899
FXUS65 KBOU 140544
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1144 PM MDT Sun Sep 13 2026

.KEY MESSAGES...

- Isolated to scattered showers overnight, along with a couple
  thunderstorms in the mountains.

- Unsettled pattern this week, but plenty of uncertainty with
  regard to daily precipitation chances.

- Cooler weather arriving for Tuesday. Temperatures average around
  seasonal normals for latter half of the week.

&&

.DISCUSSION /Through Sunday/...
Issued at 252 PM MDT Sun Sep 13 2026

It is mostly sunny across the low elevations of Colorado, and
consequently, much warmer that it was around this time yesterday
with temperature readings at Denver International Airport in the
low 90s. Cloud cover is increasing over the mountains, and a few
showers have already developed over the Park and Front Range. Weak
upper level ridging moving onto the Northern Plains has begun to
turn flow aloft a tad more southwesterly, which will help advect
monsoonal moisture into the region. For the rest of the afternoon
and evening, scattered showers and thunderstorms will be able to
produce gusty winds up to 40-50 mph. The best dry microburst
potential will be over the Denver metro and I-25 corridor, where
hot afternoon temperatures (low 90s) and surface dewpoints in the
40s will yield DCAPE values 1200-1500 J/kg. Although we expect
shower activity over the plains to cease by around 9PM this
evening, multiple rounds of showers will continue over the
mountains in the overnight hours as mid-level moisture continues
to increase. A stray shower over the Denver metro cannot be ruled
out Monday morning. However, we do not expect this rainfall to
amount to more than a trace.

An upper-level trough will track through Montana through the
day on Monday, flattening out as it progresses east, and in turn
shifting upper-level flow to the west-southwest. Near cross-barrier
flow will make for a breezy day in the mountains, with sporadic
gusts up to 50 mph over the highest peaks and ridges. Weak
downsloping and daytime mixing may also lead to periods of gusty
westerly winds (20-30 mph) for the foothills and western Denver
metro. Another round of showers will be possible over the east
Colorado plains Monday afternoon, between 2pm and 7pm.

Uncertainty remains regarding how the synoptic pattern will evolve
this week, and thus, how the rainfall chances will play out each
day. A cold front will move through the region in the very early
morning hours of Tuesday, bringing cooler air and a layer of stratus
that will likely persist through most of the day. Temperatures on
Tuesday will be cooler than normal, with afternoon highs only
reaching into the 70s at low elevations, and 50s-60s for the
mountains. Moisture Tuesday afternoon now looks less promising than
it did yesterday due to slightly more zonal mid-level flow. However,
there will likely still be enough moisture around for scattered
showers over the high terrain and some isolated showers over the
plains.

Weak ridging returns on Wednesday and temperatures will be back to
near-seasonal. Although warmer temperatures will lead to better
instability for convective development, questions remain
regarding how much moisture will be available for the plains.
Therefore, the better shower chances will likely reside over the
mountains and Palmer Divide. Daily chances for precipitation now
appear to continue through the weekend. However, there is
considerable uncertainty regarding the development and timing of a
few shortwaves Friday through Sunday. Long-range ensembles are
trending drier for next week, although precipitable water means
will remain near the climatological average.

&&

.AVIATION /06Z TAFS through 06Z Tuesday/...
Issued at 1144 PM MDT Sun Sep 13 2026

One last surge of outflow winds had moved through KDEN, which
is a brief shift to W-NW and then VRB through 07Z, before
settling into fairly normal S-SW winds overnight.

For Monday, an upper level disturbance is on track to produce a
chance of weak showers in the morning, with the best time frame
being 12Z-16Z. Aviation impacts are expected to be minimal with
ceilings well above 6000 feet and generally light winds.Confidence
is low regarding the wind direction after 16Z Monday. The HRRR
model continues to show gusty west winds up to 25 knots while
most other models show weak winds with different directions. We
think west winds are likely (>70% chance) at least after the
passage of the weak disturbance Monday morning, but the direction
becomes unclear after 18-20Z. We may just end up VRB so we opted
for VRB in the afternoon for now. Also, while the chance of
showers is limited due to lack of instability, it will still be
quite warm with high DCAPE. As a result, we`ll keep the PROB30
with VRB G30kts in the TAFS for the 21Z-01Z period. Cold front
will arrive after 06Z Tuesday, which would bring a low threat (20%
chance) of stratus impacts for the Tuesday morning rush.

&&

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

&&

$$

DISCUSSION...AA
AVIATION...20

NWS BOU Office Area Forecast Discussion