711
FXUS65 KCYS 031152
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
552 AM MDT Thu Apr 3 2025

.KEY MESSAGES...

- Below average temperatures will continue late this week and
  into the weekend.

- Periods of accumulating snow expected today through early
  Saturday morning. Travel impacts are possible, especially over
  the higher elevations.

- Warmer and drier conditions begin on Sunday and likely linger
  through much of next week.

&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
Issued at 340 AM MDT Thu Apr 3 2025

Primary forecast concern will be the potent upper level
disturbance, currently near the Four Corners region, lifting
northeast across the area later today and tonight...with a
secondary cold front sliding south out of western Canada
resulting in another round of snowfall later Friday through
Friday night. Models are trending a little more aggressive with
these two events as short range ensemble guidance and high res
guidance have trended wetter and colder compared to 24 to 48
hours ago.

For early this morning, mostly clear skies continue over much of
the area based on current IR Satellite loop. Cloud shield
associated with the upper level disturbance/trough is still
well to the south across Colorado. Fog has not formed yet across
the western Nebraska Panhandle. Will give this a few more hours
before we take it out of the forecast as surface winds have not
backed into the southeast yet. Dewpoint depressions are still
between 1 to 4 degrees C, so will keep fog in the forecast for
now. Otherwise, expect increasing clouds from south to north
this morning as a stationary front remains near the Laramie
Range. Low temperatures look on track...with readings in the mid
teens to mid 20s. As winds eventually shift into the east and
southeast, a period of fog is possible for the I-80 Summit in
this pattern, so added some fog west of Cheyenne until the snow
begins later this afternoon.

The upper level shortwave disturbance to our south, which is
part of the overall long wave trough over most of the western
third of the United States, will lift northeast today across
northern Colorado and southeast Wyoming/western Nebraska this
afternoon and this evening. Although the feature doesn`t look
too impressive, a closer look at the 700mb level and jet
dynamics show some moderate low to midlevel forcing later this
afternoon through midnight tonight. These features can surprise
us with moderate to locally heavy precipitation this time of the
year with any low level instability. In the upper levels, a 90
knot jet max will quickly move northeast ahead of the primary
vorticity max which will be located somewhere near the
Colorado/Wyoming border. Closer to the surface, a 700mb low is
forecast to develop and lift northeast...eventually stalling
near the Wyoming/Nebraska border before weakening late tonight.
In addition, the stationary front will remain near the Laramie
Range and drift east tonight, resulting in additional low level
convergence. Increased POP across most of the area with higher
QPF totals than previously expected. Precipitation will start
off as mainly rain below 5000 feet, but snowlevels should slowly
drop 3500 feet by early Friday, so most places will see all
snow by sunrise Friday. Can see a few places, especially those
above 5500 feet, getting some moderate snow bands with a half an
inch per hour rates at times. Believe these will be short-lived
as the first system looks pretty compact with two separate
peaks in precipitation and a lull in the middle (first one later
today with the second one Friday associated with the polar cold
front digging south). The question then becomes will snowfall
rates overwhelm surface/pavement temperatures for travel
impacts/hazards? This is where the most uncertainty is with the
forecast over the next 48 hours. Given the time of the day most
of the snowfall is expected to fall...which is mainly during
the daytime or evening hours along the I-80 corridor, decided
against a Winter Weather Advisory due to the pretty high early-April
sun angle. Even in the mountains, two separate periods of snow
are expected which will likely result in 4 to 9 inches of total
snowfall for the Sierra Madre Range and Snowy Range. This is
just below Advisory thresholds, so will hold off on any
headlines. Will have to monitor snowfall rates closely and areas
north of Interstate 80 once the secondary cold front arrives.
High res guidance shows a more persistent band of snowfall
developing from Lusk to Chadron and Alliance late tonight and
into Friday morning.

Pretty cold temperatures expected, especially on Friday, as the
surface cold front dives southward out of Canada. Forecast highs
are expected to be in the low to mid 30s for most of southeast
Wyoming above 5000 feet...with highs in the upper 30s to near 40
across western Nebraska and the lower elevations of far eastern
Wyoming. Another round of snow is expected with the arrival of
this front, but most models and ensembles show light snowfall
rates and maybe an other inch or two of snow. However, most of
this will fall during the day and will likely struggle to
accumulate. Very cold temperatures Friday night with clearing
skies with lows in the single digits and teens, but still not
approaching record lows for the day.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Issued at 305 AM MDT Thu Apr 3 2025

Starting Sunday morning the long term forecast is dominated by
upper level ridging and downslope flow to keep temperatures in
the 60`s to 70`s during the day and 30`s to 40`s into the overnight
hours. However, mainly on Tuesday the Intermountain West experiences
an upper level shortwave that temporarily disrupts our warmer
temperatures. The main upper level low traverses the Canadian
Providences creating a shortwave the helps to flatten our stout
ridge. This shortwave creates some small precipitation chances
for our area but currently the only area forecasted to experience
any precipitation would be mainly the mountains. This mainly
has to do with the stout dry air near the surface caused from
the downsloping off the mountains while in previously persistent
westerly flow. There is a brief instance that we enter
northwesterly flow to give a slight chance for precipitation out
of the mountains. But the most likely scenario is that the sky
becomes cloudy and most of the forecast area sees Virga in the
afternoon. The cloudy skies and virga may cool us off slightly ,
but the ensemble means still keep temperatures in the 60`s. To
add confidence in our overall dry forecast, the moisture content
at 700mb looks to be sufficient to see some light accumulations
(1-2 inches) in the mountains (mainly due to upslope), but
insufficient to produce any measurable precipitation elsewhere.
By Wednesday morning the ridge once again starts to rebuild and
temperatures return back into the 60`s.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 552 AM MDT Thu Apr 3 2025

VFR conditions will prevail through 20z. After 20z
precipitation chances will increase as the upper level low
pushes northeast from Colorado. KRWL and KSNY will be the first
terminals to receive precipitation. Ceilings will quickly drop
as mid level and lower level clouds move in from the south. IMC
conditions will soon follow around 00z for KCYS and east into
the Nebraska Panhandle. There will be a brief break in
precipitation for the Wyoming terminals around 06z. Ceilings are
expected to be between LIFR to MVFR with the most uncertainty
with KRWL with could be MVFR or VFR since it will be on the
edge. Around 10z with the exception of KCDR there will be a
brief precip break for the Nebraska Terminal before another wave
of precipitation starts for all terminals after 12z.


&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.

&&

$$

SHORT TERM...TJT
LONG TERM...MM
AVIATION...MM