321
FXUS65 KBOU 091746
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1146 AM MDT Thu Oct 9 2025

.KEY MESSAGES...

- Above normal temperatures continue through Saturday.

- Scattered showers and isolated thunderstorms return Friday,
  mainly across the higher terrain.

- Near normal temperatures with chances for showers Sunday into
  early next week, though confidence in the weather pattern is
  low.

&&

.UPDATE...
Issued at 244 AM MDT Thu Oct 9 2025

Satellite and webcams indicate that fairly widespread fog has
developed across the far northeast corner over the last hour or
two. Unlike this time last night, guidance seems to be
underestimating the fog potential. This appears to be related to
poor handling of the surface inversion/radiational cooling across
that area. Several cycles of the HRRR/RAP maintain a 2-3C T/Td
depression at the lowest model level (~8m AGL), which doesn`t
correlate well with surface observations from AKO (10.6/10.1C) and
the Holyoke CoAgMet station (6.5/6.3C). Still, the HRRR develops
quite a bit of dense fog later this morning. Though we have a
limited number of webcams/automated stations to work with, it
appears we are already ahead of schedule wrt fog, and given a
favorable setup, locally dense fog seems likely to continue into
the morning hours. Have gone for a Dense Fog Advisory through 16z
for those reasons.

Elsewhere, today should be mostly quiet with temperatures again
reaching the 70s to low 80s. An increase in cloud cover by this
afternoon and evening is likely, with perhaps an isolated shower
across the higher elevations.

&&

.DISCUSSION /Through Wednesday/...
Issued at 158 PM MDT Wed Oct 8 2025

Upper level ridge will reside over the Southern/Central Rockies
and Southern Plains through Thursday. This will bring mostly clear
skies, dry conditions, and above normal temperatures. The warmest
day of the week will be Thursday with highs in the upper 70s to
mid 80s across northeast Colorado.

For Friday and Saturday, the upper level ridge slides east of the
Rockies setting up over the plains states. Over the Pacific
Northwest and eastern Pacific, a deep upper level low slowly
progresses eastward. This will produce broad southwest flow aloft
across the Desert Southwest and across the Rockies (from New
Mexico to Montana). Hurricane Priscilla remnants get caught up in
the southwest flow aloft bringing tropical moisture to the Desert
Southwest and Four Corners Region (including western Colorado).
Precipitable water values of 200-400% of normal are expected
across southwest Colorado. Even over eastern Colorado,
precipitable water values will be 200-300% of normal and near all
time highs. Southwest flow aloft produces a rain shadow effect
across eastern Colorado, keeping the lower levels of the airmass
on the dry side. Expect scattered to numerous showers over the
mountains Friday and Saturday with showers possible east of the
mountains as well. A thick layer thick mid and high clouds will
prevail both Friday and Saturday. This will cause temperatures to
cool some, but will remain above normal for this time of year.

Zooming into northeast and north central Colorado for Friday and
Saturday, a weak and shallow easterly surge is expected in advance
of a weak shortwave trough embedded in the southwest flow. Lift
from the trough and an increase in low level moisture will bring
the best chance for showers and thunderstorms to the plains Friday
late afternoon and Friday evening. For the mountains, the better
chance for precipitation will occur earlier Friday as the wave
moves through.

On Sunday, the initial upper level low weakens and rapidly moves
eastward across the Northern Rockies. Flow aloft becomes westerly
and pushes the very moist airmass east of the area. A cold front
will accompany this bringing cooler air into the area. Downslope
flow east of the mountains is expected to result in dry conditions
while the mountains will see orographic rain/snow.

Flow aloft returns to the southwest by Monday as a new upper
level low forms over the Pacific Northwest. Models show a wide
variety of solutions where this low tracks, the strength, and the
resulting weather pattern. This will lead to a lower forecast
confidence for next week`s weather, though right now models are
leaning towards keeping the storm track to our west and north.
This would result in temperatures at or above normal with mainly
dry conditions.

&&

.AVIATION /18Z TAFS through 18Z Friday/...
Issued at 1133 AM MDT Thu Oct 9 2025

VFR conditions expected through the TAF period. The temperature
inversion has been slow to break, so SW winds have held on for the
past couple of hours. Expect a transition to ESE in the early
afternoon before returning back to light drainage winds overnight.

For tomorrow morning, there is some model variability on whether
winds will stay SW or turn SE. Most likely, stronger SE winds
(10-15 kts.) will prevail. An upper level system will arrive on
Friday, with the possibility of scattered rain showers to all
terminals in the afternoon. Have introduced a PROB30 to the TAF
for this reason. In addition, ceilings should drop down to 6,000
ft. by 15Z, although could be earlier depending on the timing of
the system.


&&

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

&&

$$

UPDATE...Hiris
DISCUSSION...12
AVIATION...MAI

NWS BOU Office Area Forecast Discussion