The Jet Stream and the General Public

I'm a meteorologist or a weather person and I generally love the weather.  I love to try to figure out what it is going to do and why.  The "nuts and bolts" of it is interesting.

But let's face it, 99% of the time a forecaster is forecasting for the general public and only a small percentage care about those "nuts and bolts".

So why show a jet stream map?

Three (3) basic traits the jet stream can illustrate:

(1) Air Mass Character:  Colder air is north of the jet stream and warmer air is south of the jet stream, relatively speaking. (See Image 1)

Image 1

(2) Changing weather patterns: How the jet stream changes over time will be associated with changes in weather.  (a) the jet stream axis dipping south (a.k.a troughing) will bring colder air in (b) the jet stream axis lifting north (a.k.a. ridging) will bring warm air in. 

Example: in Image 2 a large surface low (big "L") off the Pacific Coast at hour 0 (i.e. right now) moves toward the coastline at hour 0+24 (i.e. 24 hours later).  Another large surface low (big "L") near the Great Lakes moves toward Maine in the same time frame.  The colder air over the Pacific Northwest, Rockies and Canada shifts toward the Plains and Great Lakes and Warmer air shifts toward the Pacific Northwest. 

Image 2

(3) System movement: The jet stream may simply steer features along, rather than be a part of air mass changes.  A lot this has to do with the "scale" of the system.  Generally features will be on the 'small' scale, such as: jet streaks, weak and shallow shortwave troughs, small areas of low pressure.


Example: in Image 3, a small feature (indicated by a small "L") move in from the west, it is steered along the jet stream. (The time steps are relative.)  

NOTE: sometimes systems get "cut-off" from the main this "steering" flow and may "wander" around the atmosphere until a stronger system comes to pick it up.

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More "advanced" features of the jet stream:

Most of these "advanced" features are related to locations of enhanced upward and downward motion. In the world of weather upward motion is associated with the development of clouds and/or precipitation and downward motion is associated with the inhibition of clouds and/or precipitaton.

• Jet streak (or jet max): an area of locally higher winds within the jet stream.
• Jet streak coupling: when 2 jet streaks come together.
• Jet streak curvature: location within a trough or a ridge impacts upward/downward motion 
• Jet streak location: location of a jet streak within the larger scale flow can give clues as to whether a system will continue to strengthen or a system will begin to weaken.
• Low Level Jet (LLJ): A region of relatively strong winds in the lower part of the atmosphere. Generally NOT as strong as the upper level jet stream (ULJ)

I will address these in more depth in a separate blog post.