093 
FXUS65 KBOU 132333
AFDBOU

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

.KEY MESSAGES...

- Isolated to scattered high-based showers and thunderstorms with
  gusty winds through this evening.

- 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 /00Z TAFS through 00Z Tuesday/...
Issued at 533 PM MDT Sun Sep 13 2026

Southeast winds will continue until interrupted by outflow from 
the scattered showers and isolated thunderstorms. If not, winds 
are expected to turn south to southwest during the late evening 
hours 03-06Z. Best time for the showers and gusty outflow winds 
will be 01-04Z, though we still can't rule out a thunderstorm 
(10-20% chance) as the HRRR shows. Instability remains limited 
though according to ACARS soundings and models. The threat for 
showers ends 05-06Z with southerly winds prevailing.

For Monday, an upper level is on track to produce weak showers
Monday morning, with the best time frame being 12-16Z. Aviation
impacts are expected to be minimal with ceilings above 6000 feet
and generally light winds. Confidence is low regarding the wind
direction after 16Z Monday. The HRRR model shows gusty west winds
up to 25 knots while most models show weak winds with different 
directions. West to northeast winds are expected after the showers
Monday morning, but the direction becomes unclear after 18Z when 
winds begin to turn and outflow from showers/storms begins. 
Scattered showers and a slight chance for thunderstorms begin 
around 21Z Monday. Gusty outflow winds up to 40 knots will be the 
main threat with the showers and thunderstorms.  

&&

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

&&

$$

DISCUSSION...AA
AVIATION...BM