National Weather Service Forecast Discussion

Thornton Weather Forecast   
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005
FXUS65 KBOU 131804
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1104 AM MST Fri Nov 13 2026

.KEY MESSAGES...

- Above normal temperatures and dry conditions will prevail
  today, followed by more seasonable temperatures this weekend
  into next week.

- Chances for rain and snow showers across the high country
  Saturday, with a few showers possible over the eastern plains.

- A more active storm track next week?

&&

.DISCUSSION /Through Thursday/...
Issued at 1201 AM MST Fri Nov 13 2026

Current satellite shows a clear night for much of the state with
only a few thin high clouds over western CO. To our east, a much
cooler airmass and its accompanying cold front have pushed over the
Great Lakes and across the central Great Plains, up against our
eastern counties. Given the clear skies in place, light easterly
winds, and a somewhat of a surge in dewpoints (low to mid 30s), at
least some patchy fog is likely over the eastern CO plains and along
the South Platte River valley in the early morning hours. Areas of
fog can already be seen slowly creeping over the CO-NE border. The
fog should clear by mid morning as temperatures rise.

High clouds will continue to increase over the region Friday as the
upper level ridge axis moves off to our east and a shortwave trough
drifts over the desert Southwest. The ascent and vorticity
enhancement with this disturbance will remain well to our south,
and no precipitation is expected. However, cloud cover should keep
temperatures a few degrees cooler, in the low to mid 60s at low
elevations and 40s-50s for the mountains.

Temperatures finally cool down to near-average values for the time
of year this weekend as a broad upper level trough (remnants of what
was once a potent mid-latitude cyclone) slides southeast over our
area. Areas of fog are likely to develop as far west as the I-25
corridor in the early morning hours Saturday as temperatures drop
into the mid 30s and southerly winds, as well as a lee surface
cyclone, advect higher dewpoints. The weakening upper level
trough will also bring a plume of Pacific moisture that should
promote light mountain snow and scattered rain showers over the
plains Saturday afternoon. In terms of snow, 1 to 3 inches of
total accumulation for this event seems reasonable at elevations
above 10kft, with locally higher amounts above 12kft. For the low
elevations, rain showers should remain quite light in intensity,
with only a trace up to a few hundredths expected mainly over the
east CO plains. A few snowflakes or a rain/snow mix cannot be
ruled out over the Palmer Divide late Saturday evening as the
system exits the region and temperatures begin to drop into the
mid 30s.

Sunday is shaping up to be a mostly sunny autumn day with
temperatures in the low to mid 50s for the Denver metro and east CO
plains, which is near-average for the time of year. An upper level
ridge will begin to build over our region on Sunday into Monday,
with temperatures expected to warm back up into the 60s once again
for much of the plains and foothills Monday-Tuesday. A pattern
change is expected to arrive by Wednesday as a shortwave trough
slides over northwest CO. This is also where uncertainty enters the
picture, with ensemble guidance showing increasing spread in
temperature and moisture through next weekend. At this time, our
northern mountains look to be favored for mountain snow with the
first wave on Wednesday. We are fairly confident in temperatures
dropping to seasonable values by the end of next week. Long-range
ensemble members and deterministic runs have continued to hint at
another system bringing more mountain snow chances, and potentially
some snow for the low elevations as well. However, it is far too
early to come to any conclusions about snow amounts or even
precipitation type. At this time, global model ensembles show a 15-
degree spread in temperature between the 25th and 75th percentiles
alone. Nevertheless, more active weather and cooler temperatures
seem to be in store starting mid next week, likely continuing
through Thanksgiving week.

&&

.AVIATION /18Z TAFS through 18Z Saturday/...
Issued at 1044 AM MST Fri Nov 13 2026

This afternoon will be relatively quiet with periods of light and
variable winds interrupted by a few hours of light northeast
winds. Winds will increase this evening from the south/southwest
at APA and DEN, with speeds around 10kt to 12kts. A cyclone is
forecast to develop to the northeast of DEN overnight, slowly
turning winds W at DEN and N/NW at BJC. Fog is expected to form
to the north of DEN and BJC early tomorrow morning, progressing
south towards the airports around 11Z to 12Z. As of right now,
fog is not expected to travel far enough south to impact APA. The
fog will bring periods of ILS and LIFR conditions to both airports
through roughly 16Z to 17Z tomorrow morning. Winds during this
time will be highly dependent on the placement of the cyclone,
creating high uncertainty in the exact wind direction for tomorrow
morning at all 3 TAF sites.

Models have another circulation developing very near DEN tomorrow
afternoon. On the southeast side of the circulation, we expect
stronger south/southeast winds and on the northeast side we
expected weaker north/northwest winds. There is potential this
circulation moves over DEN tomorrow afternoon, leading to very
different winds across the field. Rain chances will start to
increase around 21Z tomorrow, but intensity should be on the
lighter side.

&&

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

&&

$$

DISCUSSION...AA
AVIATION...AP

NWS BOU Office Area Forecast Discussion