824
FXUS65 KBOU 090614
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1114 PM MST Fri Nov 8 2024

.KEY MESSAGES...

- An ongoing winter storm is generating heavy snowfall across much
  of northeast and north central Colorado through Saturday
  morning. Heavy snow will fall from the eastern foothills west of
  Denver/Boulder, south and east to the east central Plains.

- Very difficult and hazardous winter driving conditions are
  expected for much of northeast and north central Colorado,
  including the Urban Corridor.

- Warmer and drier weather returns on Sunday with a chance of snow
  returning to the high country on Tuesday. Windy Front Range
  Mountains and foothills Saturday night/Sunday morning and again
  Tuesday night into Wednesday.

&&

.UPDATE...
Issued at 825 PM MST Fri Nov 8 2024

Water vapor shows the upper level low over sern CO near the Kansas
border. The low is fcst to move almost due north with it over
swrn NE by 18z on Sat. QG analysis shows favorable ascent
overnight but decreasing by 12z. KFTG VWP shows winds are trending
to the NNE along the Urban Corridor. Radar loops continue to show
a concentrated band of moderate snow with some heavier snow along
and east of I-25 from the WY border southward to the Palmer
Divide. This activity appears to be getting locked in place with
lighter snowfall in and near the foothills. Meanwhile, across the
rest of the plains, activity continues to redevelop to the north
and west of the main low. Overall, the fcst for tonight, looks to
be mainly on track, although amounts in and near the foothills may
end up on the lower range of forecasted snow amounts.

On Sat, a deformation zone will be in place on the backside of the
upper level low as it moves into swrn NE by midday.  Thus, there
will likely be additional heavier snowfall lingering thru midday, to
the west of the main upper level low. Not exactly sure where it will
set up, but this could bring warning type amounts to portions of
Morgan and nern Weld counties before it decreases. Meanwhile, the HRRR
has this additional snowfall somewhat further west affecting
portions of the Denver metro area. Overall confidence in placement
of this activity is rather low, so will leave current highlights
as is.

&&

.SHORT TERM /Through Saturday/...
Issued at 156 PM MST Fri Nov 8 2024

GOES-16 water vapor shows an impressive storm system with a warm
conveyor belt advecting moisture all the way from Texas, wrapping
it around the center of the vorticity max into northeast
Colorado. The trough will lift north-northeast from it`s current
position over the OK Panhandle into eastern Nebraska by Saturday
evening. From this evening into the late morning hours tomorrow,
there are impressive sources of lift associated with the northwest
quadrant of the trough. First, strong QG lift will be in place
through late morning, but strongest this evening. Also maximized
this evening will be jet-induced lift, with strong diffluence
associated with a southeast to northwest-oriented 80 kt jet on
the east side of the trough. Deep upslope flow is in place with 20
kts out of the east from now through this evening. Winds at 700
turn to the NW overnight, and are fully and strongly northwest by
12Z. With the trough lifting into Nebraska, and winds going
northwest at 700, we feel snow rates will come down significantly
after midnight. However, snow won`t shut off entirely because
there is still a lot of lift associated with the TROWAL. That
seems to be the main forcing to keep snow going until late morning
across the area, but additional accumulations in the late morning
hours should be very light.

With the lifting trough to the north, snow should end first
across the hardest hit areas of Elbert and Lincoln Counties,
perhaps as soon as sunrise but for sure the snow should be light
in the early pre-dawn hours. Snow should end around midday across
the I-25 corridor and foothills to the east. There may be a few
instability snow or rain/snow mix showers Saturday afternoon in
the wake of the lifting trough, mainly north a Boulder to Fort
Morgan line. Accumulation from those showers will be minimal as
temperatures will be above freezing by then. The last place to see
a shutoff of the precip will be the northeast corner of colorado
near and northeast of Sterling. Lingering rain showers may go
until early afternoon before shutting off. It should be all rain
east of Sterling for this event. Temperatures on Saturday will
struggle to reach the 40s in most areas of the plains, though Fort
Collins eastward to Greeley and the northeast corner of Colorado
should reach the mid 40s. Elsewhere right around 40 deg is
expected.

In terms of amounts, 3-4 day totals exceeding 3 feet are likely
across eastern Elbert and Lincoln Counties. It may take a while to
clear all the roads just based on the heavy snow. Some blowing
and drifting snow is possible across east central Colorado but
mainly overnight with gusts 20-30 mph. Winds weaken out there by
Saturday afternoon which is good. Across the Palmer Divide,
another 7-14" is expected through tomorrow for totals over 2`.
The eastern foothills west of Denver/Boulder, and the metro
Denver/Boulder areas are slated for 5-14" through tomorrow.
Further north, temperatures are warmer and snowfall rates will be
a bit less, so advisories look okay for now with 2-6" possible
along and north of US-34. As before, there will be a tight
gradient in snow along the northern end. In terms of impacts: The
PM commute for pretty much everywhere south of US-34 is going to
be messy with heavy snow and accumulating snow/ice on the
roadways. Slow down, expect travel delays, and leave plenty of
room between you and the person in front of you.

The last thing to mention, which we haven`t even mentioned yet,
are the mountains and west slope. Light snow is expected across
the mountains and mountain valleys this evening and overnight.
Minor travel issues are expected across the main mountain travel
arteries west of the Divide. However, snowfall will pick up
Saturday afternoon as moist, west upslope flow returns when the
trough reaches central Nebraska. 1-5" with isolated higher
amounts should fall across the northern mountains through the
evening hours.

&&

.LONG TERM /Saturday night through Friday/...
Issued at 156 PM MST Fri Nov 8 2024

Saturday night the large upper low that brought all the snow to
eastern Colorado will have moved into the Upper Midwest with drier
conditions across the CWA. There may be just enough lingering
moisture to produce a few light snow showers over the high country,
mainly over the higher peaks. Cross sections are showing a mountain
wave setting up with wind gusts to 60 mph over the Front Range
Mountains and foothills late Saturday night into Sunday morning.

Warmer and drier weather is expected Sunday and Monday as upper
level high pressure builds over the state.

By Tuesday, we start seeing some differences between the models. The
GFS is showing a weak upper trough moving across the Northern and
Central Rockies, while the majority of the models have a deeper
trough moving across the forecast area. The GFS solution lacks
moisture and would result in little to no precipitation across the
mountains. On the other hand, some of the other models have more
moisture and quite a bit of QG lift which lends to a better chance
for snowfall across the high country with scattered showers possible
across the plains. At this time, will go with the NBM model blend
which seems like a reasonable compromise. We also could see
another mountain wave forming along the lee of the Rockies Tuesday
night into Wednesday with windy conditions across the higher
Front Range Mountains and foothills. This pattern could also
produce breezy conditions across portions of the plains as well.

Dry weather and above normal temperatures are expected for Thursday
and Friday as upper level high pressure builds over the Rocky
Mountain Region.

&&

.AVIATION /06Z TAFS through 06Z Sunday/...
Issued at 1053 PM MST Fri Nov 8 2024

Models keep the low ceilings in place, below BKN-OVC010 until
around 18Z at DIA. They keep snow around until around 21Z at DIA
with ceiling at or below 2SM through then.  For winds, models
keep NNW-erlies in place through at least 18Z Saturday. It all
seems reasonable.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until noon MST Saturday for COZ033>035-
038-042>044.

Winter Storm Warning until noon MST Saturday for COZ036-039>041-
045-049.

Winter Weather Advisory until 5 AM MST Saturday for COZ037.

Winter Storm Warning until 5 AM MST Saturday for COZ046-047.

&&

$$

UPDATE.......RPK
SHORT TERM...Schlatter
LONG TERM....JK
AVIATION.....RJK