Laramie, Wyoming 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

239
FXUS65 KCYS 180948
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
248 AM MST Sat Jan 18 2025

.KEY MESSAGES...

- An Extreme Cold Advisory is in effect from 8pm tonight through
  11am Tuesday for much of the region.

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

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

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 246 AM MST Sat Jan 18 2025

Fairly quiet night tonight behind the departing cold front, which is
well south of the CWA as of 09Z. Breezy, northerly winds have
continued behind the front leading to wind chill values between -14
and 6F. Some light snow showers are present across portions of the
area, with a low cloud deck over much of the CWA. Temperatures have
remained fairly stationary tonight, due to this cloud cover.
However, these cold temperatures will begin to get cooler throughout
the day as the cloud deck has the opposite effect during the day.
Arctic temperatures continue through much of the weekend into early
this week.

The base of the upper-level trough responsible for this arctic
outbreak is well south of the region at this time, leading to
westerly to northwesterly flow aloft, with northerly flow developing
later this afternoon. The northerly winds aloft will keep the pipe
open for arctic temperatures to continue to spill out of Canada and
into northern portions of the CONUS. As strong temperature gradients
develop between the western CONUS and the central CONUS due to the
arctic air intrusion, the upper-level jet will see an increase in
speeds by the evening hours, with a secondary jet streak positioned
across southern Canada south through eastern Montana and Wyoming.
With very cold temperature aloft and near the surface, lapse rates
will remain fairly significant, leading to the stronger winds to
slowly mix down towards the surface. A subtle shortwave will also
traverse through the 700mb flow, further increasing height gradients
and, therefore, wind speeds at 700mb, especially late this evening.
With increasing winds at 700mb and decent lapse rates, some of the
stronger winds associated with the 45-50kt 700mb jet will mix down
to the surface, increasing winds across much of southeast Wyoming
and western Nebraska throughout the day, with a secondary increase
in winds along the Laramie Range late tonight into very early Sunday
morning. While surface winds will remain well below high wind
criteria, the breezy conditions combined with -20 to -25C air at
700mb will lead to frigid temperatures at this surface for late
tonight into early Sunday morning. Wind chill values will approach
the -20 to -25F range by early Sunday morning. The Extreme Cold
Advisory remains in effect, with Extreme Cold Warnings possibly
being issued with the next forecast package. Snow chances will
slowly taper off throughout the day, but an increase in snow shower
coverage is possible with the passing 700mb shortwave trough. Did
increase PoPs across northern portions of the CWA where there were
zero PoPs. These additional snow showers should not amount to much
accumulation, likely right around 0.5in to 1.0in.

After a frigid start to the day Sunday, surface temperatures will
not warm up much under the broad, upper-level trough. Highs on
Sunday will struggle to reach the teens, with many locations seeing
single digit highs. Unfortunately, winds will remain fairly elevated
under a 700mb low-level jet, leading to wind chills values
throughout the day not making it out of the negatives and likely
remaining in the -10 to -15F range throughout much of the day for
most locations in the CWA. A secondary arctic front will push into
the region Sunday night, leading to a reinforcing shot of cold air
for early Monday morning. Temperatures will tank behind this front
with the arctic air remaining firmly in place. Overnight lows will
range from the -5 to -15F range, with light winds leading to wind
chills well into the -25 to -35F range early Monday morning. The
Monday morning lows and associated wind chills will need an Extreme
Cold headline in future updates, but wanted to give day shift
another chance to look at exactly how cold it will get. In addition
to the cold on Sunday from the passing front, another round of
widespread snow showers will be possible across the CWA Sunday
evening into early Monday morning. This round of snow will likely
drop another 0.5in to 1in for much of the region, increasing the
snow pack and favoring temperatures to drop even colder overnight
due to the fresh snow pack. More details on the upcoming cold for
the first half of the week in the long term discussion.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Issued at 246 AM MST Sat Jan 18 2025

One more reinforcing shot of arctic air on Monday with Medium
Range models in better agreement compared to yesterday. 00z GFS
has trended towards the other deterministic models with much
lower ensemble spreads this time around. Snowfall associated
with this secondary arctic front will end Monday morning with
additional snow accumulations of a half inch or so. Skies are
expected to clear during the day, but sunny skies will not make
much of a difference Monday afternoon with 850mb temperatures
remaining between -15c and -22c over southeast Wyoming and
western Nebraska. Surface temperatures will be similar with
highs in the single digits and most areas, with a few locations
remaining below zero through the day. Monday night should also
be the coldest night for many areas, but locations that see an
increasing westerly wind may not be that bad, especially later
at night with slightly warmer downslope winds expected. North
winds will eventually shift into the northwest Monday night and
increase slight, resulting in frigid wind chill temperatures
between -25 to -40f, and even as low as -45f over the more
sheltered valleys as westerly winds increase towards daybreak
Tuesday. Will likely need extreme cold headlines at some point
this weekend...for Monday and Monday night, but decided to get
through the first part of this system before we address the cold
on Monday. Thankfully, we expect these dangerous wind chills to
be pretty brief and not linger for too long into early Tuesday.
Temperatures will be tricky, but decided to lower the more
sheltered valleys, west of the I-25 corridor, into the -20 to
-25 below range. Ensembles spreads and MOS guidance continue to
trend colder in these areas. Further east, expect low
temperatures between -10 to -15f. There is a chance that these
forecast lows are a little too conservative, but expect westerly
winds to pick up over night. Low temperatures along the I-25
corridor will likely be met in the late evening hours and should
increase after midnight.

As we head into Tuesday and Wednesday, models all show a
transitive upper level ridge axis quickly moving into the area
and ejecting east Tuesday evening. Surface pressure tendencies
will likely become negative across the plains ahead of the next
clipper system to the north. A closer look at the 700mb level
shows increasing low level subsidence and strengthening surface
gradients/700mb winds over the spine of the Laramie Range and
areas to the west. There is a good chance of another wind event
for at least the wind prone areas of southeast Wyoming starting
on Tuesday. These winds should linger through Tuesday night and
into early Wednesday morning. In-house wind guidance shows very
favorable conditions for the wind prone areas with probabilities
on the order of 80% to 95%. The sub-wind prone areas are not as
clear at this time since the peak subsidence is not colocated
with the peak winds...and the peak 700mb winds are mainly across
the mountains or on the lee-side. Some mountain wave activity is
expected, so will continue to monitor. For now, increase winds
above High Wind criteria for Arlington, Bordeaux, and the I-80
Summit/foothills. Even without the strong winds, most areas will
see slowly increasing temperatures for Tuesday and Wednesday as
the arctic airmass ejects eastward while downslope winds will
result in increasing 850mb to 700mb temps each day.

For later next week, all models in better agreement showing a
steady warming trend with Friday likely being the warmest day as
700mb temperatures briefly climb above zero. However, this may
be short-lived as all model guidance is showing another strong
cold front digging southward out of Canada by next weekend,
bringing more snow and much colder temperatures to the region.

&&

.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 this evening to 11 AM MST
     Tuesday for WYZ101-102-106>110-115>119.
     Winter Weather Advisory until 5 AM MST early this morning for
     WYZ103-104-110-114-116-117.
NE...Cold Weather Advisory from 8 PM this evening to 11 AM MST
     Tuesday for NEZ002-003-019>021-054-055-095-096.

&&

$$

SHORT TERM...AM
LONG TERM...TJT
AVIATION...RUBIN