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Mac asks: So why is this the gustiest season of memory?
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Joined: 18 Mar 1997
Posts: 1561

PostPosted: Wed Jul 03, 2019 8:05 pm    Post subject: Reply with quote

us44eric wrote:
Tying in to Mac's, Mike's, and dllee's comments --- Look at the crazy anomalous conditions at Berkeley yesterday, including SE 10-17mph in July, not on a rainy day.

Often iW forecasts talk about potential East Bay shut downs or shifty conditions, particularly when there's NW wind influence. But yesterday the WSW wind at Berkeley was dismal and brief. It then began to slightly build and sustain for a few hours to ~10-17mph, BUT this occurred as it clocked back to S, SSE, SE!!!

Hi Eric,

I was not forecasting yesterday but I know the pattern was much the same as today. And today Berkeley winds graph looks dismal. So here is probably happened both days:

1. Look at the first image below notice the strong NW gusts over Marin this afternoon.

2. The second image shows the wind data from this mornings weather balloon released from the Oakland airport. Notice the very strong NW wind just aloft.

3. Today models show NW winds in the 20-40 knot range at the 975 and 950mb which is low enough to interact with Mt. Tam and parts of the Marin coast range.

4. As the NW winds just aloft hit these hills they become turbulent so you have NW winds ascending and descending above the SW wind curving through the Olympic Circle towards Pt. Isabel and Berkeley.

5. Look at my old graphic below which shows this happening. Or visit this old blog on Pt. Isabel and Berkeley:

If the NW surface wind is very strong at the surface they divert the Pt. Isabel and perhaps the Berkeley winds and you see a sudden FADE.

If the surface NW winds are weaker but there are very strong NW winds aloft you get the scenario descrived in 1-5 above.

I first figured all this out years ago after getting stranded to many times in the Olympic Circle when the winds in the Shimada Park to Pt. Isabel area died behind me.

So I bought a bunch of helium-filled silver balloons and took the ferry to Angel Island looking a complete dork. After hiking to the top of Mt. Livermore on a day when there were good winds at Pt. Isabel and Berkeley but NW wind aloft. I released the balloons one at time and watched from binoculars. Despite the SW wind curving around Point Blunt there was northerly wind atop the island. And as I watched the balloons streamed with the NW wind but moved up and down in the flow.

Unfortunately, we can not yet forecast the exact time this fade or weak winds will happen but we have gotten pretty good of at least giving a hint that it might occur.

Here is another hint: If there is NW wind on the coast and low teens SE winds going from the Pt. Isabel area to Larkspur watch out for Pt. Isabel/Berkeley issues after mid-afternoon.

Who can figure out why?

Mike Godsey

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