115 mph on Cairngorm

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Len Wood

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Aug 7, 2016, 1:12:03 PM8/7/16
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Some disruption across Scotland due to high winds

http://www.bbc.co.uk/news/uk-scotland-37002528

Len

xmetman

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Aug 7, 2016, 2:28:40 PM8/7/16
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Len


Just beat me to it - I don't think it's that unusual for Cairngorm. Gale force for over 24 hours and storm force for a good part of that, a mean max of 71 kts makes it Hurricane force 12 for a while. I made the maximum gust 98 kts at 10 UTC which I think is 112.776 mph according to Google and I didn't missed any today as far as I'm aware.


Bruce.





Smartie

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Aug 9, 2016, 4:46:53 AM8/9/16
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Max gusts 06-18 UTC from a ~2km WRF run. There is a distinct wind max off-shore of Sutherland  and ViS imagery showed a distinct cloud hole for several hours. A quick look at the model supports the idea is that it was subsidence in the strong flow in the lee of the Torridons. There was a distinct dry anomaly and intrusion aloft as well. 

xmetman

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Aug 9, 2016, 6:56:49 AM8/9/16
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Smartie 

Where do you exactly get your uk2 NWP data from?

Bruce.

Smartie

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Aug 9, 2016, 7:33:07 AM8/9/16
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This is from my own version of WRF running on a workstation. In this case initialised with GFS op data. I can give more details if people are interested.
A plot for a specific time gives a better depiction of the mountain lee wave activity.(Corresponds well with UM UKV output I've seen).
David


Richard Dixon

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Aug 9, 2016, 8:02:55 AM8/9/16
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What sort of maximum did you get on top of Cairngorm (I'm guessing the orographic smoothing reduces the peak height of Cairngorm/the range Cairngorm is in significantly?)

If it doesn't, I'd be intrigued to see what the wind at 1245m asl is across the UK to see if it's got close to that.

Richard

Smartie

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Aug 9, 2016, 8:56:04 AM8/9/16
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The max gust near Cairngorm (bullet point according to Geohack) is well below 90 kt say 60 or so. But I note the UKV doesn't have anything like that either.
Yes the orography has to be smoothed to keep the model stable and running reasonably fast. I guess the acceleration over the ridges has to be captured and more of the very small scale turbulence.
 You could build a higher resolution domain- go down to ~100m, use hires terrain etc The technology is available.


Richard Dixon

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Aug 9, 2016, 9:09:34 AM8/9/16
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David

My thought was if there is strong vertical (speed) shear in the boundary layer then would a reading in the model at the height of 1245m asl have something fairly close to that of the gusts (90kt) if the turbulent gyres bring down a bit of the higher-momentum air at the top of the boundary layer? Suspect not...!

Richard

Smartie

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Aug 9, 2016, 10:23:56 AM8/9/16
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It's bit difficult because there are interfering wave patterns from the up stream and surrounding  terrain

There is no really high speed air above ~1500m in the model. If this is correct then gusts to 40-50 m/s suggest local acceleration. I'm not sure I'm bang on the mountain peak here but it's possible as much as  a few hundred meters could have been shaved off.



Smartie

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Aug 9, 2016, 10:50:23 AM8/9/16
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There are no really high speed winds above the BL in the Lerwick 12Z sounding either-
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