Summer preview: Last weekend's rain was more than an "April Shower"

We closed out the month of April with a deluge of rain in the Tri-State area. Many spots in and around the city recorded more than 5 inches of rain between Saturday and Sunday's one-two punch of a storm system. Widespread street flooding led to several vehicles stranded on inundated roadways in New York and New Jersey. 

Storms cause flash flooding in the northwest Bronx on April 30th. 
Video courtesy of Melba Kurman/Twitter

Rainfall rates exceeded .5"/hour across the area on Sunday evening, making this late April downpour reminiscent of a July thunderstorm. And as the weekend came to a close, Central Park tallied 5.1" of rain, which is over an inch more than the Park normally records in the entire month of April. 

Rainfall totals from April 28th-30th, 2023.
Graphic created by NWS Upton, NY

A new report by Climate Central shows that these these rainfall events are becoming more common. Across most of the US, even in the desert Southwest, heavy downpours are getting heavier. 

This means that the rainfall rate is increasing, even in places where the average annual precipitation has decreased in recent decades. Why does rainfall rate matter? When rain falls in short intense bursts rather than slowly and steadily, flash flooding is more likely. Flash floods can make roadways impassable, as we experienced firsthand over the weekend. Even more importantly, people can get trapped in floodwaters, as they're more likely to be unprepared for the sudden rise in water levels. It's also bad news for agriculture and maintaining a reliable water supply, with less rainwater having a chance to penetrate into aquifers.  

The Northeast region as a whole has seen a 13% increase in hourly rainfall intensity. NYC's report, indicated by a brownish dot in the graphic above, is the only location in the region with a slight downward trend since 1970.

The trend line indicates that rainfall intensity has dropped by about 0.005"/hour since 1970. The argument could be made that this isn't a statistically significant change, as any rainfall amount under 0.01" is recorded as a trace (T) by the National Weather Service. With all other surveyed sites in the Northeast seeing an increase in heavy downpours, NYC's slight decrease is an anomaly. And with summer being the wettest season in the Tri-State, more heavy storms are likely lurking in the months to come.