About right

Houze, Robert A., Jr and Peter V. Hobbs Organization And Structure Of Precipitating Cloud Systems , Advances in Geophysics, Vol 24, 1982 p. 225-313.

We will only review P. 229-247 “Extratropical Cyclones”

Typical model of the organization of precipitation in extratropical cyclones based on the Norwegian cyclone model (note vertical scale is stretched by a factor of 30 from the horizontal)

About right

Typical evolution of a marine extratropical cyclone from its open wave stage through the occluded stage

Classification of rainbands based on studies in the Pacific Northwest

Warm-Frontal Bands

• occur within the leading portion of the frontal system• warm advection occurs through a deep layer• oriented parallel to warm front• typically about 50 km wide• can be along (1a) or ahead (1b) of warm front

Schematic cross section through warm frontal rainband

Classification of rainbands based on studies in the Pacific Northwest

Warm Sector Bands

• occur within the leading portion of the frontal system• warm advection occurs through a deep layer• oriented parallel to warm front• typically about 50 km wide• can be along (1a) or ahead (1b) of warm front

Schematic cross section through warm sector rainband

Classification of rainbands based on studies in the Pacific Northwest

Wide Cold-Frontal Rainbands

• parallel to cold front• behind or along cold front• typically about 50 km wide• in case of occlusions, associated with cold front aloft

Schematic cross section through wide cold frontal rainband

Classification of rainbands based on studies in the Pacific Northwest

Narrow Cold-Frontal Rainband

• coincides with surface cold front• typically about 5 km wide• marked difference in structure from other band types

Schematic structure of

narrow cold frontal rainbands

Classification of rainbands based on studies in the Pacific Northwest

Pre-frontal cold surge rainbands

• associated with surge of cold air aloft ahead of cold front• otherwise have characteristics of wide cold frontal bands

Schematic structure of pre-frontal cold surge rainbands and wavelike bands

Classification of rainbands based on studies in the Pacific Northwest

Post-frontal rainbands

• lines of convective clouds forming well behind cold front• Generally parallel to cold front

Example Interaction between rainbands (wide and narrow cold frontal example)

WCFR disturbs and overtakes NCFR

WCFR disturbs and eliminates NCFR

WCFR reaches NCFR and dissipates

“Although the full classification of rainbands described above is based on observations in the Pacific Northwest (refs), it is consistent with observations of rainbands in the United Kingdom (refs) and in the northeastern United States (Cunningham 1951, Boucher 1959, Austin and Houze 1972). It is also consistent with observations made in subtropical oceanic cyclones near Japan (Nozumi and Arakawa 1968). There is good reason to believe that the picture in Fig. 4 is representative of the inherent mesoscale organization of precipitation in extratropical cyclones.”

Statement of understanding in 1982 from HH (82)

Today

Classification is reasonable for marine cyclones. Does not generally apply to continental cyclones over central North America, since

1) frontal structures do not conform well to Norwegian model and2) convective instability is much different from marine cyclones