ZONE OF DOMINANT MARITIME INFLUENCE 



TRANSITION ZONE 



Ruggedness of the topography in this zone 

 markedly affects local climatic conditions. It 

 produces great differences in temperature and 

 precipitation in local areas that are not very far 

 apart. 



Climatic conditions at individual locations in 

 this zone are characterized by small variations 

 in temperature, high humidities, high fog fre- 

 quency, considerable cloudiness, and abundant 

 precipitation. 



Extremes of temperature are quite localized 

 and usually of short duration. The warmest tem- 

 peratures usually come in late July or in August. 

 Throughout the Maritime Zone only about one 

 station in 15 reaches or exceeds 90° F. The mean 

 temperature during these months is near the mid- 

 fifties. 



Temperature changes between seasons are 

 gradual; the length of the growing season varies 

 considerably from one year to another. The 

 average freeze-free period varies from 120 days 

 in the north to 150 days in the south. Freeze- 

 free periods within any given locality vary within 

 wide limits. 



The overflow of cold air from intense high 

 pressure cells over the mainland interior produces 

 downslope winds that attain destructively high 

 speeds at times. Because of its exposure to the 

 open sea, the entire Maritime Zone is vulnerable 

 to strong winds associated with intense cyclonic 

 circulations that frequent these northern ocean 

 areas. Throughout the coastal area the rugged 

 terrain produces extremely localized wind con- 

 ditions. 



Precipitation ranges from about 25 inches 

 annually in the northwest portion to 221 inches 

 in the southeast. The steep terrain, rising out of 

 the sea, creates topographic inducement for the 

 high rates of precipitation along the northern 

 Gulf Coast. 



Visibility is usually low because of cloudy 

 and foggy weather. Fog, usually the advective 

 type, occurs frequently during the summer over 

 the Aleutians and often drifts eastward to blan- 

 ket the western Gulf Coast. 



The change from a maritime to a semicon- 

 tinental climate characterizes the Transition Zone. 

 This change is rather abrupt along the boundary 

 between the South Coast and Copper River Divi- 

 sions because of the sharp ridge of mountains 

 along this boundary. The Bristol Bay and West 

 Central portions have a gradual climatic transi- 

 tion since moisture-laden air moving toward the 

 interior meets no formidable mountain barriers. 

 Typical maritime features become less prominent 

 farther inland: temperature varies more mark- 

 edly; humidities are lower,- cloudiness declines; 

 and precipitation totals recede. 



The Copper River Basin has extremely cold 

 winters, but maximum temperatures reach 90° 

 to 95° F. in summer. This climatic feature of the 

 Copper River Basin indicates that its weather pat- 

 tern approaches that of the Continental Zone. 

 In areas more directly affected by maritime in- 

 fluences, extreme highs range around the mid- 

 eighties. 



The average freeze-free season varies from 

 52 to 132 days. The 169-day freeze-free period 

 recorded at Homer one year was exceptional. 



Precipitation in the Transition Zone markedly 

 decreases from the high averages in the Mari- 

 time Zone. A drastic reduction in precipitation 

 in the Copper River Valley and land westward 

 to the upper Matanuska Valley is caused by the 

 configuration of the sheltering Chugach Range. 

 Thunderstorms are common in the Copper River 

 area during the summer. 



Precipitation generally ranges from 10 to 

 about 30 inches. A few local areas receive heavy 

 precipitation (75 to 80 inches) because south- 

 easterly winds resulting from low pressure cen- 

 tered near the Alaska Peninsula are hardly af- 

 fected by sheltering terrain. In contrast, the 

 Kenai Range shelters the western Kenai Penin- 

 sula from the southeasterly winds, and the total 

 precipitation there is comparable to that in Mata- 

 nuska Valley (15 inches at Palmer). On the more 

 exposed southern tip, annual totals average 25 

 to 40 inches. 



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