086
FXUS65 KCYS 041145
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
545 AM MDT Fri Apr 4 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 SATURDAY NIGHT/...
Issued at 305 AM MDT Fri Apr 4 2025

Relatively quiet weather last night and early this morning across
southeast Wyoming and western Nebraska. We are currently in the
brief lull between the two weather systems impacting the area
late this week. The upper level vort max/disturbance that brought
snow to the region on Thursday dissipated earlier than expected
with most of the associated dynamic forcing shearing off to the
east late Thursday evening. Most of the region still received
snowfall and/or rain and snow mix, but snowfall rates weren`t
enough to overcome the relatively warm pavement...resulting in
little to no impacts to area roadways. There is some black ice
and fog along portions of I-80 and I-25, mainly over the higher
elevations, but impacts have been minimal or limited in scope early
this morning. Otherwise, the band of snow that the 00z models from
yesterday were showing for this morning never developed due to
the weakened state of the upper level disturbance and a slight
delay in the polar cold front. Therefore, lowered POP and snow
accumulations across east central Wyoming and the northern
Nebraska panhandle between midnight and early Friday morning.

The second period of snowfall today will be associated with a
cold front diving south across central Wyoming and adjacent high
plains. Current surface observations and IR Satellite loop shows
this front across northern Carbon and Albany Counties and extending
north across western Converse county. As of 200 AM, Douglas still
shows southeast winds and a temperature of 31 while areas near
Casper and Deer Creek (roughly 35 to 45 miles away) are 5 to 8
degrees colder with brisk northerly winds between 25 to 40 MPH.
Pretty strong cold air advection with this front as it is forecast
to dive south into the I-80 corridor and eventually Colorado
this morning. Expect snow to redevelop from north to south this
morning and early this afternoon. Although 00z to 06z high res
guidance has struggled with initialization of snowfall behind
the front, it is currently snowing at Casper with a visibility
below one mile. Expect similar conditions for most of southeast
Wyoming and portions of western Nebraska today with gusty northerly
winds. This may result in greater travel impacts today with not
only the snowfall but the winds producing some drifting and
patchy blowing snow/low visibility. The updated HRRR has started
to hint at some heavier bands of snow today behind the front
across most of the area, so will continue to monitor this through
the afternoon. Expect the steady snowfall to be pretty brief,
so will not issue a Winter Weather Advisory at this time. Will
need to monitor the I-80 corridor between Elk Mountain and Cheyenne,
the northern Cheyenne Ridge including Laramie County and Banner
County, and the Highway 20 corridor along the Pine Ridge which
appear to be the most favorably areas to see Advisory conditions
due to falling snow and some blowing snow into this evening. A
quick look at the SNOTELS over the last 18 hours shows mainly 3
to 6 inches of snow with several sites lower than 3 inches from
the first batch of snow yesterday.

Coldest day of the week is expected today as the surface cold front
pushes into Colorado by early this afternoon or late this morning.
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. Low temperatures tonight will be very
tricky due to the timing of clearing skies in addition to any
observed surface snowpack. For now, kept lows in the teens with
a few places in the single digits. However, these may need to be
lowered further if either skies clear earlier or a few inches
of snow accumulate and linger into the evening hours.


All models show drier conditions on Saturday as the cold front
continues to move southeast across the central plains. Long wave
trough will still remain over the plains with northerly flow aloft
across Wyoming and western Nebraska. Not as cold on Saturday as
700mb temperatures climb above -10c, but still remaining about
5 to 10 degrees below normal with highs in the 40s to around 50.
Winds are forecast to increase across the wind prone areas, but
should remain below High Wind criteria.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Issued at 331 AM MDT Fri Apr 4 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. RH values look to drop into the teeen`s
and twenties with light winds. So there`s not too much concern with
fire weather into next week. The main time frame to focus on is
Tuesday through Thursday. Tuesday, the first shortwaves descending
down from Canada will help flatten our ridge with some light
moisture attached to it. There is a 700mb jet that is currently
progged to transit over our area for some elevated winds Tuesday
morning and lasting the evening following the diurnal trend. Given
the jet is between 40 to 50 knots theres not too much concern with
reaching high wind criteria. The shortwave would need to dig further
south to really compact the pressure gradient to achieve high wind
criteria. However, with some light moisture and northwest flow there
could be some light snow showers over the mountains as the global
models have trended upwards in QPF totals. This could possibly be
due to the models trying to resolve some possible slightly
convective showers as 200-300 joules of CAPE are also progged to be
over the Mountains and the northern portion of the Nebraska
Panhandle. Rain showers over the Panhandle may not be as likely due
to the drier low levels, and the main forcing looking to be
disconnected from the main plume of moisture.  Wednesday morning,
the wind prones will start to mix into that 700mb jet as there are
some subsidence occurring behind the shortwave that pushed through
on Tuesday. The jet gradually decreases throughout the day so there
will be some breezy winds over I-80 but it will be more to the tune
of a regular Wyoming day. Interestingly enough the 00z GFS develops
a weak lee cyclone that pushes off into the central plains Wednesday
morning. Given the associated isentropic lift there is some
possibility of brief rain showers. But it would need to overcome the
pretty stout dry layer near the surface and not confident if the
forcing will be there to overcome the dry layer. Thursday has
another weak shortwave will past through Wyoming and Nebraska
Panhandle. There is going to be more moisture with this shortwave as
the ridge does become more flat and the Intermountain west gets
blessed with remnants of a possible AR coming off the Pacific.
However, the dynamics currently progged don`t look all that
impressive but its also at the tail end of any skillful model
analysis. Given the progged NW flow we could see some light rain
showers in the northern portion of the CWA.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 545 AM MDT Fri Apr 4 2025

A cold front will push through this morning creating some light
snow showers through the early afternoon. After 19z the snow
showers will start to stop moving from north to south. By 00z
the snow shower should have stopped at all terminals with the
exception at KRWL which may have light snow persist until 01z.
There will be winds behind this front up gusts up to 30-35kts
peaking in the afternoon. By 02z the wind gusts should be over
and sustained winds between 10 to 15 kts are favored until 06z
when winds will drop below 10kts for the Nebraska Panhandle and
possibly KCYS and KLAR.

&&

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

&&

$$

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