169 
FXUS65 KBOU 230610
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1210 AM MDT Wed Sep 23 2026

.KEY MESSAGES...

- A disturbance moves through Wednesday and Thursday bringing
  increased chances for showers/storms (40-70%) and cooler
  temperatures Thursday. 
 
- Drier and warmer this weekend, but isolated showers and
  thunderstorms each afternoon and evening can't be ruled out. 

&&

.DISCUSSION /Through Tuesday/...
Issued at 242 PM MDT Tue Sep 22 2026

Water vapor imagery shows moisture starting to advect into 
Southwestern Colorado associated with the disturbance in New 
Mexico/Southeast AZ. Showers and storms are currently developing in 
the higher terrain. With the influx of moisture in the southwest 
flow aloft, more showers/thunderstorms are expected this afternoon 
in the higher terrain. Isolated high-based showers/storms could 
drift off the foothills and track eastward into the I-25 corridor 
and Denver Metro (15-20% coverage), but scattered (25-35%) coverage 
on the Palmer Divide. The eastern plains may also have a 
shower/storm linger into the late evening. Models this afternoon 
indicate DCAPE values in the 1000-1100 range, so gusty winds up to 
~25-35 mph are possible with any showers/storms today. Forecast 
soundings indicate the urban corridor remains limited in 
instability, but MLCAPE is forecasted for 500-900 and MLCIN to be 
quite minimal in the eastern plains so an isolated strong storm is 
possible but quite low. High temperatures today will favor upper 70s 
and lower 80s. 

Deterministic and ensemble model guidance are in good agreement for 
precipitable waters to increase Wednesday afternoon/late evening 
bringing our highest moisture for the week. Additionally, models 
indicate a shortwave moving through around Wednesday evening into 
Thursday morning before transitioning out of our area rather quickly 
by Thursday evening. The right entrance region of a jet streak 
moving through in the afternoon should also provide some additional 
lift. PWATs are expected across the forecast area in the 1.0-1.3 
range with the highest values in the eastern and southern plains. 
More southerly flow in the eastern plains is modeled Wednesday 
afternoon advecting greater moisture into the area increasing 
dewpoints near 60F while the Denver metro should be in the upper 
50s. We still think the greatest chance for localized heavy rainfall 
will remain over the east Colorado plains. This will increase rain 
chances Wednesday afternoon (~30%) for the urban corridor before 
increasing further towards the evening near 50-60% for most of the 
night. We decided to increase chances for rain mostly for the 
eastern plains into Wednesday night and Thursday morning since model 
guidance favors the area. However, we are still concerned about 
abundant cloud cover limiting instability leading to much less storm 
coverage. 

By Thursday morning low-level moisture will peak and cloud cover 
will dominate much of the forecast area. Nonetheless a round of 
showers/storms is modeled to move through Thursday morning in the 
eastern plains (70-80%). Isolated storms could produce localized 
heavy rainfall as warm cloud depths increase to 4,000-6,000 feet. 
The urban corridor's chances remain slightly below the eastern 
plains while the higher terrain should see shower development. 
Temperatures will only reach the upper 60s with the aforementioned 
cloud cover. We will likely see a slight decrease in shower coverage 
in the afternoon, given the expected earlier passage of the 
shortwave and less remaining instability for the eastern plains. 

On Friday, another weak shortwave will move through Colorado 
promoting isolated to scattered showers/storms over the higher 
terrain. A few showers/storms could develop in the plains, but with 
the lack of moisture aloft and instability only isolated activity is 
expected at this time. Temperatures across most of the area will 
return to the upper 70s. Saturday and Sunday deterministic and 
ensemble guidance depicts much drier weather with temperatures in 
the lower 80s slightly above normal for this time of year. Monday 
and Tuesday deterministic models depict a upper level trough 
potentially cooling us back down Tuesday near 70, along with another 
chance of showers and storms.

&&

.AVIATION /06Z TAFS through 06Z Thursday/...
Issued at 1205 AM MDT Wed Sep 23 2026

A pretty busy TAF over the next 24-36 hours....Showers and some 
gusty winds have come off the foothills over the last 90 minutes. 
Some gusts to around 25 kts remain possible at all three sites 
through about the next hour. Winds have already turned to drainage
behind this activity and will continue as drainage or a bit more 
westerly through this morning. KBJC will remain light and 
variable after these showers pass through.

Winds will turn to southeast by the early afternoon with lowering
ceilings as the afternoon progresses and moisture continuing to 
increase. The latest CAMs have pushed up the timing for the onset 
of showers. Showers are possible as early as 19-21z at all three 
sites and then become increasingly likely for much of Wednesday 
evening and overnight into Thursday morning. Generally, Wednesday
early evening (~0z to 6z Thursday) appears to be the timing of 
the heaviest rainfall through this period at KAPA and KDEN and 
have covered this with tempo groups. KBJC has a lower chance for 
showers, so have kept a prob30 there. 

KAPA will likely see the bulk of the activity and thus could have
even further lowered visibility/ceilings than the other two 
sites. BKN/OVC ceilings as low as 4,000 ft AGL at KAPA and 5,000 
ft AGL at KDEN and KBJC are in play, particularly after 0z 
Thursday along with lowered visiblities at times. Regardless, we 
are increasingly confident of at least bkn070 ceilings from 
Wednesday evening onwards at all three sites.

Showers will continue across the area (in the vicinity of all
three sites) through the overnight with the latest CAMs hinting 
at more steady and widespread rainfall at/near KAPA past 6z 
Thursday. The prob30 and tempo groups will continue to be refined 
as we approach this period.

&&

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

&&

$$

DISCUSSION...Schnell/20
AVIATION...MV