A clash of icy cloud tops and moist tropical air is expected to energize the atmosphere over South Florida Friday, boosting chances for powerful supercell thunderstorms and the possibility of golf ball-size hail.
While a period of showery weather is expected to begin today, the “interesting” part of the forecast isn’t supposed to arrive until just before quitting time Friday said National Weather Service meteorologist Robert Garcia.
That’s when the same system that pummeled Texas with window-busting ice balls this week will meet South Florida’s balmy 80-degree daytime highs with potentially combustible results.
“We’ll be warming up while there will be cold air at mid-levels where thunderstorms grow hail,” Garcia said. “That’s one of the concerns, the very cold temperatures aloft will make it possible for us to have a large hail threat.”
The Storm Prediction Center in Norman, Okla., upped South Florida’s threat for severe weather on Friday to a marginal level, which is the lowest level on a five-tier scale.
Still, forecasters noted “large hail, perhaps larger than golf ball size, may occur with the strongest storms” and that South Florida could get an upgrade to its threat level in future forecasts.
Supercell thunderstorms are characterized by a strong rotating column of air that works to suck warm moist air up into the subfreezing atmosphere.
There is no mention of tornadoes with Friday’s storms, but nearly all supercells are capable of producing hail. The size of the hail depends on the strength of the updraft – stronger updrafts can suspend frozen water droplets longer, allowing them to grow. How much melt occurs when the hailstones fall to earth also impacts size.
Bill Bunting, chief of operations at the Storm Prediction Center, said another noteworthy aspect of Friday’s storm is that the supercells could split in two because winds are not changing direction with height. That would send two supercells to the left and right.
“It’s the left mover that has really aberrant behavior and can move much faster,” Bunting said. “When you hear that one of those storms is approaching you have to get quickly to shelter.”
On Tuesday, San Antonia saw hail as large as 3.5 inches in diameter from the same system headed to Florida.
While large hail is unusual for South Florida, it’s not unprecedented.
Between 1980 and September, Palm Beach County has seen hail with a diameter of 1.75 inches (about golf ball size) 14 times, according to the National Weather Service’s Storm Events Database.
The most recent occurrence on record was on Feb. 24, 2010 when a trained weather service spotter recorded large hail west of Palm Beach International Airport during a thunderstorm that included 40 mph winds.
In late March 1996, hail damaged at least 100 vehicles at the airport and decimated a 60-acre cucumber field, according to the database.
“It’s something to keep an eye on,” Garcia said about Friday’s forecast. “It looks like it’s a bit more organized and capable of producing strong to severe thunderstorms over a good portion of the state.”
David Samuhel, a senior meteorologist for AccuWeather, was less sure about the potency of Friday’s storms and the possibility of splitting supercells.
“That’s pretty beefy wording,” Samuhel said. “It’s a sign there are really favorable conditions for the supercells to maintain themselves.”