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 dissipatedrecently 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

NWS BOU Office Area Forecast Discussion