Montesano is located at 46°59′9″N 123°35′52″W (46.985865, -123.597726). It is on the north slope of the Chehalis River valley, near the confluence of the Wynoochee River and Chehalis River. The town is bordered on the north by Lake Sylvia and on the west by Sylvia Creek.
Climate
This
region experiences warm (but not hot) and relatively dry summers, with
no average monthly temperatures above 71.6 °F (22 °C) and very wet
autumns and springs due to the maritime winds. abbreviated Cfb on
climate maps
due to frequent summer rainfall, even though there is a significant
drying trend during that season. This also renders frequent but most
often minor frosts in winter, with the climate retaining a significant
maritime influence.
| Climate data for Montesano | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Month | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Year |
| Record high °F (°C) | 58 (14) |
61 (16) |
78 (26) |
82 (28) |
97 (36) |
95 (35) |
102 (39) |
96 (36) |
94 (34) |
83 (28) |
75 (24) |
60 (16) |
102 (39) |
| Average high °F (°C) | 41.8 (5.4) |
45.8 (7.7) |
49.9 (9.9) |
57.4 (14.1) |
66.9 (19.4) |
69.3 (20.7) |
74.7 (23.7) |
74.0 (23.3) |
70.4 (21.3) |
60.3 (15.7) |
49.6 (9.8) |
44.8 (7.1) |
58.7 (14.8) |
| Daily mean °F (°C) | 36.0 (2.2) |
38.8 (3.8) |
41.4 (5.2) |
46.7 (8.2) |
53.7 (12.1) |
57.0 (13.9) |
60.9 (16.1) |
61.0 (16.1) |
57.9 (14.4) |
50.7 (10.4) |
42.8 (6.0) |
39.1 (3.9) |
48.8 (9.3) |
| Average low °F (°C) | 30.3 (−0.9) |
31.7 (−0.2) |
33.0 (0.6) |
36.0 (2.2) |
40.6 (4.8) |
44.8 (7.1) |
47.1 (8.4) |
48.0 (8.9) |
45.4 (7.4) |
41.1 (5.1) |
36.1 (2.3) |
33.4 (0.8) |
38.9 (3.8) |
| Record low °F (°C) | 1 (−17) |
5 (−15) |
14 (−10) |
13 (−11) |
22 (−6) |
32 (0) |
34 (1) |
36 (2) |
30 (−1) |
19 (−7) |
11 (−12) |
6 (−14) |
1 (−17) |
| Average precipitation inches (mm) | 18.9 (480) |
15.6 (400) |
13.4 (340) |
7.4 (190) |
4.3 (110) |
3.2 (81) |
2.1 (53) |
2.1 (53) |
4.8 (120) |
12.1 (310) |
17.2 (440) |
19.6 (500) |
120.8 (3,070) |
| Average snowfall inches (cm) | 19.9 (51) |
6.5 (17) |
5.5 (14) |
0.5 (1.3) |
0 (0) |
0 (0) |
0 (0) |
0 (0) |
0 (0) |
0 (0) |
2.1 (5.3) |
5.4 (14) |
39.9 (101) |
The
mainstem Chehalis River and its tributaries form the Chehalis River
basin, which drains approximately 2,700 square miles. The basin is
bounded by the Pacific Ocean to the west, the Deschutes River basin to
the east, the Olympic Mountains to the north, and the Willapa Hills and
Cowlitz River basin to the south. Elevations within the basin range from
sea level at Grays Harbor to over 3,000 feet in the Coast Range.
Geology
The
Chehalis Basin has several distinct geologic regions with unique
geologic history. For example, the headwaters arise out of the Willapa
Hills, which are primarily comprised of marine volcanic and sedimentary
rocks, while some other regions are primarily glacially influenced. The
hills and valleys were carved into these slabs of oceanic rock by
erosion, resulting in low rounded hills and ravines. Volcanic rocks
(primarily basalt flows) underlie most of the basin, but have been
overlain by sedimentary deposits of marine and non-marine origin or
glacial material. Near surface volcanic deposits dominate the Black
Hills west of the Black River, as well as the southern Olympic
Mountains. The younger rocks are found primarily between the Satsop and
Wynoochee River valleys.
Topography
The Chehalis
River originates in the Willapa Hills, part of the Coastal Range.
Elevations range from below 2,400 feet to 3,110 feet. The mainstem
Chehalis River flattens into an open river valley below Pe Ell. The
South Fork Chehalis River opens to a low-gradient river valley at the
Lewis County/Cowlitz County line.
Areas located north of the
lower Chehalis River are characterized by open river valley. The south
side of the river contains steeply rising hills. A portion of the open
river valley to the north transitions into tributary river valleys;
other areas transition into sloping hillsides.
Soils
The
Chehalis River basin floodplain contains five major soil associations. These soils occur in flat or gently
sloping terrain and include the major tributary systems within the
basin. In floodplain fringes, cropland, and pasture areas, dominant
vegetation includes western red cedar, red alder, black cottonwood, and
willow species. Areas of moderate to well-drained soils contain some
Douglas-fir trees.
The Chehalis River basin contains a diverse wetland
mosaic. Although the Grays Harbor area still contains an extensive
wetland system, approximately one-third of the historic wetlands in this
area have been lost to development and agricultural activities. These
include forested, scrub-shrub, emergent, and riparian wetlands. Most of
the wetland vegetation is considered broad-leaved deciduous.
The
varied habitats in the Chehalis River basin support a wide range of
wildlife. Higher elevation and forested areas support big game such as
deer, elk, and black bear and upland birds such as grouse and quail.
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