479
FXUS65 KBOU 050230
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
730 PM MST Wed Dec 4 2024

.KEY MESSAGES...

- Quiet pattern today through Saturday, with temperatures above
  normal. Exception is Middle Park with areas of fog, and possible
  patchy fog eastern plains late tonight and early Thursday.

- Pattern change late next weekend into early next week with
  colder temperatures and a chance of snow.

&&

.UPDATE...
Issued at 723 PM MST Wed Dec 4 2024

No significant updates to the forecast this evening. Weak cold
front is still dropping southward into Nebraska this evening, with
a narrow ribbon of mid-20s dew points extending from roughly
Chadron to Ogallala/North Platte. Still some potential for patchy
fog and maybe some low stratus, especially across Lincoln county.

Meanwhile, temps are quickly dropping across Middle Park, with a
handful of sites already in the single digits. Expect overnight
lows near zero, though a few of the known colder spots (Fraser
Flats, Harbison Meadow) will likely end up below zero again.
Another morning of fog/mist also expected there as well.

&&

.SHORT TERM /Through Thursday/...
Issued at 232 PM MST Wed Dec 4 2024

Quiet weather will persist through Thursday. However, there is a
weak backdoor cold front/surge which will push across the
northeast plains this evening. A brush of that could push back as
far west as DIA. That weak push will bring in slightly higher low
level moisture, with dewpoints currently in the mid 20s along a
weak moisture axis. Given a long night with lighter winds and
mostly clear skies, we`ll see strong radiational cooling and T/Td
crossover temperatures of a few degrees. Thus, there`s potential
for patchy fog development late tonight into Thursday morning.
We`ll mention that where the highest probabilities exist over
eastern Elbert, Lincoln, and Southeast Washington Counties.

For Thursday, a slightly cooler airmass will mostly hold with
shallow inversions over the plains. We`ll still see sunny skies
which will aid surface heating (once any patchy fog dissipates).
However, with little lee troughing temperatures will be a little
slower to respond than today. Thus, we`ve nudged down high
temperatures a few degrees east of the I-25 Corridor. Highs should
still be able to make it into the upper 40s to lower 50s for much
of the plains, and mid 50s for most of Denver metro. Mountain
areas will see little change from today, while inversions and late
night/morning fog remain a feature in the upper Colorado River
Valley/Middle Park.

&&

.LONG TERM /Thursday night through Wednesday/...
Issued at 232 PM MST Wed Dec 4 2024

Quiet weather is expected through Sunday as we are situated under a
ridge between two systems. Upper level analysis currently shows
northwest flow from the Polar jet that is in Canada. This will
turn into northeast flow by Saturday, as the upper level trough
to our southwest finally moves out by Sunday. Even though we have
conditions favorable for upslope flow, there is no moisture for
any precipitation. Temperatures are expected to be above normal
through Sunday.

A new upper level trough will develop in the northwest and move
eastward on Sunday. This will bring a cold front and precipitation
chances starting as early as Sunday evening for the mountains.
Breezy wind gusts up to 30 mph are expected in the northeast
Plains, where surface pressure gradients are tightest. Ensemble
forecasts have Monday being the greatest chance for precipitation
for the and Plains. 700-mb temperatures range between -12C to -13C
and QPF analysis shows enough moisture for a couple of inches of
snow due to some upsloping behind the cold front. However, there
is still some uncertainty on snow amount/duration of snowfall, as
the ECMWF shows a possibility of snow continuing to fall into
Tuesday, especially for the mountains. Regardless, most of the
ensembles are trending for a snow accumulation of 2" or less for
the Plains. Below normal temperatures are expected from Monday and
Tuesday.

&&

.AVIATION /00Z TAFS through 00Z Friday/...
Issued at 438 PM MST Wed Dec 4 2024

Fairly typical diurnal wind patterns will continue at the
terminals through Thursday with light speeds. VFR conditions are
likely at APA/BJC.

Main uncertainty is still with the potential for a brief period of
FG or low stratus behind a weak cold front tonight into Thursday
morning for DEN. Most guidance keeps this north of DEN, mainly in
Weld/Morgan counties, but this would largely be dependent on the
location of a weak Denver cyclone. Most BUFKIT profiles also favor
stratus over FG, but the signal there is hit or miss. Ultimately
opted for a few hours of a FEW003 for now and will continue to
wait out short-term model trends this evening.

&&

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

&&

$$

UPDATE...Hiris
SHORT TERM...Barjenbruch
LONG TERM...Ideker
AVIATION...Hiris