New Brunswick, NJ

Combined with below-average precipitation in August, the northern half of New Jersey has become quite dry. Conversely, rainfall has been more common in the south, thus despite a drier-than-average September, the two-month total is slightly above average. Looking first at September, statewide precipitation averaged 2.82". This is 1.25" below the 1981-2010 average and ranks as the 46th driest September since 1895. From Hunterdon, Somerset, and Union counties northward, only 1.49" fell, which is 3.00" below average and ranks as 7th driest. The southern counties averaged 3.47", which is 0.40" below average and ranks as 56th wettest.

A month ago, many NJ residents felt July was quite cool, while in fact it was just 0.4° below the 1981-2010 mean. Such was not the case in August, which truly was on the cool side. The statewide average temperature of 71.0° was 2.4° below average. It ranks as the 32nd coolest since 1895. Even when compared to the 1895-present mean, the month was 1.5° below average. Days with a maximum temperature of 90° or greater were hard to find, certainly a characteristic of the summer of 2014, which will be discussed later in this narrative.

Precipitation varied widely across the Garden State in August, rather typical of a summer month in these parts. Individual station totals ranged from 12.33” in Lacey Township (Ocean County) to 1.01” in Hillsborough (Somerset). When monthly totals from several dozen long-term stations were averaged together, the statewide precipitation was 4.39”. This is 0.18” above the 1981-2010 mean (0.26” below the 1895-present mean) and ranks as the 53rd wettest of the past 120 Augusts. It must be noted that the heavy rain that fell after 8 AM on the 31st is not accounted for in most August station totals. For the monthly state average, only several stations that observe at midnight have their full August 31st totals included, while monthly totals at most other National Weather Service Cooperative stations only run through the morning of the 31st. For more on this observing practice, see the April 2014 report.

Extremely heavy rain drenched portions of the Mid-Atlantic during the daytime hours on August 12 until after sunrise on the 13th. Starting off in the Washington-Baltimore area and moving up into central Long Island, a narrow ribbon of rainfall exceeding 5”, and over 10” in a few locales, resulted in flash flooding that resulted in water rescues and many damaged roads and vehicles. Excessively heavy rains, occasionally accompanied by lightning, traveled up a frontal boundary that was associated with an unusually strong August low-pressure system situated over the Great Lakes. The atmospheric impulses riding up this front joined forces with abundant atmospheric moisture (in the top 1% for the region) to bring multiple inches per hour rainfall rates…for multiple hours.

The heaviest rain was situated within less than a 10-mile wide path. Within 20 miles on either side, totals fell off to a mere inch or two, or even less. Such is the nature of these events, where despite the abundant atmospheric moisture, there is a finite amount of water available. The dynamics concentrated the atmospheric lifting, thus the condensation of the majority of the moisture and resultant rainfall, while adjacent areas balanced out the lifted air with subsiding air that greatly limited rainfall totals.

Another comfortable mid-summer air mass is destined to invade the Garden State this week. This arrives on the heels of several other mild, dry air masses that have contributed to making this a rather average July in the temperature department. While many may think that this has been an exceptionally cool summer, it has not. However, given that the most recent four Julys all ranked within the top six for heat dating all the way back to 1895, all are forgiven for any misperception!

The overall pattern that has led to temperatures more often being on the cool than than warm side of the ledger since last fall is one of pronounced waviness in the jet stream, with a resultant tendency for a ridge (northward swing) in western North America and a trough (dip in the jet) in the east. This allows cool and dry air to infiltrate our region, with warm and humid air kept at bay to the south. It has also kept the west in severe drought and plenty warm.