clatsop county climate
Introduction

Clatsop County lies along the Oregon coast. It is wholly within Climate Division 1 (Oregon Coast) established by the National Climatic Data Center. Below is a description of the climate of Division 1 followed by specific descriptions of Clatsop County. Climate tables for various parameters, as observed at long-term climate stations in Clatsop County, are included below.

Climate Division 1 — Oregon Coast

Stretching along Oregon's Pacific border, the coastal zone is characterized by wet winters, relatively dry summers, and mild temperatures throughout the year. Coastal terrain features include a coastal plain (extending from less than a mile to a few tens of miles in width), numerous coastal valleys, and the Coast Range, whose peaks range from 2,000 to 5,500 feet above sea level and extend down the full length of the state. Rivers such as the Coquille, Umpqua, and Yaquina dissect the Coast Range and drain its slopes. The area's heavy precipitation results from moist air masses moving off the Pacific Ocean onto land, especially during winter months. The abundant moisture supports lush pastures for dairy and animal production as well as valley crops of grass seed, flower bulbs, nuts, and fruit.

Along the lower elevations of the immediate coast, normal annual precipitation is between 65 to 90 inches. However, spots high on the west slopes of the range may get up to 200 inches. Several days of abundant rainfall can cause strong flood events. In some locations, flood control dams have greatly reduced the incidence of damaging floods. As is typical of western Oregon, the highest monthly precipitation values for the coast occur in the winter months of November, December, and January. Table 1 is a summary of mean monthly and annual precipitation for recording stations in the coastal zone. Figure 1 shows NOAA climate stations in Zone 1, which were in operation during the 1961-1990 period. Figure 2 shows the Clatsop County region from the Oregon annual precipitation map. Table 2 lists the average number of days with precipitation amounts exceeding certain thresholds.

Snowfall' in tcoastal vicinity is minimal, usually only one to three inches. Some of the higher elevations receive significant amounts of snowfall, however. For example, in January of 1982, Laurel Mountain (elevation 3,589') received 55 inches of snow. At Mary's Peak (elevation 4,097'), the highest peak in the Coast Range, snow often lasts into May. Table 4 lists average monthly and annual snowfall totals for various stations.

The months of July, August, and September tend to be the warmest, but average summer temperatures are only about 15 degrees above the coldest month, January.

Table 3 lists normal monthly temperature at stations in the area. Average heating and cooling degree days (base 65 deg F) are lower for the coastal region than any other Oregon region as a result of the mild temperatures.

Extremely high or low temperatures are rare, and the annual temperature range is lower than any other Oregon climate zone. Temperatures of 90 deg F or above occur, on the average, less than once per year, and freezing temperatures are infrequent. Newport, for example, records temperatures of 32 deg F or below an average of 30 times per year. Killing frosts are even less frequent. Most of the area averages more than 300 days between the last occurrence (in spring) and the first occurrence (in fall) of 28 deg F temperatures. Table 5 and 6 list median frost dates and mean growing seasons, respectively, for four different temperature thresholds.

Occasional strong winds strike the Oregon Coast, usually in advance of winter storms. Wind speeds can exceed hurricane force, and in rare cases have caused significant damage to structures or vegetation. Damage is most likely at exposed coastal locations, but it may extend into inland valleys as well. Such events are typically short-lived, lasting less than one day.

Skies are likely to be cloudy during winter, and only partly cloudy during summer. At Astoria, average winter cloud cover is over 80 percent, dropping only to about 65 percent in summer. Summer cloud cover is due mostly to fog and low clouds. As a result of the persistent cloudiness, total solar radiation is lower here than in any other part of the state.

Table 7 and 8 list average monthly and annual heating and growing degree days, respectively.

County Description

Established: June 22, 1844
Population: 35,850
Area: 843 sq. mi.
Economy: Fishing, tourism and forest products.
County Seat: Astoria

Clatsop County was created from the original Tuality District in 1844 and named for the Clatsop Indians, one of the many Chinook tribes living in Oregon. The Journals of Lewis and Clark mention the tribe. Fort Clatsop, Lewis and Clark's winter headquarters in 1805 and now a national memorial near the mouth of the Columbia River, also took the tribe's name. Astoria, Oregon's oldest city, was established as a fur trading post in 1811 and named after John Jacob Astor. The first U.S. Post Office west of the Rocky Mountains was also established in Astoria in 1847. The first county courthouse was completed in 1855; the present courthouse was erected in 1904. Records show that the summer resort of Seaside was founded by Ben Holladay, pioneer Oregon railroad builder, in the early 1870s when he constructed the Seaside House, a famous luxury hotel for which the city was finally named. The Lewis and Clark Expedition reached the Pacific Ocean at this spot.

(County information obtained from Oregon Blue Book)

Climate Tables (Clatsop County, Oregon)


Table 1. Precipitation, Monthly and Annual Averages (1971-2000) (back to top)
Name
Number
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Astoria WSO Airport
328
9.62
7.87
7.37
4.93
3.28
2.57
1.16
1.21
2.61
5.61
10.5
10.4
67.13
Seaside
7641
10.27
9.57
8.44
5.74
3.96
3
1.63
1.34
3
6.07
11.38
11.34
75.74

Table 2. Average number of Days with Selected Precipitation Amounts, Astoria WSO Airport, 1971-2000 (back to top)
Threshold
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
.01"or more
20.8
18.9
21
17.8
16
13.1
8.3
7.2
9.4
14.8
20.9
21.2
189.7
.10"or more
16.2
14.1
15.3
11.8
8.6
6.4
2.9
2.9
5.6
10.1
16.8
16.2
127.6
.50"or more
7.5
5.8
5.3
3
1.8
1.5
0.6
0.7
1.7
3.8
7.4
7.2
46.4
1.00"or more
2.4
1.7
1.5
0.5
0.3
0.3
0.2
0.2
0.5
1.4
2.6
3.2
14.9

Table 3. Monthly and Annual Average Temperatures (deg F), Astoria WSO Airport (1862), 1971-2000 (back to top)
Parameter
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Mean max
48.1
50.8
53.3
56.1
60.0
63.6
67.2
68.3
67.5
61.0
53.1
48.4
58.1
Mean min
36.7
37.6
38.6
40.8
45.4
49.8
52.9
53.2
49.5
44.1
40.1
37.1
43.8
Mean temp
42.4
44.2
46.0
48.5
52.7
56.7
60.1
60.8
58.5
52.6
46.6
42.8
51.0
Extreme max
67
72
73
83
87
92
93
96
95
85
71
64
96
Extreme min
11
9
22
30
31
37
39
39
33
26
19
6
6
Mean number of days
Max 90 or more
0
0
0
0
0
0.1
0.1
0.1
0.1
0
0
0
0.4
Min 32 or less
0.3
0.1
0
0
0
0
0
0
0
0
0.1
0.9
1.5
Max 32 or less
8.7
6.1
4.6
1.4
0.1
0
0
0
0
0.5
4.5
7.9
32.3
Min 0 or less
0
0
0
0
0
0
0
0
0
0
0
0
0

Table 4. Snowfall, Monthly and Annual Averages (1971-2000) (back to top)
Name
Number
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Astoria WSO Airport
328
1.2
0.4
0.2
0.1
0
0
0
0
0
0
0.3
0.6
2.5
Seaside
7641
0.4
0
0
0
0
0
0
0
0
0
0
0
0.6

Table 5. Median Spring and Fall Frost Dates, Astoria WSO Airport, 1971-2000 (back to top)
Percentile
Last Date in Spring of Low Temperatures (deg F)
First Date in Fall of Low Temperatures (deg F)
24
28
32
36
24
28
32
36
10
1-Jan
28-Jan
8-Mar
10-Apr
21-Nov
11-Nov
16-Oct
29-Sep
20
1-Jan
31-Jan
19-Mar
21-Apr
1-Dec
17-Nov
26-Oct
2-Oct
50
29-Jan
12-Feb
9-Apr
5-May
1-Dec
1-Dec
7-Nov
13-Oct
80
8-Feb
6-Mar
25-Apr
12-May
1-Dec
18-Dec
25-Nov
21-Oct
90
15-Feb
15-Mar
29-Apr
15-May
19-Dec
18-Dec
1-Dec
26-Oct

Table 6. Average Growing Season, Astoria WSO Airport, 1971-2000 (back to top)
Percentile
Length of Time (Days) Between Occurrence of Temperatures ( deg F)
24
28
32
36
10
282
245
180
143
20
293
258
199
146
50
307
290
217
167
80
334
313
244
183
90
337
321
253
194

Table 7. Monthly and Annual Average Heating Degree Days (base 65°F), 1971-2000 (back to top)
Name
Number
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Astoria WSO Airport
328
694
582
590
491
378
243
149
130
196
382
543
685
5043
Seaside
7641
636
539
553
463
358
245
169
145
189
345
513
636
4837

Table 8. Monthly and Annual Average Growing Degree Days (base 50°F), 1971-2000 (back to top)
Name
Number
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Astoria WSO Airport
328
5
10
12
33
101
210
320
341
261
108
29
8
1438
Seaside
7641
12
18
21
42
118
207
299
324
273
135
33
10
1492