Longmont, CO 80501 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 /00Z TAFS through 00Z Saturday/: Issued at 536 PM MDT Thu Oct 29 2026

VFR conditions expected to persist through the evening before fog develops and a Denver Cyclone pulls it south into KDEN and KBJC for the overnight and first half of Friday morning. For the next few hours, guidance portrays the cyclone moving northeast across KAPA/KDEN that makes for some uncertainties in the wind forecast while this occurs. The current TAF portrays the highest confidence solution, with a few hours of northeasterly winds from now until around 3Z at KDEN, before turning clockwise to the SSW by about 4Z. KAPA will likely see light and variable winds develop in the next hour before they also turn to the SSW by around 4Z. KBJC will likely see a NW transition by around 2Z before becoming light and variable through late Friday morning.

Fog is likely to make it into KDEN/KBJC sometime between 9Z-10Z, with it getting within the vicinity of both TAF sites between 7Z-8Z. Expecting visibility to drop down to 1/4SM or less once the fog settles in. KAPA remains a wildcard with low confidence in fog making it that far south, but it should make it within the vicinity by around 9Z, and will have to monitor trends and conditions to potentially add a PROB30 or TEMPO in the coming hours. Guidance does show a fairly quick clearing between 15Z-16Z Friday morning.

Friday looks similar to today, with NE winds developing by early afternoon, becoming easterly and slightly increasing in magnitude around 21Z, with another cyclone potentially moving across the TAF sites Friday evening. While it's outside of this TAF package, it does look like we will have potential for fog to return early Saturday morning that could at least make it into the vicinity of both KBJC and KDEN.

Watches, warnings and advisories

Dense Fog Advisory from 10 PM this evening to 8 AM MDT Friday for COZ046-047.