During periods of less active weather, when the storms are not hitting us regularly, a pronounced daily wind speed variation is quite evident in our region.
Winds are generally weak overnight and into the early morning and then rev up during the late morning/afternoon, often peaking around dinner time.
Consider the sustained winds (averaged over two minutes) during the last three days at four Western Washington locations.
At Westport, on the central Washington coast, the wind was near calm overnight and then sped up to around 15 mph around noon and stayed strong until around 7 PM, when it declined rapidly.
Westport
Moving to north Seattle (Sand Point), the daily (diurnal) wind variation is just slightly weaker than on the coast, with the acceleration starting a few hours later.
Seattle Sandpoint
What about the New Dungeness Lighthouse, which observes the winds in the eastern Strait of Juan de Fuca? A nice diurnal variation, but quite different. Winds peak in the evening there! Why?
New Dungeness
Finally, consider the winds at Olympic Airport, several miles from the water. They have a daily wind variation, but a bit weaker than the others, with near-calm conditions at night.
Olympia Airport
First, there is the daily variation in vertical mixing of air. Winds are generally slower at the surface, with a rough surface and structures slowing down the wind (see below)
This explains the strong sea breeze on the coast.
Seattle gets some sea-breeze action as well. In this case, the Sound Breeze, which is a sea breeze between the mostly land area of central Puget Sound and the cold water of the Straits of Juan de Fuca and Georgia (see below). It is a northerly winds the increases during the mid to late afternoon and weakens around 8 PM.
Olympia Airport has a weakened daily variation of winds, with far less sea breeze or Sound Breeze influence.
However, Olympia AP winds respond to the difference in the increased vertical mixing as the land heats up during the day (and Olympic Airport has a more continental climate and tends to warm up more during the day than Puget Sound locations).
Finally, there is the interesting case of the winds in the eastern Strait...with the Dungeness Lighthouse winds shown above.
The diurnal wind variation there is very different, peaking in the evening. Why so late?
The answer is that the winds in the Strait are responding to a larger-scale "sea breeze." One between eastern Washington and the coast.
The Columbia Basin heats up during the day, causing pressure to fall (warm air is less dense--or heavy--than colder air). So a pressure difference develops during the day (higher pressure on the coast, lower pressure east of the Cascades), and the regional winds react to that. To illustrate, below is the sea level pressure on Thursday at 6 PM--you can see the higher pressures on the coast compared to the interior.
Being larger in scale, it takes more time for the winds to react to the regional pressures...thus producing the evening maximum of westerly wind over the eastern Strait of Juan de Fuca.
Westerly (from the west) winds tend to rev up during the evening over the eastern slopes of the Cascades for the same reason. They are responding to the regional pressure differences.
In short, there are fascinating local diurnal wind variations that become quite obvious when we have sunny skies and a lack of incoming weather systems.
If you ever plan on flying a kite or taking out a sailboat, such information is of great interest.
Yes, I notice this on my bike ride home in the afternoon. Grrrrrrr. North winds make for lovely days and no so lovely bike commutes.
ReplyDeletejno62 My sentiments exactly. Riding home from work I go north and slightly uphill. The north wind does not help. In the morning there is not much wind to help going southward.
Delete“ An adiabatic process is a thermodynamic process where no heat is exchanged between a system and its surroundings. In the context of winds, this means the air's temperature changes solely due to pressure changes as it rises or falls.”
ReplyDeleteAh, so this is why I've been fighting a (sometimes quite chilly) headwind on my bicycle rides home these last few weeks. Riding north, around the eastern edge of Greenlake, the breeze coming off the lake is quite stiff, and constant. The road is flat, but it feels like a 3 or 4 percent grade with the wind.
ReplyDeleteWind on warm days doesn't bother me that much, mainly because I'm light on layers. I just get annoyed when the predominant wind doesn't align with the shore breeze along Lake Stevens.
DeleteYour timing is impeccable, as I'd been wondering about this lately. Thanks for posting about it!
ReplyDeleteI've learned this pattern well on my north-south bike commute. Great to learn something about the mechanism. So this is why I always have a &#@$^# headwind when riding home on sunny days.
ReplyDeleteCamping in the Olympics (ridgelines) during those clear, cool nights in the summer, I experience that evening breeze shutoff. Interestingly, it seems to correlate perfectly as the sun sets. I always thought it was due to the fact that solar radiation just stopped.
ReplyDeleteAlso, on those same summer nights, the winds can drastically increase as the night progresses, slowing by morning. Keeps the skeeters away for us no-tenters.
This change in wind energy is one of the significant factors that works against wind power. If one looks at the BPA wind energy graphs, there is often virtually no wind energy for days and when there is, as is shown in the wind plots, the energy is often very erratic. This makes managing the grid difficult. In California, the wind plots show a significant reduction of wind energy during the day and normally an increase in wind energy at night. This is good because there is no solar at night. However, there is a three or four to one difference between solar and wind energy in California. Even in normally breezy Hawaii there can be days and weeks of virtually no wind. It is hard to beat gravity and water as a source of energy or nuclear.
ReplyDeleteThis is the bane of my sailing schedule. I sail mostly in the North Sound. In the morning, winds are light, and sometimes southerly. In the midday hours I often bake under nearly calm conditions unless I run the motor. Then, around 3-4 PM the wind finally arrives, and peaks around 7 PM- just when I want to anchor for the night and make dinner. Contrast my upbringing in Connecticut where the wind starts around 11 AM, peaks around 3 PM, and often quits about sunset. A more accommodating regime.
ReplyDelete