2001 Boston, Massachusetts (BOS)

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2001 BOSTON, MASSACHUSETTS (BOS)

Climate is the composite of numerous weather elements. Three important influences are responsible for the main features of the Boston climate. First, the latitude places the city in the zone of prevailing west to east atmospheric flow. Both polar and tropical air masses influence the region. Secondly, Boston is situated on or near several tracks frequently followed by low pressure storm systems. The weather fluctuates regularly from fair to cloudy to stormy conditions and assures an adequate amount of precipitation. The third factor is the east–coast location of Boston. The ocean has a moderating influence on temperature extremes of winter and summer.

Hot summer afternoons are frequently relieved by the locally celebrated sea breeze, as air flows inland from the cool water surface to displace the warm air over the land. This refreshing east wind is more commonly experienced along the shore than in the interior of the city or the western suburbs. In winter, under appropriate conditions, the severity of cold waves is reduced by the nearness of the relatively warm ocean. The average last occurrence of freezing temperature in spring is early April and the first occurrence of freezing temperature in autumn is early November. In suburban areas, especially away from the coast, these dates are later in spring and earlier in autumn by up to one month in the more susceptible localities.

Boston has no dry season. Most growing seasons have several shorter dry spells during which irrigation for high–value crops may be useful. Much of the rainfall from June to September comes from showers and thunderstorms. During the rest of the year, low pressure systems pass more or less regularly and produce precipitation on an average of roughly one day in three. Coastal storms, or northeasters, are prolific producers of rain and snow. The main snow season extends from December through March. Periods when the ground is bare or nearly bare of snow may occur at any time in the winter.

Relative humidity has been known to fall as low as 5 percent but such desert dryness is very rare. Heavy fog occurs on an average of about two days per month with its prevalence increasing eastward from the interior of Boston Bay to the open waters beyond.

Although winds of 30 mph or higher may be expected on at least one day in every month of the year, gales are both more common and more severe in winter.

NORMALS, MEANS, AND EXTREMES

BOSTON, MA (BOS)

LATITUDE:    LONGITUDE:    ELEVATION (FT):    TIME ZONE:    WBAN: 14739

42 21′ 38″ N  71 00′ 38″ W  GRND: 19  BARO: 180  EASTERN (UTC + 5)

ELEMENTPORJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDECYEAR
TEMPERATURE FNORMAL DAILY MAXIMUM3035.737.545.855.966.676.381.879.872.862.752.240.459.0
MEAN DAILY MAXIMUM5636.638.345.556.166.876.881.879.972.562.752.040.959.2
HIGHEST DAILY MAXIMUM506670899495100102102100907976102
YEAR OF OCCURRENCE199519851998197619791952197719751953196319941998JUL 1977
MEAN OF EXTREME MAXS.5656.056.266.977.887.392.795.292.988.980.169.960.877.1
NORMAL DAILY MINIMUM3021.623.031.340.249.859.165.164.056.846.938.326.743.6
MEAN DAILY MINIMUM5622.023.631.240.349.859.365.264.056.747.038.127.243.7
LOWEST DAILY MINIMUM50-12-461634455047382815-7-12
YEAR OF OCCURRENCE195719611984198219561986198819862000197619891980JAN 1957
MEAN OF EXTREME MINS.563.46.115.429.640.349.457.154.744.234.624.39.530.7
NORMAL DRY BULB3028.630.338.648.158.267.773.571.964.854.845.333.651.3
MEAN DRY BULB5629.331.038.348.258.368.073.572.064.554.945.134.151.4
MEAN WET BULB1826.728.233.942.151.661.065.865.458.846.440.129.145.8
MEAN DEW POINT1818.819.724.634.743.355.861.361.354.540.933.421.539.1
NORMAL NO. DAYS WITH:
MAXIMUM 90300.00.00.00.10.52.55.42.90.8*0.00.012.2
MAXIMUM 323011.48.02.0*0.00.00.00.00.00.00.36.528.2
MINIMUM 323026.123.516.82.70.00.00.00.00.00.67.022.399.0
MINIMUM 0300.50.50.00.00.00.00.00.00.00.00.00.21.2
H/CNORMAL HEATING DEG. DAYS3011289728185072213206723215919735641
NORMAL COOLING DEG. DAYS3000001011326422066500678
RHNORMAL (PERCENT)3062626363676868717268686566
HOUR 01 LST3065656769747777798076726872
HOUR 07 LST3067686968717374777977747172
HOUR 13 LST3057565655585857595957595958
HOUR 19 LST3061606261646666697167666465
SPERCENT POSSIBLE SUNSHINE6153565756586365656360505258
W/OMEAN NO. DAYS WITH:
HEAVY FOG (VISBY 1/4 MI)671.81.72.01.72.72.12.31.81.92.21.81.323.3
THUNDERSTORMS670.20.10.61.02.33.44.23.41.70.70.40.218.2
CLOUDINESSMEAN:
SUNRISE-SUNSET (OKTAS)615.05.05.15.35.35.04.94.54.44.45.05.04.9
MIDNIGHT-MIDNIGHT (OKTAS)324.84.74.94.95.04.74.74.34.34.14.84.74.7
MEAN NO. DAYS WITH:
CLEAR629.08.27.77.06.36.66.69.110.010.77.78.597.4
PARTLY CLOUDY626.86.68.08.19.910.412.010.57.97.77.27.3102.4
CLOUDY6215.213.415.314.914.812.911.910.911.612.114.714.9162.6
PRMEAN STATION PRESSURE(IN)2929.9830.0029.9929.9029.9029.9029.9029.9929.9830.0029.9829.9929.96
MEAN SEA-LEVEL PRES. (IN)1830.0330.0330.0129.9729.9729.9529.9730.0230.0630.0830.0630.0430.02
WINDSMEAN SPEED (MPH)5313.713.814.013.512.211.611.010.811.311.912.913.512.5
PREVAIL. DIR (TENS OF DEGS)3430292930202023242424293030
MAXIMUM 2-MINUTE:
SPEED (MPH)539404641404545304741484648
DIR. (TENS OF DEGS)30270309273030092331111811
YEAR OF OCCURRENCE200020011997200020012000199919971998199919972000NOV 1997
MAXIMUM 5-SECOND:
SPEED (MPH)554545651496274376352575574
DIR. (TENS OF DEGS)30210601322925102332111825
YEAR OF OCCURRENCE200020002001199720012000199919971998199919972000JUL 1999
PRECIPITATIONNORMAL (IN)303.593.623.693.603.253.092.843.243.063.304.224.0141.51
MAXIMUM MONTHLY (IN)5010.557.8111.009.4613.3813.208.1217.099.8610.668.899.7417.09
YEAR OF OCCURRENCE197919841953198719541982195919551999199619831969AUG 1955
MINIMUM MONTHLY (IN)500.610.720.620.830.530.480.520.820.350.410.640.810.35
YEAR OF OCCURRENCE198919871981199919641999195219951957199419761989SEP 1957
MAXIMUM IN 24 HOURS (IN)502.722.684.133.325.745.693.368.405.646.633.765.148.40
YEAR OF OCCURRENCE197919691968199119541998199619551954199619921992AUG 1955
NORMAL NO. DAYS WITH:
PRECIPITATION 0.013011.09.911.611.011.210.78.99.98.48.610.912.0124.1
PRECIPITATION 1.00300.91.20.81.00.70.60.70.70.70.71.20.910.1
SNOWFALLNORMAL (IN)3011.912.36.91.10.*0.00.00.00.00.*1.38.141.6
MAXIMUM MONTHLY (IN)6439.841.338.913.30.50.00.0T0.00.210.027.941.3
YEAR OF OCCURRENCE199619691993198219771994197919381970FEB 1969
MAXIMUM IN 24 HOURS (IN)6421.023.617.713.20.50.00.0T0.00.28.013.023.6
YEAR OF OCCURRENCE197819781960198219771994197919871960FEB 1978
MAXIMUM SNOW DEPTH (IN)512629201200000061429
YEAR OF OCCURRENCE197819781978198219871975FEB 1978
NORMAL NO. DAYS WITH:
SNOWFALL 1.0302.92.72.10.30.00.00.00.00.00.00.52.511.0
PRECIPITATION (inches) 2001 BOSTON, MA (BOS)
YEARJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDECANNUAL
19722.055.295.373.345.266.762.190.835.942.987.026.0853.11
19733.122.132.205.653.764.684.832.781.952.711.747.2042.75
19743.223.244.013.862.872.291.543.417.033.121.733.9240.24
19755.703.372.742.401.782.102.355.525.494.415.134.8045.79
19765.292.452.422.001.980.584.307.991.564.160.643.3536.72
19774.412.404.764.073.522.492.212.914.034.632.546.2044.17
19788.122.872.461.794.501.531.484.621.303.132.213.6337.64
197910.553.463.033.194.240.862.365.023.613.143.291.4244.17
19800.740.885.374.362.303.052.201.550.824.143.010.9729.39
19810.956.650.623.141.171.653.471.042.543.434.786.2735.71
19824.692.662.173.422.5813.204.222.221.573.193.421.2744.61
19835.035.009.726.862.941.071.073.281.063.748.894.9453.60
19842.317.816.824.438.773.064.431.601.225.181.682.9350.24
19851.121.832.291.623.363.943.516.673.001.656.391.2136.59
19863.422.833.421.591.317.743.963.321.083.276.016.3844.33
19877.280.724.279.461.752.620.822.937.292.733.492.1245.48
19882.503.933.521.472.861.297.621.111.291.606.571.0234.78
19890.612.513.073.583.542.845.095.924.615.714.130.8142.42
19903.783.601.715.946.530.694.086.571.677.361.393.1846.50
19913.241.584.334.840.922.891.955.276.324.274.062.5842.25
19923.112.283.592.341.404.612.664.253.461.626.148.2643.72
19932.174.947.674.861.041.751.751.324.643.612.866.6043.21
19945.222.957.492.255.350.861.807.034.580.414.315.3747.62
19954.332.572.201.401.821.552.060.823.606.425.133.2035.10
19967.443.172.364.382.731.035.231.546.0910.662.295.7652.68
19972.341.284.683.462.631.410.633.011.021.785.862.2930.39
19984.765.544.153.586.8411.582.473.373.035.381.381.5953.67
19995.693.512.520.832.70T3.511.339.864.302.141.5237.91
20002.622.553.595.022.886.615.202.222.872.864.514.6745.60
20011.581.377.570.881.234.992.134.142.290.980.732.8330.72
POR=131 YRS3.673.353.893.563.243.203.123.563.253.273.863.5841.55
AVERAGE TEMPERATURE (F) 2001 BOSTON, MA (BOS)
YEARJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDECANNUAL
197233.029.636.344.957.665.473.871.565.751.842.333.050.4
197331.430.143.349.957.070.074.374.864.455.645.839.653.0
197431.729.138.750.954.764.872.472.063.750.145.337.850.9
197534.932.136.945.161.567.575.972.963.957.351.834.452.9
197626.137.341.255.160.273.472.972.064.952.341.929.052.2
197723.330.744.751.362.667.474.973.464.455.348.134.252.5
197828.527.136.248.859.368.372.171.661.452.543.635.350.4
197932.523.142.548.761.168.274.571.764.952.748.636.752.1
198029.427.936.948.759.466.375.874.267.052.441.228.650.7
198121.436.439.151.760.470.774.672.163.751.243.933.251.5
198222.930.838.748.257.863.374.970.364.154.247.639.651.0
198331.232.840.649.158.270.778.073.670.655.246.132.153.2
198426.737.631.946.158.070.574.774.662.153.344.639.551.6
198524.432.840.449.359.364.873.570.465.455.445.431.351.0
198631.428.940.748.458.466.171.070.563.254.042.335.550.9
198728.929.138.545.157.265.171.770.365.454.343.936.150.5
198827.832.239.246.857.668.573.775.564.650.846.732.851.4
198934.530.537.345.959.467.872.871.664.755.342.821.750.4
199036.434.140.147.654.966.673.173.364.658.348.540.753.2
199129.436.141.651.363.370.074.673.863.756.445.236.053.5
199231.032.435.446.455.667.869.570.463.952.542.934.850.2
199332.427.136.448.360.369.574.773.664.852.345.634.251.6
199422.226.938.251.458.471.977.572.464.255.549.038.552.2
199534.628.538.846.157.268.675.972.863.158.441.931.751.5
199630.130.936.547.957.468.171.870.964.253.240.339.350.9
199729.236.036.746.356.168.273.771.264.252.841.735.250.9
199833.935.341.549.460.364.774.472.566.354.544.639.153.0
199929.533.639.449.258.271.075.771.367.153.048.037.352.8
200027.534.243.347.357.267.370.070.363.553.943.829.250.6
200130.031.835.348.759.671.169.973.965.356.248.340.552.6
POR=129 YRS28.829.637.347.257.967.172.770.964.154.143.733.150.5

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 BOSTON, MA (BOS)
YEARJULAUGSEPOCTNOVDECJANFEBMARAPRMAYJUNTOTAL
1972-7334514056739851033971666450258245523
1973-74029428957078210231000809429335775410
1974-7502102458587836925918866590162595505
1975-7608702393959411198800733331166164897
1976-771105539368811081290956623414158435739
1977-78048530449894811271057885480209185615
1978-79111115038163591610021169691481149195615
1979-802158039048487310961071866481185665609
1980-8125723877061120134479479639320075826
1981-82269141962897913009488114962311136024
1982-83219713385157831040896749478223225136
1983-840842327561101211827901020563239365780
1984-85301423596057811255897758471204715546
1985-8631165298580103510351008746490258665595
1986-872116983446749041112997814588285765929
1987-88818573266268881145945792541253615660
1988-8991064443541992938959853565196515621
1989-9024882946601336880857762524307605774
1990-9145842364967441096803721407126354757
1991-92181112735868941049937913552317375678
1992-93211410938665693010021056880493167315745
1993-9431893875799461320105982740422675848
1994-9513612884798139321016804561258305246
1995-961211321468510231074981875510260205758
1996-9716803587397921104806868551269875661
1997-985383383693917955826736462192665321
1998-9902363216067981092872790468215295229
1999-0027393635058511152887665523250745318
2000-016210834162811031079925914488217185829
2001-2167286492753
COOLING DEGREE DAYS (base 65 F) 2001 BOSTON, MA (BOS)
YEARJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDECANNUAL
19720000267427921379000671
197300071818029631684300904
197400010228123522668130646
197500006013934526144940862
1976000432527625123161800895
1977001139212431427275600897
197800004012223722148000668
1979000035122304226851700789
1980000018114347299137100916
198100006718530623260000850
198200001567314192491020649
198300071820041028321727001162
198400033120731230662300924
19850005307227118383800652
1986000060105211190551000631
19870000488722118976020623
1988000031173287342591100903
198900102914224821489000723
1990000102116261268773480776
1991000379189304287791500956
199200003012616518983500598
199300002817331027389020875
199400012922139524144140936
1995000024147344252641500846
199600033012022219663010635
199700000189280202661200749
199800162525929824083100751
1999000011215344213110000893
200000001515116717471500583
2001000955210160283832000820
SNOWFALL (inches) 2001 BOSTON, MA (BOS)
YEARJULAUGSEPOCTNOVDECJANFEBMARAPRMAYJUNTOTAL
1972-730.00.00.0T0.63.33.62.50.3T0.00.010.3
1973-740.00.00.00.00.0T16.017.80.13.00.00.036.9
1974-750.00.00.00.02.03.62.217.01.81.00.00.027.6
1975-760.00.00.0T0.119.315.01.410.8T0.00.046.6
1976-770.00.00.00.01.017.223.25.910.7T0.50.058.5
1977-780.00.00.00.00.75.235.927.216.1T0.00.085.1
1978-790.00.00.00.04.25.810.56.6T0.40.00.027.5
1979-800.00.00.00.2T2.00.46.53.6T0.00.012.7
1980-810.00.00.00.02.45.611.91.90.50.00.00.022.3
1981-820.00.00.00.0T17.618.07.65.313.30.00.061.8
1982-830.00.00.00.0T5.54.722.30.2T0.00.032.7
1983-840.00.00.00.0T2.621.10.319.0T0.00.043.0
1984-850.00.00.00.0T3.77.010.23.72.00.00.026.6
1985-860.00.00.00.03.01.30.810.42.6T0.00.018.1
1986-870.00.00.00.03.53.424.33.73.54.10.00.042.5
1987-880.00.00.00.09.07.517.014.15.0T0.00.052.6
1988-890.00.00.0T0.03.71.56.73.20.40.00.015.5
1989-900.00.00.00.04.56.27.016.94.10.50.00.039.2
1990-910.00.00.00.0T1.211.72.83.40.00.00.019.1
1991-920.00.00.00.0T5.80.44.010.81.00.00.022.0
1992-930.00.00.00.00.69.712.919.638.92.20.00.083.9
1993-940.00.00.00.0T11.633.736.214.80.00.00.096.3
1994-950.0T0.00.00.11.54.48.50.4T0.00.014.9
1995-960.00.00.00.04.124.139.815.516.8
1996-971.6
1997-98
1998-9916.87.411.40.00.00.0
1999-000.00.00.00.00.00.013.79.22.0T0.00.024.9
2000-010.00.00.0TT4.512.49.819.2T0.00.045.9
2001-0.00.00.0T0.05.0
POR=63 YRS0.0T0.00.01.37.512.611.48.10.90.00.041.8

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