Mixed Precipitation Signals: May 2011
and a Spring 2011 Overview

Dr. David A. Robinson
New Jersey State Climatologist
Center for Environmental Prediction, School of Environmental and Biological Sciences/NJAES, Rutgers University
June 6, 2011

May Overview

A dismal mid-month period left many believing that May was a rather wet month. Truth be told, this depends on where you reside in the state, as some northern areas were almost twice as wet as average while the extreme south had just over half of average precipitation. The preliminary statewide average is 3.67". This is 0.63" below average, but somewhat above the median at 52nd wettest of the past 117 years. Morris County led the way with 8.19" and 8.10" received at two CoCoRaHS stations in Rockaway Township. Elsewhere in the county, Harding Township totaled 8.16", Boonton 7.94" Morris Township 7.91" and two Denville stations came in at 7.85" and 7.78". Totals fell off to near average levels in central NJ. In the far south, Upper Deerfield (Cumberland County) only received 1.96" and in Cape May County, Sea Isle City had 2.26" while Middle, Lower and Upper Townships caught 2.33", 2.36" and 2.37", respectively.

The first rain of the month fell in the northwest corner of the state on the 3rd. In Sussex County, Montague received 0.67", High Point 0.42" and Walpack 0.37". All of the state caught at least 0.25" on the 4th with southern coastal areas seeing as much as 1.20", with 1.13" at two Berkeley Township (Ocean) locations and 1.12" in Woodland Township (Burlington).

Conditions were quite dry from the 5th through the 13th before persistent clouds accompanied by off and on rain of varying intensities arrived on the 14th. Before conditions began to brighten and dry out on the 24th, as much as 6.45" and 6.47" had fallen at two Rockaway Township (Morris) locations. Of the 113 CoCoRaHS stations that reported on all of the nine days between the 14th and 24th, 13 received between 5.00" and 6.47", 19 caught from 4.00" to 4.99", 28 had 3.00" to 3.99", and only Wildwood Crest (Cape May) with 0.71" came in under an inch. Notable totals during this period included 4.40" at Harding Township (Morris) and 4.39" in Morris Township from the 14th to 17th.

It is difficult to subdivide totals during that period, as rains frequently came and went across NJ. However a late afternoon thunderstorm on the 15th deposited pea-size hail in Washington Township (Mercer). Wires were reported down from strong winds in Fredon Township (Sussex). Localized rains of close to 2.00" in two hours on the 16th led to flash flooding of basements, roads and streams in Bernards Township in northern Somerset County.

Late on the 18th Harrison (Hudson) saw 2.35", Saddle Brook (Bergen) 2.23" and Boonton (Morris) 2.14". A severe late afternoon thunderstorm on the 19th was concentrated in west central counties. Two stations in Liberty Township (Warren) reported hail the size of grapes and even some stones the size of golf balls, with grape size (approx. 1/2") in Franklin Township (Warren). Rain totaled 1.82" in Washington (Warren) and 1.68" at Holland Township (Hunterdon). This precipitation, on top of rains of previous days, led to flooding of streams and roads in Warren and Hunterdon counties. Later that evening, Woodbine (Cape May) received pea-size hail.

The north coast saw the most rain on the 20th with three Brick Township (Ocean) stations measuring 0.95", 0.89" and 0.83". The northern tier received most on the 21st, with 0.54" in Hawthorne (Passaic) and 0.46" at Wantage (Sussex). The episode ended with the northern half of the state getting wet on the 23rd, especially Warren County, where Washington received 1.84" and White Township 1.70". Flash flooding occurred as a result of the one hour downpour and trees were reported down in southeast Warren County.

Overall, during this damp period, thunderstorms occurred somewhere in the state on the 15th to 19th, the 21st and 23rd. Heavy fog appeared at times on the 16th (Ocean and Cape May), 19th (Cape May), 21st (Hunterdon and Camden), 22nd (Morris), 23rd (Warren) and 24th (Hunterdon and Mercer). The persistent heavy rain in the Highlands region resulted in the Passaic River in Little Falls (Passaic) cresting several inches above flood stage on the 20th and 21st, the third consecutive month that flooding occurred in the central Passaic basin. The Rockaway River at Boonton crested just over a foot above flood stage early on the 20th when the Ramapo River at Mahwah just reached flood stage.

The northwest corner was clipped with thunderstorms on the 26th, with 0.63" in Allamuchy Township (Warren) and 0.58" at Andover Township. Hail as large as 1.5" in diameter pelted Milford (Hunterdon), with pea-size hail in Greenwich Township (Warren), while trees were reported down in the Warren County communities of Allamuchy Township, Independence Township and Washington. Thunderstorms on the 28th brought central Jersey as much as 0.41" in Franklin and Montgomery Townships in Somerset County. Two other Montgomery stations caught 0.32" and 0.24". Early morning thunderstorms on Memorial Day (30th) deposited 0.61" in Hackettstown (Warren) and 0.41" in Rockaway Township (Morris), Mt. Olive (Morris) and Little Falls (Passaic).

Other than tree- and wire-felling winds in isolated severe thunderstorms during May, particularly in Warren County, it was not too windy a month. Gusts exceeding 40 mph were only observed on the 4th and 5th at Wantage (Sussex; 47 mph and 44 mph respectively) and the 30th at High Point Monument (Sussex; 42 mph). Overall, the 5th was the windiest day, with a dozen NJWxNet stations gusting between 30 and 37 mph. The highest barometric pressures of May were between 30.35" and 30.40" on the 1st and 2nd, and lowest at 29.45" to 29.50" on the 15th.

The preliminary statewide average May temperature of 63.4° was 2.9° above average and ranked as the 12th warmest since 1895 (Table 1). This continues an almost unbroken streak of above average months, with 13 of the past 15 falling into that category.

Rank Year May Temp.
1 2004 66.2°
2 1991 66.1°
3 1944 65.1°
4 1896 64.9°
5 1965 64.4°
6 2010 64.2°
7 1911 64.1°
7 1918 64.1°
9 1942 64.0°
10 1959 63.9°
11 1998 63.7°
12 2011 63.4°
12 1986 63.4°
14 1975 63.3°
15 2007 63.2°

Table 1. The 15 warmest Mays across New Jersey since 1895.

Despite the overall warmth, the first half of the month provided a few cool days with chilly mornings. The temperature fell to 31° at Berkeley Township (Ocean) and 32° at Walpack (Sussex) on the 1st. The 6th had the coldest morning of the month, with Walpack at 29°, Berkeley Township and Pequest (Warren) at 30° and Oswego Lake (Burlington) at 32°. The warm spot was West Cape May (Cape May), with a low of 54°. The last freeze of the season occurred at Walpack (32°) on the 10th, seven months to the day from the first freeze in NJ back in October 2010. The warmest morning of the month was the 30th, when Walpack (62°) was the coolest spot and Bivalve (Cumberland; 71°) the warmest.

With a rather cool start to May and then the persistent clouds of mid month, the first heat of the month did not arrive until the last week. The 26th brought the first 90° maximum temperatures to the state, with Sicklerville (Camden) coming in at 92° and nine other NJWxNet stations at 90° or 91°. The next day saw Hillsborough (Somerset) at 90°. The Memorial Day weekend was quite summer like, with temperatures in the 80°s most places, topping out at 93° in Sicklerville and Woodbine (Cape May) on the 30th and between 90°-92° at seven other locations. The monthly maximum of 95° was reached at Sicklerville on the 31st, with Upper Deerfield coming in at 93° and eight other spots at 90° or 91°.

Spring Overview

The spring season brought warmth and an abundance of rain to New Jersey. The preliminary average temperature of 52.9° was 2.2° above average. This ranks as the 10th warmest since 1895, with seven of the top 13 occurring in the past 21 years (Table 2).

Rank Year Spring Temp.
1 2010 55.3°
2 1921 54.7°
3 1991 54.0°
4 1945 53.9°
5 1977 53.7°
5 2004 53.7°
7 1998 53.5°
8 1903 53.2°
9 1985 53.1°
10 2011 52.9°
11 2000 52.8°
12 1946 52.7°
13 2002 52.6°
14 1955 52.4°
14 1942 52.4°

Table 2. The 15 warmest springs across New Jersey since 1895.

Spring 2011 brought a preliminary statewide average precipitation of 15.04". This is 2.64" above average and the 15th wettest on record (Table 3). Most of the precipitation fell as rain, although several March snow events deposited as much as 16.0" in Rockaway Township (Morris) and 13.9" at Blairstown (Warren). Rockaway came away the "winner" in the precipitation department as well, with two CoCoRaHS stations reporting totals of 25.97" and 24.62". Other hefty seasonal totals included the Morris County townships of Mine Hill (24.19"), Harding (24.17") and Randolph (23.91"). Conversely, conditions were dry for the season in extreme southern sections. Cape May County totals were as low as 8.16" in Wildwood Crest, with other locations coming in at 8.35" (Dennis Township), 8.90" (Middle Township), 9.44" (Lower Township) and 9.50" (Sea Isle City). Maximum seasonal totals from CoCoRaHS or NWS Cooperative stations with complete records in the 21 counties are shown in Table 4. With the arrival of summer, the abundant spring precipitation in northern counties has elevated reservoirs, ground water and streamflow to normal or above normal status. Such is not the case in southern areas; however there is no major concern of water deficits at this time.

Rank Year Spring Prcp
1 1983 22.25"
2 1984 20.03"
3 1953 18.11"
4 1952 17.76"
5 1940 16.76"
6 1989 16.59"
7 1998 16.00"
8 1901 15.87"
9 1980 15.71"
10 1958 15.50"
11 2010 15.36"
12 1948 15.28"
13 1973 15.16"
14 2007 15.15"
15 2011 15.04"
16 1912 14.90"
17 1933 14.57"
18 1990 14.22"
19 1947 14.00"
20 1961 13.99"

Table 3. The 20 wettest springs across New Jersey since 1895.

County Location Spring Prcp
Atlantic Buena Vista Township 12.60"
Bergen Saddle Brook 21.16"
Burlington Medford Township 14.41"
Camden Somerdale 13.78"
Cape May Woodbine 11.17"
Cumberland Vineland 13.50"
Essex Newark Airport 16.48"
Gloucester Franklin Township 13.67"
Hudson Harrison 17.94"
Hunterdon Franklin Township 21.07"
Mercer Pennington 16.55"
Middlesex North Brunswick Township 16.33"
Monmouth Eatontown 13.54"
Morris Randolph Township 23.91"
Ocean Point Pleasant Beach 12.57"
Passaic West Milford Township 24.65"
Salem Woodstown 12.54"
Somerset Bedminster Township 19.17"
Sussex Hardyston Township 22.73"
Union New Providence 17.70"
Warren Mansfield Township 19.90"

Table 4. Maximum spring 2011 precipitation by county for communities with complete records.

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