High Wind in California, February 14, 2023

Area Forecast Discussion
National Weather Service Phoenix AZ
232 PM MST Tue Feb 14 2023

.SYNOPSIS...
A weather disturbance is bringing very windy conditions ahead of
a cold front today, which will sweep through the region this
evening. The winds are generating pockets of blowing dust. This
system is also bringing precipitation to the central Arizona lower
deserts and light snow accumulations for the higher terrain east
of Phoenix. Well below normal temperatures are anticipated
Wednesday and Thursday morning followed by a gradual warming
trend. More unsettled weather will be possible early next week.

&&

.DISCUSSION...
High wind, dust, rain, thunderstorms, snow, and colder temperatures
are all anticipated through the next 24 hours as a strong trough
digs down through the region. A glance at the map on weather.gov
will quickly prove this trough is expected be impactful. Several
watches, warnings, and advisories have been issued, with nearly
all of Arizona and Southern California covered by at least one
product.

High winds are expected to be the greatest impact through tonight.
Winds have already picked up across the region early this
afternoon, with some locations having already reached advisory-
level wind gusts (40+ mph), including Northwest Pinal County and
parts of Southeast California. A very strong jet streak (150 kts
sampled around 350mb from the 12Z Medford, OR sounding) is helping
drive a deep trough rapidly down the western CONUS. Water vapor
satellite and objective analysis still have the trough near
southern Nevada. A surface cold front recently went through Las
Vegas, NV and resulted in wind gusts up to 60 mph. As the trough
axis and cold front gets closer, the gradient winds will only
increase across the area. So, surface wind speeds are still
expected to increase through the afternoon and likely peak late
this afternoon through this evening. Widespread 30-40 mph wind
gusts are likely, with ~50% chance for 40+ mph peak gusts. The
will be a chance for 50-60+ mph wind gusts as well, with HREF
probabilities favoring high terrain spots east of Phoenix and in
Southwest Imperial County CA. Wind Advisories and High Wind
Warnings are in effect and run through the late evening.

With the strong winds, blowing dust will be a threat through this
afternoon and evening. A considerable dust channel has been
observed on the satellite dust channel and webcams in northern
Imperial County this afternoon. A Dust Advisory has been issued to
cover this. A Blowing Dust Advisory is also in place across the
dust prone Pinal County through this evening. Although dust has
not been observed as of 2PM MST, dust could still become an issue
as gusts increase.

Light low-topped showers developed earlier this morning in the
foothills north of Phoenix and continue to develop further south,
now spread across most of the Phoenix area. Aircraft soundings
still show a dry stable layer between 700-600mb which is limiting
the intensity of the showers. Observed rain rates are mostly
0.10"/hr or less. However, once the colder air arrives later this
afternoon and evening, that helps destabilize the environment
more, shower shower intensity will likely increase. NBM is
maintaining a 10-20% chance for thunderstorms in South-Central AZ
this evening. CAPE overall will be limited, with HREF spread
mostly between 0-100 J/kg and a few pockets above 100 J/kg. The
best forcing will likely come with the strong cold front as it
sweeps through the region. The cold front is progged to move
through the CWA mainly between 5 PM - 12 AM MST today (7-10 MST
through Phoenix). As previously mentioned, gradient winds will be
strongest along and just ahead of the trough. With low-level winds
increasing up to 50-60 mph there will be a chance for
shower/storm driven wind gusts up to these magnitudes. A few hi-
res models even suggest some linear convection segments. Small
hail and graupel will possible with any convectively driven
shower this evening, which could briefly accumulate at lower
elevations.

The aircraft soundings out of Phoenix and the melting layer
algorithm from KIWA radar suggest snow levels are currently around
5-6 kft. Dendrite production is not great right now over South-
Central AZ due to the aforementioned dry layer existing in the
dendritic growth zone. So, any snowfall early this afternoon is
likely limited in rate and accumulation efficiency. This will
change as well this evening as the colder air arrives. The most
significant accumulations are expected to remain above 5000 feet,
though light accumulations are possible as low as 2500 feet,
north and east of Phoenix. For the Valley, snow showers will be
limited to the foothills, generally above 2500-3000 feet in
elevation. Rain amounts will vary but on average, one to two
tenths of an inch is likely. All things considered, hazardous
weather conditions are expected across much of the area today and
tonight, and motorists are urged to exercise caution.

In the wake of this system, clear skies are anticipated
Wednesday with much drier conditions as dew point temperatures
crash down to around 10F or lower by mid-day Wednesday. However,
latest model guidance continues to indicate a trailing vort max,
which will act to elongate the trough into Arizona. Consequently,
breezy conditions will continue down the Lower Colorado River
Valley and the cold will linger with well below normal
temperatures prevailing. High temperatures will struggle to even
reach the mid 50s around Phoenix, and 60 degrees across SW Arizona
and SE California Wednesday. The bigger concern though will be
temperatures Wednesday night and Thursday. Latest NBM indicates
the potential for a widespread late-season freeze event. Many
lower desert locations and valleys across Arizona may observe the
coldest readings so far this winter and Hard Freeze Warnings are
possible, particularly across Pinal County where lows may reach
the upper 20s.

Steady height rises will translate into a warming trend and a
return to near normal temperatures through Saturday. Thereafter,
forecast uncertainty increases, mainly in response to a meandering
closed low in the eastern Pacific. Low pressure systems like this
one are notoriously difficult for the models to resolve and
forecast, and this is reflected in the NBM PoPs, which show an
extended period of 20 percent 12-hour PoPs stretching from
Saturday night through next Tuesday. Model clusters also point to
high uncertainty with regard to precipitation potential, though
temperatures are generally expected to remain at or below normal.

&&

.AVIATION...Updated at 1830Z.

South-Central AZ including KPHX, KIWA, KSDL, KDVT:

Low CIGS and and windy conditions today across the region. BKN
3-4k ft cloud bases will prevail at all terminals through this
afternoon and into the evening. MVFR CIGS are possible (20-30%)
with higher probabilities (40%) at DVT and SDL. S-SE winds will go
SW over the next few hours and pick up significantly by 20-21Z.
Gusts of 35-40kt are possible (~50%) at all locations. A line of
heavy showers and possible thunderstorms along a cold front will
move through the region between 02-05Z. There may be some brief
periods where winds can gust ~50kt in association with this line.
After the front has passed through, winds will shift to the W and
decrease in strength, but gusts 20-25kt will persist through
tonight. CIGS will begin to lift between 07-08Z with skies then
clearing out between 10-11Z.

Southeast California/Southwest Arizona including KIPL and KBLH:

Windy conditions are the main aviation concern over the region.
Strong W-SW winds at both terminals with gusts 35-40kt this
afternoon and through the evening. These strong winds will create
blowing dust which can cause reduced visibilities for an extended
period of time. A few high clouds will give way to lower CIGS
between 6-7k ft this evening. 20-30% chance of showers at IPL
with higher probabilities (40%) at BLH. Winds will decrease
tonight, but gusts of 20-25kt will be possible through tonight at
both locations.

&&

.FIRE WEATHER...
Very windy conditions are expected today and tonight ahead of a
cold front that will sweep through central this evening. Wind
gusts will generally reach 35-45 mph, but there will spots in the
higher terrain potentially reaching 60-80 mph. This system will
bring another chance of precipitation for the central Arizona
lower deserts this evening and light snow accumulations for the
higher terrain east of Phoenix later tonight. Much cooler and
drier conditions are expected Wednesday. Winds will also subside
Wednesday, though general breeziness will persist. A warming trend
is then expected through the weekend. A low pressure system will
meander in the eastern Pacific early this weekend, however there
is some uncertainty with regard to if and when impacts and
precipitation will next affect the Desert Southwest.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Wind Advisory until 11 PM MST this evening for AZZ530>533-535-
     536-539-553-554-559.

     Blowing Dust Advisory until 9 PM MST this evening for AZZ551-
     553>555-559.

     High Wind Warning until 2 AM MST Wednesday for AZZ552-558-561.

     Wind Advisory until 2 AM MST Wednesday for AZZ555>557-560-562-
     563.

     Winter Weather Advisory from 5 PM this afternoon to 2 AM MST
     Wednesday for AZZ557-558-563.

     Wind Advisory until 11 PM MST this evening for AZZ534-537-538-
     540>551.

CA...Wind Advisory until 10 PM PST this evening for CAZ560-561-
     563>570.

     High Wind Warning until 10 PM PST this evening for CAZ562.

&&

DISCUSSION...Hirsch
AVIATION...Worley
FIRE WEATHER...Hirsch