283
FXUS65 KPSR 111250
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
550 AM MST Tue Mar 11 2025

.UPDATE...Updated Aviation Discussion.

&&

.SYNOPSIS...
An unsettled weather pattern for the rest of the week will result
in cooling temperatures, multiple chances for rainfall, and
breezy to locally windy conditions. The first weather system will
impact the region later today through tonight with showers and a
few isolated thunderstorms focused during the evening hours. A
more potent weather system is then expected to move in by
Thursday bringing widespread windy conditions and precipitation
before exiting Thursday night. Additional chances for light
precipitation mainly over the Arizona higher terrain are possible
Friday night into Saturday before a period of drier and warmer
conditions are anticipated for Sunday and Monday.

&&

.DISCUSSION...
A deep closed low continues to track eastward toward our region
with the low center currently 350 miles west of San Diego. High
clouds out ahead of the system are now spreading into our region
with increasing southerly winds already across southwest Arizona.
The latest model guidance continues to show the upper level low
weakening as it tracks toward northern Baja later today before
becoming an open wave tonight as it moves across northern Sonora
and southern Arizona. The main forecast concerns with this
incoming weather system will be the potential for some isolated
thunderstorms producing some localized strong gusty winds mainly
across southwest Arizona and the widespread light to moderate
rainfall through early tonight.

Hi-res guidance shows showers beginning to develop across
southeast California by mid afternoon, becoming more widespread by
late afternoon as they spread eastward into the Yuma area.
Low level moisture advection is expected to ramp up across
southwest Arizona later this afternoon with the HREF showing
MUCAPE of 100-300 J/kg developing across Yuma County and then into
portions of La Paz and Maricopa Counties early in the evening.
This should allow for a few isolated thunderstorms to develop by
early this evening likely focused in a corridor from Yuma into
western Maricopa County with sub-severe gusty winds in excess of
35 mph a possibility. The shower activity and maybe an isolated
thunderstorm or two should spread east northeastward through the
area during the evening hours with rainfall amounts anywhere from
a few hundredths of an inch to upwards of a 0.5-0,75" in the
higher terrain north and east of the Phoenix area. The latest QPF
shows amounts averaging around 0.25" for the Phoenix area, but its
likely we will see a good deal of varying amounts due to the more
scattered nature of the shower activity. During the overnight
hours tonight, the bulk of the shower activity will move into the
eastern Arizona higher terrain with most of the showers coming to
an end just after sunrise Wednesday morning. This weather system
will be on the warmer side with snow levels staying above 6500
feet. Daytime temperatures Wednesday will cool down, but readings
should still reach to around 70 degrees in the Phoenix area to
near 75 degrees across the western lower deserts.

The second weather system for this week is already starting to
take shape across the northern Pacific and is forecast to quickly
dive southeastward toward the Pacific Northwest and northern
California coastlines by midday Wednesday. There is still some
slight model uncertainty with the eventual track of the main
shortwave as it moves through our region on Thursday, but the
overall forecast remains largely unchanged. This weather system
will be larger and much colder than the first one, but it will be
less compact and contain slightly less moisture. Strong height
falls will begin to affect our region by early Thursday leading to
increasing southerly winds throughout the morning hours Thursday.
We may even see winds increasing to near advisory level across
the western deserts by mid morning before winds likely peak across
the area during the afternoon. Advisory level winds with gusts in
excess of 40 mph may impact much of the area at times from late
Thursday morning through the afternoon as the cold front sweeps
through the region.

Strong system dynamics along with strong low level forcing with
the cold front should allow for widespread rainfall to move
through the area from west to east mainly during the afternoon
hours Thursday. There still looks to be a possibility of some
isolated mostly embedded thunderstorms with the main rain band
Thursday afternoon, but the chances of a QLCS look to be less than
what we saw yesterday due to the slight northerly shift in the
trough. Either way, any stronger convection or thunderstorms could
bring localized stronger winds mixing down to the surface as
models indicate there will be roughly 45 kts at 850mb. Rainfall
amounts for this second weather system are likely to be marginally
higher than the first with the western deserts averaging between
0.1-0.2", south-central Arizona including Phoenix between
0.3-0.5", and upwards of 0.5-0.75" over higher terrain areas.

Once the cold front moves through eastern Arizona by around mid
evening, snow levels are expected to quickly fall down to around
4000 feet, but much of the initial precipitation ahead of the cold
front will mostly fall as rain with snow levels remaining above
5000-5500 feet. As the snow level drops in the evening, we should
see rain change to snow for elevations above 4000-4500 feet, but
the bulk of the accumulating snows of maybe 2-6 inches should
mostly be confined to elevations above 5000 feet. Shower activity
is expected to gradually taper off during the overnight hours
Thursday night, likely ending by around sunrise Friday morning as
the main shortwave moves well into New Mexico.

Much cooler temperatures are expected later this week with highs
on Thursday only in the mid to upper 60s (early in the day) and
highs as cool as the upper 50s in the Phoenix area on Friday. We
are likely to stay under broad upper level troughing into the
weekend with even a weak follow-on shortwave potentially bringing
some light shower activity mainly over the Arizona higher terrain
Friday night/Saturday morning. Temperatures should begin to
moderate somewhat by Saturday, but we will continue to see below
normal temperatures. Finally by Sunday, guidance favors upper
level ridging to move across the region from the west and this
should bring highs back into the normal range for a couple days.

&&

.AVIATION...Updated at 1246Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Low CIGs along with showers and perhaps a few isolated thunderstorms
will be the primary aviation weather concerns during the TAF
period. SCT-BKN CIGs down to around 8-10 kft will develop this
afternoon before continuing to lower through the evening. Showers
and perhaps a few thunderstorms will push into the metro area
around 03Z-06Z, which will promote lower CIGs. Thunderstorm
chances for this evening will be around 20%, with any thunderstorm
that develops potential resulting in erratic winds. Have added
mention of VCTS into the SDL and DVT TAFs for now where chances
look to be the best. MVFR CIGs and visibility will be possible
with any heavier showers. Any MVFR CIGs will improve overnight as
showers exit the area.

Winds will continue to favor an easterly component through the
morning before veering toward the south late morning. As this
occurs, expect to see some breezy crosswinds with gusts to around
20 kts. Winds then veer toward the southwest this afternoon and
will continue into the evening and overnight period while speeds
remain elevated.

Southeast California/Southwest Arizona including KIPL and KBLH:
The primary aviation weather concerns will be lower CIGs and
showers. Shower activity will push into southeast California later
this afternoon and will help to drop CIGs down to around 5 kft.
Any heavier showers could briefly drop CIGs lower, but chances of
seeing MVFR CIGs are relatively low (20-30%). Can`t rule out a
thunderstorm near KBLH, but confidence is too low to reflect in
the TAF at this time. CIGs will then improve through the evening
as shower activity pushes east. Winds at KIPL will favor the east
this morning with extended periods of variability before switching
to the west later this afternoon. At KBLH, winds will mostly favor
the S-SW through the period.

&&

.FIRE WEATHER...
An unsettled weather pattern will begin today as the first of two
significant weather system this week moves into the region. Today
will start off dry, but shower activity with a few isolated
thunderstorms are expected to begin across the western districts
by the afternoon and then spread into the eastern districts in the
evening. Humidities today will improve a good deal with MinRHs
mostly above 30% over the western districts to 15-20% in the
eastern districts. Breezy southerly winds will also develop this
afternoon across much of southern and central Arizona. Wednesday
will bring some additional light showers over the higher terrain,
while breezy conditions develop across the western districts.
The next weather system is forecast to impact the region Thursday
into early Friday bringing more widespread rainfall, higher
elevation snow, and windy conditions.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

DISCUSSION...Kuhlman
AVIATION...Smith
FIRE WEATHER...Kuhlman