The Presidents' Day cyclone of 18-19 February 1979 - Synoptic overview and analysis of the subtropical jet streak influencing the pre-cyclogenetic period

A detailed examination is undertaken of the subtropical jet (STJ) streak revealed by an analysis of the Presidents' Day cyclone of February 18-19, 1979. During its 24 h period, the STJ's flow became increasingly supergeostrophic and apparently unbalanced, while ageostrophic wind speeds inc...

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Bibliographic Details
Published in:Monthly weather review 1984-01, Vol.112 (1), p.31-55
Main Authors: Uccellini, L. W., Kocin, P. J., Petersen, R. A., Wash, C. H., Brill, K. F.
Format: Article
Language:English
Subjects:
Meteorology And Climatology
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Summary:A detailed examination is undertaken of the subtropical jet (STJ) streak revealed by an analysis of the Presidents' Day cyclone of February 18-19, 1979. During its 24 h period, the STJ's flow became increasingly supergeostrophic and apparently unbalanced, while ageostrophic wind speeds increased to more than 30 m/sec in association with a significant cross-contour component, directed toward lower values of the Montgomery streamfunction, as the flow along the STJ became more divergent with time. These phenomena are linked to the increasing confluence in the entrance region of the jet streak and the decreasing wavelength of the trough-ridge system in which the jet streak was embedded. The upper level divergence and upward vertical motion near the axis of the STJ are found to be important factors in the development of the cyclone's first area of heavy snow.
ISSN:0027-0644
1520-0493
DOI:10.1175/1520-0493(1984)112<0031:TPDCOF>2.0.CO;2