Drawing a Jet Stream Map (Method 2)

Method 1 is basically finding areas of of peak wind speeds, circling them and connecting them.

Method 2 is basically following the tightly packed height contours around the trough and ridge patterns.

• The basic steps for drawing a jet stream map, whether it is an analysis or a forecast model, can be broken down in easy steps.  

• BUT REMEMBER: you don't have to be perfect.  When you are drawing a jet stream map you are making "an idealized or simplified map".  You are making a continuous line for something that, in reality, is not continuous and in fact can be displaced vertically.  

•  A good tip: if you are able, looping through several forecast hours will give you better sense how things are flowing.

• I also have a post with basic information on jet streams.

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METHOD 2

Get the Level

1. Choose the appropriate level of the atmosphere.  Generally choose charts between 300mbs to 200mbs.  In an ideal depiction, choosing a layer (or slice) of the atmosphere would be more appropriate that just taking a paper a two-dimensional plane.  But, I and you, work with what is available and in the time constraints we have.

• During cold seasons, the 300mb chart might be of better use, since the air is more cold and dense in the vicinity of the jet stream during the cool season. 
• During the warm seasons, the 200mb can be used but anywhere in that range is good.

In the example for this method, I choose the 250mb level from HPC.  See Image 2.

Basic Assumptions

Some simple assumptions between the jet stream and height contours:

• the jet stream follows the trough and ridge pattern and these can be found in the height contours 
• more tightly packed height contours implies higher winds (higher "gradient").

Now the assumptions assume that you know what a height contour is and what ridges and troughs are. Here is a simple map (Image 1).

Image 1

Image 2 is from the NCEP Model Guidance website.  It is a depiction of 250 mb heights, 250 mb winds (in knots) and  isotachs.   The heights are the curving black lines.  The winds are the smaller wind barb lines. The isotachs are the shaded areas, basically areas of similar wind speeds.

As a matter of interest, I've identified the positions of the mean trough (dashed blacked lines) and mean ridge (herringbone or zig-zag line).

Image 2

What do tightly spaced height contours look like?

As stated above, Method 2, is basically following the tightly spaced height contours around the trough and ridge pattern. A quick look at what I mean by "tightly spaced" is see in Image 3.

I have placed red lines of equal length in the map.  They are perpendicular to the height contours (the black curves lines).  Areas where more height contours intersect the red line can be consider tightly spaced.

For example, Point A intersects five (5) height contours, while Point B and Point C intersect one (1) and three (3) height contours, respectively.  You can see that the region around Point A has higher winds speeds (indicated by the blue shading and the wind barbs), while Point B and C have comparatively light winds.   The higher winds speed locations are in areas where the "gradient" is higher.

A gradient is basically a rate of change over distance.  In this case, heights changing more rapidly over a distance equates to higher wind speeds.  Why?  I will likely address that in a later blog.

Where the jet stream lays in this example is basically a relation of relatives.  We want to follow the high contours where they are more tightly packed relative to other areas.

There are generally two (2) North American Jet Streams: the Polar Jet and the Sub-tropical Jet.  When making weather maps for the general public, it may not be necessary to outline both but at least know they are there.

Pop Quiz: Of the three points (A, B and C) which has the lowest winds and why?  Leave a comment to answer.

Image 3

Just draw the map already, Jeffrey!

So let's get to it.

In Image 1 and 2, we saw where the basic trough and ridge axis area lay.  In Image 3, we've located one area of tightly packed contours (relative to areas where they are less tightly packed).  So now we want to draw the jet stream.

Just draw a line that is parallel to the height contours, centered on the most tightly packed height contours.  My result is in Image 4.  The Polar Jet is indicated by the gold-toned line.

I could have also drawn the Sub-Tropical Jet.  Where would you have drawn it?  Leave a comment to answer.

Image 4

So that is it!

If you have any questions or comments, leave them below or send me a message.

Drawing a Jet Stream Map (Method 1)

Method 1 is basically finding areas of of peak wind speeds, circling them and connecting them.

Method 2 is basically following the tightly packed height contours around the trough and ridge patterns.

• The basic steps for drawing a jet stream map, whether it is an analysis or a forecast model, can be broken down in easy steps.  

• BUT REMEMBER: you don't have to be perfect.  When you are drawing a jet stream map you are making "an idealized or simplified map".  You are making a continuous line for something that, in reality, is not continuous and in fact can be displaced vertically. 

•  A good tip: if you are able, looping through several forecast hours will give you better sense how things are flowing.

• I also have a post with basic information on jet streams.

---

METHOD 1

Get the Level

1. Choose the appropriate level of the atmosphere.  Generally choose charts between 300mbs to 200mbs.  In an ideal depiction, choosing a layer (or slice) of the atmosphere would be more appropriate that just taking a paper a two-dimensional plane.  But, I and you, work with what is available and in the time constraints we have.

• During cold seasons, the 300mb chart might be of better use, since the air is more cold and dense in the vicinity of the jet stream during the cool season. 
• During the warm seasons, the 200mb can be used but anywhere in that range is good.

Here is a forecast model I choose, the GFS at 300mbs, for the morning of Friday, November 15th, 2013.   It is provided by Unisys Weather

Image 3

Where are the higher winds?

2. Circle the locations of higher winds. This can be done in a couple ways.  Many forecast models show shading, like the one I choose.  There is usually a scale included (see Image 3 above).  

Sometimes models include only wind barbs.  Such as in the image below.

Image 4

In either case, start by drawing circles contours around the areas winds, generally above 50 kts to 80 kts.  Below is rough example (Image 5).  They don't cleanly hook together do they?  In the real atmosphere they usually don't.

Image 5

Find the Core

3. Draw jet core lines: within the general area of higher wind speeds done in step #2, draw lines centered at highest wind speeds, and draw them in the direction of the wind flow.   

• Generally winds flow from west to east, but can also dive from north to south or from south to north (and in some cased west to east.  

• Wind barbs, like in the example above (Image 4), are placed where the winds are coming "from". In the (Image 4) example, in the Blue Print Example, it shows northwest winds.  
• In some forecast model depicts they show arrows, like the Image 5, above.  This generally shows the direction the winds are flowing to.  
• That is a subtle difference but it is import to know, otherwise you may be "steering" your systems in the wrong direction.  

I did some loose connections in the image below (Image 6):

Image 6

Plot the Jet Stream

4.  Make an approximate Jet Stream location.

Looking at the rough connections I made above (Image 6). I begin to connect lines, making some assumptions and keeping some things in mind:

• This is an idealized map. 
• I want smooth lines.  
• I will ignore some of the more "incongruous" 
• I will follow the flow of the wind field and the 300mb height contours (the lines in white).

My approximate jet stream location is see in the image below (image 7), as the thick white line. Notice there are two basic jet streams on this map, the northern polar jet and the southern subtropical jet.  Also, notice I didn't include every area of higher winds in the jet stream (specifically the higher winds around West Virginia into southern Pennsylvania).

Image 7

Other things to keep in mind when drawing a jet stream map:

• Jet streams flow around are areas of high and low pressure in the mid-latitudes.  .
• Generally when these idealized jet stream maps are shown, think about why you want to show them? 
• Oftentimes they can be good for showing differences in air masses. 
• Generally, when I think of jet stream maps and forecasts:  if my area is north of the polar jet, I'm expecting cooler air. If my area is south of the polar jet, i'm expecting milder air.
• That is a "dirty" assumption but it is good for general usage.  
• There are other things that come into play, such as whether there is a trough of low pressure over the region or a ridge of high pressure.  A trough of low pressure coming into the area, with the jet stream axis that was formerly north of the region now pushing south, generally means a cooling trend.  The opposite generally means a warming trend.

5.  Finalize the Jet Stream location (and if you desire) make it pretty:

I would make the lines smoother, if I were doing it for television.  The base map is there for a comparison.  

Image 8

If there are any questions or if you would like more examples, just send me a message in the Contact Me Section.