Summer 'snow' in Philadelphia breaks a confusing 154-year-old record

It's been a wild weather week across the northeastern U.S., but a report of snow in Philadelphia on Sunday amid extreme heat, thunderstorms and high winds raised more than a few eyebrows.

Small hail fell in a thunderstorm at Philadelphia International Airport on Sunday afternoon, and the local National Weather Service in Mount Holly, New Jersey recorded the observation as snow. That's because official weather service guidelines state hail is considered frozen precipitation, in the same category with snow, sleet and graupel.

The small notation in the daily climate report may have gone unnoticed but for a pair of social media posts the weather service dropped on Monday morning.

"Here's a win for #TeamSnow," the weather service posted on X at 2:12 a.m. Monday morning. The post explained that the small hail was reported as a "trace" of snow. That triggered a record event report, stating: "A record snowfall of a trace was set at Philadelphia PA yesterday. This breaks the old record of 0.0 inches set in 1870."

The weather service noted 13 other times a trace of snow had been reported due to hail from thunderstorms in June, July and August.

When asked by broadcast meteorologists around the country if they report hail as snow, weather service offices this week had varied responses. In Greenville-Spartanburg, South Carolina, the weather service office said Wednesday it's common practice at all the field offices to classify hail as a trace of snow in their climate summaries.

In fact, the office noted, historical climate records for the Greenville office show a trace of "snow" fell on the station's hottest day ever. On July 1, 2012, the temperature hit a record high of 107 degrees, but the office also observed hail that afternoon, dutifully reported as "snow."

Weather forecast offices in Dallas/Fort Worth and Tallahassee told meteorologists earlier they do not report hail as snow.

Jim Zdrojewski, a climate services data program analyst at weather service headquarters, is not sure when the weather service decided to record hail as snow.

"We've recorded it this way for a long, long time, so that it maintains the continuity of the climate record," Zdrojewski said.

The reporting forms have a column for precipitation and a column for snow. When hail is reported as "snow," the office is supposed to note in an additional column that the "snow" was really hail.

Zdrojewski said he could not speak for the service's 122 field offices and their individual dynamics. "We provide the instructions," he said.

Offices that have never reported hail as snow may continue that tradition to maintain continuity in their local climate records, he said. He also noted a difference in the words "recorded" and "reported."

Individual offices have "a little bit more flexibility in how they report things," in their social media posts for example, he said.

Zdrojewski didn't rule out bringing up the topic during a previously scheduled call with the regional climate program managers on Wednesday afternoon. But he did say: "We're always open for suggestions on how to improve things."

Dinah Voyles Pulver covers climate change and the environment for USA TODAY. She's been writing about hurricanes and violent weather for more than 30 years. Reach her at dpulver@gannett.com or @dinahvp.