Geostationary weather satellites are able to show water vapor density in the upper third of our atmosphere. As a result the upper airflow becomes visible, and ridges and troughs are easy to identify. Watch for moisture inflow. Can you identify the Tropical Jet Stream?
Sharp contrasts between black and white often indicate strong temperature gradients. We could call them “Upper air fronts”. These fronts are sure to bring unsettled weather to the surface, so as soaring pilots we do not want to see them close to our flying area.
Because big thunderstorm cells and mountain waves tend to condensate water at very high altitudes, they show up very well on water vapor images. In this picture for example we can clearly identify a Mesoscale Convective System (MCS) over Oklahoma, a cluster of thunderstorms that grew together overnight and usually dissipate by dawn.
If our “Eyes in Space” look at the earth in a spectrum just below of what the human eye can see, we are looking at the infrared spectrum (IR). In IR mode we are comparing temperatures. The cooler something is, the whiter it appears in the image.
Often times in the early morning, when we want to know whether we will be able to go to the mountains and have some fun flying, the sun has not been up yet long enough to allow us to look at a satellite loop in the visible spectrum. So we have to look at an IR image, which is independent from sunlight. What we have to keep in mind is that we are not looking at actual clouds, but simply comparing temperatures. This means that low clouds (warm) might not show up at all, while high (cold) cirrus clouds appear in bright white.
Due to their altitude and the associated cold temperatures, thunderstorm tops and mountain waves show up very well in IR. Watch for long, north-south oriented bright white clouds that do not appear to move in a loop. These will most likely be lenticular clouds indicating very high winds aloft and extreme turbulence in the mountains. Better fly another day…
Meteorologists, for whatever reason, do not like to look at the earth’s atmosphere in terms of constant altitude levels, but rather constant pressure levels. One advantage of this method is, that we always know where we are at relative to the mass of the atmosphere that weighs down on us. If we assume for example that at sea level, the earth’s atmospheric pressure is exactly 1000 milibars (mb), we know that at 500 mb we are exactly half way up through the atmosphere. This happens to be at around 18,000 feet MSL or about 5,700 meters or about 570 deca meters (dm).
A 500mb constant pressure chart is an excellent basis for looking at what is going on in the upper atmosphere. Why should I care about what is happening at 18,000 feet if I never discovered the secret of thermaling and always seem to have sled rides straight to the LZ? Well, because it is often the upper atmosphere that causes the weather closer to the surface. Think of the upper atmosphere as the master of the lower atmosphere. In order to truly understand the lower levels, we have to first figure out what the uppers are up to.
Right away we notice the black wavy lines. These are called contour lines and they are lines of equal height. What height? The height (or altitude if you will) at which we can find 500mb of pressure. The reason why heights vary is the fact that warm temperatures tend to expand, while cold temperatures contract our atmosphere. This means that our 500mb pressure level forms a landscape with hills and valleys, that meteorologist call ridges and troughs. Troughs form a U-shaped pattern and mean colder temperatures aloft, while ridges go the other way and mean warmer temperatures aloft.
We also notice that the winds aloft seem to follow the black contour lines. Not only that but there is also a direct relationship between the spacing of the contour lines and the wind strength. The tighter the contour lines are spaced, the stronger the winds aloft will be. This especially happens around and ahead of troughs, which often bring storms over the mountains. The strongest winds aloft can form a band of 50+ knot winds. This is called the jet stream and in the summer time, we usually find it far to our north at around 30,000 feet. However, in the wintertime the big scale weather patterns shift, and the jet stream can sometimes be right upon us. Beware of flying on those days.
The best flying days in the Front Range are usually brought on by a big
ridge over Colorado, which pushes the high winds to the north and sometimes
brings in stable and warm air putting a lid on afternoon thunderstorms.