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000
FXUS65 KPSR 300554
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1054 PM MST Fri Sep 29 2023

.UPDATE...06Z Aviation Discussion.

&&

.SYNOPSIS...
An approaching weather system will lead to strong winds and much
cooler temperatures this weekend. Winds are expected to be
strongest on Saturday, which could lead to areas of blowing dust
and promote heightened fire weather concerns. Below normal
temperatures set in by Sunday and continue into the start of next
week before gradually warming up through the rest of the week.

&&

.DISCUSSION...
Strong winds and much cooler temperatures are in store for this
weekend as a strong trough, currently situated near the Pacific
Northwest, digs south and strengthens over the southwest CONUS.
Today will be our last day with above normal afternoon temperatures
heading into the weekend as heights continue to fall in relation to
the approaching trough. Currently this afternoon, visible satellite
imagery shows clears skies persisting across the forecast area as
dry southwesterly flow aloft continues. Temperatures will top out in
the upper 90s to around 100 degrees this afternoon before daytime
highs dip below the triple digit mark for Saturday. Highs across the
area Saturday will range anywhere from the mid to upper 90s across
south-central Arizona to the mid to upper 80s across southeast
California.

The aforementioned trough will continue to push into northern
California later tonight into early Saturday with gradients
tightening as it approaches our region. Winds will initially be
strong in southwest Imperial County where gusts in excess of 40 mph
will occur as early as this afternoon. Thus, a Wind Advisory remains
in effect for this portion of Imperial County starting later this
afternoon. Winds will further strengthen across the entire region
Saturday as the weather system deepens into a closed low over the
Great Basin region. This will lead to widespread strong afternoon
wind gusts upwards of 30-40 mph in many areas across the CWA with
locally higher gusts in excess of 40 mph in places such as Imperial
County and the southern Gila County high terrain. The latest NBM
continues to show high confidence in peak gusts exceeding 40 mph
tomorrow in these areas. NBM probabilities for advisory level wind
gusts tomorrow across southern Gila County are around 70-80% and
greater than 90% across Imperial County. A Wind Advisory remains in
effect for these locations starting around late tomorrow
morning/early afternoon and continuing into Saturday evening. Winds
of this magnitude will have the potential to generate areas of
blowing dust, particularly in dust prone areas across Imperial
County and parts of Pinal County, which would potentially impact the
I-10 corridor between Phoenix and Tucson. Additionally, dry
conditions with low relative humidity values will be in place across
south-central Arizona tomorrow as winds ramp up. As a result, the
dry conditions combined with the strong winds will lead to elevated
to critical fire weather conditions across parts of south-central
Arizona tomorrow afternoon. A Red Flag Warning remains in effect for
Maricopa, Pinal, and southern Gila Counties. Cooler temperatures and
better moisture will preclude greater fire weather concerns across
the western CWA.

Heading through the latter part of Saturday into early Sunday
morning, a cold front will progress through the area before
stalling. Guidance suggest PWATs will increase up to around 0.70-
0.90" along/ahead of the front with forecast soundings showing a
saturated layer between 850-700 mb. This may be enough to pop off a
few weak showers along the front, which is suggested by a couple of
HREF members. However, chances for seeing any measurable rainfall
across our area looks to remain very low, with NBM PoPs remaining
less than 10%, while the best chances for precipitation reside
across the northern Arizona higher terrain. Aside from the strong
winds, the greatest sensible weather change with this weather
system will be the notable drop in temperatures this weekend as a
cooler air mass is ushered into the region. By Sunday, afternoon
highs across the lower deserts will fall into the 80s, running
about 8-14 degrees below seasonal normals. Lows will bottom out
Monday morning as morning temperatures fall into the upper 50s to
low 60s across the lower elevations.

Below normal temperatures will persist during the first part of next
week as the weather system gradually shifts eastward and allows
heights to rebound across the area. Heading into the latter part of
next week, ensemble clusters show good agreement that ridging will
build in across the western CONUS and allow temperatures to return
near to slightly above seasonal normal readings.

&&

.AVIATION...Updated at 0550Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
VFR is expected to continue through the forecast period. Winds
will shift out of the E-SE by 06Z at KIWA and 07Z at KPHX and
remain below 10 kts overnight. By late tomorrow morning, winds
will begin to veer out of the south and become elevated with gusts
up to 20 kts possible. A southerly crosswind will continue through
the early afternoon until winds finally shift more out of the SW
by 20Z-21Z. Gusts will likely increase to around 30 kts at all
terminals between the 21Z-00Z timeframe before gradually
diminishing by sunset tomorrow evening.

Southeast California/Southwest Arizona including KIPL and KBLH:
VFR conditions are expected for the majority of the forecast
period. However, there will be potential for MVFR vsbys at KIPL
tomorrow afternoon. Westerly flow will prevail overnight at IPL
with intermittent gusts possible. Winds will continue to ramp up
at IPL throughout the day with gusts over 30 kts expected by the
afternoon. There is also a 30% probability of gusts reaching 50
kts mainly during the 21Z-00Z time period. Blowing dust may reduce
vsbys below 6SM at times. Southerly to southwesterly winds will
prevail at BLH overnight with gradually increasing speeds through
tomorrow morning. Gusts up to 30 kts by can be expected at BLH by
the afternoon.

&&

.FIRE WEATHER...
An approaching weather system will bring increasing winds and much
cooler temperatures for this weekend. Dry conditions are expected
to continue through the weekend with very low rain chances (<10%)
Saturday night into early Sunday. Temperatures today will be near
to slightly above normal before below normal temperatures settle
in by Sunday. Afternoon Min RHs Saturday will range from around
10-20% across south-central Arizona to 25-40% across the western
districts. Overnight Max RHs tonight will be in the 30-60% range
and rise to 50-80% Saturday night. Winds today will be strongest
in southwest Imperial County with widespread strong, gusty winds
setting in across the region Saturday. Gusts Saturday afternoon
are expected to climb upwards of 30-40 mph in most areas with
locally higher gusts across Imperial County and the southern Gila
County high terrain. Strong winds combined with low RHs Saturday
will lead to elevated to critical fire weather conditions across
south-central and eastern Arizona. As a result, a Red Flag Warning
is in effect for Maricopa, Pinal, and southern Gila Counties late
Saturday morning through Saturday evening. Wind speeds will begin
to diminish starting Sunday, but lingering strong wind gusts are
possible across the eastern Arizona high terrain before returning
to normal by Tuesday.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Red Flag Warning from 11 AM to 7 PM MST Saturday for AZZ132-133.

     Wind Advisory from 11 AM to 7 PM MST Saturday for AZZ556>558-
     560>563.

CA...Wind Advisory from 2 PM to 10 PM PDT Saturday for CAZ563>567.

     Wind Advisory until 5 AM PDT Sunday for CAZ562.

&&

$$

DISCUSSION...Smith
AVIATION...Salerno
FIRE WEATHER...Smith