Weather
By Dan Skeldon
Spring continues to stretch its legs across South Jersey as green up is now underway. We’re back on daylight saving time and enjoying the extra evening daylight. And our average temperatures continue to slowly and steadily warm each week.
As a meteorologist, spring usually comes in a few stages, defined by the most common questions I get from March through May. In March, it’s something like “Are we all done with the snow?” or “Are you sure I can put the snowblower away?” And thankfully this year, the last measurable snow fell on February 18th.
Next comes April, when a high volume of questions come from the gardeners, landscapers, and farmers throughout South Jersey. “Am I safe to plant my tomatoes yet?” or “When is our average date for our last frost and freeze?” are some of those annual April inquiries. So the focus shifts from snow to any lingering cold nights that Mother Nature may have up her sleeve. Finally in May, attention shifts to the upcoming hurricane season and what the early outlook suggests may be on the way. And the forecast certainly calls for a future column to focus on just that in the near future.
But as we’re in the midst of April, let’s focus on the growing season, just now getting underway for some of us now or in the coming weeks. Let’s start with our average last date for 32 degrees nighttime lows. 32 degrees is of course the freezing mark, and a hard freeze can occur and kill any sensitive plants when temperatures drop below 32 degrees for several hours at night.
At the Atlantic City International Airport, where records in South Jersey are kept, the average last date for a 32-degree low temperature in the spring over the last 75 years or so is April 19th. Of course, it is just an average, although our last 32-degree night in 2020 actually did occur on April 19th last year.
In reality however, there’s more than a two month range between the extremes, the earliest and latest dates for our final 32-degree low temperature each spring. On the early side, March 14th is the earliest date for our last spring freeze, which occurred way back in 1945. Contrast that with what happened in 1992, when the temperature plummeted to a record low of 28 degrees on the morning of May 21st. Sure, the temperature soared more than 55 degrees to a high in the mid 80s that afternoon, probably one of the biggest ranges between our morning low and afternoon high we’ve ever seen in a single day. But the unusually late hard freeze had a tremendous impact on agriculture that year, most notably on the famous South Jersey blueberry crop.
Only one other year, on May 20th in 1911, did we see freezing temperatures beyond the middle of May (May 15th). That’s why when asked, I always use Mother’s Day weekend as my boundary. Once we’re past mom’s big day, you have a very good chance, let’s say close to 99 percent, of staying frost and freeze free. It certainly doesn’t mean you can’t plant before then, as many years you could be safe right now.
Also remember that areas closer to the shore, like all of our barrier islands, are more likely to remain frost and freeze free this time of year than areas farther inland. The sandy nature of the soil throughout the Pine Barrens allows for great radiational cooling on clear and calm nights anytime of the year, hence the later frost and freeze concerns each spring.
While a killing hard freeze requires below freezing temperatures, frost can form with temperatures above the 32-degree mark. Patchy frost can occur with temperatures as high as around 40 degrees, but widespread frost is more likely when lows reach the low to mid 30s, let’s say roughly 32 to 37 degrees. Of course, frost is less destructive than a hard freeze, and it’s also easier to take precautions to protect plants from a frosty night rather than a freezing one.
Given our warming climate, is there a chance that our last frost and freeze will occur earlier? That’s tough to say with any certainty, but any earlier trend has not started yet. Let’s look at the last 10 years for proof. In doing so, we’ll find that the average date for our last 32-degree night hasn’t changed, and still sits at April 19th. As recently as May 11th, 2010, we saw freezing temperatures into early May, which means some sneaky late season cold is still a possibility.
The moral in all of this: If you’re planting now, still plant with caution. While there’s a 50/50 chance you’ll be safe from freeze concerns after April 19th, there’s still a risk for a cold night or two into early May. But any plants you get for mom for Mother’s Day should be safe to go in the ground after the holiday weekend.
Meteorologist Dan Skeldon has a degree in meteorology from Cornell University. He has forecasted the weather in South Jersey for the last 18 years, first on the former television station NBC40 and then on Longport Media radio. Dan has earned the American Meteorological Society Seal of Approval for Broadcast Meteorologists, and now does television broadcasts on WFMZ-TV in Pennsylvania’s Lehigh Valley.
