Our sport is obviously heavily dependent upon the weather. We listen to forecast with nail biting anxiety to see if we are going to get a pow day or when our favorite resort will finally be able to open. Currently, those of us in the Pacific Northwest who are used to epic pow by Thanksgiving are clogging the suicide prevention hotlines now that it is December and nothing is open.
There have been many questions about why a certain weather pattern is happening and what to expect. Well, as a pilot, I have extensive training in Meteorology and understand weather, both global and regional patterns very well. When your life and those of your passengers depends on a thorough understanding of weather, you tend to pay attention.
Briefly, all of our regional weather is generally determined by the upper level winds known as the Jet Stream. In the Northern Hemisphere, The winds flow from west to east due to the Coriolis Force. These winds can be compared to a “river” of wind moving at high speed. The jet stream varies from about 100 to 400 miles wide and 1 to 3 miles thick. Its strongest winds are generally encountered at about 30,000 feet in the upper Troposphere. Jet-stream winds usually have a speed of 150 to 300 miles per hour, but speeds up to 450 miles per hour have been recorded. The most extreme differences in temperatures occur where the stream is the narrowest.
The jet stream shifts position frequently and actually migrates with the seasons. Sometimes two streams flow across the United States, one along the northern border and other well toward the south. The cruising range of aircraft flying downwind within a jet stream is greatly increased. Pilots anticipating high-altitude or long-range flights attempt to discover the location of the stream and use it to their advantage.
As these streams shift about due to changes in atmospheric pressure, they will tend to drag air masses along with them. High pressure systems rotate clock wise as viewed from space and low pressure systems rotate counter clock wise. High pressure systems bring stable and generally fair weather that is very warm in summer and very cold in winter. Lows on the other hand tend to bring unsettled and generally stormy weather.
Depending on where the air mass is located, it will determine what type of frontal system will be associated with it. Continental or “inland” is very dry while Maritime or “ocean” air is very moist. When these air masses originate from the north, they also bring cool or cold air with them. In the wintertime, air masses originating from central Canada is Arctic in nature and brings that sub zero weather well down into the United States. If, on the other hand, it originates from either the South Pacific or the Gulf, it will bring very warm air along with it, often resulting in freezing rain in the Midwest. On the west coast and in the Rockies these events are known as a “Chinook” or “Pineapple Express”
The Northeast gets a very unique situation as a result of the great lakes. As the Jet Stream draws cold Continental air from the west or northwest, it passes over these massive lakes which act like the ocean. This adds a Maritime effect to the weather, pumping in a lot of moisture which results in what is known as “Lake Effect” snowstorms. These events can bury places downwind in feet of snow.
So, what all this gobly-gook means is that by watching where the Jet Stream is located, you can make a pretty educated guess as to what kind of weather you can expect in your local area. Learning to read weather maps will really make you able to make pretty good guesses. This ability is an absolute must for any serious back country snowboarder. Just like a pilot, your life can be in danger from not understanding weather trends.
The best tools for this are the Jet Stream charts, the Satellite Images showing water vapor and infrared which shows cloud temperatures. Colder tops means bigger systems. Knowing how to read the Isobar charts is extremely valuable for determining what the winds will be like. All the lines you see are lines of barometric pressure at given altitudes. Read these like a Topographic map. The closer the lines are together the steeper the terrain; only in weather terms it means a steeper “Pressure Gradient” For your use, it is enough to know that places where these lines are really close together means very strong winds. These lines will also give you a clue as to the general wind directions since the winds flow along the Isobaric lines.
Here are some images of these charts for you to check anytime you want to get an idea of what is going on. These things are linked directly to NOAA and should update automatically.
Forecasted 300 Millibar Jet Stream Map Northern Hemisphere
Forecasted 300 Millibar Jet Stream Map North America
8 to 14 Day Outlook Charts
Usefull Weather Products