning strikes across the
area. As this corridor of instability pushes east through the
remainder of the day, it would not be surprising to see a few more
strikes over western Maricopa and the Phoenix metro this evening
and into tonight.

Regardless of any rainfall activity, marginally breezy conditions
are expected this afternoon and evening as the cut-off low helps
to tighten up the regional pressure gradient. Gusts 20-25 mph will
be common across the region, with higher gusts (30-35 mph) over
the usual breezy spots in Imperial County. Even with the
increasing cloud cover and slightly lowering heights aloft due to
the closer proximity of the low, temperatures this afternoon
across the region will be similar to yesterday, with forecasted
highs across the lower deserts between 106-111 degrees. In the
past few days, it appeared that Phoenix may potentially flirt with
a record high (114 set in 1936) this afternoon, but with
temperature forecasts responding to the expected cloud cover and
downward trend in heights aloft, it now appears that the old
record high is likely to hold for at least another year.

Model guidance has the aforementioned low quickly ejecting out of
the Desert Southwest, indicating that it will be centered over
northern Arizona by mid-day Friday. Heights aloft with the
passage of this disturbance will be closer to climatological
normals over south-central Arizona, leading a degree or two drop
in day-to-day temperatures, with highs Friday over the area
between 106-109 degrees. Further west, ridging will quickly fill
in behind the low, leading to temperatures over SW Arizona and SE
California to be a few degrees warmer, as forecasted highs there
range between 108-112 degrees. Positive height anomalies then
spread over the remainder of the region by the start of the
weekend, resulting in widespread afternoon highs at or above 110
degrees, with above normal temperatures lasting through Sunday.
The Excessive Heat Warning that was posted for south-central
Arizona has been extended through Sunday in response, while a
separate warning is in effect for parts of SE California from
Friday morning through Saturday evening.

Cluster analysis continues to remain in excellent agreement
regarding a deep trough moving over the Intermountain West during
the front half of next week. Models have trended deeper with this
system, with negative height anomalies reaching as far south as the
Desert Southwest. Previous model runs already hinted at the
potential for a cooling trend in conjunction with this system,
with the main uncertainty being how pronounced it would be. If
this more amplified solution were to be realized, noticeable
cooling would likely occur, with many areas seeing temperatures
right around, to even slightly below seasonal levels.

&&

.AVIATION...Updated at 0020Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Wind directions will continue to be variable (340v040) until the
line of virga showers moves into the Phoenix Metro around 02-03Z
when wind directions will go more westerly/northwesterly. Most of
the activity will be virga showers, but some light rain/sprinkles
will be possible. These virga showers will cause some reduction in
slantwise visibility, but cloud bases will remain around 11-15
kft. The virga showers may also cause some occasional wind gusts
of 20-25 kt. Once the virga showers exit the Metro (06-07Z) winds
will become light and variable with speeds generally aob 5 kt, but
may predominately be out of the east. Winds will then go back
westerly tomorrow afternoon, but similar to the past few days a
period of light and variable winds is expected to precede the
westerly shift. SCT-BKN mid level clouds will continue through the
evening before exiting the area tomorrow morning.

Southeast California/Southwest Arizona including KIPL and KBLH:
Gusty southerly winds at KBLH will start to diminish after sunset
when winds will turn more westerly. Winds will then become light
and variable shortly after sunrise before going easterly in the
afternoon. At KIPL, gusty westerly winds will continue through the
evening and diminish through the overnight hours. Winds will then
become more northwesterly by mid-morning tomorrow. Few mid-level
clouds will move through the area this evening.

&&

.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-
     559-560-562.

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

&&

$$

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