<P> Spring and fall can bring variable weather including warm fronts that send temperatures surging above 80 ° F (27 ° C) and cold snaps that plunge daytime temperatures into the 40s ° F (4--9 ° C). However, consistently mild temperatures in the 50s and 60s ° F (12--19 ° C) are the norm--with lengthy stretches of cloudy or partly cloudy days beginning in mid fall and continuing into mid spring . Rain often falls as a light drizzle for several consecutive days at a time, contributing to 155 days on average with measurable (≥ 0.01 in or 0.25 mm) precipitation annually . Temperatures have reached 90 ° F (32 ° C) as early as May 3 and as late as October 5, while 80 ° F (27 ° C) has been reached as early as April 1 and as late as October 21 . Severe weather, such as thunder and lightning, is uncommon and tornadoes are exceptionally rare . </P> <P> Winters are cool, cloudy, and rainy . The coldest month is December with an average daily high of 45.6 ° F (7.6 ° C), although overnight lows usually remain above freezing . Evening temperatures fall to or below freezing 33 nights per year on average, but very rarely to or below 20 ° F (− 7 ° C). There are only 2.1 days per year where the daytime high temperature fails to rise above freezing . The lowest overnight temperature ever recorded was − 3 ° F (− 19 ° C), on February 2, 1950 while the coldest daytime high temperature ever recorded was 14 ° F (− 10 ° C) on December 30, 1968 . The average window for freezing temperatures to potentially occur is between November 15 and March 19, allowing a growing season of 240 days . </P> <P> Snowfall is uncommon with a normal yearly accumulation of 4.3 inches (10.9 cm), which usually falls during only two or three days per year . Portland has one of the warmest and least snowy winters of any non-Sun Belt city in the United States, with more than 25 percent of its winters receiving no snow whatsoever . The city of Portland avoids snow more frequently than its suburbs, due in part to its low elevation and urban heat island effect . Neighborhoods outside of the downtown core, especially in slightly higher elevations near the West Hills and Mount Tabor, can experience a dusting of snow while downtown receives no accumulation at all . The city has experienced a few major snow and ice storms in its past with extreme totals having reached 44.5 in (113 cm) at the airport in 1949--50 and 60.9 in (155 cm) at downtown in 1892--93 . </P> <Table> <Tr> <Th_colspan="14"> (hide) Climate data for Portland, Oregon (PDX), 1981--2010 normals, extremes 1940--present </Th> </Tr> <Tr> <Th> Month </Th> <Th> Jan </Th> <Th> Feb </Th> <Th> Mar </Th> <Th> Apr </Th> <Th> May </Th> <Th> Jun </Th> <Th> Jul </Th> <Th> Aug </Th> <Th> Sep </Th> <Th> Oct </Th> <Th> Nov </Th> <Th> Dec </Th> <Th> Year </Th> </Tr> <Tr> <Th> Record high ° F (° C) </Th> <Td> 66 (19) </Td> <Td> 71 (22) </Td> <Td> 80 (27) </Td> <Td> 90 (32) </Td> <Td> 100 (38) </Td> <Td> 102 (39) </Td> <Td> 107 (42) </Td> <Td> 107 (42) </Td> <Td> 105 (41) </Td> <Td> 92 (33) </Td> <Td> 73 (23) </Td> <Td> 65 (18) </Td> <Td> 107 (42) </Td> </Tr> <Tr> <Th> Mean maximum ° F (° C) </Th> <Td> 58.4 (14.7) </Td> <Td> 61.4 (16.3) </Td> <Td> 69.5 (20.8) </Td> <Td> 78.7 (25.9) </Td> <Td> 87.1 (30.6) </Td> <Td> 91.3 (32.9) </Td> <Td> 96.7 (35.9) </Td> <Td> 96.5 (35.8) </Td> <Td> 90.6 (32.6) </Td> <Td> 78.2 (25.7) </Td> <Td> 63.6 (17.6) </Td> <Td> 57.5 (14.2) </Td> <Td> 100.2 (37.9) </Td> </Tr> <Tr> <Th> Average high ° F (° C) </Th> <Td> 47.0 (8.3) </Td> <Td> 51.3 (10.7) </Td> <Td> 56.7 (13.7) </Td> <Td> 61.4 (16.3) </Td> <Td> 68.0 (20) </Td> <Td> 73.5 (23.1) </Td> <Td> 80.6 (27) </Td> <Td> 81.1 (27.3) </Td> <Td> 75.8 (24.3) </Td> <Td> 63.8 (17.7) </Td> <Td> 52.8 (11.6) </Td> <Td> 45.6 (7.6) </Td> <Td> 63.1 (17.3) </Td> </Tr> <Tr> <Th> Average low ° F (° C) </Th> <Td> 35.8 (2.1) </Td> <Td> 36.3 (2.4) </Td> <Td> 39.6 (4.2) </Td> <Td> 43.1 (6.2) </Td> <Td> 48.6 (9.2) </Td> <Td> 53.6 (12) </Td> <Td> 57.8 (14.3) </Td> <Td> 58.0 (14.4) </Td> <Td> 53.1 (11.7) </Td> <Td> 46.0 (7.8) </Td> <Td> 40.5 (4.7) </Td> <Td> 35.2 (1.8) </Td> <Td> 45.6 (7.6) </Td> </Tr> <Tr> <Th> Mean minimum ° F (° C) </Th> <Td> 24.6 (− 4.1) </Td> <Td> 24.5 (− 4.2) </Td> <Td> 30.3 (− 0.9) </Td> <Td> 34.2 (1.2) </Td> <Td> 40.1 (4.5) </Td> <Td> 46.7 (8.2) </Td> <Td> 51.2 (10.7) </Td> <Td> 50.7 (10.4) </Td> <Td> 44.4 (6.9) </Td> <Td> 35.3 (1.8) </Td> <Td> 28.4 (− 2) </Td> <Td> 23.7 (− 4.6) </Td> <Td> 19.6 (− 6.9) </Td> </Tr> <Tr> <Th> Record low ° F (° C) </Th> <Td> − 2 (− 19) </Td> <Td> − 3 (− 19) </Td> <Td> 19 (− 7) </Td> <Td> 29 (− 2) </Td> <Td> 29 (− 2) </Td> <Td> 39 (4) </Td> <Td> 43 (6) </Td> <Td> 44 (7) </Td> <Td> 34 (1) </Td> <Td> 26 (− 3) </Td> <Td> 13 (− 11) </Td> <Td> 6 (− 14) </Td> <Td> − 3 (− 19) </Td> </Tr> <Tr> <Th> Average precipitation inches (mm) </Th> <Td> 4.88 (124) </Td> <Td> 3.66 (93) </Td> <Td> 3.68 (93.5) </Td> <Td> 2.73 (69.3) </Td> <Td> 2.47 (62.7) </Td> <Td> 1.70 (43.2) </Td> <Td> 0.65 (16.5) </Td> <Td> 0.67 (17) </Td> <Td> 1.47 (37.3) </Td> <Td> 3.00 (76.2) </Td> <Td> 5.63 (143) </Td> <Td> 5.49 (139.4) </Td> <Td> 36.03 (915.2) </Td> </Tr> <Tr> <Th> Average snowfall inches (cm) </Th> <Td> 0.5 (1.3) </Td> <Td> 2.1 (5.3) </Td> <Td> 0.2 (0.5) </Td> <Td> 0 (0) </Td> <Td> 0 (0) </Td> <Td> 0 (0) </Td> <Td> 0 (0) </Td> <Td> 0 (0) </Td> <Td> 0 (0) </Td> <Td> 0 (0) </Td> <Td> 0.2 (0.5) </Td> <Td> 1.3 (3.3) </Td> <Td> 4.3 (10.9) </Td> </Tr> <Tr> <Th> Average precipitation days (≥ 0.01 in) </Th> <Td> 18.0 </Td> <Td> 14.9 </Td> <Td> 17.6 </Td> <Td> 16.4 </Td> <Td> 13.6 </Td> <Td> 9.2 </Td> <Td> 4.1 </Td> <Td> 3.9 </Td> <Td> 6.7 </Td> <Td> 12.5 </Td> <Td> 19.0 </Td> <Td> 18.6 </Td> <Td> 154.5 </Td> </Tr> <Tr> <Th> Average snowy days (≥ 0.1 in) </Th> <Td> 0.7 </Td> <Td> 1.5 </Td> <Td> 0.2 </Td> <Td> 0 </Td> <Td> 0 </Td> <Td> 0 </Td> <Td> 0 </Td> <Td> 0 </Td> <Td> 0 </Td> <Td> 0 </Td> <Td> 0.5 </Td> <Td> 1.5 </Td> <Td> 4.4 </Td> </Tr> <Tr> <Th> Average relative humidity (%) </Th> <Td> 80.9 </Td> <Td> 78.0 </Td> <Td> 74.6 </Td> <Td> 71.6 </Td> <Td> 68.7 </Td> <Td> 65.8 </Td> <Td> 62.8 </Td> <Td> 64.8 </Td> <Td> 69.4 </Td> <Td> 77.9 </Td> <Td> 81.5 </Td> <Td> 82.7 </Td> <Td> 73.2 </Td> </Tr> <Tr> <Th> Mean monthly sunshine hours </Th> <Td> 85.6 </Td> <Td> 116.4 </Td> <Td> 191.1 </Td> <Td> 221.1 </Td> <Td> 276.1 </Td> <Td> 290.2 </Td> <Td> 331.9 </Td> <Td> 298.1 </Td> <Td> 235.7 </Td> <Td> 151.7 </Td> <Td> 79.3 </Td> <Td> 63.7 </Td> <Td> 2,340.9 </Td> </Tr> <Tr> <Th> Percent possible sunshine </Th> <Td> 30 </Td> <Td> 40 </Td> <Td> 52 </Td> <Td> 54 </Td> <Td> 60 </Td> <Td> 62 </Td> <Td> 70 </Td> <Td> 68 </Td> <Td> 63 </Td> <Td> 45 </Td> <Td> 28 </Td> <Td> 23 </Td> <Td> 52 </Td> </Tr> <Tr> <Td_colspan="14"> Source: NOAA (relative humidity and sun 1961--1990) </Td> </Tr> </Table>

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