069
FXUS65 KPSR 132052
AFDPSR

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

.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 1710Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Variable and potentially erratic wind directions will be the
greatest weather issue through Friday afternoon with 15-20K AGL cigs
today giving way to clear skies Friday. Confidence is good that east
winds will prevail into the early afternoon, however highly variable
directions are probable into the mid-afternoon during the typical
transition to a westerly direction. This variability may be
exacerbated by isolated, elevated convection resulting in virga and
isold SHRA; and west winds may not become truly established until
very late afternoon. While coverage and confidence of any more
direct impacts are too low to include in this TAF package, low
probabilities (~10%) exist of gusty, erratic (up to 30kt) winds
during the late afternoon through the evening.

Southeast California/Southwest Arizona including KIPL and KBLH:
A period of afternoon/evening gusty winds will be the main weather
issue through Friday afternoon as midlevel cloud decks stream north
along and east of the Colorado River. S/SE winds will be preferred
through the early evening with gusts 20-25kt initially materializing
at KBLH, then stronger westerly sundowner winds up to 30kt sweeping
into KIPL. Confidence is good that wind directions will have the
tendency to veer towards a W/SW direction through the overnight,
then trending more towards a light and variable character Friday
morning.

&&

.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...18
FIRE WEATHER...Kuhlman