773
FXUS65 KBOU 271120
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
520 AM MDT Sun Sep 27 2026

.KEY MESSAGES...

- Drier and warm today, with highs reaching into the 80s across
  the plains.

- Low chances (<30%) for light mountain snow above 12,000ft
  Monday through Wednesday.

- Potential for heavy rain Wednesday and Thursday, but confidence
  in amounts and locations remains low.

&&

.DISCUSSION /Through Saturday/...
Issued at 1110 PM MDT Sat Sep 26 2026

A potent upper level trough will move onto the West Coast on
Sunday, nudging the upper ridging over our area east. As the
ridge starts to slide east, southwesterly flow will bring
increased moisture at mid and upper levels from the Pacific. The
higher moisture in the mountains and some weak upslope from
southeasterly surface winds could produce some isolated to
scattered showers in the higher terrain and areas generally north
of I-76 tomorrow afternoon. While most of this activity is
expected to remain on the weaker side, we could see an isolated
storm or two. MLCAPE will be weak, but looking at lapse rates and
DCAPEs, any storm that can get going could have the potential for
some gusty winds (maybe around 40kts). The showers and potential storms
are forecast to move northeast into the late evening, but no
impacts are expected.

The upper trough is forecast to dive into southern California on
Monday, progressing into Arizona on Tuesday. As the trough moves
east/southeast, moisture will continue to flow into the area,
increasing PWs to around 200% of normal. A few weak disturbances
will likely move through the southwest flow at mid levels,
providing weak lift for showers and storms Monday and Tuesday.
Widespread coverage is not anticipated with this activity, with
the best chances for precip over the mountains. While coverage
will be minimal, we will want to keep an eye on the localized
heavy rain potential both days due to the anomalous moisture. A
cold front is still poised to move through the forecast are late
Monday into early Tuesday. Overall impacts from the front will be
pretty limited, other than slightly cooler temperatures for
Tuesday and Wednesday. Snow chances for the mountains continue to
decrease as each new model run comes in. While there will likely
be a few rounds of flurries and a dusting at the highest
elevations, temperatures just look too warm to support decent snow
totals (snow levels are generally 12,000+ft for Monday through
Wednesday and SLRs are below 5).

Models now have better agreement that the strong upper low will
eventually move into southeast Colorado by Thursday. The main
difference between models now is where they develop the surface
low, impacting where the heaviest rain band forms. If the surface
low ends up a bit closer to our area, we could see some wrap
around moisture, bringing heavy rain potential for Wednesday and
Thursday. However, if the surface low ends up too far south and
east, our area will end up on the drier side of things. The exact
location of the axis of heavier precip will be very difficult to
forecast, and very impactful. Models are hinting at some pretty
substantial rain amounts with this system, but right now, the
majority of ensemble members keep the highest rain totals to the
south and east of our forecast area. The best chance for heavier
rain totals for our area will be in Lincoln County. All this being
said, even if we don`t end up with the widespread heavy rainfall,
moisture will be high enough that localized flash flooding will
be a concern for any storms that pop up.

This system and the better rain chances will start to push off to
the east on Friday. The speed at which that system exits and the
next moves in is still up in the air. The GFS wants to bring in
the next shortwave and frontal system almost immediately over the
weekend, however the Euro wants to delay the second system and
hold onto the first for a bit longer. Either way, the weather with
the highest potential impacts over the next week will be that
Wednesday through Thursday time period.

&&

.AVIATION /12Z TAFS through 12Z Monday/...
Issued at 515 AM MDT Sun Sep 27 2026

Winds have been drainage through the overnight at KAPA and KDEN
and KBJC has generally had light NW winds. There will be a few
hour period of VRB winds later this morning. Winds will then turn
to SE/SSE by this afternoon. It still looks like winds will be
pretty stout- gusting to 20-25 kts. KDEN and KAPA should see the
strongest winds of the three sites. In addition, there are PROB30s
at all three sites for the possibility of high-based virga
showers from 22z/23z until about 3z. These could bring gusty
erratic winds to around 25-30 kts given soundings show DCAPE
~1100-1300 J/kg. As has been the case recently, there could be
some lingering showers for an hour or two past 3z.

Winds turn to an elevated drainage (8-12 kts) after the showers
pass through at KDEN and KAPA. KBJC should keep a light wind with
mainly a westerly component. The biggest change compared to
previous forecasts is an increase in wind speeds at KDEN and KAPA
starting early Monday morning as a jet moves in aloft. Winds could
once again gust to 20-25 kts with some hints of even a bit
stronger winds possible at KAPA starting as early as 8z and
lasting through the end of the TAF period and likely beyond. KBJC
should stay light and VRB through the end of the TAF period, but
could get in on the stronger winds later on Monday morning.

&&

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

&&

$$

DISCUSSION...AP
AVIATION...MV