Ever since the Jet Stream was originally researched by pilots trying to fly from the United States to Japan in World War II, it has played an essential role in weather analysis and forecasting. First, a few facts about the jet stream. The jet can be referred to as a ribbon of fast-moving air near the top of the troposphere (i.e. the tropopause). Jet airplanes generally travel at this atmospheric height; hence, its namesake. Wind speeds in the core of the jet can reach more than 200mph in the winter!
Jet Stream winds often produce cirrus clouds, like those pictured above.
A satellite image of clouds at the jet stream level.
In the United States, there are 2 main branches of the jet- Subtropical and Polar. The Polar Jet is the main driver of our weather here in the DC Metro during the cold weather months. As the weather gets warmer, the Polar Jet heads north into Canada. At this point, the Subtropical Jet becomes a bigger factor in our weather pattern.
The jet stream is very useful in spotting just about any synoptic weather system. As you may know, synoptic means large-scale in meteorology, so we're referring to large troughs, ridges, cyclones, and high pressure systems. Synoptic-scale low pressure systems almost always follow the track of those fast, jet-level winds. Here are a fewthings to look for:
- Troughs in the jet will contain a core of cold air. When you see one on a map, you can usually expect a big dip in temperatures, and some strong winds from the north or northwest.
- Jet ridges indicate warmer weather. In the crest of the jet ridge, winds will usually be light. On the left side of the ridge, the winds usually intensify, and this is often an area of thunderstorm activity in the spring and summer months.
- A disturbance in the jet can be spotted as a relatively slow spot in between 2 jet streaks (wind maxima). This disturbance usually corresponds to the placement of a cold front.
- A jet streak that sits just to the right of the base of a trough will have a tremendous area of rising air in the jet streak's upper left quadrant. A surface area of low pressure usually develops underneath this area of divergence.
- A strong jet can help to enhance thunderstorm development by providing wind shear. Wind shear is a change in either wind speed or direction (or both!), and a fast jet provides instant shear. If there is a fork in the jet streak, look out! This area will have massive amounts of upper-air divergence, which could lead to severe weather if other atmospheric triggers are present.
- If a tropical system (such as a hurricane) is underneath the strong winds of the jet stream, the whole system will get weaker. Unlike thunderstorms, tropical systems are vertically consistent in shape and size, so a jet stream will destroy this continuity.
Want to check out the jet for yourself? Look at the 250mb or 200mb level on model data maps. You'll see images like the one below:
The College of DuPage's website has model data for the 250mb and/or 200mb level from several different forecast models. Explore, and enjoy!