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windfind
Joined: 18 Mar 1997
Posts: 1901
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 Posted: Sun Apr 03, 2016 11:39 am Post subject: NPH Monday: Gorge, Bay Area & SoCal winds |
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Hi Gang,
It still looks like the North Pacific High slams against the west coast Monday. The North Pacific High will impact sites from the Gorge to the Bay Area to Southern California.
Take a look at the animation below.
1. Note the position of the North Pacific High. This time of year it should be W to WSW of the Bay Area. But it is actually in a position typical of mid June when its average location moves towards the Pacific Northwest. Can you see how its location Monday favors the Gorge? How does this impact the Bay Area wind?
2. Note that the biggest low pressure is in the northern Great Basin where you see much of the wind going. Note all the wind being diverted into that area rather than over the Bay Area. Typically this time of the year the low pressure is more in the southern Great Basin. How does this impact the Bay Area wind?
3. Now note the low pressure in the Central Valley is focused towards Bakersfield rather than in the Sacramento area. How does that impact the Bay Area wind Monday?
4. Note the wind being diverted from the North Pacific High into the Gorge. This time of year the Columbia Basin is relatively cool. So why would you forecast gusty Gorge winds Monday?
See the blog link tomorrow for the answers.
If anyone would like to take a stab at answering these questions I will give anyone with the right answers a custom San Carlos Baja forecast.
Mike Godsey
iwindsurf.com/ikitesurf.com
Weatheflow.com
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SpeedRoo
Joined: 27 Sep 2006
Posts: 89
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| Posted: Sun Apr 03, 2016 5:54 pm Post subject: |
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| The High pressure is centered around 40 degrees North with the Gorge at 46 degrees North. This sets up a pressure gradient with a southerly component that typically creates gusty conditions in the Gorge. Wind will be strongest in the mornings and fade in the afternoon as the thermal gradient tries to exert its influence. Winds will be strongest in areas of southerly outflow like Viento/Hatchery and Mosier.
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isobars
Joined: 12 Dec 1999
Posts: 20935
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| Posted: Sun Apr 03, 2016 7:37 pm Post subject: |
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| That, plus all push, no pull. The TriCities' high temps are dropping almost 20 degrees on Monday, decreasing any thermal boost.
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windfind
Joined: 18 Mar 1997
Posts: 1901
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| Posted: Tue Apr 05, 2016 9:41 am Post subject: |
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paypal: | Quote: | | The High pressure is centered around 40 degrees North with the Gorge at 46 degrees North. This sets up a pressure gradient with a southerly component that typically creates gusty conditions in the Gorge. Wind will be strongest in the mornings and fade in the afternoon as the thermal gradient tries to exert its influence. Winds will be strongest in areas of southerly outflow like Viento/Hatchery and Mosier. |
Hi Paypal: In the summer your analysis would be right on. That time of year there is a well established mass of marine layer air along the coast. And when the NPH is along the coast and the Columbia Basin is hot the pressure difference causes that cool heavy marine air to flow towards the Cascades. As it laps against the mountains its finds the near sea level Gorge so its flow rushes along the river towards the low pressure. And with high pressure to the SW the flow would go slightly cross Gorge making for gusty wind.
Alas this time of year the weather balloons and satellite imagery do not show much of a marine layer and the Basin is not very hot. So the cause of the gusty winds must lie elsewhere.
Isobars: | Quote: | That, plus all push, no pull. The TriCities' high temps are dropping almost 20 degrees on Monday, decreasing any thermal boost.
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Hi Isobars: Almost bingo! Since we don't have much marine layer air this time of year all that wind from the NPH is not cooler or heavier than the surrounding air so it is not as confined to the sea level gap of the Gorge. So it crashes over the Cascades which creates a lot of turbulence in the wind flow just aloft which translates as gusts at the surface. And this turbulent wind takes some time to return to the surface which is why the winds yesterday were out east.
Normally in the summer the Gorge the gust factor is somewhat compensated for by the thermal gradient wind generate by expanding air that is pulling the ocean wind inland.
This thermal wind is generated by the expansion and rising of surface air parcels out in the Basin. Since millions of tiny and huge parcels are rising randomly on hot days the resulting low pressure averages out to be a very steady gradient. This means steady winds. So the wind you feel in the summer with your sail or kite is the sum of the gusty wind of the North Pacific High and the steady wind of the thermal wind.
And yesterday that thermal wind was very weak. Hence the winds were gusty unless you were very far out east where the turbulence fades.
Now do you see why the Gorge has the steadiest but brief summer wind on those 4.7 to 5.2 days when there is only a thermal wind.
Incidentally I am leaving out the impact of topography and the strong winds aloft both of which contribute to gusty winds.
So Isobars when are you planning your San Carlos, Baja trip? Let me know and I will do a custom forecast for you.
Mike Godsey
iwindsurf.com/ikitesurf.com
Weatheflow.com
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SpeedRoo
Joined: 27 Sep 2006
Posts: 89
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| Posted: Tue Apr 05, 2016 1:32 pm Post subject: |
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| Beg to differ Windfind but the gradient level winds at 1200 feet were very southerly that day. The mixing down to river level made for very gusty winds, as it always does whatever time of the year. The locations with southerly outflow from the valleys were where the wind was, I checked them out as I drove to PDX and back during the day. There was some thermal effect wind in the afternoon once the front had cleared. Doesn't take a huge temp difference to get it going.
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isobars
Joined: 12 Dec 1999
Posts: 20935
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| Posted: Tue Apr 05, 2016 4:37 pm Post subject: |
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| windfind wrote: | | Hi Isobars: Almost bingo! So when are you planning your San Carlos, Baja trip? Let me know and I will do a custom forecast for you. |
I'd settle for reliable dawn patrol forecasts in general for the corridor or Maryhill. They -- both the dawn (instead of this 7:00 AM/mid-morning stuff) winds and reliable forecasts for them -- seem to be in short supply for a decade now.
I'm not blaming any forecasters; they are obviously very difficult to predict. I'm just disappointed to see those frequent sunrise winds fade into history, and would love to understand them better so I can better pick the best days to get up early and drive 100-150 miles to catch them.
Barring that, what's the optimal setup for those occasional, spectacular, steady evening blasts at The Wall, after everyone else gets worn out and goes home, leaving the river to us younger guys with more endurance? I just
HATE being almost the only person on the river, in the day's best wind, from 5 'til dark.
NOT! 
Mike \m/
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