449
FXUS65 KGJT 191625
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
925 AM MST Sun Jan 19 2025

.KEY MESSAGES...

- A strong Arctic outbreak is expected this weekend into early
  next week across the central CONUS. The coldest air should
  remain east of the Divide but temperatures on this side are
  forecast to be well-below normal. Overnight lows have a high
  probability of dropping well-below zero in many mountain and
  high valley/basin areas.

- The Gunnison Basin and Upper Yampa River Basin stand the best
  chance to see very cold overnight temperatures through Tuesday
  morning. Cold Weather Advisories remain in place for these
  areas through Monday morning with an Excessive Cold Watch in
  place Monday night through Tuesday morning. In addition,
  added many western Colorado mountain areas and the Central
  Yampa River Basin to the Extreme Cold Watch Monday night due
  to wind chill readings of at least 35 below zero possible.

- Light snow will continue on and off again through Tuesday
  morning with this Arctic air mass in place in addition to a
  few weak shortwaves moving through with light accumulations
  possible over the mountains.

&&

.UPDATE...
Issued at 925 AM MST Sun Jan 19 2025

Updated to expire and cancel Cold Weather Advisories for the
upper Yampa River Basin and the Gunnison Valley this morning.
Temperatures, though still quite cold, have risen above
critical levels.

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 324 AM MST Sun Jan 19 2025

The very cold Arctic air mass is settling in over much of the
region as low temperatures early this morning are already down
to -20F in Craig and Gunnison with single digits to low teens in
many of the remaining lower valleys. A Cold Weather Advisory
remains in place for the Gunnison and Upper Yampa River Basin
where forecasted lows are expected to reach at least -25F. Some
high clouds are beginning to move in from the northwest, so that
may hinder lows from realizing the full potential. Regardless,
this is evidence that the Arctic air mass is in place and is
expected to remain there through Tuesday.

These high clouds are increasing ahead of another weak
shortwave expected to move through this afternoon on the western
fringe of this Arctic trough. There is some weak instability
and steep lapse rates that will contribute to some light, fluffy
snow (20:1 SLRs) but accumulations are expected to be minimal
with a couple inches or less possible over the mountains. A bit
more cloud cover tonight could hinder lows from being as cold,
but still anticipating the coldest temps in Gunnison Basin where
a Cold Weather Advisory remains in place tonight through Monday
morning with expected lows down to -25F as much of the cloud
cover and snow showers is expected to remain further north over
the northwest Colorado mountains. Very minimal moisture is
arriving with this shortwave and in this Arctic air mass that,
despite very cold temperatures with H7 temps down to -20C, is
resulting in minimal snow accumulations well below advisory
thresholds.

Much drier northerly flow pushes in Monday afternoon and
evening on the backside of this latest shortwave that may result
in a few light orographic snow showers over the Divide
mountains but mostly clearing skies overall. The clearing skies
will lend itself to the coldest night expected Monday night as
we feel the full effects of this Arctic air mass in place.
Therefore, expanded the Extreme Cold Watch to include many
western Colorado mountains and the Central Yampa River Basin for
Monday night based on apparent temperatures or wind chill
readings, which are forecasted to reach -35F to -40F. More
details on this in the Long Term section below.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Issued at 324 AM MST Sun Jan 19 2025

We continue to anticipate low temperatures to hit their lowest
during this cold spell overnight Monday into Tuesday as the
overhead Arctic airmass begins its departure from our CWA. For
its finale, strong cold air advection from near-northerly flow
will drop overnight lows to -10 to -25F for many higher valley
and mountain regions, with single digit lows (above and below
zero) for the lower valleys. This yields the most significant
impacts over the Upper Yampa River Basin and the Gunnison Valley
where forecasted overnight lows are around -30 to -40F. This
would be near record values. Wind chills over mountains will
also be as low as -35 to -40F. An Extreme Cold Watch has been
issued for most Colorado mountain zones as a result of these
extreme wind chill values. Stay indoors if possible. If you must
go outside, dress in layers as prolonged exposure to extremely
cold temperatures such as these may lead to hypothermia. Also
issued an Extreme Cold Watch for the Central Yampa River Basin
for Monday night due to wind chill values as low as -35F. An
Extreme Cold Watch remains in effect for Monday night for the
Gunnison and Upper Yampa River Basin based on forecasted actual
low temperatures alone.

While the Arctic air moves off to the East on Tuesday,
relieving us from these extreme lows, northwesterly flow doesn`t
appear to be so quick to leave. Chilly 700mb temperatures are
likely to continue moving through on Wednesday, keeping much of
the region 5 to 10 degrees below normal for another day or two.
To those wishing for a more stark warm-up, the bad news is that
heightened confidence among deterministic model guidance
indicates that a ridge building off the West Coast will
stubbornly remain there throughout the week. Upper-level flow
over us could push into a more zonal pattern on Friday though,
bringing the area back to near-normal temperatures. The forecast
loses clarity after that, so we will have to wait to see if
next weekend will offer us warmer conditions or not.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 443 AM MST Sun Jan 19 2025

High clouds are increasing from the northwest this morning and
will continue to do so along with mid level clouds this
afternoon, becoming SCT to BKN. Light snow showers remain
possible over the mountains and northwest Colorado valleys this
afternoon and evening. Conditions expected to remain VFR with
brief MVFR or ILS cigs reached at times.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Extreme Cold Watch from Monday evening through Tuesday morning
     for COZ002-005-014.
     Extreme Cold Watch from Monday evening through Tuesday morning
     for COZ004-009-010-012-013-018-019.
     Cold Weather Advisory from 10 PM this evening to 11 AM MST
     Monday for COZ014.
UT...None.

&&

$$

UPDATE...NL
SHORT TERM...MDA
LONG TERM...MDA/BW
AVIATION...TGJT