Retrograding Low

[aveosmth]

What does this mean when a pressure system "retrogrades"? Any info would be very helpful!!!!

[ColdFront77]

Retrograding means "backwards," so a retrograding low is a low pressure system that moves "backwards" or from east to west (or even northeast to southwest) across most of the United States/in the northern hemisphere -- especially north of the Gulf of Mexico and southeast, south and southwestern U.S.

[aveosmth]

Thanks Cold Front! Is this a rare occurance or is it pretty common? Thanks!!

[ColdFront77]

You're welcome, aveosmth. It tends to be rare, but I would be more cautious to say that it is more rare than it is common.

Weather system generally always move west to east across the United States, so having a system move toward the west just can't happen for no reason at all. When a low retrogrades it can only do so at a very slow rate of speed.

Hopefully this is correct and/or others can add their feedback, as well.

You're welcome!!

[USAwx1]

You're welcome, aveosmth. It tends to be rare, but I would be more cautious to say that it is more rare than it is common.

Weather system generally always move west to east across the United States, so having a system move toward the west just can't happen for no reason at all. When a low retrogrades it can only do so at a very slow rate of speed.

Hopefully this is correct and/or others can add their feedback, as well.

You're welcome!!

Your right, Tom. In meteorology, retrogression is defined by a system which moves in a direction opposite to the basic flow.

A retrograding low pressure system (using your example) is normally cutoff from the flow--which may drift westward b/c the jet is passing off to the north of it and there is essentially nothing to steer it.

This can also be applied to high latitude blocks which move from east to west. An example of this would be an area of blocking high pressure retrograding from Scandinavia to Greenland during the winter.

DONT confuse this with the DISCONTINUOUS RETROGRESSION of the longwave pattern where one major longwave trough weakens and slides eastward while a new longwave trough forms to the west of the location of the previous through.