Information Summary

The Sea-Level Pressure Pattern across the Western U.S. and Eastern Pacific during a Catalina Eddy Event on 10/13/95

This visible satellite image/pressure field-composite map of the western U.S. and eastern Pacific Ocean shows the sea-level pressure pattern at 5:00 A.M. P.D.T., superimposed on the visible satellite image and surface weather reports at 9:00 A.M., on October 13, 1995, during the development of a Catalina eddy southwest of Pt. Conception along the Southern California coast. The information on the image includes:
(1) Contours of sea-level pressure (at intervals of 4 millibars; the analysis comes from the National Meteorological Center's eta-model initialization at 5:00 A.M. P.D.T., or 12Z);

(2) Plots of surface wind speed (in knots) and wind direction recorded at 9:00 A.M. P.D.T. (16Z); and

(3) A visible satellite image recorded at 9:00 A.M. P.D.T. (16Z) by the GOES-West (GOES-7) satellite.

This pressure map shows a region of relatively high pressure (greater than 1032 millibars in places) across the Pacific Northwest and northern Rocky Mountains. Much of California lies within a strong pressure gradient (where isobars pack relatively closely together) south/southwest of the high, where the pressure drops off rapidly toward the south. This pressure gradient drove winds across the east-to-west oriented mountain ranges along the coast of California east of Point Conception and just north of Santa Barbara, leading to the formation of a region of relatively low sea-level pressure southwest of Point Conception. The low pressure there pulled cool marine air northward along and up against the coast. Either the marine air was already full of fog and low stratus clouds, or these clouds formed in the marine air as it piled up against the coastal mountains and became deeper. The fog and low clouds are what make the eddy visible in visible satellite images such as the one shown here.

A set of companion images in our special-image archive shows a series of close-up views with surface weather observations superimposed, and a summary of information on the close-up images provides more information about them.

For more information about reading some of the meteorological information on this image, refer to the key to weather-station plots and general description of visible and infrared satellite images.

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