512
FXUS65 KPSR 240013
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
513 PM MST Sat Nov 23 2024

.UPDATE...Updated 00z Aviation Discussion.

&&

.SYNOPSIS...
Afternoon highs between 4 and 8 degrees above normal will be common
today, but on Sunday, diurnal temperature ranges will contract and
remain smaller through much of next week in response to increased
humidity and periods of thicker cloud cover. A weak shortwave trough
is expected to pass north of the area during the middle of next
week, but precipitation chances should remain confined to the
northern Arizona high terrain.

&&

.DISCUSSION...
Water vapor imagery depicts abundant mid and upper level moisture
streaming onshore along the Central California Coast at this hour,
coincident with a west southwesterly jet streak punching into the
Intermountain West. To the south of this jet streak, weak ridging
remains in place over the Desert Southwest, though the ridge axis
has shifted further east compared to the past few days. As positive
height anomalies remain overhead today, lower desert highs so far
this afternoon have been above their normal values for the date in
the upper 70s to around 80F. Positive height anomalies will
become further displaced/suppressed to the south and east over the
next 24 hours or so as a shortwave breaks off the persistent
upper low off the Pacific Northwest Coast and begins to traverse
the northern CONUS. The result will be generally zonal flow aloft.

The continuing multi-day AR event along the West Coast has now lost
much of its punch, with latest modeled IVT values over Central CA
just above the threshold that defines an AR (~250-300 kg/m/s).
However, the filament of enhanced moisture streaming inland is
advertised to translate further south throughout the day, bringing
abundant mid and upper level moisture over the forecast area by
Sunday. This southward translation of the AR is in response to an
embedded circulation rotating around the base of the broader upper
low and approaching the coast, acting to deepen the overall upstream
troughing. With enhanced IVT over the region by Sunday, the entire
profile will begin to moisten, but mostly above 500 mb. GFS bufr
soundings continue to advertise a thick, saturated layer above this
level continuing into Monday. Cloud cover on Sunday will help
keep highs in a normal range across the lower deserts, mostly in
the low to mid 70s. Modeled surface dew points from the NBM are
also shown increasing into the 30s and up to around 40F across the
forecast area Sunday, up from current observations which are in
the teens and 20s today, reflecting the shift to a more moist
environment that will persist through much of the upcoming week.

Ensembles are in good agreement that the persistent upper low off
the Pacific Northwest Coast will finally progress inland and pass
north of the region sometime Wednesday into Thursday. The track of
this system is still projected to remain well north of our region
and thus the best moisture and lift should remain focused over the
northern Arizona high terrain. Therefore, PoPs are expected to be
<10% for the entire forecast region. The shortwave trough will
bring a dry cold front through the area Wednesday, which will
only serve to lower temperatures by a few degrees. There may be
some post frontal breeziness across SE CA, however gusts are not
expected to exceed 25 mph at this time. After the shortwave passes
through, dry NW flow aloft will keep temperatures near or
slightly above average through the remainder of next week.

&&

.AVIATION...Updated at 0015Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT; and
Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather concerns are expected through Sunday afternoon
with increasing mid and high cloud cover through the course of
the TAF period. Light and diurnal winds, AOB 8 kt, with extended
periods of variability and even calm conditions, will be common.

&&

.FIRE WEATHER...
Warm and dry conditions will prevail today with highs around 5 to 8
degrees above average. Increasing cloud cover will result in slightly
cooler temperatures beginning Sunday and persisting through early
next week. Relative humidity is expected to fall below 15% across
the entire area this afternoon, but is expected to rise to around
20-35% regionwide on Sunday. Overnight recovery will range from
poor to fair across the lower deserts tonight and increase to
widespread fair to good on Sunday night. Overall light winds will
continue with only some periodic light breezes over the higher
terrain in the afternoon and early evening.

&&

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

$$

DISCUSSION...Whittock/Salerno
AVIATION...Young/Smith
FIRE WEATHER...Salerno