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690
FXUS65 KPSR 171750
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1050 AM MST Mon Jun 17 2024

.UPDATE...
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Updated 18z Aviation Discussion...
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&&

.SYNOPSIS...
Critical fire weather conditions headline the impactful weather
for the early portions of the week as breezy to windy conditions
develop today. Cooler temperatures will persist through mid-week,
with hotter temperatures and increasing moisture levels leading to
increasing thunderstorm chances late this week and into the
weekend.

&&

.DISCUSSION...
Dry, zonal flow continues to encompass the region early this
morning. However, the weather pattern is in transition as a
troughing feature currently centered over the Pacific Northwest
will continue to dig into the Great Basin, resulting in negative
height anomalies digging into the Desert Southwest going through
the middle of the week. As a result, temperatures will moderate by
several degrees back to just a few degrees above normal through
Wednesday.

While the cooling temperatures is a nice development, the
consequence of falling heights is a more energetic mid-level
troposphere, resulting in strong winds developing, especially for
today. Since the current fire danger is high to very high, a Red
Flag Warning is in effect this afternoon and evening for areas
with the strongest winds, which includes the higher terrain areas
of southcentral Arizona. Winds are expected to increase into the
15-25 mph range, with gusts up to 35 mph during this period. As
the troughing feature slowly weakens through mid-week, the fire
weather conditions should relax to elevated levels as opposed to
the critical level for today due to the weakening winds.

Heading into the latter portions of the week, ensembles remain in
good agreement of mid-level heights building again, resulting in
hotter temperatures developing once again going into this
weekend. High pressure from the Midwest region of the country will
retrograde westward, leading to this warming trend. Highs are
likely (40-70%) to reach or exceed the 110 degree mark by
Thursday, peaking on Friday (60-90%), and remaining a possibility
(30-60%) through this weekend. Another trend to monitor is the
overnight lows, as this retrograding high is projected to usher in
higher moisture levels in the low levels of the atmosphere,
resulting in warmer overnight lows. At this juncture, the
deterministic NBM is depicting lows for the Phoenix metro rising
from the mid to upper 70s early this week to lows in the mid to
upper 80s going into this weekend (20-40% chance central Phoenix
has a low of 90 degrees or warmer as early as Thursday night).
There remains a bit of uncertainty regarding the timing and
magnitude of increasing moisture levels, leading to a 5-10 degree
spread with the interquartile ranges for the low temperatures
Friday night onward. Due to this uncertainty, the level of heat
impacts will need to be monitored as overnight lows will likely be
the determining factor in whether more excessive heat products are
needed for late this week and into the weekend. At this time,
Moderate HeatRisk dominates the region on Thursday and Saturday,
with Major HeatRisk mainly across southcentral AZ developing on
Friday.

As mentioned, ensembles show a strong signal for increasing
moisture levels, at least in the lower portions of the troposphere,
late this week and continuing through this weekend. The outlook
hasn`t changed much over the last 24 hours, as the main push of
moisture commences on Thursday, as the high retrogrades and
southeasterly flow develops. The noticeable difference for the
current ensemble runs is a much more optimistic outlook from the
GEPS, as opposed to the more stable outlooks from the GEFS and
EPS. Nonetheless, thunderstorm chances are projected to increase
for the higher terrain of southcentral AZ on Thursday (5-15%
chance) and continuing into Friday (20-30%), while lower deserts
remain generally around 10% at most. PWAT`s in excess of 1.00"
is a reasonable scenario for southcentral 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 into (and
through) the weekend for southcentral AZ.

&&

.AVIATION...
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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...
A Red Flag Warning is now in effect for the higher terrain
northeast of Phoenix on Monday afternoon and evening for critical
fire weather conditions, as winds gust 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 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.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
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AZ...Red Flag Warning until 8 PM MST this evening for AZZ133.

CA...None.
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&&

$$

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