477 
FXUS65 KBOU 241833
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1233 PM 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 /18Z TAFS through 18Z Friday/...
Issued at 1154 AM MDT Thu Sep 24 2026
 
Winds will turn north/northeast as the afternoon continues. 
Rain showers are possible this afternoon, so PROB030s will start
around 22z this afternoon. Isolated showers could linger past evening
hours (~4z), so some PROB30s may need extensions depending on 
convective development. Winds should turn to drainage tonight for
KAPA and KBJC, but some uncertainty remains for KDEN tonight as
most models favor a southeasterly direction (~150) with some
indicating more of a northeast flow. NAM and GFS MOS guidance
favors the southerly drainge flow (~170-210). Guidance also shows
a cyclone developing tonight, so wind directions could be changed
for tonight. Also in play is a TEMPO for fog/low stratus at KDEN 
and KBJC from ~11-15z. Dewpoint depressions are forecasted to be 
~1 or < 1 for KDEN and KBJC, but KAPA is not expected to get this 
potential. Visibility could drop to as low as 1/2 SM for KDEN and 
KBJC if the fog comes to fruition. 

Winds in the morning look to turn variable for KBJC and KAPA while
we wait for the lower ceilings to rise (~15z). Northeast flow will
settle in the afternoon for KBJC and southeast flow for KAPA. KDEN
may remain in a southeast flow. A PROB30 for -TSRA is in place 
Friday afternoon for Denver, (22z-03z), and will likely be 
introduced for the other sites in the next TAF amend. A TEMPO was
almost used considering a majority of the models are in good 
agreement for convective development tomorrow, but for now we 
stuck with the PROB30. Brief decrease in visibilities and gusty 
winds up to 35mph are possible. After 0z chances drop quickly as
the convection shift east, but isolated may chances may linger for
a few more hours. 


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

&&

$$

DISCUSSION...AP
AVIATION...Schnell