Front Range Fans

PM10 readings at Denver-Boulder reached AQI 62 on September 24, indicating Moderate air quality. While ozone and fine particulates remain Good, coarse particulates are elevated above the Good threshold, likely from active wildfires burning in central and southern Colorado at varying containment levels.

Mean daily high and low temperatures over the past 30 days at the nearest reporting station (Boulder, CO) are running 6.1°F above normal, with average highs of 86.7°F against a normal of 80.6°F. This sustained heat stress combines with the severe drought to accelerate fuel drying and increase wildfire risk.

Water-year precipitation to September 23 at Lake Eldora SNOTEL (28 km west, 9,700 ft) recorded 21.2 inches against a median of 30 inches for this date, 71% of normal. This deficit in the high country will constrain summer 2027 streamflow to the Front Range.

Pollution-sensitive mayfly larvae were observed on September 4 in Boulder County, including Leptohyphidae species and Small Mayflies. These ephemerotera larvae require clean, well-oxygenated water and indicate acceptable conditions in tested reaches.

Great Spreadwing damselflies were observed four times between August 25 and September 18, including near Longmont. This threatened Colorado damselfly species is sensitive to habitat alteration and water quality degradation.

Boulder County moved to Exceptional Drought in the week ending September 28, with 17.32% of the county classified in the D4 category, up from 0% the previous week. Exceptional Drought concentrates water stress on fish and freshwater invertebrates as streamflow declines and water temperatures rise.

Showy milkweed displays ripe fruits through early September, observed most recently on 2026-09-09 near Boulder. Late-summer ripening allows seed pods to mature and open in preparation for wind dispersal.

Black-chinned Hummingbirds were recorded at Plaster Reservoir on 2026-09-24, with up to 3 individuals, confirmed by a regional eBird reviewer. The species is highly adaptable and currently at the tail end of its fall migration window through the Front Range, moving from breeding grounds to winter ranges in the southwest.

Boulder County's drought history this year is more of a rollercoaster than a straight slide. Severe drought (D2) has blanketed the entire county since late February. Extreme drought (D3 or worse) actually hit 100% of the county for over a month, from April 7 through May 11, then eased sharply — down to 14% through most of June and just 11% by the week of July 14 — before jumping back up. By this past week the figure had climbed to 85%, and it has held there for three straight weeks now. This is the county's second extreme-drought spike this year, not its first. The gauge record lines up with what the drought maps show. Fourmile Creek, at both Orodell and Logan Mill Road near Crisman, is running at 0.2 cubic feet per second, the low end of a 30-day range that never once climbed above that mark. For a creek of this size heading into late summer, that is barely a trickle. Upstream, the winter supply was thin too. The Niwot SNOTEL station sits at 9,940 feet, well above this ecosystem and outside the Fourmile drainage, so it is a proxy for high-country supply rather than a measure of conditions on the ground here. It banked 23.1 inches of water-year precipitation against a 28.4 inch median, 81% of normal. Snowpack and summer base flow are related in these mountains, but we don't have hydrologic data tying that specific shortfall to Fourmile Creek's specific numbers. What we have is a light snow year sitting alongside a hot, dry summer: the Boulder airport weather station has logged a mean daily high of 92.3°F over the past 30 days, six degrees above the 1991-2020 normal, hit 104°F on August 3rd, and has seen barely a fifth of an inch of rain against a normal of 1.31 inches. That is the broader pattern across the Colorado River Basin as well: thin mountain snowpack alongside an increasingly aggressive summer aridity. Eastern cottonwoods and narrowleaf willow have both been logged this summer along Boulder Canyon Drive and the Boulder Creek corridor, cottonwood as recently as August 23. Both are riparian trees that grow where shallow groundwater is reliable, which is why a creek at this level is worth keeping an eye on. No one has reported canopy stress in these stands, and we haven't measured any; if you walk this stretch, what the canopy looks like from here through September is the useful thing to note. The Boulder Watershed Collective works this ground and is worth following for anyone tracking what happens to Fourmile Creek and the county's other small streams as this drought holds, or deepens further.

The wastewater facility serving the San Souci mobile home park, in the Front Range Fans watershed near Boulder, is reporting discharge violations severe enough to leave little room for ambiguity. In its most recent reporting period the facility's own numbers to its regulator show sulfide at over 1,200 times the permitted limit and hydrogen sulfide at nearly 200 times over. Arsenic came in at 34 times the legal limit, and silver, chloride, ammonia, and total suspended solids all exceeded their permits as well. This is not a one-time lapse. Arsenic has run roughly 49 to 54 times over limit in each of the two prior quarters, and chloride, ammonia, and solids violations have now recurred for at least four consecutive quarters. That pattern, more than any single reading, is what marks this as a chronic operational failure rather than a bad week at the plant. What these figures establish is that permitted limits were broken, badly and repeatedly; they do not by themselves show a fish kill or a fouled reach downstream. No streamflow or dissolved-oxygen reading near the site was available this cycle to say what these exceedances look like in the water itself once it leaves the outfall. Context is worth holding alongside the numbers, even without a direct measured link. Boulder County's drought footprint jumped from about 11 percent in extreme drought in mid-July to roughly 85 percent by early August, the kind of shift that generally leaves less water in local streams to dilute any discharge. Whether that dynamic played out at this particular site isn't something the record confirms, but it describes the kind of summer this discharge happened into. Boulder Watershed Collective works on water quality issues in this watershed and is a reasonable point of contact for anyone following the case further.