2001 Washington, D.C. Ronald Reagan National Airport (DCA)

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2001 WASHINGTON, D.C. RONALD REAGAN NATIONAL AIRPORT (DCA)

Washington lies at the western edge of the mid Atlantic Coastal Plain, about 50 miles east of the Blue Ridge Mountains and 35 miles west of Chesapeake Bay, adjacent to the Potomac and Anacostia Rivers. Elevations range from a few feet above sea level to about 400 feet in parts of the northwest section of the city.

Observations have been kept continuously since November 1870. Since June 1941 the official observations have been taken at Washington National Airport.

National Airport is located at the center of the urban heat island. As a result, low temperatures are the highest for the area. Differences between the airport and suburban locations are often 10 to 15 degrees. There is less variation in the high temperatures.

Summers are warm and humid and winters are cold, but not severe. Periods of pleasant weather often occur in the spring and fall. The summertime temperature is in the upper 80s and the winter is in the upper 20s. Precipitation is rather uniformly distributed throughout the year.

Thunderstorms can occur at any time but are most frequent during the late spring and summer. The storms are most often accompanied by downpours and gusty winds, but are not usually severe.

Tornadoes, which infrequently occur, have resulted in significant damage. Severe hailstorms have occurred in the spring.

Tropical storms can bring heavy rain, high winds and flooding, but extensive damage from wind and tidal flooding is rare. Wind gusts of nearly 100 mph and rainfall over 7 inches have occurred during the passage of tropical storms and hurricanes.

Major flooding of the Potomac River can result from heavy rains over the basin, occasionally augmented by snowmelt, and above normal tides associated with hurricanes or severe storms along the coast. Flooding may also occur after a cold winter when the Potomac may be blocked with ice.

Although a snowfall of 10 inches or more in 24 hours is unusual, several notable falls of more than 25 inches have occurred. Normal snowfall during the winter season is 18 inches.

The average date of the last freezing temperature in the spring is April 1 and the average date for the first freezing temperature in the fall is November 10.

NORMALS, MEANS, AND EXTREMES

WASHINGTON DC, DC (DCA)

LATITUDE:    LONGITUDE:    ELEVATION (FT):    TIME ZONE:    WBAN: 13743

38 51′ 54″ N  77 02′ 03″ W;  GRND:  10  BARO:  3  EASTERN  (UTC + 5)

ELEMENTPORJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDECYEAR
TEMPERATURE FNORMAL DAILY MAXIMUM3042.345.956.566.776.284.788.586.980.169.158.347.066.8
MEAN DAILY MAXIMUM5643.446.855.366.675.783.987.986.179.668.957.646.866.5
HIGHEST DAILY MAXIMUM607982899599101104105101948679105
YEAR OF OCCURRENCE195019481990197619911994198819971980195419741998AUG 1997
MEAN OF EXTREME MAXS.5664.567.477.585.790.395.396.895.592.383.875.366.382.6
NORMAL DAILY MINIMUM3026.829.137.746.456.666.571.470.062.550.341.131.749.2
MEAN DAILY MINIMUM5628.230.037.046.356.265.470.268.862.050.240.431.848.9
LOWEST DAILY MINIMUM60-541124344754493929161-5
YEAR OF OCCURRENCE198219611943198219471972198819861963196919551942JAN 1982
MEAN OF EXTREME MINS.5612.315.322.933.243.753.560.858.648.336.626.817.435.8
NORMAL DRY BULB3034.637.547.256.566.475.680.078.571.359.749.839.458.0
MEAN DRY BULB5635.738.446.256.565.974.779.177.470.759.649.039.357.7
MEAN WET BULB1832.234.840.249.558.967.471.270.263.953.743.735.551.8
MEAN DEW POINT1824.727.131.641.953.362.766.966.159.748.437.328.545.7
NORMAL NO. DAYS WITH:
MAXIMUM 90300.00.00.00.41.57.413.810.13.90.10.00.037.2
MAXIMUM 32305.22.30.20.00.00.00.00.00.00.0*2.19.8
MINIMUM 323022.318.58.40.90.00.00.00.00.00.44.215.770.4
MINIMUM 0300.10.00.00.00.00.00.00.00.00.00.00.00.1
H/CNORMAL HEATING DEG. DAYS3094277055226460000141954567944047
NORMAL COOLING DEG. DAYS30000910431846541920331001549
RHNORMAL (PERCENT)3062605958646667697067656464
HOUR 01 LST3066666466747677797976716872
HOUR 07 LST3069697069747576808179757174
HOUR 13 LST3055524948525253555553545653
HOUR 19 LST3059565351596061646664616160
SPERCENT POSSIBLE SUNSHINE5046505557586462626159514656
W/OMEAN NO. DAYS WITH:
HEAVY FOG (VISBY1/4 MI)531.71.50.90.80.40.20.10.10.31.31.31.710.3
THUNDERSTORMS530.20.21.22.64.65.96.65.22.41.10.60.030.6
CLOUDINESSMEAN:
SUNRISE-SUNSET (OKTAS)495.45.25.25.15.14.84.84.64.64.35.05.24.9
MIDNIGHT-MIDNIGHT (OKTAS)335.15.05.04.85.04.74.84.54.54.24.75.14.8
MEAN NO. DAYS WITH:
CLEAR507.27.07.57.16.97.37.48.69.410.77.77.994.7
PARTLY CLOUDY507.46.78.39.110.111.411.810.28.47.97.86.6105.7
CLOUDY5016.414.515.213.914.011.411.411.711.611.913.815.9161.7
PRMEAN STATION PRESSURE (IN)2930.0330.0229.9729.9229.9229.9229.9429.9830.0130.0430.0330.0529.99
MEAN SEA-LEVEL PRES. (IN)1830.1130.1130.0529.9929.9929.9830.0030.0330.0730.1130.1330.1330.06
WINDSMEAN SPEED (MPH)5410.210.711.110.79.69.08.58.38.58.89.59.69.5
PREVAIL. DIR (TENS OF DEGS)3232323218181818181818183318
MAXIMUM 2-MINUTE:
SPEED (MPH)341363739374947333932343449
DIR. (TENS OF DEGS)29282831263105313235163231
YEAR OF OCCURRENCE200020012001200019991999200020002000199919991999JUN 1999
MAXIMUM 5-SECOND:
SPEED (MPH)355514851556053455541444560
DIR. (TENS OF DEGS)31272931253105353236162831
YEAR OF OCCURRENCE200020012001200020001999200020001999199919992000JUN 1999
PRECIPITATIONNORMAL (IN)302.722.713.172.713.663.383.803.913.313.023.123.1238.63
MAXIMUM MONTHLY (IN)607.115.718.456.8810.6911.5311.0614.3112.368.656.706.5414.31
YEAR OF OCCURRENCE197819611994198319531972194519551975199519631969 AUG1955
MINIMUM MONTHLY (IN)600.310.420.640.030.750.950.930.550.20T0.290.22T
YEAR OF OCCURRENCE195519781945198519861988196619621967196319811955OCT 1963
MAXIMUM IN 24 HOURS (IN)582.132.133.433.084.327.194.696.395.314.984.032.867.19
YEAR OF OCCURRENCE197619981958197019531972197019551975195519931977JUN 1972
NORMAL NO. DAYS WITH:
PRECIPITATION 0.01309.89.510.19.610.89.79.68.97.27.28.58.9109.8
PRECIPITATION 1.00300.40.50.60.40.90.81.01.31.01.00.80.79.4
SNOWFALLNORMAL (IN)306.26.31.60.*0.00.00.00.00.00.*1.03.118.2
MAXIMUM MONTHLY (IN)5823.830.617.10.6TTTT0.00.311.516.230.6
YEAR OF OCCURRENCE19961979196019721993199819901996197919871962FEB 1979
MAXIMUM IN 24 HOURS (IN)5813.818.78.40.6TTTT0.00.311.511.418.7
YEAR OF OCCURRENCE19661979199919721993199819901992197919871957FEB 1979
MAXIMUM SNOW DEPTH (IN)5518228100000012822
YEAR OF OCCURRENCE198719791960197219871973FEB 1979
NORMAL NO. DAYS WITH:
SNOWFALL 1.0301.61.50.50.00.00.00.00.00.00.00.20.74.5
PRECIPITATION (inches) 2001 WASHINGTON, D.C. DC (DCA)
YEARJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDECANNUAL
19722.455.272.273.994.7811.533.432.821.273.566.054.5551.97
19732.262.682.974.193.392.112.684.411.581.710.976.0334.98
19742.660.954.212.264.373.401.155.774.391.131.244.4335.96
19753.091.565.332.134.712.157.163.5412.362.382.054.0450.50
19763.561.552.511.173.571.214.542.137.237.760.851.9938.07
19771.500.662.172.661.733.284.064.740.325.354.814.8636.14
19787.110.424.481.385.132.434.285.851.011.162.314.0039.56
19796.645.622.451.883.552.993.435.416.645.542.330.8547.33
19802.851.165.043.282.641.683.861.111.902.592.560.6529.32
19810.382.821.492.633.422.555.693.021.943.640.292.8030.67
19822.273.332.643.195.115.412.982.681.711.752.961.7435.77
19831.693.094.846.884.627.091.783.112.904.875.095.9151.87
19841.713.436.143.713.802.014.092.302.513.183.661.1937.73
19852.113.071.880.035.792.052.912.356.673.854.470.6835.86
19862.383.490.741.980.751.293.795.330.602.015.234.9832.57
19874.902.111.542.282.543.902.592.075.112.534.492.5736.63
19883.142.522.272.004.500.953.742.391.851.755.331.3031.74
19892.492.804.303.507.776.025.661.156.685.482.372.1050.32
19902.951.302.574.095.203.143.786.740.873.302.174.7340.84
19912.900.834.421.391.571.273.762.033.502.030.855.0729.62
19922.782.233.482.553.412.355.342.483.492.033.382.8636.38
19932.902.276.823.623.401.731.363.873.682.624.764.3841.41
19944.284.208.451.581.561.593.614.352.841.191.572.3537.57
19953.221.712.141.894.192.424.030.883.738.654.772.1739.80
19965.011.993.603.174.963.145.602.637.794.043.585.5151.02
19972.552.434.152.413.042.941.143.511.593.724.601.7433.82
19985.435.235.403.964.054.421.790.591.830.590.911.7435.94
19995.422.543.872.091.282.261.015.0210.272.161.822.4940.23
20003.662.063.985.133.084.935.513.774.910.021.602.0140.66
20012.221.833.881.683.714.694.782.981.410.690.551.5329.95
POR=60 YRS2.902.563.492.813.803.303.844.013.432.902.922.9638.92
AVERAGE TEMPERATURE (F) 2001 WASHINGTON, D.C. DC (DCA)
YEARJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDECANNUAL
197238.536.545.654.164.670.277.575.971.056.046.843.656.7
197337.637.051.156.062.877.179.279.974.363.351.641.959.3
197442.939.249.258.365.171.579.078.470.257.350.943.158.8
197540.940.645.253.669.776.479.380.168.563.254.440.559.4
197633.946.951.359.965.077.678.476.770.455.443.035.557.8
197725.438.852.760.169.474.380.978.873.959.051.838.158.6
197832.531.444.457.765.876.778.881.373.659.452.243.158.1
197935.128.451.556.067.772.478.678.571.658.654.443.758.0
198037.236.146.260.169.574.882.382.877.159.948.639.859.5
198133.043.747.662.166.278.780.277.071.058.351.438.559.0
198228.138.345.754.069.072.880.375.470.660.251.845.557.6
198338.138.748.853.364.975.081.281.072.660.550.336.058.4
198432.243.841.854.964.976.976.577.868.365.246.045.657.8
198530.837.847.761.668.172.379.076.771.961.254.336.458.2
198635.435.347.456.268.176.681.174.670.961.146.539.857.8
198734.737.047.754.867.276.482.678.772.154.449.941.558.1
198831.037.347.254.465.874.481.980.768.954.449.938.757.1
198939.937.846.155.464.176.878.377.171.460.548.027.956.9
199043.645.250.256.864.375.079.476.569.662.852.044.560.0
199138.643.048.858.273.076.881.480.071.060.448.842.360.2
199238.241.245.055.462.371.779.574.069.256.048.839.656.7
199339.734.342.254.867.475.383.179.671.058.148.838.157.7
199428.836.345.462.063.179.481.875.570.259.153.444.258.3
199539.634.449.256.365.874.681.581.371.062.343.135.657.9
199632.937.342.956.863.977.277.676.570.659.444.143.056.9
199737.044.748.754.062.973.180.477.670.559.646.241.058.0
199843.043.446.957.467.573.078.979.475.460.150.344.460.0
199938.241.044.556.567.374.783.079.770.057.253.142.058.9
200035.942.551.755.667.874.774.775.167.660.246.731.857.0
200135.540.943.857.665.975.275.378.968.959.754.845.558.5
POR=60 YRS35.738.346.356.466.074.779.077.370.759.549.039.157.7

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 WASHINGTON, D.C. DC (DCA)
YEARJULAUGSEPOCTNOVDECJANFEBMARAPRMAYJUNTOTAL
1972-7300827854365484377742328610903921
1973-740041033997086777164902288543414
1974-7500262504466747406776083452403790
1975-7600201023287529565244152368003413
1976-77001130665290712217293891883234438
1977-7800119640682910019336332198604304
1978-7900919237867191810194252733003915
1979-800052313136548578305731492803640
1980-810041894877749845925361337503774
1981-82001921939981811357435923281934275
1982-830291934025978277304973657703699
1983-84003217743389010096107103029544262
1984-8500545956159410537575331663063813
1985-8600141473208799138245422676133970
1986-87013181805487759317775273046804141
1987-88004325448719104779654431769254294
1988-89001833044280777175559629711204128
1989-90003516750711446565504812856443893
1990-9100381533816308106085022372203381
1991-92002717548669682468661429512753935
1992-9300432824777817798557003073234259
1993-940033217487825111579659913513204339
1994-950051903486397828534852745903635
1995-96003014465190199379867526813104591
1996-97009182617677861564499322110303871
1997-98001423255773767559658122950113682
1998-990041534336388246676302513433637
1999-0000222403487078966494082804623598
2000-010601715441022908670654246544
2001-0044207302598
COOLING DEGREE DAYS (base 65 F) 2001 WASHINGTON, D.C. DC (DCA)
YEARJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDECANNUAL
19720035501843933461958201186
1973002214737144846928857301706
19740043396205441422192172701437
197510012177344448475132501501654
1976041928638342437017915001554
1977001049177289496434274181501762
19780001011735843451427425001732
19790014912023143142520839201479
1980000917430154656337438102006
19810064911841747838020418001670
19820006155244479330185511311464
1983000218131051050426942001737
198400049936836540415773001470
19850067013523244437322837601531
19860051016235850331820270101629
198700081463475544312220001708
1988001410131353449014411001598
19890016149136241738123333101548
19900030465030945136418388001521
19910053827836251747221441501932
199200016532144572851758001208
199300051143195694602189801702
1994001538243953033316611601621
1995000209129751551121667101718
19960002910537339736418114001463
199700105228248439918472001474
19980027111322574384563229051657
199900041113015654621806001629
2000004514330030731914629001253
2001000318831832344117147501424
SNOWFALL (inches) 2001 WASHINGTON, D.C. DC (DCA)
YEARJULAUGSEPOCTNOVDECJANFEBMARAPRMAYJUNTOTAL
1972-730.00.00.0TT0.0T0.1TT0.00.00.1
1973-740.00.00.00.00.011.01.54.2TT0.00.016.7
1974-750.00.00.0TT0.16.65.80.3T0.00.012.8
1975-760.00.00.00.00.00.40.10.90.80.00.00.02.2
1976-770.00.00.00.00.80.69.70.00.0T0.00.011.1
1977-780.00.00.00.00.10.210.33.88.30.00.00.022.7
1978-790.00.00.00.03.1T4.030.6T0.00.00.037.7
1979-800.00.00.00.30.0T8.65.16.10.00.00.020.1
1980-810.00.00.00.0T0.34.2TT0.00.00.04.5
1981-820.00.00.00.0T1.715.35.30.2T0.00.022.5
1982-830.00.00.00.00.06.6T21.00.0T0.00.027.6
1983-840.00.00.00.00.3T6.5T1.8T0.00.08.6
1984-850.00.00.00.0T0.310.0TTT0.00.010.3
1985-860.00.00.00.00.00.71.812.9TT0.00.015.4
1986-870.00.00.00.00.0T20.810.3TT0.00.031.1
1987-880.00.00.00.011.5T13.1T0.4T0.00.025.0
1988-890.00.00.00.00.01.22.91.20.40.00.00.05.7
1989-900.00.00.00.03.59.00.2T2.40.20.00.015.3
1990-91T0.00.00.00.03.04.80.3T0.0T0.08.1
1991-920.00.00.00.0T0.04.02.6T0.00.00.06.6
1992-930.0T0.00.0T1.0T4.16.60.0T0.011.7
1993-940.00.00.00.0T2.63.53.14.00.00.00.013.2
1994-950.00.00.00.0T0.03.95.80.40.00.00.010.1
1995-960.00.00.00.00.51.323.815.25.2T0.00.046.0
1996-970.0T0.00.00.20.22.34.0T0.00.00.06.7
1997-980.00.00.00.0T0.1TTT0.0TT0.1
1998-990.00.00.00.00.00.52.20.28.70.00.00.011.6
1999-000.00.00.00.00.0T14.50.90.0T0.00.015.4
2000-010.0T0.00.00.02.02.42.80.2T0.00.07.4
2001-0.00.00.00.00.00.0
POR=57 YRSTT0.00.00.82.85.35.12.20.0T0.016.2

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