547 
FXUS65 KBOU 230039
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
639 PM MDT Tue Sep 22 2026

.KEY MESSAGES...

- Isolated to scattered showers/thunderstorms this afternoon and 
  evening. 

- 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 /00Z TAFS through 00Z Thursday/...
Issued at 638 PM MDT Tue Sep 22 2026

Scattered storms and showers have been popping up off the Palmer 
Divide and lingering in the vicinity of KAPA, producing heavy rain 
and lowering cloud ceilings as low as 5000ft. Given the lack of 
instability in the latest ACARS soundings and current radar 
observations show storms weakening as they move northward, we expect 
these storms to weaken as they approach KDEN; however, they could 
still drop cigs to ~6000ft and reduce visibility over the airfield 
as they pass. Additionally, storms approaching now are producing 
gusts up to 35kts. After storms pass, winds are expected to be 
variable and mainly outflow-driven until showers clear the area, 
which is expected to be around 03Z. 

Winds should then turn south overnight and become light and variable 
in the early morning, around 12Z. Clouds are expected to linger 
overnight, but ceilings should remain high enough for VFR to 
prevail. Tomorrow afternoon/evening brings with it another chance 
for scattered showers/storms. Current model guidance suggests most 
precipitation will occur after 00Z, though we could see some showers 
pop up starting around 22Z. There's still some uncertainty on this 
timing and we'll be updating the current PROB30 and TEMPO groups 
accordingly once we get a better idea of what tomorrow's instability 
and moisture will be. Outside of any variability from storms, winds 
should be predominantly easterly throughout the afternoon and 
evening. 


&&

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

&&

$$

DISCUSSION...Schnell/20
AVIATION...AGS