Extreme Heat & Widely Variable Precipitation
July 2010 Overview
Plus a look at the Growing Season to date

Dr. David A. Robinson
New Jersey State Climatologist
Center for Environmental Prediction, School of Environmental and Biological Sciences/NJAES, Rutgers University
Aug 2, 2010

In addition to the July summary, this narrative will examine temperature and precipitation conditions across the Garden State since the growing season began in April.

July Overview

Were it not for two below-average days to start the month and a few close to average days during the last week of the month, July 2010 would have surpassed July 1955 as the warmest on record across New Jersey since statewide records commenced in 1895. Instead, 2010 will have to settle for second warmest with an average temperature of 78.8° (table 1), some 4.3° above the 1971-2000 average of 74.5°. July heat has been commonplace since 1988, with ten of the fifteen warmest Julys of the past 116 years occurring during this 23 year period.

Rank Year July Temp
1 1955 79.0°
2 2010 78.8°
3 1999 78.4°
4 1949 77.8°
5 2006 77.3°
6 1994 77.1°
7 1901 77.0°
8 1993 76.9°
9 1952 76.8°
10 1988 76.7°
11 2005 76.7°
12 2008 76.7°
13 1995 76.5°
14 2002 76.5°
15 1931 76.3°

Table 1. Ten warmest Julys across New Jersey since 1895

On 23 days this July, maximum temperatures equaled or exceeded 90° at one or more locations across the state. On twelve of these days, 95° or higher was reached, and from the 4th-7th the century mark was hit or topped. The heat started in earnest on the 4th, with Newark (Essex County) at 101° and Hillsborough (Somerset) at 100°. Jersey City (Hudson) and Eastampton (Burlington) reached 100° on the 5th, with Newark maxing out at 102°. The 6th was the hottest day across New Jersey in many years. Observing stations in every county reached 100° or higher, with the "coolest" maximum in the state the 91° at Bivalve (Cumberland) right on the Delaware Bay coast. New Brunswick reached 105°, the second highest reading at that station in over a century of observations and the warmest since 106° in August 1918. Hammonton (Atlantic) and Hillsborough both reached 104°. Fortunately, dew points were in the mid 60s during this hot afternoon. The final day of this four-day 100° spell was the 7th, when Bethel Mill Park (Gloucester) reached 103°, Hillsborough 102° and Piney Hollow (Gloucester) 101°.

There was a break from 95° or higher weather until the 18th, when Wall Township (Monmouth) and Point Pleasant (Ocean) reached that mark. Point Pleasant repeated this maximum on the 19th, with Wall Township hitting that mark again, with Hillsborough, on the 21st. The 23rd saw Hammonton reach 98° and Sicklerville (Camden) 97°. Coastal Sea Girt (Monmouth) and Point Pleasant reached 100° on the 24th, with six coastal or near-coastal stations, including the Atlantic City Marina (Atlantic) topping out at 97° on the 25th (so much for a refreshing sea breeze!).

Some cool mornings occurred early and late in July, with the upper 40°s found in a few north Jersey locations on the 1st, including 45° at Pequest (Warren). More north Jersey locations and a few in the Pine Barrens reached the 40°s on the 2nd, with Pequest bottoming out at 42°. On the 3rd, Pequest fell to 46°, with just a few other spots in the 40°s. It may be that Walpack (Sussex), a perennially cold valley location, might have been several degrees cooler on these days, but the station was out of commission until the 9th. The month ended with Walpack falling to 49° on the 30th and 47° on the 31st. To compare these observations with Pequest, the latter location fell to 54° on the 30th and 51° on the 31st.

A measure of continuous discomfort and a health risk to all occurs when nighttime temperatures fail to fall below 70°. Examining Newark Airport lows in July as an example of an urban heat island environment, lows remained at 70° or higher on 23 nights. This included three between 80° and 82°. It is also difficult to cool off coastal locations on summer nights, as witnessed by the 23 days of 70° or higher minimums at Seaside Heights (Ocean). This included a low of 81° on the 24th, when a number of other locations across NJ failed to fall below 80°.

While heat prevailed statewide in July, precipitation was all over the map! The NJ average was 3.62", which is 0.87" below the 1971-2000 average. This makes it the 36th driest of the past 116 Julys. A remarkable range of monthly totals is "hidden" in this figure, as the wettest location received 10.06" (Bethlehem Township in Hunterdon County) while the driest station caught only 1.17" (Sea Isle City in Cape May County). It just seemed to want to rain in northern Hunterdon County, where High Bridge received 8.57", Lebanon 8.56", Clinton Township 8.05" and Califon 7.56". On the dry side, Ocean County saw Brick Township catching 1.55", Lavallette 1.63" and Point Pleasant Beach 1.64". Southern Somerset County was also dry, with Franklin Township seeing only 1.62" and Hillsborough 1.84".

Measureable rain (at least 0.01") fell somewhere in New Jersey on 21 days of July. On nine of those days at least an inch fell in one or more locations. While one of those nine did not include the 8th, it marked the first day of rainfall for the month, with High Point leading the way with 0.56". Heavy rain fell in parts of north Jersey on the 9th, with Allamuchy and Oxford Township, both in Warren County, receiving 2.84" and 2.26", respectively, and Ringwood (Passaic) 2.16". The onslaught continued for Warren County on the 10th with 2.85" in Independence Township, 2.68" in Hackettstown and 2.33" at Stewartsville. Storms brought 2.27" to Winslow (Camden) on the 12th and 1.81" to Middletown (Monmouth). The stormy pattern continued on the 13th, with 2.95" in Ewing Township and 2.83" in Lawrence Township, both in Mercer County. Berkeley Township and Cherry Hill in Camden County received 2.69" and 1.92", respectively, on the 14th, with Eastampton reporting 2.54" and Lebanon 2.62".

The 19th saw a resumption of inch plus rainfall, with 1.58" and 1.05" falling in Bergen County at River Vale and Ramsey, respectively. At another Bergen location, Palisades Park received 1.43" on the 23rd and Wayne (Passaic) saw 1.21" fall. A fast moving storm again visited a swath of north Jersey on the 25th, with 1.31" in Tenafly (Bergen) and 1.07" at Charlotteburg (Passaic). Another storm dropped 1.28" in Franklin Township (Gloucester) and 1.07" in Upper Deerfield (Cumberland). The last day with rain in July was the 29th, when West Creek (Ocean) picked up 1.40", Lake Como (Monmouth) and Stafford Township (Ocean) each receiving 1.11", and Oswego Lake (Burlington) at 1.00".

Wind was not a major factor in July, except of course in some localized areas as strong storms moved through. Of the many anemometers across the state, 40 mph or higher gusts were only recorded at Cream Ridge (Monmouth) on the 19th (a 40 mph gust) and on the 25th at Harvey Cedars (Ocean) with a 52 mph gust, Seaside Heights (Ocean) at 44 mph and Bivalve at 41 mph. The lack of windy days is not unusual in July and is associated with the absence of a large range in barometric pressure. The highest pressures to be found in July were in the 30.30" range on the 2nd, with the lowest in the mid 29.70" range on the 19th and 25th (the two gustiest days of the month).

Drought concerns ramped up quickly in the month, given the general absence of rain during the last two weeks of June and the excessive heat at the end of the first week of July. Therefore the wet days that followed across portions of the state were welcome to many farmers, forestry officials and water purveyors. Still, as July ended there were localized concerns. Several 100 acre or larger forest fires occurred in the dry coastal forest towards months end. At month's end, the US Drought Monitor depicted eastern and central portions of the state within moderate drought category (D1) (note: there is no minor drought category), with other areas considered abnormally dry (D0) and the southwest corner of the state not in any drought category (note that the map resolution is too low to mark the localized wet conditions in northern Hunterdon and Warren Counties, which are surrounded by D0 conditions).

Reports of severe weather were few during the month, with localized road flooding and isolated wind damage reported on several occasions. So too did the state escape without widespread reports of health issues associated with the excessive heat.

Growing season to date

If you have read recent monthly summary reports, you already know that New Jersey is in the midst of a remarkable run of abnormally warm conditions. This has encompassed the entire growing season to date (April through July) and actually extends back to March which was the 6th warmest since 1895 (116 years). April and June were the warmest on record, May the 5th warmest and now July coming in 2nd. Thus it is not surprising that the past four months combined have averaged well above the previous record for that interval, and even 2° above 1991. This is 4.6° above average and makes this the 7th year in the top ten since 1991. Departure graphs of temperature and precipitation for each of the past twelve months are displayed on the ONJSC homepage.

Rank Year Growing Season Avg Temp
1 2010 68.3°
2 1991 66.3°
3 2006 65.8°
4 1955 65.5°
5 2008 65.5°
6 1994 65.4°
7 1949 65.4°
8 1921 65.4°
9 2002 65.4°
10 2004 65.3°

Table 2. Ten warmest April-July intervals across New Jersey since 1895

This is the 2nd warmest first seven months of the year on record, only exceeded by 1998, when large January and February positive departures started the year off on a very mild note. Looking back a full twelve months, this is the 3rd (tied with 1991) warmest August to July on record, running 2.3° above average. Only in 2002 and 2006 was this interval warmer.

Precipitation has been rather sparse since the start of the growing season. The four-month statewide average total of 11.77" is 4.74" below the 1971-2000 average. This is only 71% of normal and ranks 13th lowest since 1895 (table 3). We are indeed fortunate that March was the wettest on record, as was the 12 month period ending with March. In fact, precipitation since January totals 29.15", which makes the past seven months the 27th wettest start of the year. In addition, the August 2009 to July 2010 precipitation total of 55.01" (+7.81") is the fourth largest on record for this interval. This earlier wetness provided a substantial cushion in terms of full reservoirs, abundant ground water and above average stream flow at the onset of this dry growing season.

Rank Year Growing Season Prcp
1 1963 8.94"
2 1999 9.02"
3 1965 9.16"
4 1955 9.26"
5 1957 9.84"
6 1966 10.12"
7 1954 10.21"
8 1923 10.71"
9 1993 11.15"
10 1899 11.40"
11 1905 11.60"
12 1977 11.63"
13 2010 11.77"
14 1926 12.12"
15 1949 12.38"

Table 3. Fifteen driest April-July intervals across New Jersey since 1895

For those seeking more detailed information on hourly, daily and monthly conditions, please visit the following Office of the NJ State Climatologist's websites:

NJ Weather and Climate Network
NJ Community Collaborative Rain, Hail and Snow Network
NJ Snow Event Reports

Interested in receiving our monthly summaries at the end of each month? Send us your e-mail address here to join the mailing list.

Past Climate Summaries