Geography

The Willamette River runs through the center of the city, while Mount Tabor (center) rises on the city's east side. Mount Saint Helens (left) and Mount Hood (right center) are visible from many places in the city. Topography

Portland is located 70 miles east of the Pacific Ocean at the northern end of Oregon's most populated region, the Willamette Valley. Downtown Portland straddles the banks of the Willamette River which flows north through the city center, separating the east and west sections of the city before veering northwest to join with the Columbia River less than 10 miles from downtown. The Columbia River serves as the natural boundary between the states of Washington and Oregon and consequently divides the city of Portland from its most populated suburb Vancouver, Washington. Portland is situated near the foothills of the Tualatin Mountains, also called the West Hills and the Southwest Hills, which pierce through the Northwest and Southwest regions of the city. Council Crest Park, the tallest point within city limits, is located in the West Hills and rises to an elevation of 1,073 feet. To the west of the Tualatin Mountains lies the Oregon Coast Range, and to the east lies the actively volcanic Cascade Range. On clear days Mt. Hood and Mt St. Helens dominate the horizon while Mt. Adams and Mt. Rainier also are sometimes visible in the distance.

According to the United States Census Bureau, the city has a total area of 145.09 square miles (375.78 km2), of which, 133.43 square miles (345.58 km2) is land and 11.66 square miles (30.20 km2) is water. Although almost all of Portland lies within Multnomah County, small portions of the city lie within Clackamas and Washington counties with mid-2005 populations estimated at 785 and 1,455, respectively.

Portland lies on top of an extinct Plio-Pleistocene volcanic field known as the Boring Lava Field. The Boring Lava Field includes at least 32 cinder cones such as Mount Tabor, and its center lies in Southeast Portland. The dormant but potentially active volcano Mount Hood to the east of Portland is easily visible from much of the city during clear weather. The active volcano Mount Saint Helens to the north in Washington is visible in the distance from high-elevation locations in the city and is close enough to have dusted the city with volcanic ash after an eruption on May 18, 1980. Mount Adams, another prominent volcano in Washington state to the northeast of Portland, is also visible from parts of the city.

Climate

As with much of the Pacific Northwest west of the Cascades, Portland experiences a temperate oceanic climate typified by warm, dry summers and mild, damp winters; the city proper straddles the border between USDA Plant Hardiness Zones 8B and 9A. According to the Köppen climate classification, Portland falls within the cool, dry-summer mild temperate zone (Csb), also referred to as cool-summer Mediterranean, because of its relatively dry summers. Other climate classification systems, such as Trewartha, place it firmly in the Oceanic zone (Do).

Summers in Portland are warm to hot, dry and relatively sunny with moderately low humidity. The four months of June, July, August and September account for only 4.47 inches (114 mm) of total rain combined – a small fraction of the 36.03 inches (915 mm) inches of precipitation that falls throughout the year. The warmest month is August with a daily average temperature of 69.5 °F (20.8 °C); normal temperatures peak in late July and early August. Because of its inland location 70 miles from the coast, as well as the protective nature of the Oregon Coast Range to its west, Portland summers are less susceptible to the moderating influence of the nearby Pacific Ocean. Therefore Portland can experience heatwaves, particularly in July and August, with air temperatures rising over 90 °F (32 °C) for days at a time. Temperatures reach or exceed 90 °F (32 °C) 14 days per year and reach or exceed 100 °F (38 °C) 1.4 days per year on average. Portland has reached triple digit temperatures in all five months from May through September. The highest temperature ever recorded was 107 °F (42 °C), on July 30, 1965, as well as August 8 and 10, 1981.

Spring and fall can bring rather unpredictable weather including warm spells that send temperatures surging above 80 °F (27 °C), cold snaps the plunge daytime temperatures into the 40s, thunderstorms rolling off the Cascade Range and, although rare, occasional tornadoes. However, mild temperatures in the 50s and 60s °F (10−21 °C) and overcast skies are the norm – with rainy or partly overcast days becoming frequent in mid fall and continuing into mid spring. Portland receives less annual rainfall than most cities on the East Coast, however rain often falls as a light drizzle for several consecutive days at a time, contributing to the high number (155) of days with measurable (≥0.01 in or 0.25 mm) precipitation annually. Temperatures have reached the 90 °F (32 °C) mark as early as April and as late as October.

Winters in Portland are mild to chilly, overcast and wet with normal temperatures bottoming out in the second half of December and early January; the coolest month is December, with a daily average of 40.4 °F (4.7 °C). Approximately 55% of Portland's annual precipitation falls between November and February. Nighttime temperatures drop below freezing 33 nights per year on average, and occasionally to or below 20 °F (−7 °C) – however, there are only 2.1 days where the high fails to rise above freezing per year. Snowfall in downtown Portland is uncommon and does not happen every winter – due in part to downtown's low elevation as well as the effects of its urban heat island. Neighborhoods outside the downtown core, especially in slightly higher elevations near the West Hills and Mount Tabor, will frequently experience a dusting of snow while downtown receives no snow at all. The city has experienced a few major snow and ice storms in its past with snowfall totals occasionally reaching several feet (snowfall of 60.9 inches or 154.7 centimetres fell in the winter of 1892–93). The lowest temperature ever recorded in Portland was −3 °F (−19 °C), on February 2, 1950.

Climate data for Portland, Oregon (PDX), 1981–2010 normals Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year Record high °F (°C) 66 (19) 71 (22) 80 (27) 90 (32) 100 (38) 102 (39) 107 (42) 107 (42) 105 (41) 92 (33) 73 (23) 65 (18) 107 (42) Average high °F (°C) 47.0 (8.3) 51.3 (10.7) 56.7 (13.7) 61.4 (16.3) 68.0 (20) 73.5 (23.1) 80.6 (27) 81.1 (27.3) 75.8 (24.3) 63.8 (17.7) 52.8 (11.6) 45.6 (7.6) 63.1 (17.3) Average low °F (°C) 35.8 (2.1) 36.3 (2.4) 39.6 (4.2) 43.1 (6.2) 48.6 (9.2) 53.6 (12) 57.8 (14.3) 58.0 (14.4) 53.1 (11.7) 46.0 (7.8) 40.5 (4.7) 35.2 (1.8) 45.6 (7.6) Record low °F (°C) −2 (−19) −3 (−19) 19 (−7) 29 (−2) 29 (−2) 39 (4) 43 (6) 44 (7) 34 (1) 26 (−3) 13 (−11) 6 (−14) −3 (−19) Precipitation inches (mm) 4.88 (124) 3.66 (93) 3.68 (93.5) 2.73 (69.3) 2.47 (62.7) 1.70 (43.2) .64 (16.3) .66 (16.8) 1.47 (37.3) 3.00 (76.2) 5.64 (143.3) 5.49 (139.4) 36.03 (915.2) Snowfall inches (cm) 3.8 (9.7) 1.3 (3.3) 0.4 (1) 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0.7 (1.8) 1.6 (4.1) 7.8 (19.8) Avg. precipitation days (≥ 0.01 in) 18.0 14.9 17.6 16.4 13.6 9.2 4.1 3.9 6.8 12.5 19.0 19.0 155.0 Avg. snowy days (≥ 0.1 in) 0.4 0.9 0.1 0 0 0 0 0 0 0 0.3 0.8 2.5 Percent possible sunshine 28 38 44 50 52 55 66 64 62 44 28 23 45 Source: NOAA (extremes 1940–present, percent sunshine through 2009)