Embedded Files
In the central United States, a cold front stretches from Canada to the Gulf of Mexico. This cold front runs roughly parallel to the band of low and high clouds spiralling out from the storm system in southern Canada, stretching across the Great Lakes and across the Mississippi River Valley.
These cloud bands are excellent markers of cold fronts, but they have two problems. First, if they don't extend southward from a cyclone center, they probably don't represent a cold front. Second, it's difficult to locate the position of the surface cold front from the position of the band of high clouds. As a general rule, the cold front is near the leading edge of the cloud band to the south, and near the trailing edge of the cloud band near the low center.
Take a close look at the infrared satellite image of the Great Lakes region. A broad band of high clouds spirals out from the province of Ontario and across the eastern Great Lakes. Lower clouds are also visible in the image. But where's the cold front? By the above rule, it ought to be somewhere in Michigan, perhaps passing near Sault Ste. Marie. But the exact position is impossible to determine from this image.
Here's the surface map for the same time. The front turns out to be easily located by the wind shift and the falling temperatures behind the front. (The line of blue triangles also helps.) The front is roughly parallel to the clouds, but not really, and you can see that you wouldn't want to use a cold frontal cloud band to locate the front if you really needed to know exactly where it was.
Much farther south, the high clouds are missing, and the front over Texas is possible to identify by a thin line of shallow cumulus clouds. Here's what it looks like in the visible image. Ahead of the cold front, shallow cumulus clouds are found within the warm air. The rope cloud appears as a narrow line of cumulus clouds which is remarkably straight. Farther behind the front, stratus clouds are present.
Rope clouds such as this are always associated with convergence lines of one form or another. They can be sea breezes, thunderstorm outflow boundaries, or cold fronts. The identification of this particular rope cloud as a cold front is suggested by the fact that it extends southwestward from the larger-scale cold frontal cloud band. This identification is confirmed by the surface map. This time, I'll not be so kind as to draw the cold front for you, but I hope you can identify the cold front along the coast.
Over the Great Lakes, the surface map was needed to pin down the location of the cold front. In Texas, the satellite image can be used to determine the exact location of the cold front, much more accurately than could be done with just the surface map alone.
Report abuse