Area Forecast Discussion
Issued by NWS Flagstaff, AZ

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FXUS65 KFGZ 302153

Area Forecast Discussion
National Weather Service Flagstaff AZ
253 PM MST Mon Jan 30 2023

.SYNOPSIS...Below normal daytime high temperatures and areas of
snowfall will be the main weather highlights over the next 24
hours. Accumulating snowfall of 2 to 8 inches is currently
forecast for areas at and above 4,500 feet. Precipitation chances
diminish Tuesday with a gradual warming trend for the latter half
of the week.


.DISCUSSION...Water vapor imagery just after 2 PM MST reveals a
well-defined mid/upper level low churning across the California
coastline. This feature continues to induce modest southwesterly
upslope flow across the High Country early this afternoon. While
radar imagery has indicated the presence of a few deeper
convective elements, our 12 UTC RAOB (from KFGZ) indicates a
shallow moist layer saturation (only up through about 700mb) and
in situ observations (just looking outside the window) indicates
largely snow grains as opposed to large dendrites. Forecast
moisture profiles from short-resolution guidance indicates that
gradual saturation thanks to moisture advection and ascent will
aid in nearly total column saturation for areas near and west of
the US HWY 89 and I-17 corridors. We`re seeing some manifestation
of that with increased radar returns across Baja California and in
regional VWP data.

Low level frontogenesis in tandem with the aforementioned
moisture advection should encourage more organized banding
structures across the Vermilion Cliffs down toward the Bradshaw
Mountains. In fact, soundings from Page (KPGA) and the Grand
Canyon(KGCN) show a nearly saturated troposphere with sufficient
upward vertical motion in the dendritic growth zone. 60% of HREF
ensemble members suggest storm total snow amounts of over 5"
across the North Rim, the Kaibab, and even portions of the South
Rim. There has been a consistent signal in multiple iterations of
the hi-resolution model guidance that the greatest snowfall will
take place here and the latest snow amount grids reflect that.
Farther east, snowfall amounts of 1 to 4 inches are anticipated,
with some pockets of 4-5 inches along the highest portions of the
eastern Mogollon Rim (Happy Jack over to areas northeast of
Payson). Regardless of snow amounts, the Monday evening commute
could be tricky for areas near and west of I-17/US HWY 89 and for
areas near/east of I-17/US HWY 89, the Tuesday morning commute may
be hazardous. This will be due to the combination of snow-covered
roads (especially those that are untreated) and due to rapid
changes in horizontal visibility. The overall signal for
widespread snow-squall conditions isn`t a cause for concern, but
low level frontogenetic forcing, some instability (around 100
J/kg) and the presence of a frontal boundary are present,
particularly across the Kaibab and Western Coconino County
Plateau. Should this transpire, amounts of over 6 inches are more
probable, but nailing this down specifically (spatially and
temporally) is difficult, even at this range. Regardless of
amounts, if traveling across the High County, be prepared for
hazardous conditions over the next 24 hours. Allow extra driving
time, ensure your car is winterized, and NEVER stop along the side
of the road to play in the snow. From a weather product
standpoint, the Winter Weather Advisory that runs from the Kaibab
Plateau down through the eastern Mogollon Rim appears on track
through tomorrow morning.

The main upper low is forecast by the grand ensemble of the
Canadian, GFS, and ECMWF to exit stage right Tuesday afternoon and
into Wednesday and this will signal an end to the winter
precipitation. However, the cold front will slide southward
ushering in northerly flow and colder conditions. I`ve attempted
to anticipate some of the snow pack across the High Country with
the latest grid update. Given the high confidence in clearing
skies and diminishing winds on Tuesday and Wednesday evenings
overnight low temperatures were adjusted downward closer to the
25th percentile NBM...mainly across the western Coconino Plateau,
Kaibab, and portions of the Mogollon Rim. Lows temperatures
Tuesday night and Wednesday night are forecast to approach the
single digits. Fortunately, northerly winds will be much
diminished compared to last week, however, and wind chills (though
still in the single digits and teens), are not expected to slip
into the negative values.

A warming trend is expected to ensue with short-wave ridging
supporting more of a subsident regime across the Pacific
Southwest through the end of the work week. Snowmelt will continue
and while this may be a welcomed sign for some, areas where roads
are largely gravel or unpaved may become muddy/impassable.
Temperatures by this weekend may be as much as 5 to 8 degrees
above normal with PoPs remaining below 10%.


.AVIATION...For the 00Z TAF package...Areas of MVFR, IFR, and LIFR
conditions will continue due to low clouds and snow showers. Expect
conditions to begin to improve Tuesday, from north to south.
Southwesterly surface winds of 5-15 kts, gusting 15-25 kts will
weaken tonight and become northerly on Tuesday. Aviation discussion
not updated for TAF amendments.


.FIRE WEATHER...Rain and snow showers are expected to wind down
Tuesday, giving way to fair weather on Wednesday. Expect mainly
light, northerly winds with temperatures 5-10 degrees below average.

Thursday through Saturday...Temperatures return to near average and
winds remain light. Expect clear skies, except for some cloud cover
on Friday.


Winter Weather Advisory until 5 AM MST Tuesday for AZZ004-006-

Winter Weather Advisory until noon MST Tuesday for AZZ015-016-




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