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During the months of December, January, February, and 

 March, two to four cold front passages can be expected each 

 month, but it is estimated that only one of these is apt to 

 bring moderate onshore winds. In midsummer, owing to the 

 protective influence of the Pacific High, only the strongest 

 of these cold fronts reaches southern California, and then 

 with much reduced activity. 

 Coastal Lows 



Depressions may originate off the coast of California 

 and then move northwestwardly to the continent under certain 

 meteorological conditions. These storms may contribute swell 

 when the low remains for a few days southwest of Los Angeles 

 before moving northwest or moves to the mainland without 

 crossing the bay. In either case the period will be moderate 

 or low, probably between 8 and 10 seconds. Coastal lows may 

 move across the area shortly after developing and before swell 

 from the storm has had a chance to arrive. Under these con- 

 ditions wind waves are generated, but not always in an onshore 

 direction. 

 Thermal Lows 



During the warmer months of the year an extensive interior 

 "heat low" is situated over the arid regions of the southwestern 

 United States. On occasions this low expands northwestward, 

 especially if the high pressure belt moves northward, causing 

 southern California to come under the influence of the easterlies 

 and bringing westerly winds to Santa Monica Bay. Usually these 

 winds are weak and can be ignored in their influence on the 

 waves, except as they reinforce the sea breeze. 



