855
FXUS65 KBOU 152129
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
229 PM MST Wed Jan 15 2025

.KEY MESSAGES...

- Dry through Thursday with warmer temperatures. Big change
  arrives Friday.

- Bitter cold temperatures late Saturday through Tuesday morning.
  The low temperatures Saturday, Sunday, and Monday nights will
  all likely (>60%) be below zero across our forecast area.
  Coldest day now pointing toward Monday with highs struggling
  above zero. Wind chill values as low as -30 F possible across
  portions of the I-25 corridor and eastern plains.

- Accumulating snow potential is high (>80%) for Friday night into
  Saturday. Highest totals likely in/near the foothills and I-25
  Corridor with a few inches expected. There is a growing chance
  (50-70%) that light snow redevelops late Sunday and through
  Sunday night.

&&

.SHORT TERM /Through Thursday/...
Issued at 228 PM MST Wed Jan 15 2025

Satellite shows mostly clear skies across the forecast area, with
only some cirrus skirting the north. Skies will remain mostly
clear with a very dry airmass in place through tomorrow. That
will allow for rather strong inversions to develop once again
tonight, especially in valley locations. A few of the colder
mountain valleys will likely drop to around -20F, while the
coldest spots on the plains will drop to around +10F. Most of
Denver and locations in/near the foothills will see a little
moderation and temperatures a few degrees warmer than last night,
due to the light downslope component in place and warm advection.

The warm advection continues through Thursday, with 700 mb
temperatures warming to +4C. That, along with downslope flow just
off the deck, means inversions will be weakening and allow for
"warm before the storm" type warmth with highs near 60F in metro
Denver, and a low probability (10-20%) we get closer to the
record for the day (64F set in 1923). Adjacent plains will be a
little cooler with slightly deeper inversions, while snow covered
areas should manage to get into the upper 40s - lower 50s. Winds
start to come up across the mountains and foothills during the
day, but get stronger by Thursday evening.

&&

.LONG TERM /Thursday night through Wednesday/...
Issued at 228 PM MST Wed Jan 15 2025

Colorado will be under the influence of a weak to moderate zonal
flow aloft Thursday night with model cross sections showing a
mountain wave developing on the lee of the Rockies. Consequently,
windy conditions are expected over the Front Range Mountains and
foothills with wind gusts to 65 mph possible. Some downslope flow
east of the mountains should result in somewhat mild temperatures
across the plains with lows ranging from the upper teens to the
lower 30s.

On Friday, there will be a drastic change in the weather as a strong
short wave and associated Arctic cold front dives out of the
Northern Rockies into Colorado. The morning should start out mild
with temperatures climbing into the upper 30s to mid 40s by late
morning on the plains with temperatures sharply falling during the
afternoon behind the passage of the cold front with snow developing
by evening

There is some uncertainty in how the front will progress across the
plains as well as the intensity of the snow associated with it. When
looking at model soundings, it appears the front may come in as a
couple of pieces with the first surge around noon bringing colder
temperatures during the early afternoon. The soundings suggest the
main Arctic front will arrive late in the afternoon with sharply
colder temperatures, gusty northeasterly winds and and snow along or
just behind it. With plenty of Frontogenic lift, a favorable
Dendritic growth profile and QG lift associated with 90KT+ upper
jet, wouldn`t be surprised to see some moderate snow bands
developing along or just behind the frontal passage.

If the front is a little early, the evening commute could be
impacted along the I-25 Urban Corridor. It`s also worth noting
that there is the potential for a flash freeze if the accumulating
snow melts and subsequently freezes with the arrival of significantly
colder temperatures. After the initial heavier snow bands, light
to occasional moderate snow is expected to continue through the
night. At this time, it`s looking like we could see 3 to 5 inches
of accumulation across the Front Range Urban Corridor, including
Metro Denver with 5 to 9 inches across Front Range Mountains and
Foothills through Saturday afternoon.

Snow is expected to end by Saturday evening as moisture and lift
decrease. However, with the Arctic airmass around can`t rule out a
few lingering light snow showers and flurries.

The models are showing a secondary surge of Arctic air along with
another round of light snow moving into the forecast area Sunday
night into Monday morning with an additional inch or so across the
Front Range Urban Corridor by Monday morning.

As for the temperatures, much below normal readings are expected
from Saturday through Tuesday morning. Due to model differences and
run to run discrepancies, there still is some uncertainty when we
will see the coldest temperatures across the forecast area. However,
confidence is increasing that Monday will be the coldest day of the
period with temperatures forecasted to only climb into the single
digits across most of the forecast area. Morning lows are expected
to drop below zero Sunday, Monday and Tuesday morning. With clearing
skies, light winds and fresh snow cover, temperatures could
plummet to -20 F across some plains locations east of Denver
Monday evening or Tuesday morning.

Warmer and drier conditions are expected on Tuesday due to some
downsloping flow and upper level ridging.

&&

.AVIATION /18Z TAFS through 18Z Thursday/...
Issued at 1029 AM MST Wed Jan 15 2025

VFR will prevail through the TAF period with only FEW high
clouds. Overall, a southerly wind component is expected to
prevail through the period, although some chance (30%) winds go
light and VRB 21Z-00Z, before returning to normal south/southwest
winds around 10-12 kts tonight. Those south/southwest winds should
then hold through at least 18Z-20Z Thursday. KBJC will see more
variable wind directions, but speeds under 10 kts through 18Z
Thursday.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SHORT TERM...Barjenbruch
LONG TERM...JK
AVIATION...Barjenbruch