Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 032210
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
310 PM MST Sat Dec 3 2022

.SHORT TERM...(Tonight through Sunday)
Issued at 121 PM MST Sat Dec 3 2022

Key Impact Messages:

1) Strong winds expected across the wind prone areas and the South
Laramie Range Foothills Sunday afternoon through Monday morning.
Winds could gust up to 60 mph. A High Wind Watch has been issued
for these areas. Additional light snow accumulation and gusty
winds may create areas of blowing snow from Arlington to Elk
Mountain.

2) Steady snowfall expected across the higher elevations of the
Sierra Madre and Snowy Mountains through the short term forecast
period. Total snow accumulations of 6-9" seem likely with isolated
heavier amounts possible. These areas will be under observation
for potential winter weather highlights.

Weather Details: The warm air advection continues to push the
colder airmass out of our area as noted by temperatures rebounding
into the low to mid 40s across much of SE Wyoming. Steadily
cooling temperatures this evening will allow a refreeze of the
snow that was able to melt this afternoon.

Heading into Sunday, the main weather concern will be for the
development of strong winds across the wind prone areas and across
the south Laramie Range Foothills. While not the most impressive
setup that we have seen so far this season, both HI-RES models and
in-house models show a tightening pressure gradient Sunday
afternoon across the Laramie Range in conjunction with increasing
700mb winds around 60 knots. The bulk of these strongest winds
look to remain concentrated first around the Arlington wind prone
area and the south Laramie Range Foothills first as the better
downward omega pockets look to max out in these areas before
slowly expanding. Bordeaux may only see a brief window of high
winds with more sporadic gusts but confidence was high enough to
go ahead an issue a High Wind Watch for this zone as well.
Analyzing the potential for mountain wave activity, the GFS has
been the most aggressive in showing some minor mountain activity
around Monday morning breaking near Buford. Not the best signal
but rogue gusts could exceed 60 mph where the wave breaks. Not
expecting winds to spill into the I-25 corridor as all the high
wind parameters stay over the Laramie Range but a breezy day can
be expected with wind gusts up to 30 mph.

Outside of the wind forecast, much of the region will remain dry
with near seasonal temperatures, but prolonged orographic snow
over the Sierra Madre and Snowy mountains look likely with
gradually accumulating snow approaching 6-9" for the highest
peaks.

.LONG TERM...(Monday through Saturday)
Issued at 121 PM MST Sat Dec 3 2022

A progressive weather pattern will continue for much of the week
ahead. The main impacts will be:
* A few potential marginal high wind events for the wind prone areas
* Mountain snow opportunities on Monday through Wednesday, and again
  next weekend.
* Potential for snow on the high plains on Monday evening.

On Monday, the synoptic pattern will feature a strong, large, but
shallow trough positioned over the Hudson Bay, with a ridge over the
Eastern Pacific and a nearly closed low offshore of northern
California. Most of the CONUS will have fairly strong but mostly
zonal flow aloft. Expect strong winds to linger into Monday morning
in the wind prone areas (described above). An arctic high sliding
down east of the Rockies will push a cold front through the area
early Monday, and start to bring the winds down as higher MSLP works
into the high plains. Meanwhile, the mid-level jet on the southeast
flank of the CA upper level low will be fairly moisture rich. Models
show near saturation in the 700 to 300-mb layer with 500-mb wind
speeds around 70-knots to our west. This will produce some healthy
mountain snowfall Monday through early Tuesday, and possibly longer
depending on how quickly the moisture plume shifts southward on
Tuesday into Wednesday. WSW flow will strongly favor the Sierra
Madre range, where at least advisory criteria snowfall appears
likely. Will need to watch this for changes, as warning criteria is
not out of the question. The Snowy range will likely be partially
shadowed in WSW flow, so expecting slightly reduced totals here, but
again may need to eventually consider advisories.

We are also watching the potential for some snow to spill over into
the high plains on Monday evening into early Tuesday. The surface
high over the northern Plains could flip low-level winds around to
the east or southeast. The GFS also shows split flow at 700-mb
gaining a southerly component east of the front range and initiating
overrunning warm air advection on top of some mild frontogenesis.
With weak 500-mb vorticity maximums shifting east between the two
primary lows over the CONUS, models show higher mid level moisture
briefly being pulled eastward in the presence of this lift, leading
to some snow shower development. Currently highlighting the I-80
corridor between Cheyenne and Sidney for this potential, but also
expanded the potential slightly further north from prior updates.
Not expecting significant accumulation, but some light accumulation
is likely.

The surface high moves out quickly, and will be replaced by a weak
surface trough ahead of a subtle shortwave rotating around the broad
trough to our northeast on Tuesday. Thus, cross-barrier MSLP
gradients should come up again, and lead to elevated winds for the
wind prone areas. Can`t rule out this approaching high wind
criteria, but leaning towards just elevated at this point. On
Wednesday, the coastal upper level low will start to eject east of
the Rockies. Right now, it looks like the track will be far enough
south such that most of the mountain precip remains in CO, but could
see some snow showers creeping into our mountains on Tuesday night
into early Thursday as this system moves east. The European model is
slightly further north with this, which would bring more snow to our
mountains, and possibly to the east as well. Nudged PoPs up slightly
for the mountains on Wednesday above NBM to get a slight chance
mention in the forecast wording, but will need to monitor model
trends in the coming days. There could be some elevated winds in the
second half of the week, but this is too uncertain at this time to
discuss timing in detail. The next weather maker will be a
progressive trough moving into the west coast on Friday into
Saturday which could bring another round of wind and snow.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1040 AM MST Sat Dec 3 2022

VFR conditions expected for the forecast period. A few wind gusts
to 20-25 kts are possible in Wyoming and at KSNY/KAIA this
afternoon, which should die down around sunset. KCYS will be near
the border of SSW winds and W winds, the latter of which could
briefly creep into the terminal, but expecting winds to be mostly
SSW. Light winds overnight with continued mid level clouds
filtering through the area.

&&

.FIRE WEATHER...
Issued at 146 AM MST Sat Dec 3 2022

No fire weather concerns this weekend and next week due to near
or below average temperatures, surface snowpack, and minimum
humidities above 30 percent.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Watch from Sunday morning through Monday morning for
     WYZ106-110-116.

NE...None.
&&

$$

SHORT TERM...AW
LONG TERM...MN
AVIATION...MN
FIRE WEATHER...TJT


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