Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 10/22/22

Area Forecast Discussion

National Weather Service Phoenix AZ

 455 PM MST Fri Oct 21 2022

.UPDATE...Updated Aviation Discussion.

&&

.SYNOPSIS...
The warm and dry weather will continue today, before a low
pressure system sweeps a cold front through the region over the
weekend. For Saturday, gusty winds will impact the area,
particularly across southeastern California. Chances for showers will
also begin later Saturday, before peaking on Sunday mainly across
higher terrain areas of central and eastern Arizona. Temperatures
will turn much cooler starting Sunday, lasting through at least
early next week with afternoon highs only in the 70s across the
lower desert communities. The rest of next week looks to remain
cooler than normal with dry conditions likely prevailing through
the entire week.

&&

.DISCUSSION...
Southwesterly flow predominates across the Desert Southwest
between an anticyclone across central Mexico and a cutoff low west
of the Baja Peninsula. Influence of the ridge to the south is
evident in the latest ACARS soundings from KPHX, which show a
pronounced subsidence inversion near 700 mb. This is resulting in
above normal temperatures with only some passing high clouds.
Forecast high in Phoenix today is 91 degrees, which will likely be
the warmest temperature for at least the next week.

Well upstream, latest water vapor imagery reveals some drying off
the British Columbia coast. Not quite apparent just yet, but this
will be our next weather maker as a trough deepens rapidly across
the intermountain West Saturday. Latest models indicate height
falls and a strengthening pressure gradient with gusty pre-frontal
winds developing across portions of the Desert Southwest.

Highest EFI values reside across southwestern Imperial County and
across Pima/southwestern Maricopa and Pinal Counties Saturday
evening. This event may be unusual for this time of year, though a
lack of tails in the EFI distribution suggests extreme wind gusts
are not anticipated. Nevertheless, some members indicate gusts up
to 35-40 mph will be likely across the Imperial Valley Saturday
evening. Further east across the southwestern Maricopa County,
gusts of 30 mph are anticipated which could produce areas of
blowing dust with reduced visibilities. Latest HREF ensemble
maximum wind gusts also suggest gusts could reach 50-70 mph across
the far southwestern corner of Imperial County and a Wind
Advisory remains in effect for these areas. Across the Phoenix
area, latest blended guidance suggests gusts of 20-25 mph are
likely, though some spots will certainly be capable of hitting 30
mph.

Precipitation will also be possible Saturday night and Sunday as
the aforementioned trough digs into the Desert Southwest. However,
latest NAEFS IVT indicates the strongest moisture transport will
be bifurcated, with central Arizona situated between two more
favorable areas. Cluster analysis reveals two main clusters, one
with a deeper trough, which yields two lone outliers with QPF
above 0.5 inches for Phoenix. The other more likely cluster
indicates a high probability of light precipitation. This is
corroborated in the NBM, which indicates only a 20 percent chance
of rainfall exceeding a tenth of an inch through Sunday night.
Probabilities will be considerably higher further east across the
higher terrain east of Phoenix, where jet forced ascent will be
maximized. However, mostly likely QPF indicates storm totals of
around a half of an inch across the higher terrain northeast of
Globe.

&&

.PREVIOUS DISCUSSION...
The shortwave trough is forecast to then track eastward into New
Mexico by midday Monday with considerably drier air and
subsidence aloft surging in behind the system. Any precip chances
across far eastern Arizona should come to an end Monday afternoon.
The colder air mass across the region will drop daytime highs
well into the 70s starting Sunday and likely persist there through
at least Tuesday. Ensembles are in good agreement large scale
broad troughing will remain entrenched across the Western U.S.
through at least the middle of next week with a weak shortwave
trough potentially tracking through or near our region around next
Wednesday/Thursday. This trough should have little overall impact
on our region except for an increase in winds as it will likely
be too dry for any meaningful precip chances. NBM temperature
guidance does show some slight warming into the middle part of
next week with highs possibly reaching 80 degrees again on
Wednesday, but with the broad troughing likely persisting
temperatures are favored to remain below normal through the rest
of next week.

&&

.AVIATION...Updated 2355Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Winds through the evening will favor a westerly component before
making a diurnal switch to the east. Light winds will continue
through the overnight hours before speeds increase tomorrow morning
as winds veer toward the south. By tomorrow afternoon, winds are
expected to favor a southwesterly component with gusts climbing to
around 25 kts. Rain chances look to remain low (< 15%) across the
metro with the best chances remaining confined to the high terrain
north and east of Phoenix. FEW-SCT clouds aoa 5 kft are expected to
increase tomorrow morning along with SCT-BKN high clouds.

Southeast California/Southwest Arizona including KIPL and KBLH:
Light and diurnal winds are expected through the overnight hours
with periods of variability. By late morning/early afternoon
tomorrow, expect gusty winds to increase at the TAF sites. Gusts to
around 25-30 kts will be possible with directions favoring the W at
KIPL and SSW at KBLH. Could see some blowing dust issues,
particularly at KIPL, with the strong winds and result in a
reduction in visibility. FEW-SCT high clouds are expected through
the period.

&&

.FIRE WEATHER...
The dry and seasonably warm conditions will begin to change on
Saturday as a weather system approaches the region. The main
impact Saturday will be increasingly gusty southwesterly winds
later in the day with gusts 20-30 mph common across much of
southern Arizona to 30-45 mph across southeast California.
Minimum RHs around 15-25% today will improve starting Saturday
with readings mostly between 25-35%. The weather system this
weekend will also bring a chance for rain mainly over the high
terrain north and east of Phoenix with upwards of 50% chance of
wetting rains in Southern Gila County on Sunday. Breezy conditions
and colder temperatures will also be seen Sunday into Monday.
Much drier air will surge southward on Monday with RHs dropping to
between 10-20% across the lower deserts. The potential for
northerly gusty winds between 20-30 mph and RHs 10-15% across the
Lower CO River Valley very well could create elevated fire danger
conditions Monday afternoon. The dry conditions will then prevail
through the majority of next week with lighter winds starting
Tuesday.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...Wind Advisory from 2 PM Saturday to midnight MST Saturday night
     for CAZ560.

     Wind Advisory from noon Saturday to 6 AM MST Sunday for CAZ562.

     Wind Advisory from 4 PM Saturday to midnight MST Saturday night
     for CAZ563-564-566-567.

&&

$$

DISCUSSION...Hirsch
PREVIOUS DISCUSSION...Kuhlman
AVIATION...Smith
FIRE WEATHER...Kuhlman