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546
FXUS65 KPSR 172155
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
255 PM MST Mon Jun 17 2024

.SYNOPSIS...
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Near normal temperatures and breezy today, with widespread
elevated and locally critical fire weather conditions. A Red Flag
Warning is in effect for the high terrain east of Phoenix through
this evening. Temperatures will continue to hover near normal
through Wednesday before heating up late this week. Southeast
flow develops over the region during the latter half of this week,
bringing moisture and chances for isolated to scattered
thunderstorms over the South Central Arizona high terrain each day
starting Thursday.
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.DISCUSSION...
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Current wv imagery shows an unseasonably strong trough digging south
over the Great Basin and progressing east from the Pacific
Northwest, and as a result, winds aloft (along the base of this
trough) have increased over the Desert Southwest. ACARS soundings
from Phoenix Sky Harbor Airport show 25 kt speeds at 700 mb so far
this afternoon, and this higher momentum air is beginning to mix
down to the surface, with some automated surface observations
already reporting gusts to between 20-30 mph. The combination of low
humidity, breezy conditions, and very dry fuels has led to
widespread elevated and locally critical fire weather conditions
today for South-Central AZ. A Red Flag Warning is in effect through
8 PM MST this evening for high terrain locations to the east of
Phoenix.

As a result of height falls over the region associated with the
passage of this upper level trough, temperatures will be near normal
(but still hot) today through Wednesday, with highs generally in the
low to mid 100s across the lower deserts.

By late Wednesday, the pattern over the region changes such that
moisture can begin to enter the Desert Southwest. The aforementioned
trough will eject northeastward over the intermountain west while
another shortwave quickly dives southward from the Gulf of Alaska
and settles along the West Coast. Meanwhile, a tropical disturbance
will push eastward over Mexico bringing plentiful moisture inland as
an upper level high retrogrades southwestward from the Midwest. The
combination of the anticyclonic circulation to the north and
stronger winds associated with the tropical disturbance to the south
will allow for moisture to surge north northwestward along the AZ/NM
border early Thursday.

Daily chances for thunderstorms over the South-Central AZ high
terrain begin on Thursday thanks to the surge of moisture.
Thunderstorms chances range from 10-25% over the high terrain east
of Phoenix on Thursday and chances continue into Friday (20-40%),
while lower deserts remain generally around 15% at most. PWATs in
excess of 1.00" is a reasonable scenario for South-Central AZ
heading into the weekend, with these moisture levels (and higher,
potentially up to 1.50" in spots) looking like a good bet to
continue possibly into next week. Thus, daily thunderstorm chances
would continue for southcentral AZ, although ensembles depict the
moisture axis migrating westward through the weekend to the AZ/CA
border, thus leading to a less favorable pattern for higher (i.e.
25%+) chances for the higher terrain thunderstorms going into early
next week. Regardless, 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 through the
weekend for southcentral AZ.

Another consequence of the upper level high retrograding eastward
and settling over the Desert Southwest is increased heights aloft
and excessive heat redeveloping for portions of the region late this
week. NBM probabilities for temperatures in excess of 110 degrees
return for the Phoenix Metro Area on Thursday (40-70% chance),
Friday (70-90% chance), and continue into the weekend. On Friday,
Sky Harbor has approximately a 28% chance of tying or setting a new
daily high temperature record (previously 117 set in 2017). As a
result of these near-record temperatures and Major HeatRisk
developing over portions South-Central AZ, an Excessive Heat Watch
has been issued for Friday. Additional heat headlines (or an
extension of the current) may be considered going forward as the
forecast high temperatures on Thursday/Saturday and beyond will only
be a few degrees less than Friday, but Friday is shaping up to be
the hottest day over the next 7 days.
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.AVIATION...Updated at 1740Z.

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

Main aviation weather concern through this evening will be the gusty
winds. Southerly winds are expected for the next few hours before
switching out of the west to southwest by early this afternoon.
Wind gusts through early this afternoon will be in the mid to
upper teens before increasing further through the rest of the
afternoon peaking at 25 kts. Speeds will slacken off by the mid-
evening hours with a return to easterly winds expected during the
overnight hours. Skies will remain clear through the period.

Southeast California/Southwest Arizona including KIPL and KBLH:

Main aviation weather concern through this evening will be the
gusty winds. West winds are expected at KIPL while south to
southwest winds are expected expected at KBLH. Wind speeds are
expected to increase this afternoon and remain elevated into the
evening hours with gusts as high as 25 kts, potentially peaking
close to 30 kts at KIPL. Speeds will slacken off by later this
evening through the overnight hours. Skies will remain clear
through the remainder of the day.

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.FIRE WEATHER...
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A Red Flag Warning is in effect for the higher terrain northeast
of Phoenix through this evening for critical fire weather
conditions, as winds gust as high as 30-35 mph and relative
humidity levels as low as 6-12% 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 were to begin. Cooler temperatures
and lighter wind speeds will reduce the fire weather risk, but
remain elevated, 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.
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.PSR WATCHES/WARNINGS/ADVISORIES...
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AZ...Excessive Heat Watch from Friday morning through Friday evening
     for AZZ534-537>555-559.

     Red Flag Warning until 8 PM MST this evening for AZZ133.

CA...None.
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$$

DISCUSSION...Whittock
AVIATION...Lojero
FIRE WEATHER...Whittock/Young