Yesterday didn’t just break expectations along the Front Range — it shattered them.
On December 19, the Boulder area was placed under a PDS (Particularly Dangerous Situation) Fire Weather Alert, a designation rarely used and almost never seen in December. This wasn’t a random or sudden event. The atmosphere itself was clearly signaling a high-end fire weather day — one more typical of late summer than the doorstep of winter.
For Colorado, it was one of those days where everything had to go right to avoid disaster — and thankfully, it did.
🌀 The Atmospheric Setup: A Perfect Storm for Fire Weather
By Thursday night, the large-scale weather pattern over Colorado had already locked into place.
Strong west winds at mountaintop level intensified as flow across the Rockies turned nearly due west. This setup is notorious along the Front Range: when powerful winds aloft align just right with the terrain, they accelerate downslope and can form a mountain wave — a narrow but intense corridor of extreme wind.
In this case, wind speeds near ridge level were strong enough to support gusts well over 100 mph in exposed foothill and ridge-top locations, with the potential for those winds to surge eastward toward the Highway 93 corridor and nearby plains during the day.
At the same time, the air mass was unusually warm and exceptionally dry for mid-December. As the downslope winds developed, they compressed and warmed the air even further, stripping out what little moisture remained.
🌡️ Record Warmth Sets the Stage
The warmth arrived exactly as expected.
Denver reached 69°F, breaking a daily record that had stood since 1917. Denver Central Park climbed to 73°F, also a new record. Boulder topped out at 70°F, running roughly 25 degrees above normal.
Instead of typical December highs in the 40s and overnight lows in the teens, some locations barely cooled off at all. Boulder’s low only dropped into the mid-40s — warmer than a normal December afternoon.
That warmth rapidly dried fine fuels, even though parts of Colorado have seen precipitation this month.
💨 Winds Lived Up to the Threat
While Boulder Airport officially recorded gusts up to 73 mph, that only told part of the story.
As the mountain wave sharpened, some Front Range locations experienced wind gusts exceeding 100 mph, particularly in exposed foothill and ridge-top areas. These are winds strong enough to knock down trees, damage structures, and — most critically — make any fire nearly impossible to control.
Humidity levels collapsed at the same time. Denver dropped into the single digits, with afternoon relative humidity as low as 7–8%. The overlap of violent wind and extremely dry air is exactly what pushes fire danger into the highest category.
⚠️ A Very Close Call — But Not Another Marshall Fire
It’s important to be clear:
no major fires ignited during this event.
This was not another Marshall Fire. But the atmospheric setup bore uncomfortable similarities, and the margin for error was razor thin. One spark in the wrong place could have changed the outcome dramatically.
Recognizing that risk, power was proactively shut off to many customers along Highway 93, impacting daily life but reducing the chance of electrical equipment sparking a fire during extreme wind conditions. It was a disruptive step — but one that reflected just how dangerous the environment had become.
🌄 Why a December PDS Matters
December PDS fire weather alerts are exceptionally rare. This one occurred because multiple high-end ingredients aligned at once:
- A very dry air mass with poor nighttime humidity recovery
- Record or near-record warmth
- A significant downslope wind and mountain wave event
- Receptive fine fuels along the Front Range
Even more unusual was how long the threat lasted. Fire weather conditions remained elevated well into the evening and overnight — something typically reserved for peak fire season.
Bottom Line
Colorado dodged a bullet.
December 19 will be remembered as a near miss, not because the threat wasn’t real, but because the spark never came. It was a stark reminder that along the Front Range, fire weather doesn’t care what month it is.