Winds Hit 115 mph in the Columbia Gorge

The strongest winds in several years struck the scenic Crown Point overlook above  the Columbia Gorge:  a gust of 115 mph.  The proof, provided to me by Portland TV meteorologist Mark Nelson, is shown below.   In fact, I have receive an unofficial report that the wind at Crown point reached 118 mph.

Just to orient you, here is a picture of Crown Point and a map of its location.

Crown Point has a lot of things going for it to get strong winds.   It is on the western side of the Gorge, so that winds can accelerate down this narrow gap if there is a large pressure different down the gap, with higher pressure to the east, lower pressure to the west.  This happened yesterday as shown by a forecast for 4 AM Monday by the UW WRF model.  The solid lines are isobars (lines of constant pressure) and the shading is temperature.  A lot of isobars down the Gorge and cold air on the eastern side (this will be important).

Yesterday the pressure difference across the Gorge (Troutdale-The Dalles) got to 10 millibars....this is a lot.   But there is something else that juiced up this event:  the shallow cold air.  As shown in the figure above, cold dense air in eastern Washington was pushing up against the Cascades and then accelerating within the narrow, near-sea level gap. 

Aircraft landing at Portland (just west of the gap) documented this cold shallow flow.   Here is the proof:  a plot of winds and temperatures above the airport in time.  (time increases to the left, heights in pressure--850 is about 5000ft).   The easterly winds are very shallow (below about 925 hPa/mb, roughly 2500 ft, time in UTC:  20/18 is 10 AM Monday). There is a super inversion  above the cold air, particularly in the morning (20/12 is 4 AM on Monday).

Why is the having cold, shallow air important for getting strong winds? 

In the narrow Gorge the cold air is relatively deep, but when it gets to the western "exit" the walls fall away and the cold air collapses.   This creates a very intense local pressure difference since the cold air is dense and heavy.   Where it is deep, the pressure is high.  Where it is shallow, the pressure is less.  So a big change in height of the cold air, produces a strong temperature gradient.   The stronger the inversion above the cold air, the bigger the effect.  Here is a schematic of this process:

 As shown by the max winds for the 24h period ending 9 AM today (Tuesday), the strongest winds (these are gusts in mph) were at the exit of the Gorge where the cold air collapse was occurring.

It takes super-high horizontal resolution in a forecast model to simulate such effects. No problem!  The UW high-resolution (4/3 km grid spacing) model is up to the job.  Here is a 36 h forecast of the sustained wind speeds valid 4 AM on Monday.  The model got it right...

 One more thing.  Winds at Crown Point are also enhanced by the fact it is on a tall bluff, since winds are locally accelerated by such objects.  Just to be fair....