963
FXUS65 KPSR 101138
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
438 AM MST Fri Jan 10 2025

.UPDATE...
12Z Aviation Discussion.

&&

.SYNOPSIS...
Dry conditions, cold overnight lows, and seasonably cool afternoon
highs are expected through the weekend and into early next week. Dry
air and clear skies will result in low temperatures reaching the
freezing mark across the Arizona high terrain and some lower desert
communities, and so Freeze Warnings are in effect each morning
through Sunday. Another dry weather system will influence the region
this weekend, likely bringing breezy to locally windy conditions
over the typical wind prone areas such as along Lower Colorado River
Valley.

&&

.DISCUSSION...
Current objective/RAP analysis depicts the forecast area under
strong northerly flow aloft, with 90-100 kt speeds at 500 mb over
Arizona. This is a result of the tightened pressure gradient between
an upper low, currently centered south of the international border
and gradually shifting eastward into Chihuahua, and strong upstream
ridging along the West Coast. However, since the upper low will
continue to shift east this morning and gradients will slacken over
the area, much calmer winds can be expected today. As the forecast
area now sits solidly behind the backdoor front associated with the
upper low, cooler and drier air continues to filter into the region.
This will allow for unseasonably cold overnight lows as we head into
the weekend. Winds remained elevated well into the evening yesterday
(especially out west), and so lows this morning will not be too far
from normal in the upper 30s and 40s across the lower deserts, with
some isolated rural/higher terrain communities near freezing. Nearly
calm winds, very dry air, and clear skies tonight and Saturday night
will allow for even colder overnight lows across South-Central AZ,
between 5-8 degrees below normal. As such, expanded Freeze Warnings
are in effect for Saturday and Sunday mornings. With at least
scattered coverage of below freezing temperatures expected,
especially outside the urban core, the Phoenix Metro Area is now
included within the Freeze Warning on Sunday morning. Be sure to
protect the 4 P`s (People, Pets, Pipes, and Plants) when subfreezing
temperatures are forecast, especially for the more cold-prone, rural
and/or higher terrain communities.

The somewhat active upper level pattern over the Southwest CONUS is
expected to continue over the weekend and into early next week, with
several more shortwaves rotating through and eastern Pacific ridging
persisting. Guidance has started to hone in on a shortwave sending a
less well-defined cold front over the area later in the day
Saturday, causing breezy to locally windy conditions even into
Sunday along the Lower Colorado River Valley and portions of SW AZ
and SE CA. Aside from the increased winds out west, this will bring
little in the way of sensible weather changes and ensure that colder
air remains in place over the forecast area, allowing for very cold
overnight lows Sunday night as well. Freeze products will likely
need to be issued in future updates for a more widespread freeze
Monday morning if things shape up as anticipated.

By early next week, WPC clusters all depict a scenario where a
shortwave dives south into our region before cutting off near/off
the coast of southern California in the Tuesday-Wednesday timeframe.
Once the shortwave has moved southwest of the region, southerly flow
aloft and marginal height rises would allow for warmer temperatures
and an end to the prevalent subfreezing morning lows during the
middle of next week. Depending on where this cutoff low sets up, we
could see an influx of moisture that would result in increasing
precipitation chances across South-Central AZ. Right now the NBM has
introduced low order PoPS (15-25%) by late Wednesday and Thursday
over the higher terrain NE of Phoenix. Until then, a dry forecast is
expected to persist.

&&

.AVIATION...Updated at 1140Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
A slackening MSLP gradient will result in much lighter wind speeds
across the Phoenix Metro today. This morning we will start off
with light easterly flow with periods of calm and vrb, especially
at KPHX. Winds are then expected to shift out of the WSW this
afternoon, around 20-22Z, with speeds remaining mostly blo 10 kts.
Light easterly flow will return late tonight. SKC will prevail
through the forecast period.

Southeast California/Southwest Arizona including KIPL and KBLH:
Elevated N-NW flow will continue at KBLH this morning, however
gusts should subside after sunrise and speeds will gradually
diminish throughout the afternoon. At KIPL, light northerly flow
can be anticipated, with a return to more typical diurnal trends
by the evening as winds shift more out of the W by sunset. SKC
will prevail over both terminals through the period.

&&

.FIRE WEATHER...
Dry conditions are expected through at least early next week.
Breezy northerly winds may develop after sunrise along the Lower
Colorado River Valley and portions of SE CA, though nowhere near
as strong as yesterday, and will gradually decrease over the
course of the day. Light and diurnal to nearly calm winds are
expected areawide by this evening into Saturday. Another weather
disturbance diving into the Great Basin this weekend will act to
increase north northwest winds once again late Saturday into
Sunday along the Lower Colorado River Valley and portions of SE CA
and SW AZ. Widespread daytime gusts to between 20-35 mph are
expected. Afternoon minRHs will range between 10-20% areawide
today and Saturday, with poor to fair overnight recoveries between
25-45%.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Freeze Warning until 9 AM MST this morning for AZZ534-552-553-
     556-560>562.

     Freeze Warning from midnight tonight to 9 AM MST Saturday for
     AZZ533-534-536-550>554-556-560>562.

     Freeze Warning from midnight Saturday night to 9 AM MST Sunday
     for AZZ533-534-536>540-542>544-546-548-550>556-559>562.

CA...None.
&&

$$

DISCUSSION...Whittock
AVIATION...Salerno
FIRE WEATHER...Whittock