568
FXUS65 KBOU 241140
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
540 AM MDT Thu Sep 24 2026

.KEY MESSAGES...

- Additional rain chances Thursday and Friday (30-70%) and cooler
  temperatures for Thursday afternoon.

- Drier and warmer this weekend before an upper level trough
  brings cooler temperatures and potentially our next chances for
  showers/storms early next week.

- Medium chance (30% to 50%) for mountain snow above 10,000ft
  late Monday into Tuesday.

&&

.DISCUSSION /Through Wednesday/...
Issued at 1105 PM MDT Wed Sep 23 2026

As of 11:30pm, showers are moving northeast through our far
eastern counties. Scattered showers will continue in the eastern
plains through much of the overnight period. Rain should
generally remain light, with no hazards expected.

A surface low is forecast to develop to our southeast on Thursday,
turning surface winds more northerly in the morning and easterly by
the afternoon. PWs will decrease slightly as the turning of winds no
longer allows Gulf moisture to stream into the area at lower levels.
However, the more easterly winds will allow for upslope for much of
the afternoon and evening on Thursday. Showers and an isolated storm
or two are expected to form over the higher terrain, starting in
the southern Front Range foothills and Palmer Divide in the mid
afternoon. Rain chances will then move into northern mountains
and foothills later in the evening and early overnight period as
winds turn more southeasterly. PWs will remain around 140% to 190%
of normal and storm motions will be pretty slow (10 to 15kts), so
some localized heavy rainfall and flash flooding will be possible
in the late afternoon and evening.

On Friday, a shortwave will approach the area providing some upper
level lift and scattered showers and storms. PWs will remain high
(around 150% to 175% of normal), but storm motions are forecast to
be faster than Thursday, leading to slightly lower flash flooding
concerns. Models have rain chances increasing in the higher
terrain for the early afternoon, with the rain chances pushing
east throughout the afternoon and early evening.

The shortwave will move off to the east early Saturday, with upper
level ridging building on the backside of the shortwave for the
weekend. At the surface, a boundary looks to move through early
Saturday, turning winds more westerly. These winds will bring drier
and warmer downsloping air into the urban corridor and plains,
dropping PWs and increasing highs back above normal for the weekend.
Rain chances will decrease significantly behind this boundary and
highs will reach into the low to mid 80s for much of the plains.

Things start to get more interesting for the start of next week as a
trough approaches the area. There is still a lot of uncertainty with
this system, as some models have the trough digging south, with a
low developing near the Four Corners region. While other models
keep the trough more north, before it digs further south to our
east. The positioning and strength of the trough will have
significant impacts on the strength and timing of a cold front,
our precip chances, and temperatures for Monday through Wednesday.
Right now, models are showing a decent cold front moving through
the area sometime late Monday through early Tuesday. The
positioning of that trough will determine if we can pull those
colder temperatures aloft south behind the front. This has lead
to a pretty significant spread in temperatures between ensemble
members, with highs on Tuesday ranging anywhere from the low 50s
to near 70 (25th to 75th percentiles) for the plains. The
temperatures will have impacts on the snow chances in the higher
terrain as well. Areas above 10,000ft are currently sitting at a
20% to 40% chance for at least an inch of snow from late Monday
through late Tuesday. If we can get those colder temperatures and
better lift in our area, we could see those chances increase as we
get closer.

&&

.AVIATION /12Z TAFS through 12Z Friday/...
Issued at 535 AM MDT Thu Sep 24 2026

Rain showers have gradually upticked in coverage in the vicinity
of KAPA over the last 90 minutes. Have kept a VCSH through 14z
this morning at KAPA. There is a ~10% chance that KDEN sees a rain
shower over the next hour or two.

Winds are light and variable across much of the area and will
eventually turn to the northeast/east by the afternoon. More rain
showers are possible this afternoon, so have PROB30s at all three
sites starting around 22z- when showers could move off the higher
terrain- and lasting through at least 2z. Instability is forecast
to be rather low. Showers could linger a bit past 4z at KAPA and
KBJC. Winds should turn to drainage for a few hours after the
showers end.

The main focus then turns to the potential for fog/low stratus on
Friday morning. Models and BUFKIT soundings continue to be in
relatively good agreement that the lowest 1-2 km of the atmosphere
will be rather saturated. Dewpoint depressions are forecast to be
< 1 degree at KBJC and KDEN. Winds look to turn to the north or
northeast early on Friday morning, introducing upslope flow to
the area with lowering ceilings/VCFG. The period of highest
concern as it looks now is from about 11z to 14z on Friday
morning. There is now enough confidence to introduce a TEMPO at
KDEN and KBJC. Visibility could drop to 1/2 SM or less at KDEN and
KBJC for this period if the fog potential were to be realized. At
KAPA, the majority of guidance does not turn winds fully to the
north, so the fog potential is lower there. Have included some
ceilings around 4000 ft AGL given the saturated environment.

Once any fog and/or low clouds erode around 15z Friday, winds
will turn to the southeast ahead of another potential afternoon of
showers/t-storms.

&&

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

&&

$$

DISCUSSION...AP
AVIATION...MV

NWS BOU Office Area Forecast Discussion