2001 Wilmington, Delaware (ILG)

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2001 WILMINGTON, DELAWARE (ILG)

Delaware is part of the Atlantic Coastal Plain consisting mainly of flat low land with many marshes. Small streams and tidal estuaries comprise the drainage of the State. Wilmington, at the northern end of the State, marks the beginning of low rolling hills extending northward and northwestward into Pennsylvania. The Delaware River, the Delaware Bay, and the Atlantic Ocean are along the eastern boundary of the State. The broad Chesapeake Bay lies 35 miles, or less, to the west of the western boundary of nearly the entire State. These large water areas considerably influence the climate of the Wilmington, Delaware region.

Summers are warm and humid, winters are usually mild. During the summer maximum temperatures are usually in the 80s. The temperature reaches 100 degrees on the average once in six years. During January, the coldest month of the year, the daily average temperature is 32 degrees. Temperatures of zero may be expected once in four years. Most of the winter precipitation falls as rain. Seasonal snowfall has been as little as 1 inch, and as much as 50 inches. Snow is frequently mixed with rain and sleet, and seldom remains on the ground more than a few days.

The proximity of large water areas and the inflow of southerly winds cause the relative humidity to be quite high all year. During the summer months the relative humidity is approximately 75 percent. Fog is relatively frequent and may occur in any month. Light southeast winds blowing up the Delaware Bay favor the formation of fog. Light north–northeast winds bring in smoke from Philadelphia and from the heavy industry area located along the Delaware River north of Wilmington.

Rainfall distribution throughout the year is fairly uniform, however, the greatest amounts normally come during the summer months. Mostly, the summer rainfall comes in the form of thunderstorms. Moisture deficiencies for crops occur occasionally, but severe droughts are rare. During the fall, winter, and spring seasons, much of the rainfall comes from storms forming over the southern states or the South Atlantic and moving northward along the coast. During the late summer and early fall, hurricanes occasionally cause heavy rainfall, but winds seldom reach hurricane force in Wilmington. Heavy rains occasionally cause minor flooding, but the streams and rivers of northern Delaware are not subject to major flooding. Strong easterly and southeasterly winds sometimes cause high tides in the Delaware Bay and the Delaware River, resulting in the flooding of lowlands and damage to bay front and river front properties.

Based on the 1951–1980 period, the average first occurrence of 32 degrees Fahrenheit in the fall is October 29 and the average last occurrence in the spring is April 13.

NORMALS, MEANS, AND EXTREMES

WILMINGTON, DE (ILG)

LATITUDE:    LONGITUDE:     ELEVATION (FT):    TIME ZONE:    WBAN: 13781

39 40′ 22″ N  75 36′ 03″ W  GRND: 92  BARO: 95  EASTERN (UTC + 5)

ELEMENTPORJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDECYEAR
TEMPERATURE FNORMAL DAILY MAXIMUM3038.741.952.162.672.981.485.684.177.766.655.543.963.6
MEAN DAILY MAXIMUM4539.342.451.463.072.881.585.584.177.666.355.444.163.6
HIGHEST DAILY MAXIMUM547578869496100102101100918575102
YEAR OF OCCURRENCE195019851998198519961994196619551983195119501998JUL 1966
MEAN OF EXTREME MAXS.5459.862.473.081.988.493.395.493.590.081.872.663.979.7
NORMAL DAILY MINIMUM3022.424.833.141.852.261.667.165.958.245.737.027.644.8
MEAN DAILY MINIMUM4523.225.432.942.052.261.666.965.657.945.636.927.844.8
LOWEST DAILY MINIMUM54-14-621830414843362414-7-14
YEAR OF OCCURRENCE198519791984198219781972198819821974197619551983JAN 1985
MEAN OF EXTREME MINS.547.09.418.028.838.548.955.753.442.531.822.312.530.7
NORMAL DRY BULB3030.633.442.752.262.571.576.475.068.056.246.335.854.2
MEAN DRY BULB5432.034.142.252.662.471.576.374.767.656.446.036.054.3
MEAN WET BULB4929.030.537.246.155.764.268.767.861.651.341.532.648.8
MEAN DEW POINT4922.223.329.238.750.260.064.664.257.747.335.826.443.3
NORMAL NO. DAYS WITH:
MAXIMUM 90300.00.00.00.20.73.37.64.91.90.00.00.018.6
MAXIMUM 32308.85.00.60.00.00.00.00.00.00.00.13.918.4
MINIMUM 323026.022.014.53.30.10.00.00.00.01.99.622.299.6
MINIMUM 0300.60.30.00.00.00.00.00.00.00.00.00.11.0
H/CNORMAL HEATING DEG. DAYS301066885691384122000352885619054937
NORMAL COOLING DEG. DAYS3000004419935331012515001046
RHNORMAL (PERCENT)3068656262676870727271696968
HOUR 01 LST3072717071778081838381767477
HOUR 07 LST3074747372757779838484807678
HOUR 13 LST3059565149535454565654565955
HOUR 19 LST3066636057626364687069686865
SPERCENT POSSIBLE SUNSHINE
W/OMEAN NO. DAYS WITH:
HEAVY FOG (VISBY 1/4 MI)544.23.52.72.12.21.71.62.32.43.83.33.433.2
THUNDERSTORMS540.20.31.12.33.85.56.15.42.40.90.60.228.8
CLOUDINESSMEAN:
SUNRISE-SUNSET (OKTAS)16.05.0
MIDNIGHT-MIDNIGHT (OKTAS)
MEAN NO. DAYS WITH:
CLEAR12.02.06.08.09.03.07.05.09.05.0
PARTLY CLOUDY11.01.06.04.05.01.04.03.02.02.0
CLOUDY14.05.011.06.08.02.07.03.08.0
PRMEAN STATION PRESSURE (IN)2930.0029.9929.9429.9029.9029.9029.9229.9629.9930.0230.0230.0129.96
MEAN SEA-LEVEL PRES. (IN)4930.0830.0730.0229.9930.0029.9830.0030.0230.0830.1030.0730.1030.04
WINDSMEAN SPEED (MPH)429.810.111.010.48.88.27.77.37.78.09.09.18.9
PREVAIL. DIR (TENS OF DEGS)2630303030301830183231303030
MAXIMUM 2-MINUTE:
SPEED (MPH)751434546484145403936444351
DIR. (TENS OF DEGS)15292833242732143529142715
YEAR OF OCCURRENCE199919961996199519991998199519972001199519992000JAN 1999
MAXIMUM 5-SECOND:
SPEED (MPH)761545653615255535246575361
DIR. (TENS OF DEGS)23292733232732153626132823
YEAR OF OCCURRENCE199919961996199519991998199519972001199919992000MAY 1999
PRECIPITATIONNORMAL (IN)303.032.913.433.393.843.554.233.403.432.883.273.4840.84
MAXIMUM MONTHLY (IN)548.417.029.176.807.387.4912.6312.0912.688.017.847.9612.68
YEAR OF OCCURRENCE197819792000198319831972198919551999199519721996SEP 1999
MINIMUM MONTHLY (IN)540.520.830.810.350.220.210.160.250.820.080.490.190.08
YEAR OF OCCURRENCE198119801966198519641988195519721970200019761955OCT 2000
MAXIMUM IN 24 HOURS (IN)542.532.294.872.562.724.356.834.118.433.883.832.338.43
YEAR OF OCCURRENCE199819662000196119901972198919711999196619561996SEP 1999
NORMAL NO. DAYS WITH:
PRECIPITATION 0.013010.39.59.910.611.29.89.18.87.87.39.49.8113.5
PRECIPITATION 1.00300.70.61.00.70.90.81.20.91.10.70.81.010.4
SNOWFALLNORMAL (IN)307.66.92.40.3T0.00.00.00.00.*0.73.421.3
MAXIMUM MONTHLY (IN)5026.227.520.32.6TTT0.00.02.511.921.527.5
YEAR OF OCCURRENCE1996197919581982199119921990197919531966FEB 1979
MAXIMUM IN 24 HOURS (IN)5022.016.515.62.4TTT0.00.02.511.912.422.0
YEAR OF OCCURRENCE1996197919581987199119921990197919531966JAN 1996
MAXIMUM SNOW DEPTH (IN)4613208200000T91220
YEAR OF OCCURRENCE1987197919561987196219531966FEB 1979
NORMAL NO. DAYS WITH:
SNOWFALL 1.0302.31.70.80.10.00.00.00.00.00.00.21.06.1
PRECIPITATION (inches) 2001 WILMINGTON, DE (ILG)
YEARJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDECANNUAL
19722.505.432.404.473.857.492.070.251.644.207.845.9948.13
19733.813.424.026.575.565.192.822.443.022.220.677.3147.05
19742.921.734.563.083.963.971.495.115.651.771.194.1839.61
19754.232.954.633.035.656.165.532.556.193.062.633.0049.61
19764.211.702.251.405.052.144.332.002.116.120.491.7933.59
19772.181.094.553.910.964.411.384.821.293.596.145.8140.13
19788.411.775.592.166.943.005.535.972.181.482.695.5651.28
19797.617.022.614.033.104.014.766.115.943.453.231.4453.31
19802.440.836.224.552.404.233.491.091.443.992.410.8333.92
19810.523.231.263.545.054.502.523.383.822.840.673.9535.28
19823.752.712.875.413.724.702.704.682.301.973.872.3941.07
19832.983.556.846.807.383.942.331.293.443.875.486.8054.70
19841.254.275.404.245.034.546.531.562.023.311.631.9441.72
19851.562.052.030.355.521.376.912.284.561.844.460.8033.73
19864.212.771.192.771.694.053.992.882.754.046.426.1142.87
19874.351.521.162.633.152.314.094.214.852.313.501.9035.98
19882.464.141.822.594.950.218.293.032.181.945.290.9037.80
19892.482.753.692.766.575.4312.631.974.313.921.991.2749.77
19903.561.352.153.427.033.944.276.152.642.851.615.1644.13
19914.300.974.643.281.983.413.715.385.361.271.264.2639.82
19921.051.814.361.764.483.144.342.214.301.114.274.2137.04
19932.643.117.505.873.951.604.042.656.262.772.853.5146.75
19945.003.557.362.853.692.117.015.682.100.852.962.2445.40
19953.082.282.472.103.501.262.892.035.178.014.312.1739.27
19964.581.193.634.983.275.006.253.044.054.703.257.9651.90
19971.831.833.491.490.821.753.083.661.932.333.242.5728.02
19984.802.954.862.914.134.662.183.141.762.801.261.0136.46
19995.413.513.963.363.561.620.894.2412.683.422.092.9447.68
20003.832.009.173.432.944.834.642.477.300.082.542.8046.03
20013.132.815.621.435.334.282.352.652.570.740.991.9533.85
POR=108 YRS3.343.013.813.463.673.704.504.443.722.993.193.4143.24
AVERAGE TEMPERATURE (F) 2001 WILMINGTON, DE (ILG)
YEARJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDECANNUAL
197236.132.641.350.062.568.676.975.569.653.545.241.654.5
197335.635.549.454.761.475.878.178.170.459.949.137.757.1
197436.233.144.355.562.470.476.776.166.553.246.638.955.0
197537.535.940.647.565.271.575.776.365.460.051.036.255.2
197627.741.246.554.759.972.474.273.766.952.540.431.053.4
197720.833.347.254.463.968.976.475.469.353.446.633.453.6
197827.222.837.650.360.370.673.477.166.754.146.837.252.0
197931.422.145.450.663.867.975.375.068.255.049.638.153.5
198032.429.940.054.664.968.977.778.271.354.843.333.154.1
198125.437.940.255.062.572.377.173.566.953.045.334.253.6
198224.234.241.850.665.069.977.372.067.456.047.541.353.9
198335.235.345.953.161.071.877.677.069.356.946.732.155.2
198424.838.635.650.761.273.875.275.263.761.243.342.153.8
198527.537.447.158.065.970.676.674.469.158.351.032.955.7
198632.231.643.652.465.772.177.172.567.557.244.137.354.4
198731.431.944.652.363.173.579.174.368.351.747.438.654.7
198827.434.844.250.862.971.679.477.365.851.046.735.153.9
198936.034.342.151.662.174.375.974.468.457.644.625.053.9
199040.541.146.053.761.572.177.474.666.760.048.441.056.9
199134.339.744.954.769.173.677.376.767.257.646.839.556.8
199235.237.241.552.060.769.676.372.267.353.247.238.354.2
199337.631.039.052.865.372.879.477.868.755.747.436.455.3
199426.331.641.858.460.075.879.873.267.253.949.740.054.8
199536.630.345.351.562.272.078.777.168.259.341.331.354.5
199629.933.338.452.660.173.074.174.067.755.140.139.253.1
199731.838.943.250.358.669.675.972.865.555.643.637.653.6
199839.841.044.754.265.370.575.175.570.957.046.941.056.8
199934.836.941.752.762.971.680.075.868.153.849.438.855.5
200031.536.647.351.963.872.072.972.765.056.444.230.153.7
200131.636.239.853.362.773.072.777.365.656.750.842.555.2
POR=107 YRS32.333.542.252.362.771.476.174.367.856.545.835.554.2

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 WILMINGTON, DE (ILG)
YEARJULAUGSEPOCTNOVDECJANFEBMARAPRMAYJUNTOTAL
1972-73002035658671690282047732214304342
1973-74001517946983988688763530013774354
1974-7500653625538058478087535208454802
1975-7600561774188881149681567341178314486
1976-77044438773410471361884546333107325479
1977-78013135355097511651179842433191175737
1978-7960603375428541037119760542489285179
1979-8047313184588271004100976830783354851
1980-810020322645985122275276329913545147
1981-820057370585947125985571542669125295
1982-830142930551972491982258736816374457
1983-8400742755421013124075890442216255395
1984-850211314964170111547665502487374404
1985-860045213411986101193065337399114732
1986-8702736276619848103292362837414324908
1987-8802224065218111159869637419121385005
1988-89305243454192389385471039514204947
1989-900254236605123174966159336812764632
1990-9121692144947349437006173206154160
1991-920064244541785914799723386169124637
1992-93015736352781784394579936064124788
1993-940055286526879119392971522318924997
1994-95002934345477087596759840112204559
1995-96004120870310331083912816378206105390
1996-9700433047417941025729672436201565001
1997-98207132463584477566764531789274396
1998-9900222415367389267827153629574424
1999-0001363404628071032816544390117154560
2000-01029927461910741029801776361110105155
2001-1073271418691
COOLING DEGREE DAYS (base 65 F) 2001 WILMINGTON, DE (ILG)
YEARJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDECANNUAL
19720020351433763341658001063
1973000194233241641318329001434
197400024641753703551132601109
19750000972073373557327501101
197600037252602912781066001003
197700520801563603281660501120
19780000481882733831177001016
19790041571233273241381600990
198000008315940041721410001283
19810009622283812701203001073
198200027516339123810732101009
1983000174721839837820929001296
19840000502763213278034001088
19850044710618136630017413001191
1986000012922737926711640001158
19870003912644462951290001228
1988000062242455389805001233
198900606128734529916217001177
19900010362322739530412766001188
19910011819727139037113523201408
1992000339156358230134300923
19930001792524524051763401372
19940003241334466260994001236
199500044221843438114839101267
199600013642542912851292001038
199700009204348248924000941
1998002201061953203372042001186
19990000402114763421391001209
20000003892302532471061100939
2001000164625724738810021001075
SNOWFALL (inches) 2001 WILMINGTON, DE (ILG)
YEARJULAUGSEPOCTNOVDECJANFEBMARAPRMAYJUNTOTAL
1972-730.00.00.0TTTT1.2TT0.00.01.2
1973-740.00.00.00.00.06.12.411.5TT0.00.020.0
1974-750.00.00.00.0TT5.14.81.1T0.00.011.0
1975-760.00.00.00.00.00.34.51.76.7T0.00.013.2
1976-770.00.00.00.00.13.214.5T0.0T0.00.017.8
1977-780.00.00.00.00.40.916.018.49.9T0.00.045.6
1978-790.00.00.00.04.5T12.027.50.2T0.00.044.2
1979-800.00.00.02.50.01.46.10.85.10.00.00.015.9
1980-810.00.00.00.00.51.46.5T3.70.00.00.012.1
1981-820.00.00.00.0T2.814.64.50.42.60.00.024.9
1982-830.00.00.00.0T5.8T18.50.30.50.00.025.1
1983-840.00.00.00.0TT9.7T5.2T0.00.014.9
1984-850.00.00.00.0T0.314.20.7T0.40.00.015.6
1985-860.00.00.00.00.01.43.19.7TT0.00.014.2
1986-870.00.00.00.0T0.321.415.70.22.40.00.040.0
1987-880.00.00.00.00.72.110.81.1TT0.00.014.7
1988-890.00.00.00.0T0.26.72.91.20.00.00.011.0
1989-900.00.00.00.05.68.91.51.01.31.60.00.019.9
1990-91T0.00.00.00.06.45.20.60.9TT0.013.1
1991-920.00.00.00.0T0.21.51.30.5T0.0T3.5
1992-930.00.00.00.0T0.11.410.013.90.00.00.025.4
1993-940.00.00.00.0T2.42.79.23.40.00.00.017.7
1994-950.00.00.00.0T0.0T8.3T0.00.00.08.3
1995-960.00.00.00.03.27.126.27.56.05.9T0.055.9
1996-970.00.00.00.00.0T0.85.66.52.80.00.015.7
1997-980.00.00.00.00.0TT0.0T0.00.00.0T
1998-990.00.00.00.00.02.04.50.02.00.00.00.08.5
1999-000.00.00.00.00.00.014.24.00.02.10.00.020.3
2000-010.00.00.00.00.02.14.85.00.7T0.00.012.6
2001-0.00.00.00.00.00.0
POR=51 YRST0.00.00.10.93.16.96.03.10.2TT20.3

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