Here’s when to expect New Jersey’s first frost of the season

What is Frost?

According to the Glossary of Meteorology, the official definition of frost is:

"The fuzzy layer of ice crystals on a cold object, such as a window or bridge, that forms by direct deposition of water vapor to solid ice."

Fuzzy ice!

Temperatures actually do not need to register at or below 32 degrees Fahrenheit for frost to form. We generally look for those ice crystals at an air temperature around 37 degrees. That is because the coldest air tends to sink and pool right at the surface, at grass blade height, allowing for ice crystals to form.

A freeze, of course, occurs when the thermometer drops below 32 degrees.

The colder it gets and the longer it remains colder, the harsher the frost/freeze effects on the surrounding environment.

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Who Cares?

For most New Jerseyans, the only real effect of the season's first frost is purely psychological. That initial blast of ice crystals and cold temperatures serves as an important seasonal milestone, as summer turns to autumn. Time to put away the flip-flops and bathing suits, and dig out the winter clothes. Shed a tear, and reach for the pumpkin spice.

There are two groups for whom the first frost is especially important, and potentially catastrophic: Farmers and gardeners.

There are many plants and crops that have very low or even no frost tolerance. Citrus trees are the classic example. In New Jersey, particularly sensitive plants include corn, peppers, eggplant, cucumbers, squash and melons (including pumpkins). A single cold night can lead to massive crop and financial losses.

On the other hand, it is worth mentioning that certain plants love a good frost/freeze.

One of my favorite delicacies, ice wine, requires harvesting grapes that have frozen on the vine. Apples tend to ripen and sweeten faster following a period of frosty temperatures. And maple trees produce the best maple syrup harvest when a series of light freezes is followed by thaws, squeezing the sap out of the wood fibers.

When is the First Frost/Freeze?

For New Jersey, the short answer is October.

For some reason, frost is a hot topic in the Farmer's Almanac each year, as reported on by this season some of my colleagues on this very site:
—First fall frost is closer than you think
—Farmer's Almanac says this NJ town will get the first frost

However, this is an area of meteorology and climatology that does not require a specific prediction from an almanac or a crystal ball. We know based on history when frosts and freezes are likely to start, putting an inevitable end to the Garden State's growing season. It is more of a short-range forecasting issue, as we try to predict exactly which calm, clear, cold autumn nights may produce ice crystals a few days in advance.

As you might suspect, there are some geographical and topological differences in average first frost timing. Let's look at more specific dates for four reference stations across the Garden State.

NORTHWEST: Sussex Airport

Traditionally, higher-elevation northwestern New Jersey is the coldest corner of the state. Therefore, it makes sense that Sussex, Warren, and Morris counties experience the earliest annual frost/freeze.

—Last 37° Frost Occurred... April 27, 2024 (33 degrees)
—Earliest First Frost... September 15 (2001)
—Average First Frost... September 30
—Latest First Frost... October 24 (2021)

—Last 32° Freeze Occurred... April 26, 2024 (30 degrees)
—Earliest First Freeze... September 21 (2020)
—Average First Freeze... October 14
—Latest First Freeze... November 3 (2021)

NORTHEAST / URBAN: Newark Liberty International Airport

Due to the urban heat island effect, the NYC-adjacent industrial and urban area of northeastern New Jersey tends to be one of the warmest spots in the state year-round.

—Last 37° Frost Occurred... March 25, 2024 (33 degrees)
—Earliest First Frost... September 27 (1940 and 1947)
—Average First Frost... October 23
—Latest First Frost... November 21 (1978)

—Last 32° Freeze Occurred... March 24, 2024 (32 degrees)
—Earliest First Freeze... October 8 (1935)
—Average First Freeze... November 6
—Latest First Freeze... December 2 (1985)

INLAND: New Brunswick

I debated whether to include both an "inland central" and "inland south" station in this analysis. But the statistics are remarkably similar across the board — so I opted to show New Brunswick numbers, to be representative of most of New Jersey. (It is worth noting that the heart of the Pine Barrens trends colder on mornings where radiational cooling is in full effect — therefore the growing season is likely a bit shorter there.)

—Last 37° Frost Occurred... April 27, 2024 (35 degrees)
—Earliest First Frost... September 20 (1979 and 1993)
—Average First Frost... October 10
—Latest First Frost... November 5 (1971)

—Last 32° Freeze Occurred... April 22, 2024 (32 degrees)
—Earliest First Freeze... October 4 (1974)
—Average First Freeze... October 23
—Latest First Freeze... November 11 (2017)

COAST: Atlantic City Marina

The warming influence of the ocean and bays prevents temperatures from really bottoming-out along the Jersey Shore. (Especially on barrier islands.) The southern coast in particular tends to be the warmest corner of the state on cold season mornings.

—Last 37° Frost Occurred... March 24, 2024 (32 degrees)
—Earliest First Frost... September 30 (1888)
—Average First Frost... October 28
—Latest First Frost... November 19 (1978 and 2016)

—Last 32° Freeze Occurred... March 24, 2024 (32 degrees)
—Earliest First Freeze... October 10 (1888)
—Average First Freeze... November 12
—Latest First Freeze... January 4 (2015-2016)

Dan Zarrow is Chief Meteorologist for Townsquare Media New Jersey. Check out Dan's weather blog or follow him on Facebook for your latest weather forecast updates.