High Wind and Strong Wind in California, December 14, 2021

Area Forecast Discussion
National Weather Service Phoenix AZ
124 PM MST Tue Dec 14 2021

.SYNOPSIS...
A low pressure system and attendant cold front will quickly sweep
eastward through Arizona this evening, bringing strong winds,
showers, and areas of blowing dust. Much cooler temperatures are
expected Wednesday, with a slight warming trend thereafter though
the weekend. Another less impactful storm system will move into the
Southwest this weekend, but most areas are expected to remain dry.

&&

.DISCUSSION...
A powerful upper level trough and associated PV max are located
south of KMRY this afternoon. Water vapor imagery clearly depicts
all the classic features associated with this system, with a mid-
level dry slot longitudinally oriented across southeast California
and western Arizona. The bulk of significant moisture advection and
rainfall is being absorbed by the coastal ranges in California,
where widespread showers have been occurring for most of the
morning. The most impactful part of this storm system continues to
be the potential for strong winds. SPC mesoanalysis shows 850-mb
winds of 30-50 kt in place across southern California, which will
contribute to increasing winds from west to east through this
evening. Already, localized gusts to 50 mph have been observed at
JTNP, where a High Wind Warning is in effect. This trough is
forecast to accelerate eastward this evening and be accompanied by a
110-120 kt 500-mb jet streak moving directly across south-central
Arizona. Most forcing for ascent accompanying the trough will remain
focused across northern Arizona, but significant low-level
frontogenetical forcing will likely result in a shallow convective
frontal band quickly advancing eastward this evening. HREF and HRRR
timing suggests a 10 PM to 1 AM time frame for this to affect the
Phoenix area. Along this band, strong winds, showers, and
potentially a few embedded thunderstorms are likely, with enhanced
wind gust potential possible given the very strong kinematic profile
in place. Most areas across the lower deserts are forecast to
receive between 0.10" to 0.25", but NBM the percentile QPF values
are close to 0.50" across the Phoenix area. Areas north and east of
Phoenix could potentially receive localized totals up to 1", which
could cause minor flooding issues. Tonto Creek is forecast to
briefly rise above action stage this evening. A dusting of snow is
also possible in parts of JTNP and southern Gila County as snow
levels fall from around 8000 feet down to around 4000 feet in the
wake of the cold front amidst lingering light precipitation.
However, any accumulations outside of the highest peaks should
remain at 1 inch or less.

The aforementioned storm system will rapidly advance eastward on
Wednesday morning and give way to a quieter, quasi-zonal westerly
flow pattern over the Southwest. Significant cooling will take
place, with temperatures expected to run about 10 degrees cooler
than Tuesday. In fact, the official forecast has most areas
(including Phoenix) staying in the upper 50s for highs. Another
concern will be the potential for freezing temperatures on Thursday
morning. NBM probabilities of temperatures below 32 degrees are
highlighting potential freezes in parts of Yuma and La Paz Counties,
the lower Colorado River Valley, and southeast California. Will have
to assess the potential for a Freeze Watch or Warning for this time
period in later shifts.

By this weekend, a weak trough will develop again over the
Southwest, but will have little to no impact on weather given the
lack of moisture in place. It will at least keep the well above-
normal temperatures at bay. Ensemble guidance is showing a more
significant storm system potentially bringing rain back to the
region late next week.

&&

.AVIATION...Updated at 1756Z

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

A very strong and fast-moving Pacific weather system and associated
sfc cold front do bring significant weather impacts will be this
afternoon into tonight. Breezy southerly crosswinds will develop by
18z with sustained speeds around 10-12 kts and perhaps a few gusts
into the teens. Gusty southerly winds will increase by this evening
as a cold front approaches. By 03-04Z this evening, we can expect
southerly cross winds to approach 20-30 kts. The strongest winds
will occur as the cold front pushes through the area around 06-09Z
with westerly wind gusts upwards of 40-45 kts. Due to these strong
winds this afternoon and evening, blowing dust will also be
possible. Winds just above the surface will be even stronger, with
winds at 2k feet AGL getting as strong as 50-06 kts. Thus, have
introduced LLWS in the Phx area TAFs. Showers will push through as
well with the frontal passage (06-09Z also best time frame), however
chances for any thunderstorms are expected to remain low (<10%). The
most likely solution is a band of showers and very strong winds
moving through the terminals. CIGs are expected to fall to around 3-
5 kft and perhaps briefly lower as showers move through. Winds
expected to weaken by 12Z tomorrow morning. The combination of dust
and showers will likely reduce visibilities at times. After a period
of light SE-ly winds during the morning hours, more typical light
westerly winds to return during the late afternoon hours on
Wednesday.

Southeast California/Southwest Arizona including KIPL and KBLH:

A very strong and fast-moving Pacific weather system and associated
sfc cold front do bring significant weather impacts will be this
afternoon into tonight. Southerly winds will start to ramp up by
late morning and continue to increase through the afternoon with
gusts around 20-30 kts. As the cold front moves through between
roughly 0-3Z, expect westerly gusts to climb near or in excess of 40
kts. There is roughly a 20% chance that wind speeds will end up
exceeding 48 kts at KIPL and roughly a 50% chance at KBLH. May see
some slantwise and surface visibility concerns due to the potential
for blowing dust associated with the strong winds. Expect some
showers as the cold front moves through, with the best chances
expected at KBLH. CIGs will mostly remain aoa 15 kft through the mid
afternoon before dropping to around 8 kft. As showers pass through,
CIGs around 5 kft may become BKN to OVC briefly. Winds are expected
to diminish rather rapidly after midnight, with speeds dropping into
the 8-12 kt range by daybreak on Wednesday

&&

.FIRE WEATHER...
Thursday through Monday:
Cool, dry weather is forecast. Winds will be light and diurnally
influenced. MinRH each afternoon will be 20- 30% in most areas.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Blowing Dust Advisory from 6 PM this evening to 5 AM MST
     Wednesday for AZZ540-542>544-546-548-550-551-553-554.

     Wind Advisory from 6 PM this evening to 5 AM MST Wednesday for
     AZZ537-540>544-546-548>555.

     High Wind Warning from 7 PM this evening to 8 AM MST Wednesday
     for AZZ545-557-558-563.

     Wind Advisory from 7 PM this evening to 8 AM MST Wednesday for
     AZZ547-556-560>562.

     Blowing Dust Advisory from 5 PM this afternoon to 3 AM MST
     Wednesday for AZZ530>533-535-536-538-539-559.

     Wind Advisory from 5 PM this afternoon to 3 AM MST Wednesday for
     AZZ530>536-538-539-559.

CA...Blowing Dust Advisory until 1 AM PST Wednesday for CAZ563>567-
     569-570.

     Wind Advisory until 1 AM PST Wednesday for CAZ563>567-569-570.

     Wind Advisory until 1 AM PST Wednesday for CAZ561-568.

     Blowing Dust Advisory until 1 AM PST Wednesday for CAZ562.

     High Wind Warning until 1 AM PST Wednesday for CAZ562.

     High Wind Warning until 8 PM PST this evening for CAZ560.

     Wind Advisory from 8 PM this evening to 1 AM PST Wednesday for
     CAZ560.

&&

DISCUSSION...Rogers
AVIATION...Percha/Feldkircher
FIRE WEATHER...Heil