The “BIG picture” suggests, not!

by Mike Godsey, mike@iwindsurf.com

Funny, forecasting is a lot like growing up. As a kid you can only focus on the obvious. As you mature your world expands.NORTH PACIFIC HIGH ridge

When I first started forecasting I looked at the things right in front of me: the fog, the ocean buoys, the SFO-SAC pressure gradient etc. And in simple patterns and in the simpler weather years ago that sometimes worked. But then all of a sudden a marine surge would appear out of nowhere. Or on a ripping NW day at the ocean buoys Bodega and the Peninsula would be dead and Pt. Isabel blow.

Gradually as my skills improved along with my tools I began to widen the scope of my vision and found that subtle events 10’s to 1000’s miles away often impacted the local winds.

First there was that memorable Usafishing.com fishing trip when I found that the winds between Bodgea and Pt. Bonita radically changed from strong NW to mild SW along our course.

Listening to the old salts talk about these nasty days with a steep southerly chop formed on the big NW swell was an aha experience. I realized that there had to be a tiny eddy that formed on some days that blocked the NW wind from the Peninsula but shot southerly wind through the Golden Gate.

So I started looking at the fuzzy satellite imagery even more closely and found I in certain patterns I cold  discern an eddy even
before first light when I was preparing the forecast. But it took more years for me to realize what caused the eddy and to be able to forecast in advance. And I am still waiting tor at aha insight when I figure out how to forecast what time of the day it will die.

So this meandering story applies today since this is exactly the sort of Thursday when, looking at the small picture, I would have forecast powerful NW winds on the coast for day since everyone knows that a NW blows lasts at least 2 or more days. Perhaps weakening a bit each passing day but… lasting.

Looking at the first image you can see the small picture even at dawn powerful NW wind just off the beaches.

But now let’s zoom out and look at the 2nd. image Big Picture. The difference is subtle but it makes strong NW wind Friday unlikely for the AWT Waddell contest.

First find the center of the North Pacific High. Remembering that the NPH is a huge dome of high pressure air you can see that it is extending a ridge from it’s center towards the Pacific Northwest. This has 2 impacts on the wind Friday:

1. As this happens the wind in far Northern California Cascades becomes more North. It is hard to see this in the image since the mountains weaken and divert the wind. But as this wind comes down the mountains tomorrow it compresses, heats and creates low pressure in the Redding area.

This process has already started today. Looking at the tiny pressure gradient graph to the right and you can see that the SFO-Redding pressure gradient modeled for today is much weaker that yesterday.

I expect that pressure gradient to become negative tomorrow creating a South to North pressure gradient which causes southerly wind to ramp up on the coast Friday morning and Sherman Island Friday late afternoon and especially Saturday.