205
FXUS65 KBOU 210022
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
522 PM MST Mon Jan 20 2025

.KEY MESSAGES...

- Bitter cold through Tuesday morning.

- For the plains, wind chills -15F to -25F tonight into early
  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 Tuesday/...
Issued at 332 PM MST Mon Jan 20 2025

Much drier air has spread across the area with dew points of 5 to
15 below on the plains and 15 to 30 below in the mountains. The
only thing to stop the temperatures from plummeting this evening
will be winds. The winds over the northeast corner will diminish
this evening, then start to increase out of the southwest by
morning. For the Denver area, the current light winds will persist
through early evening, but will shift to southwesterly which will
begin a weak downsloping which will then increase as the night
goes on. Temperatures should drop sharply in the areas with light
winds in the first few hours of the night, more slowly over the
northeast corner. For Denver, lows will likely be this evening
with rising temperatures later tonight, perhaps to as warm as it
is this afternoon. Areas further east will likely have steady
temperatures or a little rise later in the night. For low lying
areas like the broader South Platte River valley north of Denver
including Greeley, Fort Collins, Longmont, and Fort Morgan, the
winds will stay light and there will be maximum conditions for
radiational cooling. We`re forecasting lows in the minus teens for
these areas, and the coldest spots may drop a little lower than
that.

Meanwhile, the higher mountains will have wind overnight. They are
quite cold now (mostly minus teens) but probably won`t get much
colder. As the winds spread down into the foothills, those areas
will warm up a bit and the foothills will be the warmest place
which is why they are not in the advisory or warning. The mountain
valleys will have excellent cooling all night, and they`re
starting cold with temperatures around zero. There`s also already
dry air, so there won`t be much energy absorbed in forming frost,
it`ll all be going to space. Spots that are zero now with a minus
20 dew point will probably have lows in the minus 30s, and the
coldest spots could be -40.

On Tuesday, most places should warm up pretty quickly as strong
warming aloft will mix down. Current forecast has most lower
elevations getting above freezing, then the snow cover will limit
further warming but places near the mountains could poke into the
lower 40s. Wind sheltered cold pool areas will lag behind, and
some of the mountain valleys could be much colder. We`re looking
for teens in Grand County, but that could be optimistic. Winds
will gradually increase over the Front Range, getting pretty windy
with 40 to 60 mph gusts in the foothills and some 30-40 mph gusts
along the base of the mountains by the end of the day.

&&

.LONG TERM /Tuesday night through Monday/...
Issued at 332 PM MST Mon Jan 20 2025

Gusty winds are expected Tuesday night as models are in agreement of
a mountain wave. The forecast Sangster model shows a 35% chance of
of wind gusts exceeding 70 mph overnight Tuesday. However, model
soundings are showing a weak inversion layer so confidence is low
that winds will reach high wind warning criteria. More likely places
just east of the foothills could see wind gusts up to 50 mph.
Regardless, blowing snow will be an issue through Tuesday night.

On Wednesday, we will be under northwest flow aloft as a trough
traverses the area. The low-pressure system, which will be situated
along the Nebraska/South Dakota border, will bring a cold front
through our area. The tightening of the pressure gradients from this
system will bring gusty northwest winds, up to 40 mph, for the
majority of the plains. Models don`t show much moisture in our area,
so no precipitation is expected with this system, except for a snow
shower in the mountains where orographics are favored. Temperatures
are still expected to be below normal, with highs in the mid 30`s
for most of the plains.

By Friday, a ridge will build over southern California, with the
axis oriented SW to NE. This will keep Colorado in a northwest flow
aloft again. By the afternoon, a trough will make its way south from
Canada, shifting our flow aloft to be more westerly. This will
allow warmer temperatures to enter our region. Friday is expected
to be our warmest day of the week where we will see seasonal
temperatures due to downslope flow.

As the trough dips south Friday night, flow aloft turns
southwesterly. Looking at the 700-mb winds, they shift from westerly
flow to more southwesterly. This will allow WAA to filter through
our area. At the surface, there will be northerly flow. With the
lift and some moisture, snow showers could persist through the day
Saturday and possibly into Sunday. As of right now, only a couple
of inches are expected. This system will bring our temperatures
down again, with Saturday`s high temperatures expected to be in
the 20`s for the plains.

Ensemble models show agreement that a positively-tilted trough will
split into two systems. The first system will travel south to
California and become a closed low. The second system will be a weak
trough to the northeast of Colorado. Weak southwest flow aloft will
prevail for the next couple of days due to the closed low sitting
over California. Monday will see a gradual warmup, although still
below normal temperatures.

&&

.AVIATION /00Z TAFS through 00Z Wednesday/...
Issued at 521 PM MST Mon Jan 20 2025

Models show normal drainage wind patterns tonight at DIA, maybe a
bit more southwesterly then usual. These winds are expected to
continue into the early afternoon hours of Tuesday. There will be
no ceiling issues at DIA.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Extreme Cold Warning until 9 AM MST Tuesday for COZ030>034-037.

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

&&

$$

SHORT TERM...Gimmestad
LONG TERM....Gimmestad/Ideker
AVIATION.....rjk

NWS BOU Office Area Forecast Discussion