836 
FXUS65 KBOU 240555
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1155 PM MDT Wed Sep 23 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 /06Z TAFS through 06Z Friday/...
Issued at 1153 PM MDT Wed Sep 23 2026

Rain showers have affected all three sites this evening with some 
rain showers still lingering south of KAPA at this hour. Expecting 
the bulk of any shower activity to stay near the Palmer Divide 
overnight. There is good model agreement of a push of monsoonal 
moisture between 9z and 12z, so have a PROB30 at KAPA for rain. This 
could also bring the potential for lowered visibility and cloud 
decks to ~4000 ft AGL at KAPA. There is a ~20% chance that KDEN 
has a shower during this period, but confidence is low in this 
scenario. Model guidance has backed off on any stratus development
potential tonight, but there is still a ~10% chance that stratus 
could develop.

Otherwise, winds will settle into drainage overnight and then turn 
to the northeast/east by the afternoon. More rain showers are 
possible Thursday 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 will remain low. 
Showers could linger a bit past 3z at KAPA and KBJC. Winds should 
then 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 are in relatively good 
agreement that the lowest 1-2 km of the atmosphere will be rather 
saturated. Winds look to turn to the north or northeast early on 
Friday morning introducing upslope flow to the area. The period of 
highest concern as it looks now is from about 9z to 13z on Friday
morning. For now, have included VCFG and ceilings to 5000 ft AGL 
at KDEN for this period. If confidence increases, there is the 
possibility for MVFR or IFR conditions due to visibility of 3 SM 
or less and/or ceilings less than 3000 ft AGL.

&&

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

&&

$$

DISCUSSION...AP
AVIATION...MV