030
FXUS65 KPSR 042310
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
410 PM MST Sat Jan 4 2025

.UPDATE...Updated Aviation Discussion.

&&

.SYNOPSIS...
Cooler temperatures have settled in across the region, but weather
conditions will remain pleasant through the weekend. Above normal
temperatures will continue into early next week, although the
weather pattern is trending more unsettled, which could result in
near normal temperatures through the end of the week. Should the
weather pattern become more active, more widespread breezy to
windy conditions and increasing precipitation chances can be
expected through the middle portions of next week.

&&

.DISCUSSION...
A large area of low pressure over the Rockies has brought in
cooler conditions today, as the ridging from yesterday has
retreated across the Plains. Mostly clear skies now exist across
the region, as any residual clouds from this low pressure have
moved east of the region. Cooler temperatures just a few degrees
above normal will persist into next week, as the troughing feature
across the Rockies slides to the southeast into the Plains.

Strong positive height anomalies will build across the eastern
Pacific and extend into western Canada heading into early next
week, resulting in a highly amplified pattern that may resemble a
Rex Block by the middle of next week. Deterministic solutions
depict a shortwave sliding downstream of this amplified ridge
going into the middle of next week, which will work to deepen the
longwave troughing that will bring the active winter weather
across the central US late this weekend.

Ensembles are now in better agreement with this longwave
continuing to deepen, with negative height anomalies now extending
westward into Arizona as early as Tuesday. Therefore, the
forecast for the middle of next week is trending more active,
although details of the trough (i.e. positioning and whether the
trough will cutoff from the main flow) will dictate whether the
region could receive some higher potential for precipitation
through the middle portions of next week. Cluster analysis depicts
a cutoff low by Wednesday for the majority of the clusters,
although it is worth noting that the differences of the
positioning of the low is affecting the precipitation outlook for
the region. The best precipitation chances look to be Wednesday
into Thursday where the cutoff positioning is most favorable to
advect sufficient moisture into the region. The more certain
impact at this point would be breezy to windy conditions
developing, first out west as early as Tuesday, and spreading
eastward across south-central Arizona on Wednesday.

.PREVIOUS DISCUSSION...
Heading into the latter half of next week, the forecast
uncertainty increases as the ensembles differ in terms of the
positioning of the upper-level low. Some ensemble members show the
low becoming cutoff from the main jet stream flow and
retrograding a bit southwestward near northern portions of the
Baja Peninsula while other members show the low a bit more
progressive with more of an eastward movement. Depending on the
scenario that materializes will determine whether or not there
will be additional precipitation chances heading towards the end
of next week. The cut-off low scenario would certainty increase
precipitation chances whereas the more progressive solution would
keep conditions dry. Nevertheless, what is a bit more certain are
that temperatures are likely to cool off due to the close
proximity of the low with readings at more seasonable levels, in
the mid to upper 60s for highs across the lower deserts.

&&

.AVIATION...Updated at 2310Z.

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

No aviation concerns are expected during the TAF period under
FEW to occasionally SCT high clouds. Winds will continue to follow
their diurnal trends with some isolated gusts in the mid-teens
through sundown. The typical nightly E shift at KPHX may not
become fully established until mid morning Sunday, with moment of
variable directions occupying the majority of the nighttime hours.

Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation concerns are expected during the TAF period. Winds at
both terminals will contain a W/NW`rly component through Sunday
afternoon. SCT high clouds over the region will be common over
the next 24 hours

&&

.FIRE WEATHER...
Dry conditions along with above normal temperatures will persist
throughout the weekend. Winds will be a bit breezy out of the
north later today through Sunday, mainly along the Lower Colorado
River Valley, with fairly light winds expected elsewhere. MinRHs
mainly in the teens will be common into early next week before
some improvement occurs by midweek. A more unsettled weather
pattern is expected by midweek as a weather system passes through
the region and delivers a period of breezy to locally windy
conditions as well as modest precipitation chances across the
higher terrain areas of south-central AZ. Temperatures mid to
late next week are forecast to cool down closer to seasonable
levels.

&&

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

$$

DISCUSSION...Young
PREVIOUS DISCUSSION...Lojero
AVIATION...RW
FIRE WEATHER...Lojero