553
FXUS65 KBOU 201942
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
142 PM MDT Sun Sep 20 2026

.KEY MESSAGES...

- A chance for thunderstorms this afternoon through tonight,
  mainly over the eastern plains. A fewstrong to severe storms
  are possible.

- Expect cooler conditions linger Monday, with more limited
  shower and thunderstorm coverage.

- Gradual warming returns Tuesday onwards, with generally isolated
  precipitation chances each day.

&&

.DISCUSSION /Through Sunday/...
Issued at 142 PM MDT Sun Sep 20 2026

It has become unstable over the Palmer Divide and eastern plains
with SBCAPE of 400-1000 J/kg. This combined with good shear is
expected to produce a few strong to severe thunderstorms. Main
area of concern is from the Palmer Divide northeast to Akron to
Sterling and eastward. Farther west, subsidence is expected to
limit convective activity this afternoon, but this may change this
evening.Models have been trending towards scattered to numerous
thunderstorms developing over southeast Colorado tonight, after
sunset. This activity appears to be triggered by the left exit
region of a jet streak moving through. The uncertainty in the
forecast is how far north the thunderstorms will develop. The 12Z
NAMNest and some of the HRRR runs show storms as far north as the
Denver metro area in the 02-04Z time frame. Hail will be the main
threat given the steep lapse rates and cooler mid level
temperatures. The thunderstorms are expected to continue after
midnight over southeast Colorado and then exit the state.

Weak ridingbuilds over Colorado Monday bringing dry conditions.
Temperatures will be a littlecooler than what we have
recentlyseen, but they will be near normal with highs in the mid
70s across northeast Colorado. Models show light
precipitationforming over the eastern plains (south of I-76)
Monday night. Confidence isn`t the highest that we will see rain
showers or thunderstorms Monday night, but we have enough moisture
and instability for them. If we get enoughlift, some showers or
storms could develop. The models do show an increasing jet over
the area. Therefore, we will include some PoPs in the forecast for
this.  A closed low will be over southern Nevada on Monday. It
weakens and lifts northeast across Utah and Wyoming Tuesday and
Tuesday night in the southwest flow aloft. Best lift with this
feature is on track to be later on Tuesday with Tuesday evening
seeing the best chance for showers/storms. Temperatures warm with
highs in the mid 70s to lower 80s.

On Wednesday, temperatures will be a few degrees warmer with
highs in the upper 70s to lower 80s. Chances for showers and
thunderstorms look low at this time, but they can`t be ruled out
with slightly above-normal moisture lingering around.

For Thursday through Sunday, an upper level high will be over
Texas and northern Mexico with an upper level trough roughly
centered over the Pacific Northwest. This will maintaina
southwest flow aloft over the Central Rockies. Models hint at some
sort of shortwave trough lifting northward out of the subtropics
for Thursday. The timing and location of the trough and its
associated precipitation are not agreed upon by the models.
However, models are starting to show it will be moist with
precipitable water values climbing well above normal reaching
130-180 percent of normal and slightly higher on the GFS.
Precipitable water values will stay near or slightly above normal
Friday through the weekend. Main chance for showers/storms will be
over the mountains, but we could see them spread onto the plains
if we get a disturbance or two to help with lift.Temperatures
during this period are expected to be slightly above normal, with
highs in the upper 70s to lower 80s. Temperatures will be closer
to normal on the days with more moisture/cloud cover.

&&

.AVIATION /18Z TAFS through 18Z Monday/...
Issued at 1108 AM MDT Sun Sep 20 2026

Expect VFR conditions thru the period. Light and variable winds
will gradually become NE in the 19z-20z time period. By 01z winds
will become more easterly and then turn more SE by 04z. Overnight
winds will go light and variable by 08z. There is a very low chc
(5%) of an isold shower at APA and DIA between 03z and 06z.

&&

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

&&

$$

DISCUSSION...BM
AVIATION...RPK

NWS BOU Office Area Forecast Discussion