Keystone

000
FXUS65 KBOU 312341
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
541 PM MDT Sat Oct 31 2026

.KEY MESSAGES...

- Areas of fog again late tonight through Sunday morning across
  portions of northeast and eastern Colorado.

- Unsettled weather returns late Sunday and Monday.Mountain snow
  is likely (>70% chance) above 8500ft during thistime, with a
  few inches of snow expected.

- Scattered rain showers for the plains on Monday.

&&

.DISCUSSION /Through Saturday/...
Issued at 308 PM MDT Sat Oct 31 2026

A blanket of fog over most of the I-25 corridor and parts of the 
eastern Colorado plains made for ominous conditions to start the 
day. In fact, satellite still showed a stubborn patch of mist and 
low level clouds over Denver International Airport and its 
surroundings just under one hour ago. Despite the passage of a 
very weak shortwave over the area this afternoon, we expect mostly
sunny skies east of Continental Divide with high clouds moving in
late in the day. Southwest flow aloft will begin to transport 
Pacific moisture towards the Four Corners this afternoon, which 
will promote some isolated rain/snow showers over the high 
terrain. Areas of fog will be possible once again tonight, 
developing over the eastern plains first and slowly making its way
west to the Denver metro and I-25 corridor by dawn. However, we 
expect the bulk of the fog to remain north of I-70.

The pattern turns more active tomorrow as a closed-low off the 
Pacific Northwest coast and longwave trough extending south to Baja 
California briefly split up and then merge again as both features 
move east over the Great Basin. A subtropical jet will also slide 
north over the Four Corners with the broad wave, bringing 
precipitable water (PW) values that are 4-5 standard deviations 
above climatology for the time of year (0.60-1.00"). However, with 
such limited lift and instability, this plume of moisture may only 
amount to light rain over the plains and Denver metro, with a trace 
up to a few hundredths at most. Lee cyclogenesis east of Denver 
will bring breezy southerly winds with gusts up to 30 mph for 
portions of the east Colorado plains and Palmer Divide. Winds 
should remain light for areas west of I-76. More widespread 
stratiform rain is expected over the mountains, particularly 
Sunday evening during the peak of moisture transport. In terms of 
snow, snow levels looks to be too high for impacts during the day 
with only light accumulations possible above 11,500ft. Snow levels
will begin to lower late Sunday night as the center of the cutoff
low drifts closer to the area. 

A strong cold front will push through northern Colorado late Monday 
morning, leading to a slight drop in temperatures over the plains. 
The primary concern with this front will be the strong northerly 
winds that will develop on the backside, potentially reaching speeds 
up to 25-30 mph, and isolated gusts up to 55 mph over parts of the 
east Colorado plains. Light intermittent rain will be possible 
across the low elevations, with temperatures struggling to rise 
above the mid 50s. For the mountains, snow levels will continue to 
drop, likely reaching the 8,500-9,000ft level by late afternoon on 
Monday, and continuing to drop overnight into Tuesday. Snow 
accumulations will range between 2 and 5 inches, with the highest
amounts above 10,000ft. This will lead to periods of slick roads 
and hazardous travel conditions late Monday afternoon through 
Tuesday morning. Although snow amounts are just shy of Winter 
Weather Advisory criteria at this time, an advisory may be 
considered in the next forecast package for parts of the northern 
mountains if model guidance trends any wetter. Snow levels may 
drop as low as 6,500- 7,000ft by Tuesday morning. If enough 
moisture lingers into Tuesday morning, a few flurries to a light 
dusting of snow cannot be ruled out over the crest of the Palmer 
Divide.

Looking ahead, temperatures will remain near normal to slightly 
below normal for the rest of the work week with a period of quieter 
weather expected as an upper level ridge forms over our region. 
However, long-range ensemble means do hint at another period of 
active weather and mountain snow chances for next weekend. 

&&

.AVIATION /00Z TAFS through 00Z Monday/...
Issued at 541 PM MDT Sat Oct 31 2026

Main concern is potential for another round of fog. There is more
uncertainty, however, regarding whether that fog gets into KDEN 
tonight. We expect a more southerly wind to develop over the next 
few hours through 04Z and then hold most of the night. However, a 
weak Denver Cyclone is still expected to form, with a possible 
shift to more westerly winds on the back side of it 11Z-16Z. At 
the same time, we'll likely have more mid level moisture and 
cloudiness move in, which could diminish our radiational cooling 
component slightly....thus the uncertainty. Given the already 
moist/cool boundary layer and little mixing today, we still have 
around a 60% chance of fog developing at KDEN, 70-80% at KBJC, but
only 10% at KAPA where more southerly downslope winds are almost 
certain to prevail. Given the uncertainty about the clouds and
above mentioned probabilities, we've kept the TAFs relatively 
unchanged for this forecast cycle. This means TEMPO FG at KDEN
12Z-16Z, prevailing FG at KBJC 11Z-16Z, and no fog at KAPA. 

A shortwave trough lifts northeast across the area late Sunday 
morning, helping to break up the fog and possibility of a brief 
light rain shower. By 18Z Sunday the shortwave is expected to be 
northeast of the area with south winds prevailing 18Z-23Z with 
gusts to 20-25 kts at KDEN and KAPA. Another shear zone is 
expected to develop with a shift to W-NW winds 23Z Sunday - 01Z 
Monday. 

&&

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

&&

$$

DISCUSSION...AA
AVIATION...20