853 
FXUS65 KBOU 121810
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1210 PM MDT Sat Sep 12 2026

.KEY MESSAGES...

- Slightly cooler today, then unseasonably warm along the Front
  Range and I-25 Corridor Sunday. Isolated showers and storms, but
  some uptick over the mountains Sunday. 

- Unsettled pattern next week, with cooler weather arriving by
  Tuesday. 

&&

.DISCUSSION /Through Friday/...
Issued at 223 AM MDT Sat Sep 12 2026

Cold front has pushed across northeast Colorado in these wee
morning hours. This will support cooler weather today, although 
high temperatures will still be near normal for this time of year.
A couple showers may linger over the northern plains early this 
morning, with redevelopment mainly over the mountains and Palmer 
Divide area this afternoon where airmass is less strongly capped. 
A few of these high based showers and storms could drift onto the 
adjacent plains as usual late in the afternoon/evening, but no 
significant precipitation is expected. 

We'll see low level moisture gradually return to the eastern
plains tonight, with areas of stratus likely developing 
along/east of a Limon to Sterling line. That does offer up some 
uncertainty for Sunday's high temperatures. Lee troughing indeed 
looks slow to develop, and thus the cooler and more moist boundary
layer conditions will likely persist more than most models 
advertise. While Denver and the I-25 Corridor is still shaping up
to be quite hot (lower 90s), somewhat cooler weather will likely 
hold over the eastern plains. While we've trimmed those 
temperatures from previous forecasts, further trimming is quite 
likely for the eastern plains due to the morning stratus and 
deeper moist boundary layer. Regarding convection, the mountains 
will see an uptick in convective coverage and intensity as another
monsoonal moisture plume pushes northeast into the state. 
Precipitable Water values increase to >150% of normal over the 
mountains, and thus a couple stronger storms could produce brief 
heavy rain. They will likely tend to weaken as they attempt to 
move off the higher terrain given locally drier airmass. At this 
time, the prospects of these tapping into the richer air over the
eastern plains also seems slim. 

For Monday, it still looks quite warm with more pronounced lee
troughing and downslope in west-southwest flow aloft. Regarding
convective potential, the plume of mid/upper level moisture shifts
across Colorado, but may end up being pushed too far south/east  
for higher shower/storm coverage. PoPs originating from model 
blends were still rather aggressive but wouldn't be surprised to 
see the higher coverage shift well southeast of the I-76 Corridor,
especially considering the eastward scouring of low level 
moisture ahead of the lee trough. 

Tuesday through Thursday is shaping up to have the highest
coverage of showers/storms for the week ahead. On Tuesday, the
monsoonal moisture plume is advertised to shift northward slightly
as an upper level trough digs into the western U.S. At the same
time, a more significant cold front will be pushing southward
across the plains, lending itself to a stronger low level upslope
component east of the Front Range. High temperatures are still
looking to cool into the 70s, with a 30-40% chance of highs 
holding below 70F on the plains. For Wednesday and Thursday, the 
forecast area would get into a more favorable location for weak 
synoptic scale lift as models are in better agreement with a weak 
shortwave lifting slowly east across the northern Great Basin into
Wyoming. We'll still need a weak front or two to help our upslope
in order to see higher shower/storm coverage, but trends have 
been in our favor here for light to locally moderate precipitation
amounts. Trends would then be for drier weather and near normal 
temperatures for later next week. 

&&

.AVIATION /18Z TAFS through 18Z Sunday/...
Issued at 1134 AM MDT Sat Sep 12 2026

Winds are beginning to settle into an easterly component across
the TAF sites early this afternoon. Expect wind speeds to see a
slight strengthening through the afternoon, but keep the easterly
component outside of any outflows or microbursts. Mid-level
moisture is expected to increase with showers and thunderstorms
already present across the higher elevations. This will increase
potential for afternoon/evening virga showers if things can hold
together coming off the higher terrain. A PROB30 has been
introduced to now include KDEN to account for this potential from
22Z to 1Z this afternoon. Microbursts/gusty outflows around 30kts
will be possible with any passing showers. Expecting winds to 
turn to the southeast then settle into drainage at KDEN/KAPA, with
KBJC remaining light and variable through the overnight hours. 

Slightly higher confidence in afternoon showers and maybe a weak
storm to pass across the TAF sites on Sunday. DCAPE looks slightly
more impressive and instability will be marginal for lightning
potential, but a PROB30 has been introduced at KDEN at 21Z, with
potential for a TEMPO to be considered for the evening hours in
the next TAF package. Gusts between 30-40kts will be possible with
any passing showers/storms Sunday afternoon/evening. 


&&

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

&&

$$

DISCUSSION...20
AVIATION...9