2001 San Francisco, California International Airport (SFO)

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2001 SAN FRANCISCO, CALIFORNIA INTERNATIONAL AIRPORT (SFO)

The station is located in the central Terminal Building of the San Francisco International Airport, which is on flat filled tideland on the west shore of San Francisco Bay. The bay borders the airport from the north to the south–southeast. San Bruno Mountain, 5 miles to the north–northwest, rises to 1,300 feet. A north–south trending ridge of coastal mountains, 4 miles to the west, varies in elevation from 700 to 1,900 feet, being highest southward along the peninsula. The Pacific Ocean west of the ridge is 6 miles from the airport. A broad gap to the northwest of the station, between San Bruno Mountain and the coastal mountains, allows a strong flow of marine air over the station and dominate the local climate.

San Francisco Airport enjoys a marine–type climate characterized by mild and moderately wet winters and by dry, cool summers. Winter rains, occurring from November through March, account for over 80 percent of the annual rainfall, and measurable precipitation occurs on an average of 10 days per month during this period. However, there are frequent dry periods lasting well over a week. Severe winter storms with gale winds and heavy rains occur only occasionally. Thunderstorms average two a year and may occur in any month.

The daily and annual range in temperature is small. A few frosty mornings occur during the winter but the temperature seldom drops below freezing. Winter temperatures generally rise to the high 50s in the early afternoon.

The summer weather is dominated by a cool sea breeze resulting in an average summer wind speed of nearly 15 mph. Winds are light in the early morning but normally reach 20 to 25 mph in the afternoon.

A sea fog, arriving over the station during the late evening or night as a low cloud, is another persistent feature of the summer weather. This high fog, occasionally producing drizzle or mist, usually disappears during the late forenoon. Despite the morning overcast, summer days are sunny. On the average a total of only 14 days during the four months from June through September are classified as cloudy.

Daytime temperatures are held down both by the morning low overcast and the afternoon strengthening sea breeze, resulting in daily maximum readings averaging about 70 degrees from May through August. However, during these months occasional hot spells, lasting a few days, are experienced without the usual high fog and sea breeze. September, when the sea breeze becomes less pronounced, is the warmest month with highs in the 70s. Low temperatures during the summer are in the mid–50s.

A strong temperature inversion with its base usually about 1,500 feet persists throughout the summer. Inversions close to the ground are infrequent in summer but rather common in fall and winter. As a consequence of these factors and the continued population and economic growth of the area, atmospheric pollution has become a problem of increasing importance.

NORMALS, MEANS, AND EXTREMES

SAN FRANCISCO, CA (SFO)

LATITUDE:    LONGITUDE:    ELEVATION (FT):    TIME ZONE:    WBAN: 23234

37 37′ 11″ N  122 23′ 53″ W  GRND: 86  BARO: 89  PACIFIC (UTC + 8)

ELEMENTPORJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDECYEAR
TEMPERATURE FNORMAL DAILY MAXIMUM3055.659.460.863.966.570.371.672.373.670.162.456.165.2
MEAN DAILY MAXIMUM5655.659.060.963.866.469.971.271.973.370.162.756.365.1
HIGHEST DAILY MAXIMUM747278859297106105100103998575106
YEAR OF OCCURRENCE194819301952198919841961198819931971198719671958JUN 1961
MEAN OF EXTREME MAXS.5664.568.372.978.984.188.486.686.090.185.974.064.678.7
NORMAL DAILY MINIMUM3041.845.045.847.249.752.653.955.055.251.847.142.749.0
MEAN DAILY MINIMUM5642.044.645.847.449.952.453.754.654.451.647.142.848.9
LOWEST DAILY MINIMUM7424253031364143423834252020
YEAR OF OCCURRENCE192819291929192919291932192819351929192919311932DEC 1932
MEAN OF EXTREME MINS.5633.536.838.741.344.748.150.050.649.445.039.034.742.7
NORMAL DRY BULB3048.752.253.355.658.161.562.763.764.561.054.849.457.1
MEAN DRY BULB5648.951.853.455.658.361.262.563.363.960.954.949.557.0
MEAN WET BULB1747.348.750.251.253.255.457.057.857.355.250.846.752.6
MEAN DEW POINT1744.045.146.246.848.750.953.054.253.750.946.442.948.6
NORMAL NO. DAYS WITH:
MAXIMUM 90300.00.00.00.10.40.90.70.31.40.40.00.04.2
MAXIMUM 32300.00.00.00.00.00.00.00.00.00.00.00.00.0
MINIMUM 32301.20.1*0.00.00.00.00.00.00.00.01.02.3
MINIMUM 0300.00.00.00.00.00.00.00.00.00.00.00.00.0
H/CNORMAL HEATING DEG. DAYS305053583632872181219268791353064843016
NORMAL COOLING DEG. DAYS3000050162128641100145
RHNORMAL (PERCENT)3078767371717173747272757874
HOUR 04 LST3086848181838486868382848584
HOUR 10 LST3079757065636365676568727769
HOUR 16 LST3066646259595859615859636761
HOUR 22 LST3080787776787982827877778079
SPERCENT POSSIBLE SUNSHINE
W/OMEAN NO. DAYS WITH:
HEAVY FOG (VISBY 1/4 MI)643.32.60.40.10.10.00.00.20.61.32.13.013.7
THUNDERSTORMS740.40.40.30.20.10.10.10.10.20.30.10.22.5
CLOUDINESSMEAN:
SUNRISE–SUNSET (OKTAS)555.05.04.64.23.63.02.42.62.63.14.24.73.8
MIDNIGHT–MIDNIGHT (OKTAS)324.74.94.63.93.43.22.62.82.63.04.04.33.7
MEAN NO. DAYS WITH:
CLEAR698.57.89.510.813.516.220.318.817.915.511.19.4159.3
PARTLY CLOUDY697.57.38.79.39.78.67.58.68.28.98.37.5100.1
CLOUDY6915.013.112.89.97.85.22.83.33.66.510.614.1104.7
PRMEAN STATION PRESSURE(IN)2830.0930.0530.0330.0329.9729.9529.9529.9429.9330.0030.0830.1130.01
MEAN SEA–LEVEL PRES. (IN)1730.1230.0830.0630.0530.0029.9629.9629.9629.9430.0130.1130.1330.03
WINDSMEAN SPEED (MPH)437.79.011.012.513.914.113.712.811.49.78.17.711.0
PREVAIL. DIR (TENS OF DEGS)2714302929282830303030301430
MAXIMUM 2–MINUTE:
SPEED (MPH)543444645464338373240464546
DIR. (TENS OF DEGS)17272626262626262626241624
YEAR OF OCCURRENCE199720012000200119991997199719991997199720012001NOV 2001
MAXIMUM 5–SECOND:
SPEED (MPH)556595154545344463949555559
DIR. (TENS OF DEGS)16182628262626262529241618
YEAR OF OCCURRENCE199719992000199919991997199720011997199720012001FEB 1999
PRECIPITATIONNORMAL (IN)304.353.173.061.370.190.110.030.050.201.222.863.0919.70
MAXIMUM MONTHLY (IN)7411.2613.649.016.363.810.860.350.662.307.307.9412.3013.64
YEAR OF OCCURRENCE199319981958195819571967197719761959196219731955FEB 1998
MINIMUM MONTHLY (IN)740.24TTT0.000.000.000.00TT0.000.010.00
YEAR OF OCCURRENCE199119531934197720011928193019961995197819291989MAY 2001
MAXIMUM IN 24 HOURS (IN)745.713.412.462.661.540.830.350.602.303.742.433.335.71
YEAR OF OCCURRENCE198219981982195819571967197719971959196219941955JAN 1982
NORMAL NO. DAYS WITH:
PRECIPITATION 0.01309.88.910.46.12.30.70.40.61.43.68.19.461.7
PRECIPITATION 1.00301.40.80.50.20.00.00.00.00.00.40.60.74.6
SNOWFALLNORMAL (IN)300.1T0.00.00.00.00.00.00.00.00.0T0.1
MAXIMUM MONTHLY (IN)691.5TT0.00.00.00.00.00.00.00.01.01.5
YEAR OF OCCURRENCE1962199619951932JAN 1962
MAXIMUM IN 24 HOURS (IN)691.5TTT0.00.00.00.00.00.00.01.01.5
YEAR OF OCCURRENCE19621996199519871932JAN 1962
MAXIMUM SNOW DEPTH (IN)480000000000000
YEAR OF OCCURRENCE
NORMAL NO. DAYS WITH:
SNOWFALL 1.0300.*0.00.00.00.00.00.00.00.00.00.00.00.0
PRECIPITATION (inches) 2001 SAN FRANCISCO, CALIFORNIA CA (SFO)
YEARJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDECANNUAL
19721.091.350.181.20T0.06TT0.305.245.152.4016.97
19738.326.822.930.110.07TTT0.041.607.943.5531.38
19743.211.704.212.32T0.140.23TT0.930.502.3615.60
19752.603.945.911.660.020.040.130.21T2.270.260.2117.25
19760.372.131.220.92T0.01T0.660.300.341.372.7010.02
19772.221.042.01T0.41T0.35T0.470.152.203.6912.54
19788.904.924.904.500.02TTT0.26T1.670.6425.81
19796.615.872.740.690.13T0.09TT2.201.944.3024.57
19804.857.622.650.900.240.030.10TT0.100.121.7318.34
19815.922.213.600.240.07TTT0.282.354.893.9123.47
19828.812.827.633.25T0.06TT0.961.955.343.9934.81
19836.836.648.503.110.32T0.01T0.570.106.036.2338.34
19840.461.471.360.68T0.03T0.110.051.966.121.8914.13
19850.742.353.300.120.050.290.030.020.180.693.191.6112.57
19864.048.095.840.390.15T0.01T0.470.020.061.6620.73
19872.803.521.980.160.06TTTT0.931.644.5115.60
19883.920.380.052.020.290.60TT0.030.422.313.6513.67
19891.251.284.000.780.040.01TT1.241.401.340.0111.35
19903.062.280.790.201.55T0.01T0.200.190.281.7910.35
19910.243.766.070.610.210.11T0.270.041.730.232.7015.97
19922.046.444.120.25T0.390.000.14T1.120.156.0420.69
199311.264.682.340.410.550.16TTT0.451.472.1923.51
19942.505.260.241.121.520.03TT0.100.335.732.4919.32
19958.890.388.751.410.930.60TTT0.030.026.4127.42
19966.926.032.891.401.24TT0.00T0.762.566.9728.77
19977.520.310.250.300.210.24T0.60T0.686.413.8720.39
19988.2013.642.052.242.370.03T0.000.090.622.430.9632.63
19992.964.592.802.180.100.180.000.060.270.461.470.4315.50
20005.838.461.741.300.530.140.000.010.072.140.910.4421.57
20013.876.121.021.560.000.100.000.000.110.314.518.5426.14
POR=74 YRS4.473.502.881.330.390.130.020.050.200.972.403.4219.76
AVERAGE TEMPERATURE (F) 2001 SAN FRANCISCO, CALIFORNIA CA (SFO)
YEARJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDECANNUAL
197245.652.055.355.457.660.964.364.062.661.053.244.956.4
197348.052.951.456.758.763.562.160.763.560.753.950.056.8
197448.649.753.454.856.260.463.063.762.562.053.848.656.4
197547.450.951.450.658.459.861.863.061.458.852.249.355.4
197648.550.551.053.358.363.262.564.363.361.357.048.856.8
197747.053.250.955.555.860.462.464.163.560.555.352.356.7
197852.552.857.054.960.460.461.463.265.861.152.546.057.3
197947.550.354.555.560.461.063.863.767.362.654.150.957.6
198050.554.453.055.956.359.963.061.563.261.255.650.757.1
198151.154.053.256.259.065.061.763.062.758.656.352.257.8
198245.151.751.354.657.459.761.763.364.061.152.348.955.9
198348.053.454.154.757.861.565.166.968.364.455.553.458.6
198451.352.957.056.061.861.365.664.469.760.453.847.758.5
198546.451.651.459.058.665.264.864.063.260.752.047.157.0
198653.756.357.156.258.662.562.461.262.961.457.150.358.3
198749.353.354.959.261.662.463.165.164.063.957.050.558.7
198850.654.556.558.159.562.565.365.063.161.456.550.458.6
198948.348.454.960.859.862.762.864.061.460.856.450.157.5
199049.949.253.358.559.062.464.566.366.463.156.046.457.9
199150.155.352.255.756.959.463.764.462.962.857.550.857.6
199248.956.157.460.663.463.665.863.865.365.456.849.859.7
199349.352.557.558.162.264.864.867.363.163.456.350.159.1
199451.550.656.056.858.561.562.164.564.160.149.948.057.0
199552.254.153.955.057.060.864.863.063.262.558.453.758.2
199651.854.956.059.160.461.563.262.763.060.956.353.958.6
199750.953.456.158.264.462.364.066.968.361.857.751.159.6
199852.852.355.055.757.761.662.864.364.360.354.247.057.3
199949.350.451.054.655.559.661.963.863.662.557.151.156.7
200052.453.554.458.260.262.961.463.666.260.052.651.658.1
200148.851.055.753.662.662.662.763.262.962.457.351.757.9
POR=74 YRS48.751.553.355.258.060.862.162.763.460.554.649.656.7

REFERENCE NOTES:

PAGE 1:

THE TEMPERATURE GRAPH SHOWS NORMAL MAXIMUM AND NORMAL MINIMUM DAILY TEMPERATURES (SOLID CURVES) AND THE ACTUAL DAILY HIGH AND LOW TEMPERATURES (VERTICAL BARS).

PAGE 2 AND 3:

H/C INDICATES HEATING AND COOLING DEGREE DAYS.

RH INDICATES RELATIVE HUMIDITY

W/O INDICATES WEATHER AND OBSTRUCTIONS

S INDICATES SUNSHINE.

PR INDICATES PRESSURE.

CLOUDINESS ON PAGE 3 IS THE SUM OF THE CEILOMETER AND SATELLITE DATA NOT TO EXCEED EIGHT EIGHTHS (OKTAS).

GENERAL:

T INDICATES TRACE PRECIPITATION, AN AMOUNT GREATER THAN ZERO BUT LESS THAN THE LOWEST REPORTABLE VALUE.

+ INDICATES THE VALUE ALSO OCCURS ON EARLIER DATES.

BLANK ENTRIES DENOTE MISSING OR UNREPORTED DATA.

NORMALS ARE 30–YEAR AVERAGES (1961–1990).

ASOS INDICATES AUTOMATED SURFACE OBSERVING SYSTEM.

PM INDICATES THE LAST DAY OF THE PREVIOUS MONTH.

POR (PERIOD OF RECORD) BEGINS WITH THE JANUARY DATA MONTH AND IS THE NUMBER OF YEARS USED TO COMPUTE THE MEAN. INDIVIDUAL MONTHS WITHIN THE POR MAY BE MISSING.

WHEN THE POR FOR A NORMAL IS LESS THAN 30 YEARS, THE NORMAL IS PROVISIONAL AND IS BASED ON THE NUMBER OF YEARS INDICATED.

0.* OR * INDICATES THE VALUE OR MEAN–DAYS–WITH IS BETWEEN 0.00 AND 0.05.

CLOUDINESS FOR ASOS STATIONS DIFFERS FROM THE NON–ASOS OBSERVATION TAKEN BY A HUMAN OBSERVER. ASOS STATION CLOUDINESS IS BASED ON TIME–AVERAGED CEILOMETER DATA FOR CLOUDS AT OR BELOW 12,000 FEET AND ON SATELLITE DATA FOR CLOUDS ABOVE 12,000 FEET.

THE NUMBER OF DAYS WITH CLEAR, PARTLY CLOUDY, AND CLOUDY CONDITIONS FOR ASOS STATIONS IS THE SUM OF THE CEILOMETER AND SATELLITE DATA FOR THE SUNRISE TO SUNSET PERIOD.

GENERAL CONTINUED:

CLEAR INDICATES 0–2 OKTAS, PARTLY CLOUDY INDICATES 3–6 OKTAS, AND CLOUDY INDICATES 7 OR 8 OKTAS. WHEN AT LEAST ONE OF THE ELEMENTS (CEILOMETER OR SATELLITE) IS MISSING, THE DAILY CLOUDINESS IS NOT COMPUTED.

WIND DIRECTION IS RECORDED IN TENS OF DEGREES (2 DIGITS) CLOCKWISE FROM TRUE NORTH. "00" INDICATES CALM. "36" INDICATES TRUE NORTH.

RESULTANT WIND IS THE VECTOR AVERAGE OF THE SPEED AND DIRECTION.

AVERAGE TEMPERATURE IS THE SUM OF THE MEAN DAILY MAXIMUM AND MINIMUM TEMPERATURE DIVIDED BY 2.

SNOWFALL DATA COMPRISE ALL FORMS OF FROZEN PRECIPITATION, INCLUDING HAIL.

A HEATING (COOLING) DEGREE DAY IS THE DIFFERENCE BETWEEN THE AVERAGE DAILY TEMPERATURE AND 65 F.

DRY BULB IS THE TEMPERATURE OF THE AMBIENT AIR.

DEW POINT IS THE TEMPERATURE TO WHICH THE AIR MUST BE COOLED TO ACHIEVE 100 PERCENT RELATIVE HUMIDITY.

WET BULB IS THE TEMPERATURE THE AIR WOULD HAVE IF THE MOISTURE CONTENT WAS INCREASED TO 100 PERCENT RELATIVE HUMIDITY.

ON JULY 1, 1996, THE NATIONAL WEATHER SERVICE BEGAN USING THE "METAR" OBSERVATION CODE THAT WAS ALREADY EMPLOYED BY MOST OTHER NATIONS OF THE WORLD. THE MOST NOTICEABLE DIFFERENCE IN THIS ANNUAL PUBLICATION WILL BE THE CHANGE IN UNITS FROM TENTHS TO EIGHTS (OKTAS) FOR REPORTING THE AMOUNT OF SKY COVER.

HEATING DEGREE DAYS (base 65 F) 2001 SAN FRANCISCO, CALIFORNIA CA (SFO)
YEARJULAUGSEPOCTNOVDECJANFEBMARAPRMAYJUNTOTAL
1972–736442751313506135213344162411971033087
1973–74100129761283274595014243542982701453211
1974–7583541011173294995403874154242201513320
1975–76109751201883774805044154273442221363397
1976–777238791272314945493264322782781413045
1977–7810348551392843853813352382951611352559
1978–7911165321433715815364063192771481323121
1979–80555613853204314412983662692611552750
1980–817610974145275436424301358279180532710
1981–8211265711972523896113644163072411543179
1982–8310063471303764915213223303012251133019
1983–8433118432813544153422422691241152237
1984–8543345147328527570370416180192272839
1985–86495160158382546343236239260191782593
1986–877711362122228447477320309168128852536
1987–8860164070233445440296259212184782333
1988-89402971128246447511455308162160942651
1989-907038103138249454459437356189185942772
1990-9133138772625704542653872732441662752
1991–925744659622343449425222613352582134
1992-9320493440235466480346225201100542250
1993–94331171672564554083962732382001182526
1994–959143461544465223883013382932421433007
1995–96487973981923443982892701871491282255
1996–9775737115525533343131727019476742324
1997–9832821092224223703483012692181092410
1998–998159571473205504834034283152891703302
1999–00104477592229423381327328207169942476
2000–011065632151367409497384282334107952820
2001–766074100225408
COOLING DEGREE DAYS (base 65 F) 2001 SAN FRANCISCO, CALIFORNIA CA (SFO)
YEARJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDECANNUAL
19720010714491681400109
1973000076418237100129
197400006112722313000127
1975000021415191920080
197600002188423332300192
1977000001030261750088
19780000240718623300144
1979000011192521881800182
19800000010227303310103
1981000171611777300113
1982000112571523120075
1983000071642661193200282
1984000433107024152900302
198500081385028113300169
19860012011507160042
198700042915926174300143
1988000111985534232400174
19890004063581521600122
199000013232358582400190
19910000062129133320104
1992000910215318495800218
1993000018583391192610246
199400004184302780091
199500000264826252900154
1996000181630229213600152
199700106515781071570279
19980000013234445600131
199900090151719412400125
200000210273622073100171
2001000038301310162800135
SNOWFALL (inches) 2001 SAN FRANCISCO, CALIFORNIA CA (SFO)
YEARJULAUGSEPOCTNOVDECJANFEBMARAPRMAYJUNTOTAL
1972–730.00.00.00.00.0T0.00.0T0.00.00.0T
1973–740.00.00.00.00.00.00.00.00.00.00.00.00.0
1974–750.00.00.00.00.00.0T0.00.00.00.00.0T
1975–760.00.00.00.00.00.00.0TT0.00.00.0T
1976–770.00.00.00.00.00.00.00.00.00.00.00.00.0
1977–780.00.00.00.00.00.00.00.00.00.00.00.00.0
1978–790.00.00.00.00.00.0T0.00.00.00.00.0T
1979–800.00.00.00.00.00.00.00.0T0.00.00.0T
1980–810.00.00.00.00.00.00.0T0.00.00.00.0T
1981–820.00.00.00.00.00.0T0.0T0.00.00.0T
1982–830.00.00.00.00.00.00.0TT0.00.00.0T
1983–840.00.00.00.00.00.00.00.00.00.00.00.00.0
1984–850.00.00.00.00.00.00.00.00.00.00.00.00.0
1985–860.00.00.00.00.00.00.00.00.00.00.00.00.0
1986–870.00.00.00.00.00.00.0T0.00.00.00.0T
1987–880.00.00.00.00.00.00.00.00.00.00.00.00.0
1988-890.00.00.00.00.0TTT0.00.00.00.0T
1989-900.00.00.00.00.00.00.00.00.00.00.00.00.0
1990-910.00.00.00.00.00.00.00.00.00.00.00.00.0
1991–920.00.00.00.00.00.00.00.0T0.00.00.0T
1992–930.00.00.00.00.0T0.00.00.00.00.00.0T
1993–940.00.00.00.00.00.00.0T0.00.00.00.0T
1994–950.00.00.00.00.00.00.00.0T0.00.00.0T
1995–960.00.00.00.00.00.00.0T0.00.00.00.0T
1996–970.00.00.0
1997–98
1998–99
1999–00
2000–01
2001–
POR=68 YRS0.00.00.00.00.00.00.0TT0.00.00.0T

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