214 
FXUS65 KBOU 161928
AFDBOU

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

.KEY MESSAGES...

- Unsettled pattern rest of this week. This afternoon/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 /18Z TAFS through 18Z Thursday/...
Issued at 1217 PM MDT Wed Sep 16 2026

Light, variable winds expected to continue for the next couple hours 
before settling in an east/northeast pattern for most of the 
afternoon. The main concern this evening and overnight will be the 
potential for showers/storms. Models are fairly consistent on rain 
chances starting around 23Z and lasting through at least 10Z across 
the area. While today's southwesterly flow aloft is dragging in 
plenty of monsoonal moisture, conditions in the low levels should 
remain stable throughout the afternoon, which will hinder any 
convective development. As such, we've opted to keep tonight's rain 
chances at a PROB30. Outside of any variability from showers/storms, 
winds overnight should stay at drainage before becoming variable 
starting around 15Z, followed by another east/northeast pattern for 
the morning and afternoon. 

Conditions are more favorable for thunderstorms/rain tomorrow, with 
above normal moisture and greater instability across the area 
expected. Following model guidance, we've started a TEMPO for -TSRA 
at 21Z and lasting through the end of the TAF period. Should current 
forecast/model trends continue as they have, we'll likely be 
extending that TEMPO through 01/02Z for KDEN at the next regular TAF 
update.

&&

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

&&

$$

DISCUSSION...BM
AVIATION...AGS