433
FXUS65 KBOU 221756
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1056 AM MST Fri Nov 22 2024

.KEY MESSAGES...

- Dry with well above normal temperatures through Saturday.

- Mountain snow and a rain and snow mix for the plains late
  Sunday into Monday morning.

- Mountain snow Tuesday through Thanksgiving morning, with
  widespread travel impacts likely.

- Snow may spread into the urban corridor and plains Tuesday
  night/Wednesday morning.

&&

.UPDATE...
Issued at 1056 AM MST Fri Nov 22 2024

Mountain wave clouds are winning.

This would be the second day in a row where our forecasted highs
were warmer than the observations. This morning, major changes to
decrease afternoon temperatures and increase the sky clover were
introduced. It is possible clouds could remain over the I-25
corridor and parts of the foothills through this evening. A few
spots outside of the cloud deck south of Denver are reporting mid
50s so there is a chance of parts of the urban corridor mainly
from Broomfield to south Denver to increase this afternoon.

&&

.SHORT TERM /Through Tonight/...
Issued at 136 AM MST Fri Nov 22 2024

Water vapor imagery shows anticyclonic flow within a ridge over
Colorado. There is a decent amount of high level moisture that is
streaming across northern Colorado and a large mountain wave cloud has
developed across the Front Range as a result. This high level
moisture and mountain wave will continue through the day today. As
a result, the high level mountain wave clouds will persist and
this may create a nice sunrise and sunset. In addition, it will
also keep high temperatures down a couple of degrees compared to
what they could be under sunny skies. Nonetheless, subsident flow
will allow for temperatures to warm well above normal today. Highs
will be in the 60s across the I-25 corridor and northeast plains
while the areas that have snowpack will stay around 50 degrees.
Otherwise, there will be light winds which will make for a
pleasant day.

Tonight, temperatures will be quite mild with lows potentially
staying in the 40s along the banana belt of the western I-25
corridor. The high clouds and dry conditions will continue.

&&

.LONG TERM /Saturday through Thursday/...
Issued at 136 AM MST Fri Nov 22 2024

Despite the upper-level ridge axis displacing eastward Saturday,
ample subsidence will remain in place, with compressional flow in
the lee of the Front Range making it the warmest day of the week
for the urban corridor and a large swath of the plains. Highs
will climb well into the 60`s in those areas, although high level
cloud cover will serve as a buffer to the warming. Tightening
surface pressure gradients will lead to an uptick in breezy
conditions across the higher terrain.

Westerly flow aloft becomes more prevalent Sunday as a shortwave
pushes across the northern plains. Zonal cross sections indicate
moistening low to mid-levels later in the day across the high
country, and a weak cold front traversing the lowlands in the
afternoon/evening. The bulk of the moisture will affect the
mountains, where favorable orographics will promote snow showers
through Monday morning leading to a few inches of snow
accumulation for the higher elevations. However, a period of snow
showers is also favored (70% chance) for the urban corridor
Sunday night into early Monday morning as low-level moisture, cold
air, and shallow upslope flow converge. Any accumulations would
be light and under an inch for most locations.

A lull in activity can be expected much of the day Monday as
transient ridging sneaks into the region, although there`s enough
uncertainty in timing between the successive systems to sustain at
least a slight chance of snow showers in the high country through
the period. Regardless, Monday will be cooler in the post-frontal
regime, with temperatures holding in the 30`s for mountain
communities, and 40`s for the lower elevations.

Precipitation potential ramps back up Tuesday in the high country
as a deeper trough advances into the Intermountain West,
reinvigorating the westerly flow and advecting better moisture
into the region, so travelers can expect deteriorating conditions
for mountain roadways, especially later in the day. Subsidence
east of the Rockies will keep the lower elevations mostly dry and
slightly milder compared to Monday.

The overall picture for Wednesday remains largely unchanged since
24 hours ago. Ensembles support the trough dipping southeast as an
open wave, with a much deeper saturated layer in place and the
development of more impactful snowfall across the higher terrain.
Clusters still differ in terms of the trough amplitude and
position, but these variations are more relevant to low elevation
winter weather potential, as any of the favored scenarios would
support a healthy mountain snow event, albeit with different
degrees of impact. Between 60-80% of ensemble members favor
precipitation extending into the plains and urban corridor, with
QPF ranges remaining quite significant, which is not surprising
considering we`re still 5 days out. Deterministic runs will
assuredly tiptoe around over the next couple of days, so patience
and monitoring of ensemble trends will be the name of the game.

The potential for the trough to slow and precipitation to linger
into Thanksgiving does appear to be dwindling however, especially
outside of mountainous terrain, with a better defined
precipitation window beginning to show up in ensemble guidance.
The probability of precipitation Thursday afternoon is thus less
than 15% for the lower elevations, although chilly conditions
remain favored.

&&

.AVIATION /18Z TAFS through 18Z Saturday/...
Issued at 1056 AM MST Fri Nov 22 2024

VFR conditions are expected this TAF period. Southeasterly wind
are possible this afternoon through this evening due to cyclone
development not occur. This might be due to snow cover ground
south of the terminals and mountain wave cloud cover. Wind speeds
remain between 8-10kts through the TAF period. Typical drainage
winds are possible overnight tonight for all sites. There is some
uncertainty in wind direction Saturday but there is potential for
northerly winds at all terminals by the afternoon hours due to
wind boundaries.

&&

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

&&

$$

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