2012-01-17/18 - Mountain wind storm: CO front range
A fairly typical mountain wave-generated windstorm is well underway across the Front Range vicinity in Colorado. Boulder seems to be one of the places most notably being impacted, mostly because there's more sensors there. The NCAR mesa and foothills lab sites are a good way of viewing this event. Looks like gusts up to almost 80 MPH have been reported so far there. I've seen a max gust of 92 MPH just southeast of Boulder so far. The high wind warning for this event told of possible gusts as high as 100 - 120 MPH at higher altitudes.
I'm not 100% sure what specifically is causing this event, but I'm pretty sure the following factors are involved:
-Strong cross-barrier (in this case, west winds across the peaks of the Front Range) flow. This event has winds that are more NWly than Wly, but speeds approaching 80-90 kts around 500 mb is apparently enough to get it done.
-A stable layer at the altitude of the terrain so that the first parcels forced up and over the peaks cannot continue to rise, thus starting the oscillation.
-Not too stable of lapse rates in the lowest layers to get vertical transport of strong winds
-Some factor involving the Freude number or something relating to the gravity wave phase speed sqrt(g*H)
The 00Z DEN sounding is showing the strong NW winds aloft, a pretty strongly stable layer about 50 mb deep centered around 600 mb (well within the range of the tallest peaks), and a stable, but not too stable (except for the lowest few hundred meters), lower atmosphere.
Sometimes the strong winds are produced by rotors created by the shape of the waves and the differential friction in the lowest levels of the atmosphere. Not sure if this is happening with this event.
These types of events are very mesoscale, and the E-W extent of this event is pretty thin. Generally only locations within a few miles of the really complex terrain features are seeing the stronger winds from this event. In this case, locations east of I-25 in Colorado are pretty much not being affected.
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