We go back once again to Dr. Dale Ireland over in Silverdale, whose nifty HD web camera over on the western shores of the Kitsap Peninsula continues to capture the incredible sights of weather.
In this video, captured Wednesday, you can see the wind blowing in different directions at different altitudes -- also known as vertical wind shear.
First, here is the video:
Now, here, thanks to the UW's Mark Albright, is a snap shot of the vertical wind pattern during the day, also known as a "sounding". (This is what weather balloons capture, but is also done today using radio waves and acoustic soundings to determine atmospheric conditions.)
This is a bit of a spaghetti mess, but the bottom of the graph is the ground, and then it shows the conditions as they change vertically as you go up chart. (I think the units on the left are meters). Each vertical bar represents one hour, with the time in GMT on the bottom.
The blue barbs are the wind direction, and it works like a weather vane, to where the tail is where the wind is coming from, and the "point" at the start of the barb is where the wind is blowing toward -- sort of like an archery arrow.
In this case, the wind is blowing from the south in the lower layers, but then veers to the west and then the north. The video above is looking west, so you can see the lower clouds are blowing south to north while the higher clouds are blowing northwest to southeast.
You've probably heard the term wind shear in regards to aviation. What you're seeing in our example above is high enough and not abrupt enough to cause any aviation problems. But when you get strong wind shear near the ground, it can be a pilot's worst enemy.
Wind shear is defined by any area where you have two different winds blowing nearby -- and not necessarily a change in wind direction. It can be a change in speed such as wind going immediately from fast to slow, or an updraft right next to a downdraft. These differences cause eddies in the air and strong turbulence.
The most dangerous are areas of strong upward winds near areas of strong downward winds (usually near thunderstorms).
A pilot flying near the ground might encounter a strong updraft. If the pilot then pushes the nose down to counterbalance, then the plane could suddenly enter a strong downdraft that, combined with the pilot still trying to descend from the updraft, can push the plane farther down and into the ground.
Technology to the rescue: Most aircraft are now equipped with wind-shear sensors, and many airports now have wind sensors along the tarmac to help alert pilots to wind shear potential. If a pilot knows it's coming, they can avoid problems.
And there's good news for the Northwest. One of my pilot sources, who has flown large jets around the Northwest for nearly 15 years, says our weather around here is great for flying compared to other parts of the country, and that severe wind shear around here is incredibly rare.
For Seattle, he says the most common times they get any sort of wind shear is not due to thunderstorms, but usually in the winter "when a storm is coming in and the winds are smoking out of the west above 2,000 feet, at speeds at least 50 knots."
He says the wind drops off over Boeing Field at about 1,900 feet.
"Usually it is a slow drop-off as you keep descending, but I have had several times where you are at only 200-300 feet above the runway and the winds are still at 35-40 knots, but the surface winds are only in the 20’s. When you get in that situation all you can do is be prepared for it and be ready to add a bunch of power as you come over the end of the runway. Also, as we train for, if it doesn’t look or feel right just “go around” and try it again."
Here are some more links for information on wind shear in general: