032
FXUS65 KBOU 080230
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
730 PM MST Fri Feb 7 2025

.KEY MESSAGES...

- Much cooler temperatures for Saturday behind a cold front
  passage overnight tonight.

- Snow will move across the mountains tonight, producing slippery
  high country roads into Saturday morning. A few light snow
  showers could spill onto the plains.

- Another round of mountain snow (light) Saturday night/Sunday,
  once again possibly spilling onto the plains.

- There will be two systems that bring widespread light snow to
  our area and cold temperatures late Monday into Tuesday morning
  and Tuesday night and into Wednesday.

&&

.UPDATE...
Issued at 724 PM MST Fri Feb 7 2025

As of this writing, our incoming cold front is sweeping through
the Cheyenne Area, with an imminent crossing into Colorado as it
marches ahead at a robust 35 mph or so. With some acceleration off
the Cheyenne Ridge, this should have the front traversing our
northern urban corridor through the next couple of hours before
reaching the Denver metro near or even a little before 10pm.

There is a lot of dry air ahead of it to erode, and not a huge
amount of moisture with it. That being said, low-level
frontogenesis looks very strong with and immediately following the
front and, with some northwest flow aloft, would suggest higher
potential for precipitation in the Denver area overnight than
currently advertised. Have therefore made targeted upward
adjustments to precipitation probabilities for areas with maximum
frontogenesis, which may allow to a dusting to half inch or so of
accumulation locally east of the mountains. Speaking of the
mountains, snow is ramping up on schedule and the forecast remains
on track, so no changes made there.

&&

.SHORT TERM /Through Saturday/...
Issued at 301 PM MST Fri Feb 7 2025

Current water vapor imagery shows dry conditions remain across the
plains of Colorado this afternoon as moisture is beginning to
increase to the north over Wyoming.  Downsloping winds have brought
widespread 60s to areas along the base of the foothills and adjacent
plains, making for a mild day for this first week of February.
Temperatures are expected to cool significantly tonight, especially
over the northeastern plains as a cold front slides south out of WY.
Looking at observations to the north, Casper, WY dropped 28 degrees
between 2pm and 3pm this afternoon as the aforementioned cold front
passed through. By its expected arrival time to northern Colorado
late tonight, we are expecting this to bring overnight lows down
into the teens across the northeastern plains, while downsloping
winds keep locations along the foothills and adjacent plains in the
20s and 30s.

On top of the cold front tonight, a 150-160kt jet-level speed max is
expected to push into northern Colorado, setting up directly over
the forecast area. Westerly flow aloft will increase as it
approaches, and Pacific moisture will make its way into the
mountains, which will induce some orographic snow showers. At the
500mb level, a shortwave will pass over the Rockies and QG ascent
will peak overnight. Frontogenesis is expected to be at its max
after midnight and persist into the morning. The heaviest snowfall
is expected first over the northern mountains this evening,
before shifting southward over the I-70 corridor after midnight.
We expect some impacts to this evenings commute for the northern
mountains including Rabbit Ears Pass, and some lingering slick
conditions for the morning ski traffic along the I-70 corridor.
Winter Weather Advisories are in effect from 5PM this evening
through 7AM Saturday for the northern mountains, where we are
expecting 6 to 12 inches with some locally higher amounts.
Additionally, for RMNP and the Medicine Bow Range where 4 to 10
inches are expected with some locally higher amounts. From 9PM
tonight through 7AM Saturday another Advisory will be in place for
the mountains of Summit County, the Mosquito Range, and the
Indian Peaks where 4 to 10 inches with some
locally higher amounts are also expected.

While the main impacts are expected in the mountains, with the cold
front and frontogenesis in place, there could be some snow bands
that setup over portions of the plains late tonight into early
tomorrow morning. PoPs were adjusted upwards for this reason in
this forecast package, mainly along the I-25 corridor and east to
DIA.

Temperatures will be  much cooler tomorrow behind the front, with
30s expected across the plains. Downsloping winds will keep
temperatures milder along the base of the foothills and west of I-
25, where we might make it into the 40s. Snow showers will
diminish through the morning and clearing skies are expected for
a few hours in the afternoon ahead of our next approaching system.

&&

.LONG TERM /Saturday night through Friday/...
Issued at 301 PM MST Fri Feb 7 2025

The long term period will be very active with a series of shortwave
troughs moving right over Colorado. With that being said, each
shortwave will pass by so quickly that they will not have time to
deepen and create more substantial low pressure systems.
Therefore, each wave will bring light precipitation.

The first shortwave during the long term period will move over
Colorado Saturday night into Sunday morning. It will begin as a
slight trough at 500 mb and will end up as zonal flow by midday
Sunday so the forcing with this system will be very weak. There will
be some Pacific moisture that may bring 1-4" of snow the western
slopes of the mountains, mainly the I-70 corridor. There will be a
short period where warm air advection along with 700 mb
frontogenesis will provide enough low level lift to create a
couple of bands of precipitation that may spread onto the plains.
But snow amounts will be less than an inch on the plains and the
snow will move out as quickly as it began. Nonetheless, the roads
could be a tad slick Sunday morning for those traveling about.

The next shortwave trough will move through Colorado on Monday night
and will be similar to the Saturday night/Sunday one. This wave will
be slightly stronger and snow will be more widespread. The warm
air advection at 700 mb will be decently strong but limited
moisture will mean snow amounts will generally remain light. The
mountains will likely see around 2-8" from this system and the
I-25 corridor and plains will likely be around 1-3".

The most amplified shortwave of the long term will move through
Tuesday night and into Wednesday. Widespread snow is expected once
again due to the combination of warm air advection and frontogenesis
around 700 mb. Looking at forecast soundings, the upslope flow will
be very weak and very shallow so there will not be much forcing from
that aspect. As a result, the snow`s intensity will be light and
similar amounts to the previous system are expected.

Wednesday night and Thursday will be dry before another system
brings ample Pacific moisture Thursday night through the
following weekend. Early indications are that the mountains may
see moderate to heavy snowfall during this period with very light
snow on the plains.

As for temperatures, the series of fronts will keep conditions on
the colder side. The coldest nights will be Tuesday night and
Wednesday night. Lows will drop to the single digits across the
plains each of those nights. The wind chill may be lower on Tuesday
night given that there will be more wind and wind chill values may
reach -15 F on the far eastern plains. On Wednesday night, the
fresh snow cover, light winds, and clear skies will allow
temperatures to get well below normal. There are quite a few
members of the ECMWF that take Denver below zero and this seems
reasonable. The low temperatures were decreased in the forecast
but kept just above 0 F.

&&

.AVIATION /00Z TAFS through 00Z Sunday/...
Issued at 434 PM MST Fri Feb 7 2025

For wind...difficult forecast for next few hrs at KDEN preceding
FROPA, but lean towards shift from NE to lighter ESE for 2-3 hrs
before FROPA brings NE wings 04-05Z with gusts near 20 kts. These
shouldn`t be too long lasting, with mostly NE/E flow prevailing in
the morning before SE winds becoming more prevalent in the
afternoon and evening.

All terminals will be VFR through at least 08Z. Trended fcst
towards increased moisture and lower CIGS, with 3-5 hr period
mainly 10-15Z where BKN025-030 will be possible, along with light
SN showers. Best potential for showers will be in vcnty of KDEN,
hence the TEMPO for occsnl reductions to ~6SM, although confidence
is low given initially dry low levels.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 7 AM MST Saturday for COZ031-033.

Winter Weather Advisory until 7 AM MST Saturday for COZ034.

&&

$$

UPDATE...Rodriguez
SHORT TERM...Bonner
LONG TERM...Danielson
AVIATION...Rodriguez