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 satelliteimagery 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
becomingfavorable for locally heavy rain. Precipitable water
values grow to over 200% ofnormal, and above daily observed
maximums (outside ofclimatology).

There are two areas of numerous showers and thunderstormsat 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 bringa 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 levellow 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 southernCalifornia coast. Ridging is expected to
prevailbetween 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

NWS BOU Office Area Forecast Discussion