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The 300 mb map features height contours in black, wind barbs (also in black, and isotachs (lines of constant wind speed) represented by the progressively "hotter" colors.
This map and the others in this module can be accessed through the UCAR Weather numerical model web site.
This map is ideal for practicing your wind skills. Want to find the strongest winds? One technique is by color: Southern New Jersey is bright red, which means wind speeds exceed 125 knots according to the scale at the bottom of the image. Color-blind? Look at the wind barbs. The wind barbs in that area have two pennants and three long barbs, for a total of 130 knots (each pennant is 50, each barb is 10). Can't make out those tiny wind symbols? Look at the height contours. They are closest together across the mid-Atlantic states, implying the strongest geostrophic wind speeds.
Consistent with geostrophic balance and the earlier examples, notice how the winds tend to be parallel to the height contours. Also, notice that in the southern part of the map, that rule doesn't work so well. A general truth: the closer you get to the equator, the less well geostrophic balance works.
A couple of other things are unexpected.
At the center of the low over Hudson's Bay, the wind speed is relatively weak, even though there are lots of height contours. Why? It's like being in a steep-sided valley: the slopes surrounding you are large, but right at the bottom of the valley it's level. In calculus you'll learn that if the height reaches a maximum or minimum at a particular point, the height gradient there is zero.
Where there is strong cyclonic (leftward) curvature in the height contours, such as over Washington State, the wind speeds seem to be unusually weak. This is generally true, and stems from the fact that for air to curve to the left, the pressure gradient force must be stronger than the coriolis force. The opposite situation occurs when there is strong anticyclonic (rightward) curvature.
Did you understand that? If so, answer this question: Why does the wind speed tend to be weak when the airflow curves to the left?
Finally, notice how the strongest winds form bands of color that are much longer than they are wide. These are the "jet streams", ribbons of strong wind that are good or bad for air travel, depending on which way you happen to be going at the time.
The pressure gradients (and winds) are much stronger aloft, at jet stream level, than at the ground. Through a somewhat tricky argument that I won't go into here (but which depends on the relationship between vertical pressure differences and temperature), the cold lower-tropospheric air tends to be located north of the jet stream, with its southern edge aligned with it, and the stronger the jet stream winds, the stronger the temperature gradient beneath the jet stream.
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