244
FXUS65 KBOU 162357
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
557 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 /00Z TAFS through 00Z Friday/...
Issued at 557 PM MDT Wed Sep 16 2026

A series of outflows from the north have kept winds more northerly
this afternoon and evening. Some variable gusty winds are still
possible, especially if showers continue to linger over the
foothills and Palmer Divide. Latest ACARS soundings show very little
instability around KDEN, so we don`t expect to see any organized
convection this evening over the airfield. Given the proximity of
current storms to KAPA, we`ve kept -TSRA in the PROB30 there, but
bumped down to -SHRA for KDEN and KBJC. Storms/showers will be
possible tonight through around 10Z. After any outflows/gusts move
out of the area, winds should turn to drainage before becoming
variable in the early morning hours.

Tomorrow afternoon will have better chances for storms/showers
thanks to some more instability and plenty of moisture across the
area. We expect localized heavy rainfall to be the primary hazard
with tomorrow`s convection, with some gusty outflows possible.
Because of this, prevailing winds tomorrow afternoon will likely be
outflow-driven, and so there`s some uncertainty with regards to the
dominant direction. While most storms should pop up in the late
afternoon/early evening (21Z-01Z), some model guidance keeps showers
in the area as late as 04Z, prompting a PROB30 for the end of the
TAF period.

&&

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

&&

$$

DISCUSSION...BM
AVIATION...AGS

NWS BOU Office Area Forecast Discussion