Secondary Low = Coastal Low?

[EEL]

Question came to mind looking at description of the weather for the next couple of days. Marine forecasts often speak of a coastal low and they seem to be the harbingers of strong NE winds and storms. Current discussion talks of coastal low to south and then east as cause of impending snow event, but the low on the weather charts appears to be headed well north of us. Is a coastal low the same as a secondary low and do they always appear when there is a "primary" and larger low to the NW of the coastal low? So the odds are of strong NE winds from the coastal low closely followed by strong NW winds on the back side of the primary low? Google did not help me on this so asking here with hopes Huth is about.

Ed Lawson

[JohnHuth]

Question came to mind looking at description of the weather for the next couple of days. Marine forecasts often speak of a coastal low and they seem to be the harbingers of strong NE winds and storms. Current discussion talks of coastal low to south and then east as cause of impending snow event, but the low on the weather charts appears to be headed well north of us. Is a coastal low the same as a secondary low and do they always appear when there is a "primary" and larger low to the NW of the coastal low? So the odds are of strong NE winds from the coastal low closely followed by strong NW winds on the back side of the primary low? Google did not help me on this so asking here with hopes Huth is about.

Ed Lawson

These are two different things:

A coastal low is a shallow low pressure system limited to the lower layers of the atmosphere and is formed when the wind blows from the land to the sea.

Secondary lows are small scale cloud vortices which develop within already mature occlusion cloud bands. A secondary low, by definition, will occur when there is a larger, primary low, which is characterized by counter-clockwise circulation in the northern hemisphere, and typically happens with occluded fronts.

In not sure that in the description of what you're saying, Ed, is what is classically known as a coastal low - it may simply be a low that happens to be on the coast. A classic coastal low has to do with a land/sea heating effect - although I'm not excluding this as the case. I do that, in Nor'easters, one finds lows that work their way up the coast and bring snow etc from offshore from the counterclockwise circulation.

This URL has a a very nice satellite photo of a secondary low:

http://www.zamg.ac.at/docu/Manual/SatManu/...s/SLC/index.htm

This one describes coastal lows

http://www.1stweather.com/regional/educati...oastallow.shtml

[EEL]

These are two different things:

********

In not sure that in the description of what you're saying, Ed, is what is classically known as a coastal low - it may simply be a low that happens to be on the coast.

John:

Thanks for the links.

I asked because the last two storms have been caused by lows which developed along the coast to our south and traveled up into the gulf of Maine. From looking at the NOAA charts, it appeared these formed south of and were secondary to a low which passed north of us. It seems these lows are far larger and more than something created by changes only at low altitude which you described as a coastal low. In one forecast discussion from Gray, ME they called source of the storm as a "coastal low" and described it has forming in midatlantic states and then moving upward. Based on the info in you post it seems the lows causing the storms are secondary lows and perhaps they are referred to informally as coastal lows since they are the harbinger of coastal storms/nor'esters even though they are not coastal lows in a technical sense.

I did notice that the folks on the Weather Channel called these storm producers secondary lows.

Ed Lawson

[JohnHuth]

John:

Thanks for the links.

I asked because the last two storms have been caused by lows which developed along the coast to our south and traveled up into the gulf of Maine. From looking at the NOAA charts, it appeared these formed south of and were secondary to a low which passed north of us. It seems these lows are far larger and more than something created by changes only at low altitude which you described as a coastal low. In one forecast discussion from Gray, ME they called source of the storm as a "coastal low" and described it has forming in midatlantic states and then moving upward. Based on the info in you post it seems the lows causing the storms are secondary lows and perhaps they are referred to informally as coastal lows since they are the harbinger of coastal storms/nor'esters even though they are not coastal lows in a technical sense.

I did notice that the folks on the Weather Channel called these storm producers secondary lows.

Ed Lawson

Sounds like secondary lows and the "coastal" just means they're on the coast.

Nor'easters are strange. I recall one nor'easter a couple of years ago that the forecasters completely missed - it was a low that seemed to be moving offshore, and then completely stalled and brought 5 days straight of rain. (also odd that it was in early summer)