National Weather Service forecasters are getting a bit more confident in the storm predictions for tomorrow and Thursday, saying while tornadoes are still a low risk factor, the atmosphere is primed for their development.
According to the Miami weather service office, low level winds early Wednesday and into Wednesday night could help tornadoes to develop as a significant disturbance higher up in the atmosphere moves toward Florida preceding a cold front.
The so-called “shortwave trough” coming in from the Gulf of Mexico promotes upward movement of air, which in turn can produce thunderstorms as the air cools high in the atmosphere.
The Storm Prediction Center has South Florida under a marginal risk for storms with a 5 percent chance of severe storms occurring. Forecasters at the Norman, Okla.-based prediction center also said the thunderstorms may include a “couple of supercells.”
Supercells are thunderstorms with vigorous and persistent rotating updrafts.
Some strong winds may also be possible with wind gusts up to 60 mph Wednesday.
The raucous weather, however, needs two key ingredients to mix before it can form up. And one will trigger the other.
“There’s a good set up for something to happen,” said Brian Edwards, a meteorologist with AccuWeather. “But you need some juice or there won’t be as much instability.”
A stout low pressure system that was over the desert southwest on Monday is cruising on the subtropical jet stream east with an ETA in Florida on Wednesday. At the same time, warm, moist air from the Caribbean is creeping its way into the Peninsula through the Keys.
The forecast as of Monday put the two systems on a collision course. The large low pressure system pushing a cold front acts as the match to light up the smaller weather pattern, lifting air into the atmosphere where it cools and can become a thunderstorm.
“The warm moist air doesn’t necessarily mean anything will happen. We have to have something to get it going,” said Arlena Moses, a meteorologist with the National Weather Service in Miami.
The cold front will bring temperatures to a low of 48 overnight Thursday and keep the high Friday to the mid 60s.
As much as 2 inches of rain could fall Wednesday and Thursday, raising the risk of urban flooding and adding to already above normal rain totals for the year.
According to the South Florida Water Management District, Palm Beach County has received 3.07 inches of rain in January, more than an inch above the historic norm. Broward and Miami-Dade counties are also above normal with an added 2.27 inches and 1.73 inches, respectively.
The extra wet weather _ December had about 4 more inches of rain than normal in Palm Beach County _ hasn’t helped farmers, who said crops have grown too quickly or are more susceptible to disease and rot.
Meteorologists warned last year that the strong El Nino would lead to a wet winter with cooler temperatures on average because of increased cloud cover.
“Widespread rain event unfolding for Wednesday and Thursday with a few strong storms possible,” is how National Weather Service meteorologists in Melbourne described what may be coming.
The Melbourne office handled the EF-1 tornado that hit Hobe Sound early Jan. 17, but forecasters don’t expect that kind of turbulence Wednesday.
“It doesn’t appear to be as significant a threat,” said Scott Kelly, an NWS meteorologist in Melbourne. “However, there is a threat for some strong, possibly isolated severe storms.”
If rain moves in late Tuesday, temperatures may cool down enough that Wednesday just gets heavy rain and no thunderstorms. That’s what happened Friday when forecasters initially predicted 60 mph wind gusts along an advancing cold front. Friday’s highest gust at Palm Beach International Airport was 28 mph, although Saturday recorded a 47 mph gust as cold air rushed in behind the front.
“Some of our forecast models are trying to bring in rain as early as late Tuesday night and that’s a concern if you’re trying to get severe storms firing up,” Edwards said. “That may kill instability.”