915
FXUS65 KBOU 121133
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
533 AM 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 /12Z TAFS through 12Z Sunday/...
Issued at 533 AM MDT Sat Sep 12 2026

A patch of stratus near 3000 ft AGL had developed around KDEN and
KAPA, which could last until 14Z-15Z given weak upslope
component in place behind last night`s cold front. Then daytime
heating will burn off any lingering stratus. NE-E winds (nearly
VRB at KBJC and KAPA) are expected to trend more easterly
15Z-18Z.

Another round of virga showers will be possible this afternoon,
likely starting 21Z-22Z. Although conditions look slightly less
favorable than Friday, a few microbursts with gusty winds up to
30 kts cannot be ruled out, particularly near KAPA and KBJC so we
included a PROB30 at both of those TAF sites. Low enough threat
(20%) at KDEN to keep it out of the TAF for now. Otherwise, winds
will gradually turn more SE-S 00Z-06Z but could be gusty to ~20
kts due to outflows from greater probability of showers occurring
on the Palmer Divide. Winds eventually return to fairly normal
S-SW by 05Z-06Z Sunday. Any stratus after 06Z Sunday is expected
to stay over the eastern CO plains, so 10% chance of less at KDEN.

&&

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

&&

$$

DISCUSSION...20
AVIATION...20

NWS BOU Office Area Forecast Discussion