101
FXUS65 KBOU 181746
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1146 AM MDT Fri Sep 18 2026

.KEY MESSAGES...

- Increasing coverage and intensity of afternoon/evening showers
  and t-storms for the lower elevations, peaking Saturday when
  locally heavy rainfall can be expected across the plains.

- Warm temperatures through Saturday to give way to more seasonal
  conditions Sunday onwards.

- Trending drier Sunday into Monday, although at least isolated to
  scattered showers will remain each day.

&&

.DISCUSSION /Through Thursday/...
Issued at 1144 PM MDT Thu Sep 17 2026

Though not as climatologically anomalous as the last couple of
days, precipitable water values will remain plenty elevated today,
combining with a hair higher instability to promote renewed
scattered showers and a few generally weak thunderstorms this
afternoon through the evening. As was the case over the past few
days, steering level flow should remain above 20-25 kts, thus
keeping storms on the move and limiting overall accumulations for
most areas (with some locations, per usual, remaining dry).
Temperatures will continue to hold 5-10 degrees above normal for
the date.

Saturday remains the day to watch in terms of both severe threats
and localized flooding potential. Despite a small downtick in
available moisture, PWs will remain elevated, with moderately
deep warm cloud depths and increased instability as cool air
advection returns aloft with the approaching upper-level low.
Steering level flow will continue to be hefty, but improved shear
and higher coverage of late day convection will lead to a greater
potential for heavy downpours namely over the plains. The
exception to the above trend will be the high country, where drier
air will steadily gain influence through the weekend and reduce
precipitation coverage and intensity. Scattered afternoon showers
and thunderstorms look to continue into Sunday with the passage of
the upper-level trough and sufficient shear and instability,
however a more noteworthy decline in PWs and cooler surface
conditions would suggest a slight reduction in activity compared
to Saturday.

Transient ridging emerges by Monday, providing for a drier day
across most of the region with afternoon showers becoming much
more isolated in nature, albeit not disappearing entirely.
Temperatures will be fairly seasonal if not a touch below average,
with highs in the mid 70`s Monday for the lower elevations.

Southwest flow aloft will dominate past Monday, allowing for the
intrusion of a few shortwaves through the week and keeping
opportunities for additional precipitation in place most days,
with the mountains being best positioned for the better coverage given
the flow pattern. Beyond that, there`s still ample variance in
model guidance, limiting how much detail we can extract.

&&

.AVIATION /18Z TAFS through 18Z Saturday/...
Issued at 1140 AM MDT Fri Sep 18 2026

Afternoon convection still appears likely today. Recent clearing
evident on satellite has allowed temperatures to reach the upper
70s with dew points still hovering around 50F. ACARS profiles have
also shown a gradual increase in instability over the last couple
hours, with MLCAPE approaching 500 J/kg. Most guidance develops
convection over the southwest metro before 20z, which then lifts
northeastward through the terminals between roughly 21-23z. Some
SHRA may linger beyond 00z but most impacts from TS or gusty
outflow winds would be before that time.

Winds are a bit uncertain today. There should be light upslope as
a prevailing direction early this afternoon, before becoming more
variable in the vicinity of convection. A return to drainage is
expected this evening. Some guidance hints at some stratus or fog
potential overnight though this would be almost certainly be
dependent on getting meaningful precipitation across a large area
near the terminals today.

Tomorrow`s forecast is largely similar to today, with convection
likely developing during the early afternoon hours, lingering into
the evening.

&&

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

&&

$$

DISCUSSION...BRQ
AVIATION...Hiris

NWS BOU Office Area Forecast Discussion