955 
FXUS65 KBOU 170547
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1147 PM MDT Wed Sep 16 2026

.KEY MESSAGES...

- Unsettled pattern rest of this week. Tonight, Thursday, Friday,
  and Saturday all look fairly active. Locally heavy rainfall 
  will be the greatest threat. 

- Temperatures warm through Friday, then settle back closer to or
  slightly below seasonal normals this weekend. 

- Trend toward drier weather by early next week.

&&

.DISCUSSION /Through Wednesday/...
Issued at 128 PM MDT Wed Sep 16 2026

Water vapor satellite imagery shows a plume of moisture traveling
north-northeast out of Mexico and across the Four Corners region.
DEN ACARS soundings indicate this moisture has yet to reach 
northeast Colorado with precipitable water values around 0.80 
(in). Moisture increases tonight and Thursday with ingredients 
becoming favorable for locally heavy rain. Precipitable water 
values grow to over 200% of normal, and above daily observed 
maximums (outside of climatology). 

There are two areas of numerous showers and thunderstorms at this
time across the southwest part of the country. One is over 
northwest Colorado/northeast Utah, associated with the right 
entrance region of the jet. A second area of numerous storms is 
over Arizona, triggered by a shortwave trough lifting northward 
from the eastern Pacific and Mexico.  Some of the showers and 
storms over northwest Colorado are creeping into north central 
Colorado bring a brief period of heavy rain and gusty winds. 
Additional showers and thunderstorms are expected to form over the
mountains and higher foothills this afternoon and early evening. 
It's still unclear how many showers and storms will spill onto the
urban corridor and nearby plains. Models and ACARS soundings show
little instability, so most of this initial convection is 
expected to dissipate as it leaves the higher terrain. Lift 
increases this evening and tonight as a shortwave trough over 
Desert Southwest moves into the Central Rockies. Scattered showers
and thunderstorms are expected to lift northward over night and 
into Thursday morning due to lift from the shortwave. The 
shortwave trough continues northward, bringing numerous showers 
and thunderstorms to southeast Wyoming, western Nebraska and 
possibly far northern Colorado early Thursday afternoon. Even 
though the shortwave trough will be north of the state Thursday 
afternoon, a surface low with a warm front like feature may 
promote storm development Thursday afternoon. The boundary is 
expected to run roughly from Loveland to Greeley to Akron. Because
of the very moist airmass, heavy rainfall and localized flooding 
will be the main concern with the thunderstorms Thursday.

Southwest flow aloft will prevail Friday and Saturday around the 
upper level low off to our northwest while ridging remains to the 
southeast. The airmass stays very moist with precipitable water 
values of 160-220% of normal. Scattered afternoon/evening showers 
and thunderstorms are expected both days. Saturday looks slightly 
better for precipitation chances as the upper level low will be 
closer (offering better lift), and instability will be greater. 
Temperatures are expected to top out in the upper 70s to mid 80s 
with Friday being a little warmer. 

The upper level low tracks eastward across Wyoming on Sunday. 
With troughiness over eastern Colorado, enough moisture is 
expected to hang on for a round of showers and thunderstorms.  A 
northwest flow aloft will bring cooler air into the state with 
highs expected to be in the 70s across northeast Colorado. Some 
60s will be possible across northern parts of the state if the low
takes a more southerly track and clouds persist most of the 
day.  

On Monday, the upper level low weakens and lifts northeast into 
the Great Lakes region. Meanwhile, a new upper level low moves 
onto the southern California coast. Ridging is expected to 
prevail between these systems over Colorado on Monday. This 
ridging could linger into Tuesday, depending on how much eastward 
progress the upper level low to the west makes. Temperatures will 
be seasonal under this pattern with highs in the mid 70s to low 
80s on Monday and Tuesday. Flow aloft across the Central and 
Southern Rockies is expected to back to the southwest or perhaps 
south ahead of the upper level low on Tuesday and Wednesday. This 
could send another surge of subtropical moisture northward. One 
would think dry conditions should prevail under the ridge Monday 
and maybe into Tuesday. Precipitable water values stay slightly 
above normal Monday and Tuesday, so we can't rule out isolated 
showers and thunderstorms, especially towards Tuesday if we start 
to see another surge of subtropical moisture. Wednesday could hold
a better chance for showers and thunderstorms, but this will 
depend on the strength and track of the upper level low.

&&

.AVIATION /06Z TAFS through 06Z Friday/...
Issued at 1147 PM MDT Wed Sep 16 2026

Winds are attempting to settle from the S-SW, and for the most 
part rain showers were focused to the west and south of KDEN. 
Thus, a mostly S-SW component should remain in place. There hasn't
been too much outflow from these showers since the airmass is 
finally more moist and less DCAPE. We will keep a PROB30 of -SHRA  
through about 10Z as some showers are still coming up from the 
south. KBJC and areas west of I-25 should see a little better 
chance of showers overnight given current trajectories and a 
little easterly component still in place. 

Thursday afternoon will have higher chances for showers and storms
due to an increase in moisture and weak lift from a passing
weather disturbance. Due to the increase in moisture, if a
shower/storm moves directly across an airport visibility could be
briefly reduced to 1-2SM. The odds of that are low so we've only
gone with the TEMPO -TSRA for now, with gusty VRB winds to 30 kts,
of course. There is minimal DCAPE (~500 J/kg), but enough
environmental wind and potential precipitation loading for the
gusty outflow winds. That TEMPO will be for the highest
probability period of 21Z-01Z, but could be an hour or two later.  
Some model guidance keeps showers in the area as late as 04Z, 
prompting a PROB30 on the back end. Finally, regarding winds 
tomorrow, there is low confidence but for now we think we'll start
mostly VRB by around 14Z, transitioning to a SE or even S-SW wind
depending on arrival time of showers. Those should could be in 
the vicinity as early as 16Z. Post-convection winds look pretty 
messy at the time, but in this scenario they would favor a 
northeasterly backflow for a few hours before transitioning to 
normal S-SW again after 06Z with sufficient clearing.

&&

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

&&

$$

DISCUSSION...BM
AVIATION...20