Laramie, Wyoming 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

296
FXUS65 KCYS 180532
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1032 PM MST Fri Jan 17 2025

.KEY MESSAGES...

- An arctic cold front will continue to bring widespread light
  to moderate snow followed by frigid temperatures through the
  weekend. Winter Weather Advisories are in effect for the
  higher terrain.

- A reinforcing shot of bitterly cold air and light snowfall is
  possible Sunday into Monday.

- Slow warming trend Tuesday through Thursday with increasing
  winds across the wind prone areas of southeast Wyoming.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 230 PM MST Fri Jan 17 2025

Surface observations have tracked the passage of a strong cold
front through southeast Wyoming and western Nebraska early this
afternoon. As of 19z, this front has cleared south of the
Colorado border with wind shifts noted at all surface
observation sites along I-80. With north to northeasterly
upslope flow in place behind this front, uplift of the moist
post-frontal airmass has resulted in snowfall commencing across
much of southeast Wyoming and western Nebraska. Recent obs from
KCYS and highway weather stations indicate anywhere from 2 mile
to less than 1 mile visibility in some of the heavier bands of
snowfall. These trends will continue through the day with
snowfall accumulating almost immediately on non-paved surfaces.
As the sun angle lowers later this afternoon, expect snow to
accumulate on any untreated surfaces. Forecast soundings
indicate that saturation in the dendritic growth zone will
quickly decrease this evening in areas east of I-25. Therefore,
despite some lingering light snow falling through the night,
accumulating snowfall will likely be over with prior to midnight
east of I-25. Farther to the west in the slopes of the Laramie
Range as well as the mountains and basins of southeast Wyoming,
a more favorable northerly upslope flow regime will keep better
snowfall rates and accumulation going through the night. No
major changes were made today with regard to either the forecast
snowfall totals or the Winter Weather Advisories in effect with
this system.

As the arctic cold front pushes well south into the southern
plains on Saturday, flow aloft will turn to more north-
northwesterly as cold air continues to filter southward from
Canada. Temperatures aloft reach their minimums over southeast
Wyoming and western Nebraska on Saturday evening and a bitterly
cold day is expected with wind chills likely remaining below
zero even during the afternoon hours. Isolated snow showers will
remain possible on Saturday afternoon with such potent cold air
aloft, however any additional accumulations will be limited to
the highest elevations in the Snowy and Laramie ranges. Forecast
high temperatures will remain around 15 degrees below average.

The remainder of the short-term forecast will focus on cold
weather challenges with another reinforcing shot of arctic air
arriving on Sunday afternoon and evening as a secondary arctic
trough dives southward. Recent changes to NWS headlines have
introduced the "Cold Weather Advisory", replacing the former
"Wind Chill Advisory" products. Cold Weather Advisories
highlight extreme cold conditions regardless of wind chill, and
can be issued for either cold or wind+cold situations. Each
night from Saturday night through Sunday night and Monday night
supports apparent temperatures (wind chills) below at least -25
degrees for much of southeast Wyoming and western Nebraska.
Afternoon temperatures/wind chills will rise above these
thresholds, but not by much at times. With such a prolonged cold
weather event forecasted, in addition to a very mild winter
thus far, we have opted to issue a Cold Weather Advisory for
most of southeast Wyoming and all of the Nebraska panhandle from
Saturday night through Tuesday morning. Locations in open
country will see the most extreme wind chills, with the coldest
night of the period likely coming on Sunday night into Monday
morning. Short and medium-range ensemble guidance is somewhat
split with regard to the extent of the cold, with the ECMWF
Ensemble members generally colder than the GEFS by around 5 to 8
degrees. Still, despite this slight uncertainly, enough
confidence in very cold weather is still present to support the
Cold Weather Advisory product.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Issued at 230 PM MST Fri Jan 17 2025

On Monday morning, the arctic airmass is still hanging out over
the region keeping temperatures rather frigid. There is a small
shortwave with a little plume of moisture associated with it
over Carbon county. Given that the pattern at this time is
northwesterly, this favors upslope with the Sierra Madres and
Snowy Range and downsloping for the areas along and East of
I-25. Therefore, pops were kept over and near the mountain
ranges with some uncertainty as to whether Rawlins should be
included in the pop distribution. Tuesday, the arctic airmass
starts to peel off through the day with a ridge and warmer air
pushing eastward. Looking the global ensemble members, there is
some uncertainty with how fast this ridge will begin to
influence the area. This is particularly highlighted with how
dispersive the ensemble outcomes are with the surface max/min
temperatures. At the 700mb level there is a jetstreak that moves
over southeast Wyoming on Tuesday and persist until Wednesday
morning as well. Given the strong subsident flow expected over
our wind prones, winds were also increased. Looking at our
machine learning high wind algorithm, the probs were increased
to 85 to 90 percent chance for wind gusts meeting high wind
criteria for our wind prones. The algorithm also increased the
probs up to 70 percent for the WY37 area between Laramie and
Cheyenne. So we will be keeping a close eye on this period for
possible headlines. Wednesday through Friday, our warm ridge
pattern is short lived as another shortwave descends from
Alberta, Canada to flatten our ridge Wednesday into Thursday.
There is some arctic air dragging with this wave but nowhere
near the capacity of the previous arctic airmass. While this is
still the point where the ensembles start to lose skill,
temperatures aren`t expected to rise above 30 degrees area wide
these two days. On Friday, a larger ridge starts to push east
into the Rocky Mountains giving us warmer temperatures Friday
and possibly the weekend.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1024 PM MST Fri Jan 17 2025

Northwest flow aloft will continue as cold air continues to
invade the region with surface high pressure building in.

Wyoming TAFS...Ceilings will range from 2500 to 5000 feet, with
occasional light snow reducing visibilities to 1 to 3 miles and
ceilings to 1500 feet until 15Z, then scattered clouds from
2500 to 4500 feet will develop after 01Z. Winds will gust to
28 knots at Cheyenne until 01Z.

Nebraska TAFS...Ceilings will range from 5000 to 9000 feet until
00Z, with occasional ceilings around 1500 feet at Chadron,
Alliance and Scottsbluff until 09Z, then scattered clouds from
5000 to 9000 feet will prevail after 00Z. Winds will gust to
25 knots at Chadron and Alliance until 09Z, and to 30 knots at
Alliance, Scottsbluff and Sidney from 15Z to 00Z.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Cold Weather Advisory from 8 PM Saturday to 11 AM MST Tuesday
     for WYZ101-102-106>110-115>119.
     Winter Weather Advisory until 5 AM MST Saturday for WYZ103-104-
     110-114-116-117.
NE...Cold Weather Advisory from 8 PM Saturday to 11 AM MST Tuesday
     for NEZ002-003-019>021-054-055-095-096.

&&

$$

SHORT TERM...MAC
LONG TERM...MM
AVIATION...RUBIN