Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 082359
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
450 PM MST Thu Dec 8 2022

.SHORT TERM...(This evening through Sunday)
Issued at 215 PM MST Thu Dec 8 2022

Forecast concerns in the short term deal with strong winds leading
to wind headlines through Saturday. Major winter storm still
possible the start of next week with significant snowfall and
strong winds possible.

Currently...Frontal boundary lays from western Nebraska near
McCook to Gordon Nebraska to Gillette Wyoming up into central
Montana this afternoon. Upper vort max pushing into western
Nebraska at this time riding over the front. Winds behind this
upper shortwave have really increased. We have seen 60+mph winds
at Arlington...the Summit and eastern foothills from late morning
that are continuing this afternoon. Bordeaux has begun to increase
with 50mph gusts reported at the WYDOT site. No plans on changing
any of the current wind warnings at this time. Current Craig to
Casper 850/700mb height gradients near 55/56mtrs
respectively. GFS 700-800mb winds increasing to 45 to 50kts
through 00Z this afternoon over Cheyenne and south Laramie Range.
Wind gusts at Cheyenne currently at 40kts. With these winds
continuing to increase through the afternoon...do feel Cheyenne is
going to hit.

One note of caution for the evening shift. May need to extend the
High Wind Warning a few more hours this evening as gradients
remain high through 06Z. May be a last minute update to extend
warnings based on current observations later today.

As for winter headlines...SNOTELs in the Sierra Madre have
reported roughly .6 inches of liquid. Snowing pretty good at
Chadron. Just got a report at Chadron of 3 inches with snow
continuing to fall. So will keep the advisories going as they are.

Upper low tracks east this evening...with winds easing overnight.
Shortwave ridge moves fairly rapidly across the CWA Friday morning
as next low pressure system moves into northern Utah. Looking at
increasing Craig to Casper 850/700mb height gradients Friday
evening as upper shortwave moves into central Wyoming. GFS
700/750mb winds up to 50kts Friday evening over Arlington and
Bordeaux. Decided to issue a High Wind Watch for Friday night into
Saturday.
In Wyoming, the main aviation hazard will be strong winds this
afternoon. KCYS and KLAR can expect frequent wind gusts between 30
and 40 kts, with occasional gusts above 45 kts. MVFR CIGs are
lingering at KRWL, but this should improve in the next 1-2 hours
with wind gusts of 30 to 35 knots likely this afternoon. Winds will
die down after sunset. A reprieve in the weather for Saturday
afternoon through Sunday as upper ridge resides over the area. A
very strong low pressure system moves into northern California
Sunday morning and afternoon. This is the low that could bring
significant winter weather to our area for Monday through Wednesday
next week.

.LONG TERM...(Sunday night through Thursday)
Issued at 215 PM MST Thu Dec 8 2022

KEY MESSAGES:

1) Strong winter storm remains possible in the long term forecast
with weather impacts beginning early Monday morning and lasting
through Wednesday. Primary hazards will be heavy snowfall and strong
winds.

2) Uncertainty remains high at this time as even a slight shift
north or east could leave southeast Wyoming and the Nebraska
panhandle receiving minimal impacts.

3) Strong winds following the initial snowfall possible, resulting
in blowing snow, especially in east central Wyoming and the Nebraska
panhandle.

DISCUSSION: The primary forecast concern for the long term forecast
period is a potential strong winter storm starting Monday over
western portions of our cwa, lasting through Wednesday. Confidence
is HIGH that the main hazards with this storm will be heavy snowfall
and strong winds, however confidence is LOW on where exactly these
impacts will occur. The location will be heavily dependent on how
the system sets up synoptically. The current GFS and ECMWF
deterministic model runs have the low dropping south along the
western edge of the Rockies Monday, then swinging back north to the
borders between WY/NE/CO/KS, tapping into deep Gulf moisture, and
remaining almost stationary through Wednesday night until it ejects
northeastward Thursday. If this set up remains consistent between
model runs, east-central Wyoming and the Nebraska panhandle,
particularly the Pine Ridge area, will receive significant impacts
due in part to the wrap around moisture and strong pressure gradient
resulting in heavy snowfall and very strong northerly winds.

As this system is still 5+ days out, it is a guarantee that the
forecast will change, either trend higher or lower depending on
where the models show the low closing off and becoming stationary.
The snowfall accumulation forecast is currently near GFS Ensemble
means and NBMv4.1 50th percentile everywhere, except the Pine Ridge,
Chadron to Douglas area, where it is closer to the NBMv4.1 75th
percentile. In general what this means is we are most confident in
the Pine Ridge, Chadron to Douglas area, receiving the strongest
impacts and our confidence decreases moving south.In Wyoming, the
main aviation hazard will be strong winds this afternoon. KCYS and
KLAR can expect frequent wind gusts between 30 and 40 kts, with
occasional gusts above 45 kts. MVFR CIGs are lingering at KRWL, but
this should improve in the next 1-2 hours with wind gusts of 30 to
35 knots likely this afternoon. Winds will die down after sunset.
Another area to note is the Laramie Valley, mid-level winds appear
to start off southerly, transitioning to easterly by Tuesday,
turning northerly by Wednesday. As southerly and easterly are both
downsloping, the Laramie Valley will start off shadowed by the
mountains, decreasing the snow potential until the winds turn
northerly, which is a more favorable direction.

Stay tuned in the coming days for forecast updates!

&&

.AVIATION...(For the 00Z TAFS through Friday afternoon)
Issued at 455 PM MST Thu Dec 8 2022

Snowfall and low CIGS will impact KCDR early this evening before
conditions quickly improve around 03z. Southwest flow expected
tomorrow with increasing mid to high cloudiness through the day.

HAZARDS/WEATHER TRENDS: Near IFR conditions will continue at KCDR
with mainly MVFR VIS expected in light snow. Conditions are expected
to improve shortly (between 00z and 03z) with VFR conditions at all
terminals tonight through Friday morning. Otherwise, gusty winds up
to 30 MPH this evening across the eastern plains tIn Wyoming, the
main aviation hazard will be strong winds this afternoon. KCYS and
KLAR can expect frequent wind gusts between 30 and 40 kts, with
occasional gusts above 45 kts. MVFR CIGs are lingering at KRWL, but
this should improve in the next 1-2 hours with wind gusts of 30 to
35 knots likely this afternoon. Winds will die down after sunset.
erminals will likely become light and variable after 02z.


&&

.FIRE WEATHER...
Issued at 215 PM MST Thu Dec 8 2022

Strong winds this afternoon across the wind prone areas of
southeast Wyoming. Afternoon humidity has remained well above
critical levels this afternoon...so critical fire weather
conditions not expected. Another high wind event for the wind
prone areas of southeast Wyoming Friday evening into Saturday with
High Wind Watches in effect. Another strong low pressure system
forecast to move into the central Rockies Sunday into Tuesday that
could bring substantial snowfall to much of the forecast area.
Substantial snow amounts possible Tuesday and Wednesday with very
strong north to northwest winds. Standby for further updates over
this weekend.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...

WY...High Wind Warning until 8 PM MST this evening for WYZ106-110-
     116>118.

     High Wind Watch from Friday evening through Saturday morning for
     WYZ106-110-116-117.

     Winter Weather Advisory until 5 PM MST this afternoon for WYZ112.

NE...Winter Weather Advisory until 8 PM MST this evening for NEZ002.

&&

$$

SHORT TERM...GCC
LONG TERM...LK
AVIATION...TJT
FIRE WEATHER...GCC


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