Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 10/07/23

Area Forecast Discussion

National Weather Service Phoenix AZ

 445 PM MST Fri Oct 6 2023

.UPDATE...
Updated Aviation section.

&&

.SYNOPSIS...
Generally dry conditions and above normal temperatures
will continue through at least the first part of next week as
high pressure prevails across the region. A slight increase in
moisture over the weekend may allow for some showers to develop
over the higher terrain areas of eastern AZ. An area of low
pressure moving across the Intermountain West and Central Rockies
will result in a cooling trend as we head through the middle and
latter half of next week.

&&

.DISCUSSION...
A ridge of high pressure is currently entrenched across the region
with the 500 mb height field ranging between 588-589dm. The
latest ACARS sounding from Phoenix show that the lower troposphere
has a warmed a couple of degrees Celsius compared to 24 hours
ago. As a result, high temperatures today will be slightly warmer
with highs across the lower deserts between 100-105 degrees. There
is still a decent chance that the daily record high temperature
for Phoenix, which is 105 degrees last set in 1917, may be
reached. With temperatures this afternoon topping out above 100
degrees, the HeatRisk will be in the moderate category across most
of the south-central AZ lower deserts and thus the necessary heat
precautions will need to be taken if partaking in outdoor
activities for an extended period of time.

Even though high pressure will remain in place through the weekend,
a weakening upper-level low over the eastern subtropical Pacific
will be approaching the northern Baja Peninsula through Saturday.
This feature in combination with strong surface high pressure
building over the Plains will set up a tight easterly pressure
gradient across most of central and eastern Arizona. This will cause
an increase in the winds, especially by later tonight and continuing
into early Saturday afternoon, as gusts will likely range between 30-
40 mph across the higher terrain areas east of Phoenix and between
20-30 mph at times across the south-central Arizona lower deserts.
Winds will subside as the afternoon progresses as the pressure
gradient weakens. With the elevated winds overnight tonight through
Saturday morning, overnight low temperatures will remain fairly
warm with lows in the Phoenix area likely not dropping below the
mid 70s. In fact, there is a very high likelihood (>80% chance)
that a record warm low at Phoenix Sky Harbor will be broken with a
forecast low of around 80 degrees (previous record warm low was
77 degrees last set in 2003). With heights aloft slightly lowering
with the approaching trough, temperatures this weekend will be
slightly cooler with highs ranging between 98-102 degrees across
the lower deserts.

With the easterly flow, there will be a slight increase in moisture
across the region as precipitable water values will rise from 0.4-
0.5" they are currently to 0.8-1.0" through the weekend. However,
this moisture increase will be insufficient for rainfall across the
lower deserts and this is reflected in the latest NBM PoPs which
is near zero percent. There is better chances for shower
development and maybe an isolated thunderstorm across the eastern
Arizona High Terrain in the area of the Mogollon Rim and the
White Mountains.

As we head into next week, ensembles remain in pretty good agreement
on the overall synoptic pattern in showing a Pacific trough moving
across the Pacific northwest and then diving southeastward into the
Intermountain West Region and Rockies through the middle and latter
half of next week. However, examining the ensemble cluster analysis,
there is still disagreement with respect to the depth and
location of the trough with the EPS members favoring a deeper
trough solution while the GEFS members favor a shallower and more
progressive trough solution. Nevertheless, a cooling trend and
potentially some breezy conditions can be expected but to what
degree is still uncertain as it will be dependent on how deep the
trough will be.

&&

.AVIATION...Updated at 2345Z.

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

Over the Greater Phoenix Area, there is is a modest E/NEly
pressure gradient causing atypical afternoon winds from the
northeast mixed in with light and variable conditions. A backdoor
cold front will push westward across western New Mexico and into
eastern AZ tonight. This will lead to a tightening pressure
gradient over the northeastern two- thirds of AZ. Though surface
winds will favor northeast and east directions tonight, sustained
speeds are anticipated to remain below 10kts most of the time
(except for foothill locations with a W/SW facing aspect).
However, in the lower levels above the surface, speeds will be
significantly stronger after 05Z with up to 30-35kts at 2000ft AGL
which would be flirting with LLWS criteria for the TAFs.
Confidence in LLWS meeting criteria too low at this time to
reflect in the TAFs. With surface heating Saturday morning and
associated mixing, easterly surface winds strengthen between
16Z-17Z with gusts of 25 kts common before beginning to weaken
after 20Z. As for sky cover, a weak upper level disturbance will
produce minor amounts of mid- high clouds.


Southeast California/Southwest Arizona including KIPL and KBLH:

Over far southeast CA, there is a modest N/NWly pressure gradient
driving light northerly winds. Anticipate light winds to continue
at KBLH through Saturday morning before trending to light and
variable. At KIPL, light and variable winds early this evening
will become light westerly and continue that way until 17Z or so
with light north/northeasterly developing. Skies will be clear
except for some very minor amounts of mid-high clouds during the
day Saturday.



&&

.FIRE WEATHER...
Above normal temperatures and dry conditions will continue into
the weekend with only slight improvement in moisture levels.
Minimum afternoon humidity levels will generally fall to between
10-15% today before rising to 15-20% by Sunday. Poor to fair
overnight recoveries of 20-35% can be expected through tonight
improving to 35-55% by Sunday night. Atypical winds will begin
today with breezy easterly winds across much of southern Arizona
and northerly winds across the western districts. Winds across
south-central Arizona will pickup later tonight through Saturday
morning with gusts ranging between 30-40 mph across the higher
terrain and between 20-30 mph across the lower deserts. Winds be
subsiding beginning Saturday afternoon. An increase in moisture
into the weekend may result in a few light showers over higher
terrain of eastern districts, but chances for wetting rainfall are
expected to be less than 5%.

&&

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

$$

DISCUSSION...Lojero
AVIATION...AJ
FIRE WEATHER...Lojero/Kuhlman