681
FXUS65 KPSR 181126
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
426 AM MST Fri Oct 18 2024

.UPDATE...Updated 12z Aviation Discussion...

&&

.SYNOPSIS...
A weather system impacting the region today into Saturday will
push a cold front through the area by early this afternoon.
Scattered showers and isolated thunderstorms are expected across
south-central Arizona this morning before moving into far eastern
Arizona this afternoon. Breezy to locally windy conditions will
also be seen today, as well as much cooler temperatures. Pleasant
weather is expected this weekend, with Saturday`s temperatures
being similar to today`s. Temperatures are then expected to warm
during the first half of next week as high pressure settles back
over the region, with readings across the lower deserts
approaching the century mark by mid week.

&&

.DISCUSSION...
Strong height falls are beginning to occur over the Desert
Southwest as a deepening upper level low digs southeastward from
the Great Basin into our region. The center of the low is
currently over central Nevada with a cold front advancing east
southeastward across northwest Arizona into southeast California.
Winds have already become gusty at times over our area as the
system approaches from the northwest, especially across southeast
California. Closer to cold core, showers and thunderstorms have
been impacting southwest Utah and now portions of northwest
Arizona since late evening.

The main forecast concern for our area today will be the
increasing winds and the development of showers and isolated
thunderstorms over south-central Arizona by sunrise this morning.
As the low continues to move into our region and the cold front
marches into southwest Arizona over the next few hours, Hi-Res
CAMs are in good agreement scattered showers and isolated
thunderstorms will develop just ahead of the front. This line of
broken showers and thunderstorms may eventually fill in more by
mid morning as it moves across the Phoenix area, before tracking
through Gila and Pinal Counties late morning. HREF shows
sufficient (~500 J/kg) MUCAPE for thunderstorm development with
this line of convection and we can`t rule out one or two of these
storms becoming strong to severe given the ample (50+ kts) of
0-6km Bulk Shear. Fairly limited moisture with PWATs mostly
between 0.6-0.9" just ahead of the advancing front and a fast
storm movement will limit rainfall amounts today with lower desert
locations seeing mostly below 0.10", while higher terrain areas
northeast of Phoenix may see 0.25-0.50". Gradient winds behind
the cold front will increase by late morning into the afternoon
with gusts commonly reaching to between 25-35 mph with the
strongest winds of up to 45 mph across southeast California.

Much cooler temperatures will finally be seen across the region
today with highs mostly in the 70s across the lower deserts, which
would be the coolest day since mid April. The core of the low is
expected to briefly stall out over central Arizona tonight into
Saturday allowing colder air to be remain in place. Overnight
lows tonight/Saturday morning should easily dip into the 50s
across the lower deserts to the 30s and 40s over higher terrain
areas. Depending on the position of the low center during the
daytime hours Saturday, we are likely to see some daytime
convective showers across the higher terrain northeast and east of
the Phoenix area but rainfall amounts should be quite limited due
to the drier air that gets pulled into the system later today.
Conditions elsewhere on Saturday should be quite pleasant with
sunny to mostly sunny skies and highs in the mid to upper 70s in
the Phoenix area to the lower 80s across the western lower
deserts.

Starting Sunday, the upper level low will quickly weaken while
lifting northeastward into the Central Rockies. Upper level
heights over the Desert Southwest will rapidly rise Sunday with H5
heights already recovering to between 582-585dm. As a result,
temperatures will begin a fairly quick warming trend which should
persist through the middle of next week as stronger high pressure
eventually settles over the region. NBM forecast highs quickly
approach 90 degrees on Monday and then into mid to upper 90s by
Wednesday. Ensemble guidance then favors H5 heights near 590dm
during the middle part of next week before potentially gradually
lowering ever so slightly late next week. NBM forecast highs are
now showing around a 50/50 chance for some lower desert locations
reaching 100 degrees again for next Wednesday and Thursday. These
above normal temperatures are likely to persist into the following
weekend, although we should begin to see highs dropping back into
the lower to mid 90s.

&&

.AVIATION...Updated at 1125Z.

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

A cold front moving through the area this morning will result in a
broken line of -SHRA and embedded TS activity across the
terminals with the most likely impacts expected to occur between
13-16z. As this line of -SHRA moves across, BKN CIGS between
030-040 kft are expected before cloud coverage decreases to FEW-
SCT and CIGS rise, most likely after 16z. Winds along and ahead of
the cold front will be mainly from the south and switch out of
the west behind the cold front. Wind speeds behind the cold front
are expected to substantially pick up with potential gusts in
excess of 25-30 kts at times through the afternoon. Wind speeds
are expected to diminish below 15 kts heading into this evening
with wind directions switching out of the east to southeast.

Southeast California/Southwest Arizona including KIPL and KBLH:

Strong winds out of the northwest are expected through this
afternoon as gusts exceed 25-30 kts, with KBLH potentially
reaching 35 kts at times with areas of BLDU. Winds will begin to
diminish by this evening to less than 10 kts at KIPL but likely
remain elevated to near 15 kts at KBLH. Skies will remain clear
throughout the TAF period.

&&

.FIRE WEATHER...
A strong, but somewhat dry weather system will move through the
region through Saturday dropping temperatures to below normal.
There will also be chances for showers and isolated thunderstorms
today across south-central and eastern AZ with lingering showers
over higher terrain areas on Saturday. Breezy to windy conditions
are also expected today with afternoon gusts of 30-40 mph in many
locations. After a brief bump in RHs this morning, drier air
surging eastward throughout the area will drop RHs into the teens
this afternoon across the lower deserts leading to a period of
elevated fire danger conditions. RHs Saturday will improve
slightly with MinRHs mostly between 20-25%, while winds drop off
considerably. Temperatures will begin to moderate starting on
Sunday, with above normal readings returning by early next week.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Wind Advisory until 5 PM MST this afternoon for AZZ530.

     Wind Advisory from 11 AM this morning to 6 PM MST this evening
     for AZZ560-562-563.

     Freeze Warning from midnight tonight to 9 AM MST Saturday for
     AZZ563.

     Freeze Warning from midnight Saturday night to 9 AM MST Sunday
     for AZZ563.

CA...Wind Advisory until 5 PM PDT this afternoon for CAZ560-561-564-
     568>570.

&&

$$

DISCUSSION...Kuhlman
AVIATION...Lojero
FIRE WEATHER...Kuhlman