132 
FXUS65 KBOU 271950
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
150 PM MDT Tue Oct 27 2026

.KEY MESSAGES...

- Another night of fog with visibility below 1/4 mile in the South
  Platte River Valley and the far eastern plains of Colorado. 

- Mild and mostly dry through the work week.

- Unsettled weather potentially returning late in the weekend and
  early next week. There are many scenarios for how the weather
  will turn out but snow in the mountains is the most likely
  impact from this system. One possibility results in the lower
  elevations seeing their first snowfall of the season.  

&&

.DISCUSSION /Through Tuesday/...
Issued at 124 PM MDT Tue Oct 27 2026

The fog and low clouds have mostly dissipated today except for Morgan
County which has held onto some low clouds. With some low clouds 
lingering and a mountain wave cloud over Boulder, Larimer, Weld, 
and Morgan Counties, the high temperature forecast was lowered 2-3
F in those areas. Otherwise, there are no impacts expected today 
with dry conditions. 

Overnight tonight, there will continue to be weak lee cyclogenesis 
over the eastern plains. The light easterly low level flow across 
the plains will push the low clouds and moisture currently over 
western Kansas and Nebraska back into Colorado. This will lead to 
another night of fog and low clouds. The worst visibility as low 
as 1/4 of a mile will be in the South Platte River Valley from 
Julesburg to Greeley. This fog will likely extended throughout the
majority of southern Weld County but may not reach Adams, 
Boulder, or Larimer Counties. With that being said, the cities of 
Fort Collins and Longmont will have a 50% chance of fog tonight. 
This fog was added to the forecast generally from midnight to 9 AM
Wednesday. There may need to be Dense Fog Advisories for the I-76
corridor. 

Southwest flow aloft will be over Colorado Wednesday and Thursday 
with very dry air. This will keep conditions dry at the surface with 
generally pleasant conditions and seasonal temperatures. 

On Friday, there will be a weak shortwave trough that will move over 
the panhandle of Texas. Our forecast area should be to the northwest 
of the precipitation and affects from this trough. However, some 
light precipitation could occur over Lincoln and Washington Counties 
as well as the central mountains. Otherwise, there will be seasonal 
temperatures and light winds. 

Saturday and Sunday will have strong southwest flow aloft as a broad 
trough moves over the West Coast. There will be an initial very 
light wave of moisture that will move over the mountains of Colorado 
on Saturday that will produce light rain/snow. The plains will 
remain dry. On Sunday and into Sunday night, mid to upper level 
moisture with origins from the tropical Pacific will move from 
southern California to Colorado. This will bring another shot of 
rain/snow to the mountains of our forecast area. Since this 
moisture has tropical origins, snow levels will be high, likely 
above 9,500 feet or even above 10,000 feet. The other thing to 
note about the Sunday and Sunday night system is that in southwest
flow aloft, the mountains of our forecast area usually under 
perform because the mountains of southwest Colorado usually 
receive the bulk of the moisture. 

There remains considerable uncertainty for the Monday and Tuesday
period. Models indicate a piece of the broader western US trough 
will break off and become cutoff. This cutoff trough will 
generally move from the Idaho/Montana region towards Colorado and 
then to the Central Plains. There are many scenarios that could 
play out with this system. It could track east of our forecast 
area bringing light snow to the northern mountains and mostly dry 
conditions to the plains. It could track well west of our forecast
area, perhaps in Utah, and provide some mountain snowfall and 
light precipitation across the plains. Another possibility is that
it tracks just to the west of our forecast area and creates 
strong easterly flow in the low levels and a more significant 
precipitation event for our area. Given that the trough is 
breaking off of a larger trough and becoming cutoff, the 
predictability is quite low and none of the scenarios are favored 
at the moment. Expect forecast models to vary greatly from run to 
run over the next few days. Nonetheless, it is a system worth 
watching.

&&

.AVIATION /18Z TAFS through 18Z Wednesday/...
Issued at 1145 AM MDT Tue Oct 27 2026

VFR conditions are expected through the TAF period. There is a 
low (~20%) chance that FG/low stratus could make it into KDEN 
tonight explained in more detail below...

Fog was prevalent and quite dense at KBJC and KDEN for several 
hours this morning and has finally been lifting over the last 2-3 
hours. Each site is back to VFR conditions at this time. There is 
a channel of stronger winds (gusts up to 20 kts) affecting KAPA, 
but these are expected to lighten up in the next 60 to 90 minutes.
Additionally, satellite and web cameras show that there is a 
mountain wave cloud near and west of KBJC. For this afternoon, 
winds will turn to the east and stay under 12 kts. At KDEN, winds 
could increase a bit to 10-15 kts later this afternoon. A weak 
Denver cyclone looks to form tonight in Weld County causing rather
variable winds this evening. At this time, the cyclone is 
expected to move far enough away from KDEN that drainage flow 
occurs by about 5z- perhaps a bit later at KBJC- at all three TAF 
sites through the overnight. Model guidance is in good agreement
that this would keep an fog to the north and east of KDEN from 
far northern Adams County into Weld County. If the cyclone were to
be positioned further south, some fog could make it into KDEN and
approach KBJC, but there is only about a 20% chance that this 
scenario could play out tonight. We have covered this potential 
with a lengthy period of VCFG and a few low clouds in the TAF.

For tomorrow, winds will be vrb and light in the morning and 
transition to an east/southeast wind with speeds slightly 
increasing to 8-12 kts by the late afternoon.

&&

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

&&

$$

DISCUSSION...Danielson
AVIATION...MV