097
FXUS65 KBOU 201150
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
450 AM MST Mon Jan 20 2025

.KEY MESSAGES...

- Bitter cold through Tuesday morning.

- For the plains, wind chills of -15F to -25F this morning and
  again this evening through Tuesday morning.

- For the mountains and mountain valleys, the coldest conditions
  are expected tonight and Tuesday morning with wind chills
  falling to -35F to -45F.

- Windy with areas of blowing snow Tuesday and Tuesday night in
  the Front Range Mountains as well as in and near the foothills.

- Temperatures moderating somewhat through the rest of the week.

&&

.SHORT TERM /Through Tonight/...
Issued at 247 AM MST Mon Jan 20 2025

Radar shows weak dbz across much of our forecast area this
morning. Reflectivities have come down in the past hour or two
and snowfall rates seem to be less than a quarter inch per hour
now. The upper level shortwave trough that is moving through our
forecast area is currently providing QG ascent. But around 5-6 AM,
the axis of the trough will pass through and the QG ascent will
switch to subsidence. So snow showers will substantially degrease
in coverage after 6 AM and the majority of the area will see dry
conditions by the late morning. Drier air aloft will arrive by the
afternoon and the sun will come out across much of our forecast
area. Tonight is expected to be dry as well.

A surge of northerly winds around 2-3 AM brought in a wave of
colder temperatures from the north. Temperatures are just starting
to dip below zero across the plains. Meanwhile, there are
northerly winds up to 30 mph in spots that have produced wind
chills as low as 25 F below zero. Temperatures will fall to around
-4 to -7 F by sunrise this morning. There will not be much
 warming throughout the day today but with afternoon sunshine
 expected, highs should be between +4 to 8 F across the plains
 today.

Clear skies, a fresh snowpack, and light winds this evening will
allow temperatures to free fall. The usual cold spots like Greeley
and Limon could reach -16 F tonight. The Denver metro may see
temperatures reach -10 F this evening before drainage winds
develop. There will be ridging aloft that moves over Colorado
tonight with warm air advection and downslope winds across our
forecast area. These conditions will result in temperatures
increasing from the late evening through Tuesday morning so the
lows will likely occur before midnight. A Cold Weather Advisory
was kept in place since wind chills will reach -25 F.

Across the mountains and mountains valleys, temperatures will be
extremely cold tonight. The usual cold spots of Kremmling, Fraser,
and Antero Reservoir may reach -35 F. In the mountains, the added
elevation will make them more exposed to wind. The combination of
bitterly cold temperatures and winds gusting up to 45 mph will
create wind chills as low as -50 F. Therefore, an Extreme Cold
Warning was issued for the mountains and mountain valleys.

&&

.LONG TERM /Tuesday through Sunday/...
Issued at 247 AM MST Mon Jan 20 2025

Tuesday will start off chilly, but temperatures will be warming
at most locations by sunrise under strong warm air advection.
Though cold pools, especially the mountain valleys will be very
cold to start the day. Strong high pressure over the Great Basin
and lowering pressure across the Central Plains will bring west to
southwest winds, helping to scour out the very cold air. Highs
are expected to top freezing with mid to upper 30s across most of
northeast Colorado. With the help of downslope winds, some lower
40s will be possible in/near the base of the foothills. Where the
winds slide over the cold pools, expect much cooler temperatures
here. It`s looking quite windy on the east slopes of the Front
Range Mountains and Foothills Tuesday and Tuesday night with gusts
to 50 mph possible. Blowing snow may become an issue because of
these winds and recent snowfall.

On Wednesday, an upper level trough embedded in the north-
northwest flow aloft tracks across the area. This will bring gusty
northwest winds to the plains, as well as the foothills and
mountains. Temperatures will take a step back with highs in the
upper 20s to mid 30s. There`s not much moisture with this system,
but some light snow and/or flurries will be possible, mainly over
the mountains. On Thursday, north-northwest flow aloft continues,
which will keep temperatures below normal. Can`t rule out light
orographic snow showers over the mountains, but it should be dry
for nearly all of the area.

For Friday and this weekend, a westerly flow aloft will prevail
over the Central Rockies Friday ahead of a large upper level
trough pushing south out of Canada. Dry conditions are expected
Friday, and areas east of the mountains will be mild due to the
downslope flow. This is expected to be the warmest day of the week
with temperatures near normal (mid to upper 40s over northeast
Colorado). The upper level trough continues to track southward
Saturday. General model trend is to split this system in two. The
main trough eventually forms a closed low somewhere over the Great
Basin of perhaps as far west as California. The second piece of
this system end up being a weak trough passing over or east of
Colorado. There`s still a lot of uncertainty on how this system
eventually evolves. Model ensembles are in good agreement that
temperatures will cool below normal this week, but not bitterly
cold like this past weekend. They also tend to show a period of
light snow, most likely Friday night/Saturday.

&&

.AVIATION /12Z TAFS through 12Z Tuesday/...
Issued at 434 AM MST Mon Jan 20 2025

Radar reflectivities have decreased substantially this morning and
visibility at all three terminals has increased as a result.
Expect light snow with visibility between 3-5 SM through around
15Z this morning. In addition, ceilings will be in the 3,000-5,000
range. The QG forcing from a passing trough will turn to
subsidence in the afternoon. This will end snow and will clear out
ceilings around 19-20Z at all terminals with a return to VFR
conditions. These VFR conditions will continue through Tuesday
night with moderate drainage winds.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Extreme Cold Warning from 6 PM this evening to 9 AM MST Tuesday
for COZ030>034-037.

Cold Weather Advisory until 9 AM MST Tuesday for COZ038>051.

&&

$$

SHORT TERM...Danielson
LONG TERM...Meier
AVIATION...Danielson