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000
FXUS65 KPSR 241809
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1109 AM MST Wed Apr 24 2024

.UPDATE...Updated 12z Aviation Discussion.

&&

.SYNOPSIS...
Noticeable cooling will take place over the next few days as an area
of weak low pressure traverses the Desert Southwest. This system
will help generate breezy to locally windy conditions over the next
few days while potentially sparking a few light showers over
southwestern Arizona Thursday morning. Another more potent low
will then affect the region through the end of the week and into
the start of the weekend, ushering in the return of rain chances
Friday night into Saturday morning and helping to keep cooler and
breezy conditions in the forecast.

&&

.DISCUSSION...
The ridging pattern that resulted in several days of well- above
normal temperatures has started to push of to the east as a weak
area of low pressure advances towards the southern
California/northern Baja Coast. As these two features continue
their easterly progressions`, a noticeable cooldown occur over
the next few days once the aforementioned low moves to a close
enough proximity to the southwestern CONUS. Temperatures this
afternoon will be around 10 degrees cooler than what was observed
Monday, with daytime highs in the upper 80s and lower 90s across
the lower deserts. Highs by Thursday will then fall another 5-10
degrees, with only low to middle 80s in the forecast for lower
elevation communities, a good 15-20 degrees cooler compared to
where we started the week.

The other noticeable impact of this approaching system will be
the generation of breezy to locally windy conditions across the
region. Today, the strongest winds will focus over parts of
southeast California, where gusts in over 40 mph will be common.
Due to the high likelihood of gusts exceeding that threshold, a
Wind Advisory was posted for much of Imperial County and the area
around Joshua Tree NP that goes into effect this afternoon/evening.
Another Wind Advisory may be posted Thursday afternoon and
evening for areas in and around the Imperial Valley and Salton
Sea, as advisory level gusts will once again be possible
(60-70%). Elsewhere, winds over the next 1-2 days should remain
below advisory criteria, gusting primarily between 20-30 mph
across the lower deserts, with higher gusts of 25-35 mph expected
over the Arizona high terrain.

Moisture with this system will be lacking, yielding very low rain
chances across the Desert Southwest. However, recent model runs
have this shortwave trending slightly deeper as it pushes east,
resulting in a slight increase in PoPs over parts of southwestern
and south-central Arizona for early Thursday morning. Though
chances remain only around 10-15%, a stronger trough could
conceivably help spark some virga and very light showers due to
the greater degree of forcing and cooler air aloft. This shower
potential is now being highlighted in the CAMs, with members
showing activity over parts of La Paz and far northern Yuma
Counties, as well as western Maricopa County during the above-
mentioned window. Any totals observed with this activity will be
minimal, amounting to only a few hundredths of an inch at most.

Another more potent trough will dive south from the Pacific
Northwest toward our forecast area on Friday, yielding a
continuation of cooler-than-normal temperatures through at least
Saturday and persistent breezy to locally windy conditions. Model
trends now have the base of the cold core moving over the Desert
Southwest earlier than previous runs, and as a result, forecasted
wind speeds have trended upwards for Friday afternoon and
evening. Widespread gusts of 30-35 mph now look likely across much
of the region, with advisory-level gusts possible for the high
terrain areas of south-central Arizona, and once again for parts
of southeast California. However, any subtle shifts in the
forecast back to a slower progression of this system may result in
a very different wind forecast for Friday as the strongest winds
aloft associated with this trough would arrive outside of the
window of peak mixing, making it harder to get those higher
momentum winds down to the surface.

Dynamically, this trailing system will be much more impressive than
the proceeding shortwave. The better kinematics combined with
greater regional moisture flux compared to its predecessor has
resulted in increasing rain chances for parts of the region,
specifically for Saturday morning, when the area of greatest
forcing and coldest air aloft will move over the region. PoPs
during that timeframe have risen to around 30% over northern
Maricopa and southern Gila Counties, while other areas across
Maricopa, Pinal, and La Paz Counties have seen PoPs rise to
15-25%. Initial QPF totals are light, ranging from 0.01-0.20",
with the higher totals focused over higher terrain areas.

Global ensembles show this disturbance quickly ejecting out of the
region by Sunday, allowing for ridging to build in its wake,
resulting in a quick warm-up back towards above-normal
temperatures by the start of next week. A fair amount of
temperature spread remains as long-range guidance currently does
not agree on how amplified the ridging may be and where the axis
will be located. Nonetheless, the return of middle to upper 90s
across the lower deserts appears likely by as early as Monday.

&&

.AVIATION...Updated at 1808Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Southerly winds, with some SW-SE variability is anticipated
through 22-23Z this afternoon before a more distinguished SW
develops. Winds increase this afternoon, with occasional SW gusts
up to 20-25 kts. Confidence in wind directions tonight is low.
Surface decoupling should allow winds shift back to an E to SE
component, however it may be brief and winds may veer back S-SW
with a weather system moving through. There is a low chance
(5-10%) for some showers to sneak into Phoenix Thursday morning
between 12-17Z. Most activity will pass to the north, where a few
thunderstorms may also develop. FEW to SCT high clouds will clear
by this evening. Then FEW, to briefly SCT, clouds as low as 5-6K
ft may develop Thursday morning and then rise to 10-12K ft during
the day.

Southeast California/Southwest Arizona including KIPL and KBLH:
Very breezy to windy conditions are expected at both terminals
through most of the TAF period. Winds will be strongest during the
late afternoon and evening, with westerly gusts peaking up to
35-40 kts at KIPL this evening and southwesterly gusts peaking up
to 25-30 kts at KBLH. Some reprieve from the gustiness is
anticipated overnight, but sustained speeds will likely remain
elevated in the 10-20 kt range. The strong winds will be capable
of kicking up dust, but the wind direction at KIPL is not ideal
for significantly reduced visibility (MVFR or lower). There is a
low chance (5-10%) for a high-based shower to develop near KBLH
between 5-10Z before quickly moving off to the east. SCT mid-level
clouds will develop Thursday morning and clear by the afternoon.

&&

.FIRE WEATHER...
Multiple systems will impact the region through the start of this
weekend helping to cool temperatures and generating daily
occurrences of breezy to locally windy conditions. Elevated fire
weather conditons will exist this afternoon across the western
districts due to gusts approaching 40 mph and RH values hovering
around 10-15%. Elsewhere, similar RH values will be observed but
winds will not be as gusty, though isolated instances of elevated
fire weather conditons cannot be ruled out. Though widespread
gusty winds are likely to continue through this at least the start
of this weekend, any further fire risk should be limited by
increasing RH levels, which will rise to about 20-25% by
Thursday. Decent to good overnight recoveries will be common
across the region over the next few days, with MaxRHs ranging
between 45-75% before those values increase further by the start
of the weekend.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...Wind Advisory from 5 PM this afternoon to 3 AM PDT Thursday for
     CAZ560-563-565>567.

     Wind Advisory from 5 PM this afternoon to midnight PDT Friday
     night for CAZ562.

&&

$$

DISCUSSION...RW
AVIATION...Benedict
FIRE WEATHER...RW