Viii. Climatic conditions
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- TABLE 4 4, 8
- Month Heating
- TABLE 7a 4, 5, 8
- TABLE 7b 2
- TABLE 8a AVERAGE PERCENT DAYTIME CLOUD COVER
- TABLE 8b 4,12
- Average and Peak Wind Data
| INTRODUCTION
This Local Climate Report is excerpted from the Cranford Environmental Commission’s Natural Resource Inventory. The original Natural Resource Inventory was published in December of 1993. The updated Natural Resource Inventory was published in December of 2003. The original text of the 1993 Natural Resource Inventory appears below with the 2003 updates and additions in red italics. The data tables presented show a ten year difference in data and may be used as a micro analysis of weather changes over the ten year period. VIII. CLIMATIC CONDITIONS 1,6(2001 update)
A major regional weather characteristic is instability caused by high pressure air masses which move in from Canada and conflict with low pressure air masses moving from the south. This results in periodic cool spells during the summer and periods of relatively warm, spring-like weather in winter. The storms experienced in Cranford are classified in four general groups: thunderstorms, cyclonic or transcontinental storms, extratropical storms, and hurricanes. Thunderstorms normally occur with the most frequency in the months of July and August. They are usually of brief duration and are limited in area. These storms, when intense, can cause local flooding in areas of the Township where storm sewers are not of sufficient size to accommodate the resulting surge flows. The general path of these storms is in a northeasterly direction. During autumn, winter and spring, cyclonic storms predominate. These storms are due to movements of transcontinental air masses with attendant high and low pressure areas. Intense storms of this type are potent flood producers over large areas because of their wide range. These storms can cluster together and last for many days, depositing four, five or more inches of precipitation over their duration. The duration of these storms, coupled with the continuous rainfall, can cause the Rahway River to rise above the storm sewer stream encroachment near the end of the storm event. This slows storm sewer drainage and causes street flooding as a result. In extreme cases, the Rahway River rises so high that river water will enter the street, causing flooding that will linger until the river recedes below the storm sewer encroachment elevation. Extratropical storms are due to the rapidly convective circulation that results when tropical marine air masses are lifted suddenly on contact with hills and mountains. They usually cause heavy rain in the summer and autumn seasons. A hurricane is defined as a spiraling tropical low pressure system, formed by the release of latent heat from ocean water condensation, with sustained wind speeds of 74 m.p.h. or greater. Because of its size and duration, a fully developed hurricane is the most destructive of storms. Hurricanes only form in certain areas of the earth at specific times of the year. Those affecting the United States form in the western Atlantic Ocean, near the Cape Verde Islands, and in the western Caribbean Sea. Hurricane season there runs from June 1 to November 30. METEOROLOGICAL DATAThere are no official meteorological stations located in Cranford. 2The Cranford station (located at 40'North Latitude, 74 18' West Longitude) on the grounds of Union County College is a National Weather Service Cooperative Observing Station. The station’s personnel manually take and manually record singular daily temperature and precipitation data only. It has been in existence for about 30 year; thus it does not have a long record of observations useful in assessing the magnitude of recent events. Observations from Newark are rather adequate surrogates for Cranford, and as noted above they are the only local observations for variables other than precipitation and temperature. All variables are automatically recorded instantaneously or hourly depending upon the parameter, and are electronically entered into the climatic database. The Newark weather station is located at Newark International Airport, approximately 10 miles east northeast of the Township (located at 40 42' North Latitude, 74 10' West Longitude). This station measures and keeps records on various weather-related phenomena such as temperature, barometric pressure, relative humidity, wind and cloud cover. Summaries of each are presented below: 1. Temperature In the last ten year period, the mean annual temperature at the Newark station increased from 54.2 degrees to 54.8 degrees Fahrenheit. The coldest month is January, with an average temperature of 30.6 degrees, a decrease from 31.5 degrees Fahrenheit in the last ten years. July is the hottest month of the year, with an average temperature of 77.8 degrees increased from 76.8 degrees Fahrenheit in the last ten years (see Table 5a). Temperature readings of above 90 degrees and below 0 degrees Fahrenheit are not unusual occurrences. The record high of 105 degrees Fahrenheit was first set in July of 1966 and equaled during July of 1993. The record low temperature of -8 degrees Fahrenheit was set in January of 1985. The average annual heating degree days decreased in past ten years from 4,972 to 4,888 and ranges from 5,577 to 4,086. The average annual cooling degree days increased over the past ten year period from 1,091 to 1,201 and ranges from 1,490 to 982 (see Table 5b).
2. Barometric Pressure Barometric pressure averages 1,016.1 millibars annually, with monthly averages ranging from 1,013.7 to 1,018.1 millibars (see Table 6a). 3. Relative Humidity Depending upon the time of day, the average annual relative humidity ranges between 53 and 73 percent (see Table 6b). 4. Precipitation An average of 42.34 inches of rain falls annually at the Newark station. Normally, this rainfall is distributed evenly throughout the year, with average monthly rainfall ranging from 2.94 to 4.3 inches each month. 2Neither Hurricane Floyd of September 16, 1999, nor the two major preceding storms of July 25, 1997 and October 20, 1996 altered the record for the maximum monthly rainfall which stood at 11.84 inches in August of 1955 and now stands at 22.48 inches. The minimum monthly rainfall was recorded in June of 1949 at 0.07 inches. The maximum rainfall that occurred in a 24-hour period occurred in August of 1971 and amounted to 7.84 inches. 2Neither Hurricane Floyd of September 16, 1999, nor the two major preceding storms of July 25, 1997 and October 20, 1996 altered the maximum 24-hour period rainfall record. Precipitation data is summarized in Table 7a. The abundant precipitation in the Cranford area has made groundwater recharge adequate and has helped the area's vegetative ground cover and tree population to temporarily retain water and minimize erosion. Precipitation during the winter months often falls in the form of snow (see Table 7b). The average annual snowfall in Cranford is approximately 27.7 inches. The monthly maximum of snow for the area stood at 29.1 inches, recorded in December of 1947, a portion of this amount (26.0 inches) was the result of a record 24-hour snowfall. 2Recently, however, a new record was set when Newark Airport recorded 33.4 inches of snow in February of 1994. Newark Airport also recorded 31.6 inches of snow in January of 1996, 27.8 inches of which were attributable to the blizzard that occurred on January 7 and 8, 1996. Snow can be expected to fall from October to May. The average monthly snowfall at the Newark station is shown below in Table 4. TABLE 44, 8AVERAGE MONTHLY SNOWFALL, ICE PELLETS, AND SLEET – (inches)Month Snowfall - (inches) September Trace October Trace November December January 7.7 February March April 0.7 May Trace Annual 27.7 Rainfall of 0.01 inches or more occurs on an average of 121.7 days annually and ranges from 11.3 to 15.4 days per month. Snowfall of 1.0 inch or more occurs on an average of 7.1 days annually and ranges from 0.0 to 2.2 days per month. TABLE 5a
TABLE 5b
TABLE 6a
TABLE 6b4, 9
TABLE 7a4, 5, 8
TABLE 7b2
5. Wind The normal prevailing wind direction is from the west to east for eleven months of the year. January is the exception, when the prevailing winds are from the northeast. Average monthly wind velocity ranges from 8.7 miles per hour (mph) to 11.9 mph, with an annual average of 10.2 mph. The peak gust recorded at the Newark station was 83 mph. Average and peak wind data is presented in Table 9. 6. Cloud Cover The mean annual amount of cloud cover is 62 percent. There is no data for the amount of cloud cover between sunset and sunrise. The following data in Table 8 is a list of daytime cloud cover only: TABLE 8aAVERAGE PERCENT DAYTIME CLOUD COVERMonth Average Cloud Cover – (percent) January 65 February 64 March 63
April 64 May 65
June 62 July 62
August 60 September 57 October 55 November 64 December 64
AVERAGE NUMBER OF CLOUDY DAYSMonth Clear Days Partly Cloudy Days Cloudy Days January 8 8 16 February 7 8 13 March 8 8 15 April 7 9 14 May 6 11 14 June 7 11 12 July 7 12 12 August 8 12 12 September 10 9 12 October 11 8 12 November 8 8 14 December 8 8 15 Annual 93 112 160 TABLE 91, 4, 10
* - fastest observed in one minute. Cranford has a wide variety of weather styles which contribute to the distinct seasonal differences experienced by the Township. These include rainfall, snowfall, thunderstorms, hailstorms and windstorms and are generally neither extreme nor severe. Table 10 below presents a listing of the average duration of the distinct weather types by month. TABLE 10
Notes: a = 0.01 inches or more. b = 1.0 inches or more of snow, ice pellets, and hail. c = 0.25 mile or less visibility. d = sunrise to sunset. New Jersey’s Weather2 New Jersey’s weather and climate offer something for everyone. In a month’s time one might observe record high and low temperatures being broken, tornadoes touching down, severe thunderstorms passing through, and a snowstorm blanketing the region. While rare, all occurred in November of 1989. A single year may bring a serious drought, an inundating flood, extreme heat, numbing cold, a damaging hurricane, a stinging blizzard. All but the cold and snow were exhibited in 1999. A relatively cool summer, sunny fall, manageable winter, and mild spring are also enjoyed from time to time. This weather and climate potpourri is a result of New Jersey’s middle latitude location. This geographic positioning results in the state being influenced by wet, dry, hot, and cold air streams, making for four relatively well defined seasons and leading to potential clashes between cold and warmth, triggering occasional severe conditions. This introduction will discuss the wettest time of the year, New Jersey drought frequency, long term monthly means, and variability over time. Cranford geographically lies at the southern portion of the northern land area as it boarders the central land area. From a climatalogical standpoint, Cranford lies in the northern region and enjoys the climate of the elevated region with the moderating effect from ocean on–shore air masses. It is important to know how precipitation data is gathered. Since the late 19th century, trained observers at several dozen National Weather Service observing stations across the state have taken daily observations of precipitation, snow, and temperature. National Weather Service professionals operate some stations, but volunteers at Cooperative Observing Stations record most of the data. Manual and electronic gauges are used to measure rain and melted snowfall, which, combined, equal precipitation. The statewide values presented in this introduction are calculated as an average of all of the stations operating at a given time; regional values are for northern and southern counties, with a narrow strip of coastal counties comprising a separate region. The data and figures discussed are from monthly and annual precipitation for the state and sub regions from 1895 to present. An excellent climatology of New Jersey’s annual precipitation regime is available for scrutiny because of over a century of data on file. Between 1895 and 2000, the average annual precipitation across New Jersey was 44.80 inches. From year to year this has varied by as much as plus or minus 35% of the mean, with as little as 29.36 inches in 1965 and as much as 59.98 inches in 1996. On average there is an equitable distribution of precipitation throughout the year. The wettest month, August with 4.59 inches is only 1.44 inches greater than the driest month, February with 3.15 inches. Of course, many months vary considerably from the long term mean, witness the driest month on record, 0.24 inches in June of 1949, and the wettest, 11.44 inches in August of 1955. Regionally, the northern division is the wettest, followed by the southern, and then coastal divisions. Annual precipitation from 1895 to 2000 averages 46.05 inches in the north, 44.33 in the south, and 42.04 along the coast. Precipitation in the north is enhanced by atmospheric lifting provided by its elevated terrain. The coast has less rain in the summer, as the stable, cooling influence of the ocean results in fewer drenching thunderstorms. The long-term annual mean is 2.3 inches less than the 1971-2000 mean of 47.19 inches. This clearly indicates that, in addition to the marked year-to-year variability in precipitation, there are also longer-term variations. On a decade basis, the last half of the 20th century included the 1st (1971-80), 2nd (1981-90), 3rd (1951-60), 4th (1991-2000), and 10th (1961-70) wettest decades of the century. With the exception of the drought-filled 1960s, New Jersey has experienced a much wetter regime of late, with approximately a 5 % increase in precipitation over the past century. The long-term increase in precipitation is seen most strongly in the northern half of the state. This region experienced an approximate 10% increase over the century, even with the dry decade of the 1960s. New Jersey has its share of flooding events, be the flash floods or major river floods, as seen in recent years, including the Sparta/Hopatcong event in August of 2000 and the Hurricane Floyd flood of September 16, 1999. Human development, heavy rain, sometimes in combination with a rapidly melting snow pack, are the major dictating factors. In contrast, a dearth of reduced winter storminess, non existent tropical moisture, and meager thunderstorm rains can lead to protracted periods of dry conditions or drought. The past two decades saw precipitation deficits in 1980-81, 1984-85, 1994-95, and 1998-99. However, these extended periods of below average precipitation have not lasted for more than a year. None have come close to matching the drought that occurred in the early and middle 1960s, the most severe drought of the 20th century, and perhaps for many centuries based on tree ring analysis, nor has any had the longevity of several other droughts earlier in the 20th century. It is impossible to predict whether the wet precipitation regime of the past four decades will persist into the early decades of the 21st century, or whether the drier pattern of the first half of the 20th century becomes reestablished. Nor can it be determined if the tendency for the reservoir-rich northern part of New Jersey will continue to exhibit a greater increase in precipitation than the remainder of the State. The protracted drought of the 1960s was a seemingly rare situation; so too may be the conditions experienced in recent decades, with extended periods of below average precipitation not lasting more than a year. Results of continued monitoring and research of New Jersey’s precipitation regime will be useful in preparing for floods, droughts, and any hydrologic changes in the 21st century. Notes: Updates are in red Italics. Updates are as of November 1, 2001 1 The Normals database report is updated on a 10 year basis. The decade ending 2000 will be added to the database report which is due out by mid 2002 or later. That will span the period 1961 to 2000. Because this NRI publication deadline is earlier, most of the data in this section of the NRI is from the data report dated from 1961 to 1990. 2 Data, information, text, and analysis supplied by the New Jersey State Climatologist. 3 From the New Jersey State Climatological data. 4 From the National Climatic Data Center – National Oceanographic and Atmospheric Agency and the National Weather Service. 5 From Newark Weather Almanacs. 6 Data and substantive text changes and text additions are in red. 7 30 years of data. 8 59 years of data. 9 35 years of data. 10 52 years of data. 11 158 years of data. 12 53 years of data Friday, January 07, 2005 01:58:19 VIII-
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