483 
FXUS65 KBOU 151757
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1157 AM MDT Tue Sep 15 2026

.KEY MESSAGES...

- Cooler weather today. Limited shower and storm chances, mostly 
  over the higher terrain. 

- Unsettled pattern rest of this week, but still some uncertainty
  with regard to daily precipitation chances. Thursday looks like
  the highest opportunity of measurable rain (50-70%) and a 
  locally heavy rainfall threat. 

- Temperatures bounce back Wednesday, but then average near or
  even slightly below seasonal normals through next weekend. 

&&

.DISCUSSION /Through Monday/...
Issued at 228 AM MDT Tue Sep 15 2026

A cold front moved across the plains early this morning, which 
will bring a marked change to the weather. Cooler temperatures 
can be expected in all areas east of the Front Range mountains, 
with highs mostly in the upper 60s to lower 70s. There is still 
some uncertainty with the amount of cooling, as models vary 
considerably on the low level moisture and stratus potential. At 
this point, we do think we'll see at least areas of stratus this 
morning, with the highest concentration generally Denver and
Boulder to points south and southeast. Given the somewhat limited
extent, we do expect that to break up by late morning although 
mid level clouds could slow that dissipation and warming. As a 
result, we'll lean toward the cooler side of any short term 
guidance. With regard to shower and storm chances, a few showers 
and even a couple rumbles of thunder continues over the mountains 
early this morning. Those should gradually dissipate as we lose 
any upper level support (right entrance region of the upper jet). 
However, sufficient daytime heating over the mountains will allow 
scattered showers and a few storms to redevelop this afternoon. 
The plains will be much more stable, making it difficult for any 
showers drifting off the mountains to survive very far east onto 
the I-25 Corridor and adjacent plains.

For Wednesday, we'll see flat upper level ridging which will allow
temperatures to warm to above normal readings again (mid 80s for 
most of the plains). Instability will increase slightly, with a 
few hundred J/kg of MLCAPE. Most convective initiation will once 
again be over the mountains, but given improving thermodynamic 
profiles we should see eventual development and movement of 
scattered showers and storms into the I-25 Corridor and adjacent 
plains through the late afternoon and evening hours. Some of these
showers and storms will likely continue overnight given further 
moisture and mid level theta-e advection. 

Thursday is still shaping up to be a more active weather day. Two
reasons for this; Precipitable water values climbing to 200% of
normal and upper level support from a disturbance originating from
the northeastern tropical Pacific (currently near the southern 
tip of the Baja California peninsula, or vicinity of Cabo San 
Lucas). However, timing of this feature may be key in potential 
convective coverage and intensity, as too early of an arrival 
(like the GFS) could mean we'll just see scattered and lighter 
showers and a few storms. A later arrival during peak heating 
could mean more numerous showers and storms with locally heavy 
rainfall. While the EC and GEM are a little slower than the GFS, 
they could still be a bit on the early side. In any case, 
something to monitor over the next couple days as warm cloud 
depths are forecast to increase to 3,500-6,000 feet, fairly 
impressive for this time of year. 

The weather still looks fairly active into Friday. While there is
less moisture, there is still some upper level support due to a 
trough drifting slowly east across the Northern Rockies and
northern Great Basin. Timing is uncertain here, but appears
Saturday could still be quite active before drier weather more 
likely arrives late in the weekend. Temperatures will be holding 
near or even slightly below normal for this period. 

&&

.AVIATION /18Z TAFS through 18Z Wednesday/...
Issued at 1157 AM MDT Tue Sep 15 2026

Low clouds have dissipated recently dissipated and VFR conditions
are expected to prevail for the rest of the TAF period (thru
Wed). ACARS and forecast soundings show a strongly capped 
airmass. The chance a shower survives off the higher terrain and 
reaches DEN and APA is very low, therefore removed the PROB30 for 
showers. Kept the PROB30 for showers at BJC since it is closer to 
the foothills and mountains. Southeasterly winds will prevail this
afternoon and a Denver Cyclone is expected to form. Models show 
the cyclone tracking north of DEN and APA, which would cause 
southeast winds to shift to the southwest this evening. Cross 
sections show a good amount of mid and high cloud cover for 
tonight and Wednesday with ceilings expected to stay above 6000 
feet. Models do not show this, but if the Denver Cyclone tracks 
farther south than expected, northerly winds could pull in enough 
low-level moisture for low clouds towards 12Z Wednesday. A storm 
system moving out of the Desert Southwest will bring scattered to 
numerous showers and thunderstorms to the Central Rockies 
Wednesday afternoon, but the best chance for showers and 
thunderstorms in the Denver area is expected to be after 00Z 
Thursday.

&&

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

&&

$$

DISCUSSION...20
AVIATION...BM