453
FXUS65 KBOU 220257
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
757 PM MST Thu Nov 21 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.

- Periods of mountain snow next week. Likely impacting travel
  Tuesday through Thanksgiving morning. Snow may spread onto the
  urban corridor and eastern plains as well Wednesday.

&&

.UPDATE...
Issued at 754 PM MST Thu Nov 21 2024

Only minor changes to the forecast at this hour. There`s some
cirrus in addition to the wave cloud, and we`ve upped the cloud
cover a bit. Less wind than the last few nights. Nudged tonight`s
lows down just a little in most places, but warmer in the areas
that still have wind, mainly mountain ridges and the foothills.

&&

.SHORT TERM /Through Friday/...
Issued at 220 PM MST Thu Nov 21 2024

Weak northwesterly winds continue aloft under the upper level
ridge across northeastern Colorado. GOES-18 West GeoColor shows a
few mountain wave clouds over the urban corridor which has lead to
a slight delay in warming but overall, afternoon temperatures
were decreased. Snow packed areas across the plains will be
slightly cooler. Overall, light winds are expected tonight with a
few clouds along the foothills and mountains. Temperatures drop
the single digits and upper teens for the higher elevations. Low
temperatures for the plains drop to the mid 20s to mid 30s. Dry
conditions and light winds continue Friday. With cloud cover
mainly west of the Divide, afternoon temperatures for the plains
could reach the lower 60s.

&&

.LONG TERM /Friday night through Thursday/...
Issued at 220 PM MST Thu Nov 21 2024

Southwest flow aloft to increase through Saturday as the ridging
that was over the region moves off to the east. There will be
enough moisture streaming in from the Pacific to produce high
clouds for most of the day. At the surface, a lee side trough
forms near the base of the foothills. This is expected to bring
breezy to windy conditions to the mountains and higher foothills.
Across the lower elevations, southerly flow is expected with it
turning eastward into the foothills. The airmass will be very warm
Saturday. Downslope off the Palmer Divide will push temperatures
well into the 60s with a few lower 70s possible. It will be
difficult elsewhere to maximize this warm air off the surface.
Cloud cover and easterly winds will limit heating with highs in
the upper 50s to mid 60s across most of the plains.

Flow aloft increases and slowly turns to the west Sunday. The
westerly flow is a better direction for orographic lift and
mountain snow. However, most of the snow (at least the heaviest)
is expected to be accompanied when the left exit region of a jet
moves over Sunday night. This may also bring rain and/or snow to
the Denver area and eastern plains Sunday night. As far as
temperatures go, easterly flow across the plains continues through
Saturday night and into Sunday with highs in the lower to mid 50s
expected. Over the higher terrain, the Pacific airmass will lead
to mild temperatures, possibly mild enough for rain in the valleys
through Sunday early evening.

For Monday through Wednesday, strong westerly aloft off the
Pacific will persist. This pattern will bring periods of mountain
snow. A lull or break in the snow is expected on Monday when the
subsident side of the jet passes over the region. Snow
returns/increases over the mountains Monday night. Expect a period
of heavier mountain snow sometime Tuesday/Wednesday when jet lift
returns. Models starting to agree an upper level trough holds
together as it crosses the Great Basin and Central Rockies Tuesday
and Wednesday. Still plenty of disagreement on timing and
strength, but generally enough agreement that we should see a
period of better snowfall with this as it moves across the
mountains Wednesday. If this system holds together as it tracks
across the Central Rockies, it likely brings snow to the Front
Range, Denver area, and eastern plains Wednesday/Wednesday night.
Roughly 80-90 percent of the ECMWF ensemble members show snow for
the Denver area with this system, while only 40-50 percent of the
GFS ensemble members have snow.

For Thanksgiving day, the upper level trough is expected to be
southeast of the region resulting in a cool and dry day. There
will be low PoPs in the forecast. This will be for the chance of
snow during the morning if this trough happens to slow. Highs are
expected to be in the mid 30s to lower 40s across northeast
Colorado. Though it could be cooler if there is widespread snow
cover across the area.

&&

.AVIATION /00Z TAFS through 00Z Saturday/...
Issued at 524 PM MST Thu Nov 21 2024

VFR through Friday. South winds under 12 knots at KDEN/KAPA
becoming light and variable by 18z Friday. Light winds at KBJC.

&&

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

&&

$$

UPDATE...Gimmestad
SHORT TERM...AD
LONG TERM...Meier
AVIATION...Gimmestad