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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS65 KCYS 171726
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1126 AM MDT Wed Apr 17 2024

.KEY MESSAGES...

- Widespread rain and snow showers will return to much of the
  area on Wednesday and Wednesday night. Accumulating mountain
  snow is possible, especially in the Snowy Range with 6 to 12
  inches of new accumulation possible above 9000 feet.

&&

.SHORT TERM /THROUGH THURSDAY NIGHT/...
Issued at 319 AM MDT Wed Apr 17 2024

Beginning of an extended unsettled pattern for the region will
unfold as we head throughout the day today as we wait for a
strong north to south moving cold front to push through the
region. Ahead of this cold front south to southwesterly
downsloping winds will keep most areas east of the Laramie Range
dry. With the approach of both the surface front and upper
level trough, pressure gradients at the surface and aloft will
increase which could prompt the development of some elevated
winds across Albany and Carbon counties. HI-RES models show some
subtle hints of mountain wave activity and if this comes to
fruition then some strong winds may develop across the I-80
Summit and the south Laramie Range foothills and a short fused
high wind warning may be needed if this mountain wave activity
does development. Expect a quick reduction in the winds as the
front pushes through as pressure heights immediately build into
the region post FROPA. Moisture pooled along the main frontal
boundary will slam into the higher terrain and with a steady
feed of cold moisture air, the high elevation mountain peaks
could see some modest amounts of snow accumulations today in
Thursday. The main question will be where does this cold front
stall and transition into a stationary boundary as this will
effect where the heaviest valley snow will fall. Still expecting
scattered to widespread snow showers to imp areas south of the
North Platte River valley but accumulations overall look low
with minimal impacts expected.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
Issued at 319 AM MDT Wed Apr 17 2024

The first half of the long term will feature cooler and wetter
weather due to an active synoptic pattern, while the later half
of the extended forecast will see the return of warmer and
potentially drier weather.

By the time Friday rolls around, cold air will already be locked in
place from an upper-level trough over much of the northern tier of
the country. The main part of the trough will be pushing into the
Great Lakes region by Friday afternoon, leaving the back edge of the
trough over the CWA. Friday night into Saturday, one final push of
colder air will move into the region from a shortwave on the
trailing edge of the trough. 700 mb temperatures will be in the -8C
to -12C range. This will likely lead to the coldest temperatures in
this cold spell, with morning lows on Saturday dropping into the
20s, and high temperatures in the low 40s. Some locations may not
even make it out of the 30s! These temperatures will be well below
average for April and lead to the potential for snow. Besides the
cold, this shortwave comes with an increase in moisture and energy
which will lead to the development of precipitation over much
of the CWA. Models are in fairly good agreement on where snow
will occur, however QPF amounts differ from model to model,
which will have a profound impact on snowfall amounts. As
mentioned, models are fairly consistent with showing snow in the
high terrain, as well as areas east of the Laramie Range. For
the lower elevations, it looks like areas along the Interstate
80 corridor between Cheyenne and Sidney could see the highest
QPF amounts. Again, models are in disagreement with QPF/snowfall
amounts. There is even a fair amount of member spread between
the GFS and ECMWF ensembles. For now, trended snowfall totals
closer to the ECMWF ensemble mean and the NBM. Both of these are
less than the GFS/GEFS which show a pretty good swath of
snowfall accumulation along the Interstate 80 corridor. Being
that its late April, the sun angle may make it difficult for
snow to accumulate, especially during the day. Hence, the trend
towards lower snowfall amounts.

A quick warm-up is in store on Sunday as a broad ridge building over
western CONUS allows 700 mb temperatures above 0C to move back over
the region. High temperatures could warm over 20 degrees compared to
Saturday`s highs! This will put temperatures back to slightly above
average. A shortwave passing north of the CWA on Monday may cool
temperatures off a few degrees and bring a slight chance of showers.
Temperatures continue to warm on Tuesday, but long range models
begin to disagree on potential precipitation chances.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
-- Changed Discussion --
Issued at 1123 AM MDT Wed Apr 17 2024

Showers will remain scattered throughout the afternoon in
southeast Wyoming and western Nebraska although rain will not
reduce VIS at any terminals to below MVFR levels. A cold front
will move southward through the high plains, reaching CYS around
23z. This will bring a northerly wind shift as well as low
ceilings to most areas east of I-25. MVFR is likely at CYS with
IFR possible after 2z if moisture is more pronounced in the
lower levels.
-- End Changed Discussion --

&&

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

&&

$$

SHORT TERM...AW
LONG TERM...SF
AVIATION...MAC