Miller Type A and B storms

[CatullusA]

Since this comes up periodically (and I've seen several questions wrt recently on WWBB), I thought it was worth recapitulating the differences between these types of storms. These desigantions were coined in 1946 by James Miller in the paper "Cyclogenesis in the Atlantic Coastal Region of the United States."

Miller on Type-A cyclones:

"Type A.- Type A appears as a cyclone wave along the front of a cold outbreak. This type of cyclogenesis is not peculiar to the Atlantic coastal region or even east coasts in general. It is a common occurence in regions where cold outbreaks occur frequently, but it is most often observed along east coasts in the colder part of the year. At the tiemof origin of a type-A cyclone in the Atlantic coastal region the characteristic features of the surfaceweather map are:

1. A cold anticylcone covering most fo the United States east of the Rocky Mountains.
2. A cold, continental airmass flowing off the continent.
3. A current of warm, maritime air from a southerly or southeasterly direction in the western Atlantic, associated with a more or less well developed warm anticyclone and opposed to the offshore flow of cold air.
4. A retardation of a portion of the cold front in such a way that the front is distorted into a wave form.
5. A spreading of middle clouds and precipitation over the retarded portion of the cold wedge.

Type-A cyclones generally originate over the ocean and move in a northeasterly direction so that in many cases they do not have much impact on the weather of coastal stations."




Miller on Type-B cyclones:

"Type B.- Type-B originates near the coast line to the southeast of an older cyclone. Its point of origin is along the warm front, or what appears to be the warm front, of the older storm. There is some reason to believe that this type is not as common in other parts of the world and owes its frequency to the peculiar topography of North America. It is not often recognized elsewhere and not always recognized in this region. In many cases detailed study of a close network of observations is necessary to identify type B; consequently the historical northern hemisphere maps, having been anaylzed from an open network, sometimes do not distinguish between the primary cyclone and the secondary that forms near it. The characteristics of type-B are:

1. An occluding or occluded primary cyclone in the region of the great lakes, nearly stationary or moving northeastword.
2. A shallow wedge of cold continental air and associated pressure wedge, lying between the Appalachian Mountains and the Gulf Stream, the wedge line oriented southwestward from a cold anticyclone centered in eastern Canada or over the Grand Banks and crossing the 45th partallel near longitude 68 W. The shallow, cold airmass is sluggish and tends to remain along the coast during cyclogenesis.
3. A warm, maritime airmass flowing northward against the sluggish cold wedge, creating and maintaining a frontal discontinuity between the two arimasses.
4. A spreading of middle coulds and precipitation over the cold wedge, partially separated from the cold and precipitation area of the primary cyclone.
5. A local area of falling pressure dissociated from the isallobaric minimum preceding the primary cyclone, but associated with the front of the cold wedge in the region where the airmass contrast and the convergence are the greatest. The cyclone forms in this area.

As this cyclone type originates near the coast line and usually moves northeastward it affects the coastal weather much more frequently than does type-A."


Note that this is taken from Miller (1946), which appeared in Vol. 4 of J. of Meterorology. An updated scheme was produced in the early nineties by Davis et al in (1993).

-Miller, James. (1946) "Cyclogenesis in the Atlantic Coastal Region of the United States." Journal of Meteorology., 3, 31-44
-Davis, R.E., and Dolan, R. (1993) "Synoptic climatology of Atlantic coast noertheasters." International Journal of Climatology., 13, 171-189[/u]

[paul e]

Good job with the descriptions. I was just going to ask for a site to clarify, but this is perfect. I question one thing; the assertion that A type storms "...in many cases they do not have much impact on the weather of coastal stations. "

It asserts tha tbecause they originate over the ocean, and move northeast, they are too off shore to effect much land.. But, hey, all we need to do is remember the 93 superstorm, or the other classics like it that originate in the gulf, round the trough base, and chug up the east coast while developing rapidly to know that the worst of all storms to bring snow to the northeast are often these A type storms: the TRUE nor'easters!

[Chris the Weather Man]

What website did you get this information?

[Anonymous]

Good in-depth explanation of the two types of East Coast cyclogenesis. Will have to save this on my computer.