214
FXUS65 KPSR 071103
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
403 AM MST Thu Nov 7 2024

.UPDATE...Updated Aviation Discussion...

&&

.SYNOPSIS...
A weather system remains parked over the Desert Southwest today,
bringing us some of the coldest temperatures of the season so far.
Some communities in the higher terrain east of Phoenix are likely to
see freezing temperatures early this morning. As the weather system
moves off late this week, temperature will gradually warm each day,
eventually reaching a near normal range Sunday into early next week.

&&

.DISCUSSION...
Current 500 mb RAP analysis places the center of a potent upper
level low over the northeastern portion of AZ, with the associated
circulation in the process of becoming somewhat closed/detached from
the northern stream. As the overall motion of this system has
slowed, and dry, colder air continues to surge southward along the
low`s western flank, satellite imagery shows mostly cloud-free skies
across much of the state, except over the far Northern AZ high
country and portions of the Mogollon Rim. Over the course of the
day, models advertise the center of the closed low meandering south
southeastward, passing over the White Mountains, and then moving off
into New Mexico by early Friday. The colder air in place over the
region, particularly over the eastern CWA, is expected to bring the
first widespread freeze of the season to several high desert
communities such as Globe/Miami this morning. A Freeze Warning
remains in effect through 9 AM MST for those higher terrain
locations east of Phoenix, as well as for the higher elevation areas
of western Joshua Tree National Park. Northerly flow aloft remains
strong, with global guidance showing 850-700 mb wind speeds to 25-30
kt this morning, though speeds will diminish over the day as the low
weakens and shifts eastward. Despite the weakening trend, daytime
mixing will be capable of bringing widespread breezy conditions to
the western deserts once again, particularly along the Lower
Colorado River Valley. Gusts to 25-35 mph will be possible, likely
peaking around late morning/midday.

By Friday, a gradual warming trend will commence, more noticeably
for the western deserts at first. Ensemble guidance is in quite
excellent agreement that weak ridging will translate over the Desert
Southwest over the weekend and prevail into early next week, leading
to temperatures in a near-normal range by Sunday. However, the upper
level pattern is somewhat complex this weekend, with most ensemble
members showing an elongated, positively tilted shortwave
disturbance stretching from Western Canada down into the eastern
Pacific well off the coast of Baja California. Meanwhile, an
anticyclonic curved jet streak sets up over the Desert Southwest
by Sunday into Monday. The result of the evolution described is H5
heights near to only slightly above average for this time of year
over the CWA, peaking on Monday at around 581-583 dam. With
heights aloft peaking Monday, lower deserts highs will reach the
upper 70s to lower 80s, only a few degrees warmer than forecast
highs on Sunday.

The pattern described for this weekend into early next week resolves
with a trough over the Gulf of Alaska deepening and moving onshore
along the Pacific Northwest Coast early next week. Cluster analysis
still shows uncertainty with regard to timing of the trough and how
much it will deepen, though all the clusters currently advertise
at least a somewhat progressive system remaining well north of the
region (30% of members comprise a solution with a deeper trough
impacting the region by Tuesday). With the most likely solution
described above, the sensible weather impacts would be cooler
temperatures during the middle of the week, breezy conditions for
at least a portion of the region, and continued dry conditions
(PoPs remain near zero).

&&

.AVIATION...Updated at 1100Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Northerly winds are expected to persist through this afternoon
with some fluctuation from the northwest to the northeast late
this morning before settling back out of the northwest this
afternoon. Wind speeds will be fairly light with the highest
speeds up to 10-12 kts. Eventually winds are expected to settle
out of the east later in the evening. Mostly clear skies will
prevail, aside from occasional FEW to SCT mid-level clouds late
morning and afternoon over the mountains north and east of the
metro.

Southeast California/Southwest Arizona including KIPL and KBLH:
Northerly winds are expected to persist across the area through at
least the afternoon with fairly light wind speeds aside from
during the late morning and afternoon at KBLH when gusts to
around 25 kts are likely. By this evening, winds will shift out of
the west at KIPL and northwest at KBLH. Expect clear skies to
persist through the entire period.

&&

.FIRE WEATHER...
Below normal temperatures will prevail through the end of the
work week. A mostly dry weather system will meander over Arizona
today and move off to the east by Friday. Breezy daytime conditions
are once again expected across the western districts, with wind
gusts along the Lower Colorado River Valley and portions of
Southeast California to between 25-35 mph today. Winds return to
mostly light and diurnal tendencies across the region Friday.
Light shower activity will be possible across the eastern Arizona
higher terrain through this afternoon, but CWR for the high
terrain of far eastern Gila County is 5% or less. MinRHs today and
Friday will fall mostly between 15-20% across the eastern deserts
and 10-15% across the western deserts, with readings closer to
20-30% over higher terrain areas each day. Dry conditions will
persist through the weekend into early next week, with weak high
pressure eventually pushing temperatures from below normal into
the normal range over the weekend.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Freeze Warning until 9 AM MST this morning for AZZ557-558-560-
     562.

CA...Freeze Warning until 8 AM PST this morning for CAZ560.

&&

$$

DISCUSSION...Whittock
AVIATION...Kuhlman
FIRE WEATHER...Whittock