Stubborn clouds persist over Mid-MO due to stable conditions
It feels like the sun has gone into hiding for early fall, as most of Mid-Missouri has been stuck under a thick, stubborn cloud deck for days. Forecasters at the National Weather Service don't expect it to clear out anytime soon.
The setup started early in the week, with a cold front bringing in cool air and moisture. A large area of high pressure parked over southern Canada behind the front, locking in a light easterly-to-northeasterly flow at the surface. Those winds have been feeding us a steady supply of cool, damp air all week.
"That air mass is very cool," said NWS meteorologist Brad Charboneau. "And because there's not a lot of wind to push it out, it's just kind of stuck in place."
Northerly winds are supplying moisture and chill, and other factors are also allowing the clouds to linger for longer. While it's cool at the surface, there's actually warm air sitting aloft, which is creating a very stable atmosphere.
"When you have a lot of stability like that, it's hard to move air masses out of the way," Charboneau explained. "You end up with these stagnant patterns where you have day after day of the same kind of conditions."
That warm air acts like a lid on a pot, trapping the moisture beneath it. And because the clouds are so thick, they're almost self-sustaining.
Normally, sunshine heating the ground helps stir up the atmosphere and break up cloud cover. But when clouds are this thick and persistent, sunlight can't punch through to warm the ground in the first place. "It's kind of what we call a positive feedback loop. If we could get some mixing from heating from the sun, that could also help dissipate the clouds." Charboneau says.
Our pattern will change this weekend with an incoming system, but it may only bring more clouds and rain chances. Charboneau says we could see some breaks in the clouds here and there, but widespread sunshine likely won't arrive until early next week after the system clears the area.
This bout of cloud cover has brought a welcome reprieve from the heat; the first three weeks of September were the hottest start to the month on record. But with the clouds, we've seen temperatures drop to near or below average for several days, though this month will likely land in the top 5 warmest Septembers on record for Mid-MO.
