A rare setup leads to the potential for a storm with rotation.
UPDATE: Severe thunderstorm watch issued for Lehigh Valley region
This is going to be one of those days where you need to pay attention to weather warnings, a local meteorologist says.
The National Weather Service's Storm Prediction Center has upgraded the chance of severe weather from slight to enhanced -- the third level on the five-level scale -- in its morning update.
The upgraded risk of severe weather, as shown by the National Weather Service's Storm Prediction Center. (Courtesy photo | For lehighvalleylive.com) "It looks like from after 5 and before 9 that the window is ideal," Mike DeFino, of the Allentown-based Eastern PA Weather Authority, said late in the morning.
While the threat includes an isolated tornado, DeFino said, the potential is there for wider-ranging damage than there was nine days ago, although the wind shouldn't be quite as severe as the microburst that whipped through Whitehall Township. Last Tuesday there was a tornado warning but no tornado, even though funnel clouds were spotted in Lehigh County.
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"We see a very active day for the Lehigh Valley -- for most of eastern Pennsylvania," DeFino said Thursday.
Winds could exceed 60 mph in thunderstorms and the rain could be torrential, the weather service said, extending the storm window from 3 p.m. to midnight. Flash flooding is possible, according to the regional briefing.
An approaching low pressure area will bring winds from the south, but the winds at the lower level will be coming from the west, setting up the chance of a rotating storm, DeFino said.
While weak tornados aren't rare in this part of Pennsylvania, the way Thursday's storm is setting up only happens about twice a year and could lead to significant non-tornadic wind damage, he said.
"A setup like this one, where the winds switch and give you the potential that you don't see that much, there's a potential there for dangerous storms," he said.
With the morning rain over and the sun heating up the atmosphere, then the front arriving adding energy to the mix, it's not a surprise the prediction center has increased its confidence that rough weather is on the way, DeFino said.
Unlike last week, where clouds built up in an intimidating show of fierce potential before the rain tore through, this time rain will hide the possibly rotating clouds from a person on the street.
"You won't be able to see it coming," he said.
But the National Weather Service and other forecasting operations will be able to see on radar what's actually going on, DeFino said.
"Pay attention to the warnings," he said. "Take them seriously. We're in good hands with the National Weather Service; they're very smart."
Tony Rhodin may be reached at arhodin@lehighvalleylive.com. Follow him on Twitter @TonyRhodin. Find lehighvalleylive.com on Facebook.