Portland ME Jetport Normals based on NWS Observations 1961-1990 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year
Temperature ( f )
Daily Maximum 30.3 33.1 41.4 52.3 63.2 72.7 78.8 77.4 69.3 58.7 47.0 35.1 54.9
Daily Minimum 11.4 13.5 24.5 34.1 43.4 52.1 58.3 57.1 48.9 38.3 30.4 17.8 35.8
Monthly 20.8 23.3 33.0 43.3 53.3 62.4 68.6 67.3 59.1 48.5 38.7 26.5 45.4
number of days with:
maximum 90 degrees or above 0 0. 0 0 0.2 0.9 1.9 1.2 0.3 0 0 0 4.5
maximum 32 degrees or below 17.2 12.9 4.1 0.1 0 0 0 0 0 0 1.0 12.4 47.7
minimum 32 degrees or below 29.9 26.5 25.2 13.5 2.0 0 0 0 0.8 8.6 19.3 28.9 154.7
minimum 0 degrees of below 6.1 3.9 0.5 0 0 0 0 0 0 0 0 2.8 13.3
Degree Days
Heating (base 65f) 1370 1168 992 651 363 100 11 39 189 512 789 1194 7378
Cooling (base 65f) 0 0 0 0 0 22 123 111 12 0 0 0 268
Precipitation
water equivalent 3.53 3.33 3.67 4.08 3.62 3.44 3.09 2.87 3.09 3.90 5.17 4.55 44.34
Snowfall 19.2 16.5 11.6 3.4 0.1 0 0 0 0 0.4 3.1 17.0 71.3
Relative Humidity
normal daily (in percent) 67 65 66 67 71 75 75 76 77 74 73 70 71
@ 1 am EST 72 70 72 77 82 87 88 88 88 83 79 75 80
@ 7 am EST 73 73 73 72 75 79 81 84 85 84 80 77 78
@ 1 pm EST 58 56 56 54 58 60 60 60 60 58 61 60 58
@ 7 pm EST 66 64 66 66 69 73 73 76 78 75 73 69 71
Mean Number of days with: 
Fog (visibility 1/4 mile or less)  2.1 2.1 3.4 3.1 5.1 5.1 6.4 5.6 5.1 4.6 3.6 2.0 48.2
Thunderstorms 0 0.1 0.4 0.5 1.9 4.1 4.5 3.5 1.5 0.6 0.4 0.1 17.6
        Percent of Possible Sunshine 
56 60 56 55 54 60 63 64 63 57 48 53 57
        Winds 
mean speed (MPH) 9.3 9.4 10.1 10.1 9.1 8.4 7.7 7.7 8.1 8.5 8.9 8.9 8.8
prevailing direction (in degrees) 360 340 320 180 180 180 180 180 180 340 360 360 180
Wind Rose
Source: NOAA/NCDC publication Climatography of the U.S. #84

 
 
The Portland Jetport is located 2 3/4 miles west of the site of the former city office. The surrounding country is mostly open, rolling and sloping generally toward the Fore River, a body of brackish water about l,000 feet wide at a distance of about l/2 mile from the station and forming one boundary (north through east) of the field. The airport is about 5 l/2 miles west–northwest of the open ocean. A slight rise reaching an elevation of l00 feet, lying northwest of the field, cuts down the wind slightly from that direction. The older portion of the city is situated on a hill rising abruptly from sea level to l70 feet, l l/2 miles east of the airport and on the opposite side of the Fore River. A line of low hills southeast of the airport, near the ocean, which reach a maximum height of l60 feet, shuts off sight of the ocean from the airport. Sebago Lake with an area of 44 square miles is situated about l5 miles to the northwest and 45 miles farther are the White Mountains, averaging 3,000 to 5,000 feet in height. As a rule, Portland has very pleasant summers and falls, cold winters with frequent thaws, and disagreeable springs. Very few summer nights are too warm and humid for comfortable sleeping. Autumn has the greatest number of sunny days and the least cloudiness. Winters are quite severe, but begin late and then extend deeply into the normal springtime. Heavy seasonal snowfalls, over l00 inches, normally occur about each l0 years. True blizzards are very rare. The White Mountains, to the northwest, keep considerable snow from reaching the Portland area and also moderate the temperature. Normal monthly precipitation is remarkably uniform throughout the year. Winds are generally quite light with the highest velocities being confined mostly to March and November. Even in these months the occasional northeasterly gales have usually lost much of their severity before reaching the coast of Maine. Temperatures well below zero are recorded frequently each winter. Cold waves sometimes come in on strong winds, but extremely low temperatures are generally accompanied by light winds. The average freeze–free season at the airport station is l39 days. Mid–May is the average occurrence of the last freeze in spring, and the average occurrence of the first freeze in fall is late September. The freeze–free period is longer in the city proper, but may be even shorter at susceptible places further inland. Daily maximum temperatures at the present airport site agree closely with those near the former intown office, but minimum temperatures on clear, quiet mornings range as much as l5 degrees lower at the airport.

 

updated 2/01
by ES