Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 240056
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
556 PM MST Sat Mar 23 2024

.UPDATE...Updated Aviation Discussion.

&&

.SYNOPSIS...
Unsettled weather will encompass the region the next several days
with cooler temperatures, locally windy conditions, and increasing
rain chances. The most notable winds will affect SE California this
evening with modest breeziness elsewhere. Rain chances increase
markedly tonight with additional rounds possible later on Sunday,
then again on Tuesday across south-central Arizona. Warming and
drying conditions are anticipated during the latter half of next
week ahead of another potential unsettled weather pattern next
weekend.

&&

.DISCUSSION...
Expansive troughing was translating onshore this afternoon with
numerous vorticity centers pivoting within the greater circulation.
Objective analysis indicates impressive 60-90dm H5 height falls
already entering the western CWA with H7 winds rapidly intensifying
above 30kt. This setup along with a strong cold front crashing
onshore and a deepening marine layer have already supported
downsloping winds and mountain rotors affecting SE California as
evidenced by standing gravity waves on visible satellite. Per model
output and forecast soundings, wind gusts should intensify this
evening as fropa shifts towards the Colorado River. Some of these
stronger winds will shift into SW Arizona later in the evening
associated with the pressure packing along the front, however
duration of advisory type winds should be temporally limited in
these locations. Otherwise, the proximity of the trough base and
additional height falls over western Imperial County should create
another round of stronger gusts Sunday, however the majority of the
area should merely experience a continuation of typical spring
gustiness.

Satellite imagery and objective analysis also shows a narrow plume
of modest moisture being advected northeast along the cold front,
albeit with a portion of the total PWAT being blocked by the Baja
spine. Nevertheless, forecasts still indicate a brief period of
mixing ratios reaching 6 g/kg and PWATS near 0.75" coincident with
fropa across south-central AZ overnight. HREF members remain fairly
consistent in depicting broken lines of showers ahead of the front
sweeping through the Phoenix metro and higher terrain areas prior to
sunrise, and have boosted NBM POPs somewhat given the favorable
synoptic setup. The quick movement of the front out of the CWA by
mid morning should result in lesser rainfall chances through the
day, however with cold air aloft, steep lapse rates, and residual
moisture, instability may develop in the afternoon (perhaps ~100
J/kg MLCape) supporting isold/sct showers. However, with the main
vorticity lobe digging south into Mexico, forcing will be rather
limited during the afternoon and evening precluding a more
widespread higher POPs.

On Monday, the main trough axis slides east of the region with some
measure of weak subsidence entering the CWA. With this lack of any
discernible forced ascent and poor thermodynamic profiles, rainfall
chances appear minimal during the daylight hours. However, another
shortwave ejecting from the Pacific Northwest, and absorbing into
the NW flow aloft on the western side of the trough axis Monday
night into Tuesday will enhance rain chances once again across south-
central AZ. This type of pattern historically has supported showers
moving off higher terrain into parts of the Phoenix metro far more
efficiently than global model indicate, and have increased POPs
slightly over the mandated NBM as a result. This overall multi-day
unsettled pattern should result in modest rain accumulations to
around 0.05-0.25" for the Phoenix metro and 0.25-0.75" over higher
terrain of the eastern CWA.

During the middle and latter half of the week, drier conditions will
quickly settle into the region with flat ridging moving into the SW
Conus. Ensembles are somewhat more in line with the trailing ridge
pattern being somewhat stronger than previous iterations, however H5
heights peaking near 576dm may only hover over the region briefly
before the next East Pacific trough and cyclonic flow edges into the
region late in the week. As a result, numerical guidance spread is
rather narrow suggesting good confidence of temperatures returning
to a near normal range in the Wed-Fri time frame. Discrepancies
amongst the ensembles grow rapidly heading into next weekend as the
aforementioned trough moves towards the west coast. Recent trends
among operational and ensemble members suggest a far slower forward
progression to the wave structure such that a quasi-blocking pattern
may materialize yielding very low forecast confidence.

&&

.AVIATION...Updated at 0056Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Gusty SW winds will continue through the rest of the afternoon and
evening with gusts to around 20 kts. Between 4-11Z tonight a cold
front will move west to east through the metro. Winds will
increase, with speeds climbing up to 12-17 kts and gusts to around
22-27 kts. There will also be a 30% chance for gusts in excess of
30 kts as the front rolls through and with VCSH/-SHRA. There will
be a 10% chance for TS as well. CIGs will fall to 5-7K ft during
this time. The front will pass through the terminals around 09-10Z
and push showers off to east. Winds will also subside slightly
following the front. Clouds should improve post-front becoming FEW
to SCT 7-8K ft before becoming BKN again by around 13-14Z. West
winds and SCT-BKN 6-7K ft clouds will prevail Sunday, with daytime
wind gusts to around 20-25 kts. There will be a slight chance
(20%) for showers, and lower chance for a thunderstorm, beginning
after 20-21Z Sunday. The showers will be capable of producing
stronger wind gusts and sudden wind shifts from outflow boundaries
that may emanate a distance away from the activity.

Southeast California/Southwest Arizona including KIPL and KBLH:
Blustery conditions will prevail through most of the TAF period at
both terminals. Winds will be strongest at KIPL, expected to peak
this evening with westerly gusts up to 40 kts, mainly between
02-06Z. Otherwise, gusts between 25-35 kts will prevail. At KBLH,
west to southwest gusts to around 30 kts should continue through
midnight before subsiding. The gusts this evening will be capable
of kicking up some blowing dust, which could temporarily lower
visibility. Gusty conditions at KBLH will pick up again later
Sunday morning, with gusts through the afternoon mainly between
20-25 kts. VCSH and virga has developed near KIPL late this
afternoon and is only expected to last to as late as 02-03Z. A few
isolated showers may also pop up near KBLH Sunday afternoon, but
confidence is too low to include in the TAF. SCT to BKN clouds
between 6-10K ft will be common through the TAF period.

&&

.FIRE WEATHER...
Windy conditions will develop today and last through tomorrow with
areas across the western districts gusting in excess of 40 mph (up
to 55 mph in higher terrain areas). MinRH 15-25% today will increase
above 25% for the lower deserts ahead of the next rain chances
Sunday into Monday. Lingering enhanced moisture levels are
anticipated for southcentral AZ through Tuesday, while the western
districts will begin to dry to around 20%. Wetting rain chances are
highest in the higher terrain areas of southcentral AZ for Sunday
into Monday around 20-40%, with higher chances around 30-60% for
Tuesday. Expect lower desert wetting rain chances to be no more than
10-20%. Generally drier and warming conditions expected going
through the middle of next week.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...Wind Advisory until 6 AM PDT Monday for CAZ560-562>567.

&&

$$

DISCUSSION...18/Young
AVIATION...Benedict
FIRE WEATHER...Young


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