607
FXUS65 KPSR 131709
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1010 AM MST Thu Jun 13 2024

.UPDATE...
Updated Aviation

&&

.SYNOPSIS...
Very hot and overall dry conditions will persist through the 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 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 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...Kuhlman
AVIATION...18
FIRE WEATHER...Kuhlman