Derby, CO 80024 Weather

Key messages

- Mild and mostly dry through the work week.

- Unsettled weather returns late this weekend and early next week. Mountain snow is likely (>70% chance) above 8500ft during this time. High uncertainty remains for the foothills and plains.

.DISCUSSION /Through Thursday/: Issued at 1257 PM MDT Thu Oct 29 2026

We're looking at another potential fog event tonight. Light winds and surface conditions near or at saturation could lead to dense fog development overnight tonight and tomorrow morning. High res models have fog developing over Kansas and the eastern plains and a surface cyclone to the northeast of Denver. This circulation could usher fog right into the urban corridor from the north. High res ensembles currently have a medium to high chance (50% to 80%) that patchy dense fog (vis <0.5mi) will develop across the urban corridor, northern I-25 corridor, and portions of the eastern plains. This could lead to dangerous travel conditions for the Friday morning commute. A similar fog setup will be in place for Saturday morning, leading to additional fog and travel concerns for portions of the urban corridor and eastern plains for Saturday morning.

A shortwave will move to the southeast of the area on Friday. While most of the forcing and precipitation from the shortwave will be to our east/southeast, our far eastern counties could be clipped by a weak shower or two. No impacts are expected. On Saturday, another shortwave will move through the southwest flow aloft bringing isolated to scattered showers to our higher terrain in the afternoon.

On Sunday, things start to get more uncertain. Late Saturday into early Sunday there will be two upper level low pressure systems off the west coast of North America. One will be off the coast of Baja California while the other will be closer to the Pacific Northwest. The southern one will bring significant moisture transport into the four corners region on Sunday, bringing our PW values into the 200% to 300% of normal range for Sunday and Monday. The northern system will dig southeast, phasing with the other system sometime Sunday or early Monday. Models tend to struggle with exactly how two troughs phase together, which brings high uncertainty on the exact path of the resulting system and the potential impacts for our area.

There will be widespread upper level support for showers ahead of the approaching trough. Right now, peak QG forcing looks to be Monday afternoon, which is when we'd expect the most widespread showers. However the timing and strength of the trough could very well change between now and late this weekend. A strong surface front will move through sometime late Sunday and Monday, bringing strong north/northwesterly winds to the plains. The current forecast upper level and lower level winds, don't look great for additional topographic forcing and higher precip totals, with the exception of maybe the Palmer, which tends to do better with northerly winds than the rest of our area. However, we will be keeping an eye on the development of the surface low and any potential eastward turning of the winds, which would impact precip totals in our area. Currently, liquid precip amounts look to stay under an inch for our area, with much of the area remaining below half an inch. In terms of snow, snow levels are forecast to start out around 10kft or 11kft, dropping closer to 7,500ft by Tuesday morning. Models remain too warm for snow on the plains, with the NBM giving the plains a 0% chance of any measurable snowfall.

This system will move off to the east on Tuesday, bringing weak upper level ridging and drier conditions. Northerly surface winds will continue for Tuesday and Wednesday, helping keep temperatures near or below normal.

.AVIATION /18Z TAFS through 18Z Friday/: Issued at 1257 PM MDT Thu Oct 29 2026

Light east winds will develop this afternoon and will slowly strengthen at DEN. East winds will likely be between 8-12 knots during the late afternoon and early evening. There are no other concerns through midnight.

Later tonight, easterly low level winds will advect moist air and low clouds westward from the eastern plains of Colorado. This cool and moist air will move into the South Platter River Valley and develop fog/low clouds. As a weak cyclone develops on the east side of Denver, light northwesterly winds will likely move low clouds/fog southward across BJC and DEN. A TEMPO for 1/4 SM fog was added to both TAFs. The most likely time for fog will be roughly 10-15Z although fog and low clouds could occur from 08-17Z. In the worst case scenario, fog could reduce visibility to 1/8 of a mile at both DEN and BJC. There is around a 20-30% chance of fog at APA. Therefore, no fog was included in the APA TAF but a FEW001 cloud group was added to indicate the possibility of the fog/low clouds.

The fog/low clouds will slowly clear out tomorrow morning. No impacts are expected the rest of the day tomorrow given light winds and high clouds.

Watches, warnings and advisories

None.