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487
FXUS65 KPSR 170542
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1042 PM MST Sun Jun 16 2024

.UPDATE...Updated Aviation Discussion.

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.SYNOPSIS...
A troughing pattern will encompass the western U.S. through the
first half of this week, resulting in cooler temperatures and breezy
conditions across the lower deserts of AZ and southeast CA. Another
pattern change will arrive late this week as a strong ridge sets up
over the area allowing temperatures to climb back to well above
normal. An increase in low level moisture will result in daily
thunderstorm chances across the higher terrain of southcentral AZ
beginning on Thursday and persisting through next weekend.

&&

.DISCUSSION...
Dry, zonal flow aloft is prevalent over southcentral AZ as
indicated by GOES-18 WV imagery. 500 mb hghts are beginning to
decrease across the northern and western portions of the region,
however 585-588 dam hghts are still present over southcentral and
southeastern AZ where temperatures are expected to remain well
above normal this afternoon. An Excessive Heat Warning remains in
effect through 8 PM MST for high temperatures between 105-112
degrees across the lower deserts of southcentral AZ including the
Phoenix Metro area. Another tranquil night is expected with lows
in the low to mid 70s across the region with the exception of Sky
Harbor Airport which will see a low around 83 degrees.

On Monday, a deep upper trough located over the Pac NW will move
further inland toward the Intermountain West, resulting in a
decrease in 500 mb hghts over our forecast area. In fact, negative
hght anomalies will be present across the entire western U.S.,
leading to a cooling trend which will last through the middle of
this week. Highs across the lower deserts on Monday will top out
around 100-106 degrees which is right around normal for this time of
year. Due to an increased sfc pressure gradient and strengthening of
the mid lvl wind field, we are expecting a breezy day to set up
across the area tomorrow with gusts reaching 20-30 mph. Locally
higher gusts up to 35 mph will be possible in southeast California
as well as the higher terrain of Gila and Maricopa Counties. Due to
the stronger winds and very low relative humidity, fire danger will
be high to very high, especially for the higher terrain areas
north and east of Phoenix (see fire wx disco for more details).

Near normal temperatures will continue through the middle of the
week as negative 500 mb hght anomalies overspread the forecast area.
The coolest day of the forecast period looks to be Tuesday when
highs are expected to remain below 105F across the lower deserts.
Unfortunately these near normal temperatures are not expected to
last as a strong subtropical ridge rebuilds over the region on
Thursday. Latest NBM temperatures are forecast to rise back around
110F across southcentral AZ on Thursday afternoon and increase
further on Friday to around 110-115F. The NBM probability to tie the
record high of 117F in Phoenix on Friday is currently around 40%.
Therefore, excessive heat criteria will likely be met later this
week as HeatRisk increases to major by Friday.

&&

.PREVIOUS DISCUSSION...
Another development with the expected pattern change late this week
is enhanced moisture levels advecting into the region (most notably
into southcentral AZ), with the surface high pressure setting up in
the vicinity of the NM/TX border beginning Thursday. Current
ensemble guidance depicts PWATs exceeding 1.00" or around 150% of
normal beginning Thursday and persisting into the weekend. There are
definite timing and magnitude differences between the ensembles in
regards to this moisture advection, but thunderstorm chances will
begin to increase across eastern AZ on Thursday and continue through
at least Saturday. The latest NBM PoPs continue to range between 10-
30% for the higher terrain of southcentral AZ, with the lower
deserts remaining low (10% or less). Monitoring the high pressure
development and evolution/movement will be key in determining how
good (or bad) thunderstorm chances will truly become late week and
into the weekend for southcentral AZ.

&&

.AVIATION...
-- Changed Discussion --
Updated at 0542Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

W to SW winds will continue for another couple hours and then
shift E between 6-9Z. A persistence forecast is expected Monday,
with a period of S winds between ~14-21Z and afternoon W to SW
gusts peaking as high as 25-30 kts again. SKC will prevail.

Southeast California/Southwest Arizona including KIPL and KBLH:

W winds will prevail at KIPL, while S to SW prevails at KBLH.
Elevated wind speeds and occasional gusts will continue for
another hour or two before subsiding at both terminals. Breezy
conditions are expected Monday, with peak afternoon and evening
gusts around 25-30 kts. SKC will prevail.
-- End Changed Discussion --

&&

.FIRE WEATHER...
Hot, dry, and windy conditions will lead to elevated to locally
critical fire weather across the region on Monday. A Red Flag
Warning is now in effect for the higher terrain northeast of Phoenix
on Monday afternoon and evening where gusts as high as 30-35 mph and
relative humidity levels as low as 7-12% are anticipated. Fuel
moisture across southcentral AZ is now critically dry with ERCs
exceeding the 90th percentile, or near the climatological maximum
for this time of year. These conditions will result in the rapid
spread of wind driven wildfires if one was to occur. Cooler
temperatures and lighter wind speeds will reduce the fire weather
risk by the middle of this week, however relative humidity will
still remain around 10-15% on Tuesday and Wednesday. Overnight
recovery will remain at or below 40%. Strong high pressure is
expected to build back over the region by Thursday resulting in
very hot temperatures, but wind speeds are expected to remain
light. Mid-range models are in agreement that we will see an
uptick in low level moisture across the eastern districts late
this week into this weekend, resulting in a low chance (10-30%)
of thunderstorms across the higher terrain of southcentral AZ.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
AZ...Red Flag Warning from 11 AM to 8 PM MST Monday for AZZ133.

CA...None.
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&&

$$

DISCUSSION...Salerno
PREVIOUS DISCUSSION...Young
AVIATION...Benedict
FIRE WEATHER...Salerno