IAP 12.310
January 2008
Significant U.S. Weather Events
Classical Low Pressure System (Jan 10-11, 2008)
The evolution of a "textbook" low-pressure system is
happening before our very eyes. A low-pressure forms east of
the Rockies on Wednesday evening:
With southerly flow in front of the low, the system
can gather moisture from the Gulf of Mexico.
Recall from Wednesday's class what the 500 mb
flow looked like:
Do you recall why we look at the 500mb charts? This
level is important because this is often called the "steering
level." So if you know where the storm is, looking at this chart **
you, yourself ** can predict where the storm will go.
In fact, if you assumed this pattern stays the same,
on Wednesday, you could have predicted the rainfall today without
even looking at any of the computer models! Using the chart
above, if you follow the 500 mb jet, you'll notice if the
low-pressure system is over OK, it will go into Indiana and towards
Michigan.
What happened the next day? On Thursday, As
we had expect, the low is now over Indiana as shown below.
With the help of the counter-clockwise flow, a cold front develops.
This cold front can be seen from space:
With the Gulf of Mexico nearby, notice the moisture
associated with this cold front, as shown in the following radar
image.
