080 
FXUS65 KBOU 131803
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1203 PM MDT Sun Sep 13 2026

.KEY MESSAGES...

- Unseasonably warm along the Front Range and I-25 Corridor today. 

- Isolated to scattered high-based showers and thunderstorms with
  gusty winds late this afternoon and 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 Saturday/...
Issued at 240 AM MDT Sun Sep 13 2026

Flat upper level ridging is building across the forecast area as
evident in the latest water vapor imagery, as well temporary 
drying aloft. Meanwhile, a low level moisture surge of 
moisture/cooling was originating from the convective complex in 
the eastern portions of Kansas and Oklahoma. 

With the ridging aloft, we'll be heating up again with plenty of 
sunshine. Summer-like heat is expected to return for the Front 
Range and I-25 Corridor, with highs in the metro areas reaching 
the 90-95 degree range. There is more uncertainty about warming 
farther east across the eastern plains, given the weak surge noted
at the present time and also lack of lee troughing. A lot of the 
details hinge on the convective evolution in the Central Plains, 
but we do see cooler temps (highs closer to 80F) over the far 
northeast corner. With regard to convection, we do expect a late 
day/evening surge of mid/upper level moisture approaching from the
Desert Southwest. Given we'll likely warm dry adiabatically to 
550 mb and DCAPE increases to nearly 1500 J/kg, the main threat 
from any showers and storms late this afternoon and evening would 
be gusty microbursts. Peak winds could easily reach 50 mph given 
the DCAPE. We'll continue with the low PoPs in the forecast (very 
light rainfall) and added gusty winds as an attribute. 

Mid and upper level monsoonal moisture will continue to increase
late tonight through Monday morning, which will keep a chance of
showers in the forecast. By Monday afternoon, the deepest plume
shifts to areas southeast of I-76. At the same time, mid level
cloud cover could also limit daytime heating (still very warm!), 
and keep a weak cap in place for the afternoon. Thus, the 
development of afternoon storms may be limited to the mountains 
and Palmer Divide area. We do get into the right entrance region 
of an upper level jet, so that could help carry some convection 
east/northeast across the I-25 Corridor and plains through Monday 
evening. 

A stronger cold front is still on track to arrive Monday night,
ushering in much cooler weather for Tuesday. Guidance continues to
slowly slip for high temperatures, although we still think they 
may be too warm. While deterministic forecasts still lie in the
lower to mid 70s for the plains, forecast experience would 
suggest many locations of the plains would more likely (>60% 
chance) stay in the upper 60s. Of course this will depend heavily
on extent of post-frontal stratus. That cooling also means we'll 
be struggling to produce much instability, and any of that would 
have to come from the mid levels and/or convective initiation over
the mountains. Overall the chances of precipitation have 
decreased somewhat as the best plume of monsoonal moisture is now 
expected to stay to our south.

That may change as we head closer to Wednesday but more likely
Thursday or even Friday. Guidance suggests a slower approach of
the next trough moving across the northern Great Basin and Central
Rockies. In fact, this leads to considerable uncertainty for the
forecasts later this week, with Thursday now trending to be the 
wettest day (as hinted to yesterday). However, that trough is 
slowing so perhaps we could see daily chances of showers and 
storms last into next weekend. 

&&

.AVIATION /18Z TAFS through 18Z Monday/...
Issued at 1203 PM MDT Sun Sep 13 2026

Light and variable winds are expected to turn southeast by 19-20Z
as a surface trough forms along the base of the foothills. We are
still on track for scattered showers and a slight chance (~10%) 
for a thunderstorm, mainly after 00Z. Given the warm and dry low 
levels and DCAPE of 1000-1500 J/kg, gusty outflow winds are 
likely. A wind shift to the west (possibly NW or SW depending on 
the convection's location) is expected to accompany the showers. A
gust up to 45 knots can't be ruled out, but there's a much better
chance for gusts to be in the 25 to 35 knot range. The threat for
showers ends 04-05Z.

For Monday, there will be a chance (30%) for showers during the 
morning. Ceilings are expected to be above 6000 feet and winds 
will be southwesterly. Confidence is low regarding the wind 
direction after 18Z Monday. The HRRR model shows gusty west winds 
up to 25 knots while most models show weak winds with different 
directions.  There will be another chance for showers Monday 
afternoon (after 21Z) with outflow winds being the main threat 
again.  

&&

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

&&

$$

DISCUSSION...20
AVIATION...BM