000
FXUS65 KPSR 011144
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
444 AM MST Sat Oct 1 2022

.UPDATE...Updated Aviation Discussion.

&&

.SYNOPSIS...
Anticipate an uptrend in thunderstorm activity this weekend over
south-central and southwest Arizona with ongoing chances Monday
and Tuesday. Rain chances over the lower deserts will remain
modest at only 10 to 20 percent. Storm chances will retreat to the
higher terrain of south-central Arizona by Wednesday. High
temperatures will remain slightly above normal before a subtle
cooling trend during the latter half of the next workweek.

&&

.DISCUSSION...
Though the Monsoon season (calendar based definition) is over,
there will still be varying amounts of thunderstorm coverage over
AZ for several days to come. The flow pattern isn`t classic
Monsoon though. There is a cutoff low centered over Sonora,
Mexico, another larger one centered over eastern Idaho, a narrow
high amplitude ridge centered near the West Coast, and another
ridge centered over the Plains states. Precipitable water values
are relatively for this time of year being above the 90th
percentile over portions of southern AZ and into far southeast CA.
Surface dew points reflect this as well with afternoon readings
in the 60s in those areas. It`s a been a bit dryer over south-
central AZ.

There is generally good agreement amongst the global models on the
evolution of the synoptic scale features for this weekend through
next Friday. For today, the low to the north drifts a bit further
north as does the low to our south. A pattern change starts
Sunday where a strong short wave in the northern branch of the
Westerlies starts budging the upper low to our north beginning a
transition to an open wave. Meanwhile, the West Coast ridge starts
moving inland. It regains some amplitude on Monday which aids in
southward elongation of the trough to the north. That in turns
leads to a weakening of the Sonora low. But, that also enables a
short wave to track through Arizona. Speaking of short waves,
deterministic data indicates a short wave may at least brush the
forecast area Sunday (ahead of the larger one later Monday). As
for PoPs, those trend up modestly east of the Lower Colorado River
Valley - though not dramatically. Made some subtle manual
adjustments to NBM PoPs to align better with WPC QPF guidance.
Highs will remain slightly above normal because strong ridging
doesn`t build right over us. Thus, HeatRisk levels remain in the
Low category.

The short wave for late Monday may be followed by a couple of
additional short waves in the northerly flow which eventually
appear to reform another closed low centered near the Mexico
border. That northerly flow will lead to drier air and thus a
downtrend in the PoPs. But, the presence of the closed low will
make for a slow downtrend. Highs will be slightly cooler during
latter half of the workweek (more noticeably over south-central
AZ) due to the influence of the short waves and cutoff low.

&&

.AVIATION...Updated 1144Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Winds through the TAF period will mostly follow light and diurnal
tendencies with speeds generally staying below 8 kts. Showers and
thunderstorms are expected to mostly remain focused over the high
terrain areas north and east of Phoenix this afternoon with chances
remaining low (~15%) within the metro. Could see outflows from
distant high terrain thunderstorms make it into the Valley and lead
to enhanced east to southeast winds later this evening. FEW-SCT
mid and high clouds are expected throughout the period.

Southeast California/Southwest Arizona including KIPL and KBLH:

Winds at KIPL will generally favor the SE, while winds at KBLH favor
the S. Expect speeds to mostly remain aob 10 kts at the terminals
aside from some gusts into the teens later this morning into the
afternoon at KBLH. Otherwise, expect FEW-SCT mid and high clouds
throughout the next 24 hours.

&&

.FIRE WEATHER...
Anticipate an uptrend in thunderstorm activity this weekend over
south-central and southwest Arizona with ongoing chances Monday
and Tuesday. Rain chances over the lower deserts will remain
modest at only 10 to 20 percent (20-40% higher terrain). Storm
chances will retreat to the higher terrain of south-central
Arizona by Wednesday with lingering chances of 15-30% through
Friday. High temperatures will remain slightly above normal
before a subtle cooling trend during the latter half of the next
workweek. MinRH will range from 25-35% across the forecast area
through Monday before decreasing 5-10% by Wednesday - mainly over
southeast CA and southwest AZ (little change or even slightly
higher over the higher terrain of south-central AZ). Max RH will
range from 50-90% tonight before decreasing 10-20% by Monday night
over southeast CA and southwest AZ with an additional 5-10%
decline by Wednesday night across the forecast area. Apart from
thunderstorms, winds will tend to follow familiar diurnal
patterns.

&&

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

$$

DISCUSSION...AJ
AVIATION...Smith
FIRE WEATHER...AJ

NWS PSR Office Area Forecast Discussion