I have visited Boulder, Colorado many times because of the National Center For Atmospheric Research, which is located there. The news about the fast moving fires in the surrounding areas made me sad. I know someone who is adversely affected. A colleague asked how it could happen so quickly. The initial meteorology breakdown points to strong winds in the mountains. Here is a brief description of what happened.
Smoke and ash can be seen on the radar.
The NWS.
The National Weather Service warned of strong winds on the morning of the fires. Confidence is increasing in very strong winds across much of Larimer, Boulder counties. There is a chance for gusts up to 90 mph for wind-prone areas. The NWS discussion noted that mountain waves may amplify cross-barrier flow and weak shear aloft.
Let's quickly understand the meteorological jargon. The cross-barrier flow shows that the wind was blowing in a different direction than the mountainous terrain. There was no change in wind speed or direction with altitude because of weak wind shear. The radar image of the smoke-ash plume associated with the Marshall Fire is a strong indicator of the westerly flow.
The Marshall Fire can be seen from the weather satellites.
The NWS.
A deeper dive into the NWS forecast discussion on Thursday morning hints at the emerging concern. They wrote, "If this does mix down, I can't rule out strong winds at lower elevations for a few hours." One of the high resolution weather models showed gusts up to 90 mph and could spread eastward, as highlighted by the forecaster on duty. The forecaster wrote, "I can't ignore what I'm seeing so will issue a High Wind Warning for zones 36,38 and 39." The graphic below shows how mountain waves and stronger winds can play out in complex terrain.
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Waves, turbulence, and winds are mixed.
NWS Reno.
The media is reporting that the fires in the region were caused by downed power lines. The tragic set of circumstances were caused by the double-whammy of winds and the human footprint. The area is bracing for a winter storm after the winds died down. This will be an impact event, but it may help fight the fires.
Predicted snowfall amounts on New Year's Eve.
The NWS.
