Several cold air funnels have been reported within showers and thunderstorms which have been forming northwest of Chicago in Wednesday afternoon's unstable atmosphere. Cold air funnels tend not to be damaging--often spinning beneath towering cumulus clouds without touching the ground. Thunderstorms--some towering as high as 31,000 ft.--but topping out at 29,000 ft. as of this 2:45pm posting---have been developing and dissipating across sections McHenry County--some producing nickel size hail. Doppler radar indicates there has been slow southward development---even as remnant showers attempt to move southeast with with northwesterly upper steering winds. Thunderstorms weaken as they move into counties immediately adjacent to Lake Michigan as they encounter cooler air there. Weather Bug sensors are indicating temperatures are in the mid to upper 60s near the lake and in the vicinity of this afternoon's showers and thunderstorms--but in the low 80s at the warmer inland locations which haven't been subjected to cooling rainfall and storm outflows. A funnel cloud was reported around 1:55 pm near Woodstock also in Mc Henry County--something which may happen from time to time with any of these thunderstorms. The situation doesn't support damaging or an organized outbreak of tornadoes.
Temperatures are falling with height at a faster than normal pace which means the atmosphere is unstable. The set-up is just the latest ramification of the cooler than normal air which northwest upper steering winds have continued to deliver and replenish so often this summer. Daytime heating encourages air near the surface of the earth to warm, rendering it buoyant. This heated air then ascends and cools prompting the thunderstorm development we've been observing much of the afternoon. It's a situation likely to spawn additional (though scattered) thunderstorms over at least sections of the Chicago area into evening. The thunderstorm development is being further enhanced by the convergence of ground level winds along inland-moving easterly winds off Lake Michigan. The cooling these winds promote across the counties closest to the lake has been--and is likely to continue--inhibiting thunderstorm development by stabilizing the air. Only sprinkles or light showers--remanants of the west and north suburban thunderstorms---are able to make it into these lakeside counties.
Indications are areas west and north of the Chicago--including DeKalb, Kane, McHenry, Boone, Ogle and Lee Counties will be affected from time to time by these thunderstorm clusters--any of which may spawn some cold air funnels and produce hail and some downpours.
We'll have more on WGN News at 5:30 pm and 9PM tonight--and also a look at a surge of warmth Friday which appears poised to bring us July's warmest temperatures to date. That warmth may be followed by vigorous if not some possibly severe thunderstorms later Friday night into a portion of Saturday.
Tom Skilling
Temperatures are falling with height at a faster than normal pace which means the atmosphere is unstable. The set-up is just the latest ramification of the cooler than normal air which northwest upper steering winds have continued to deliver and replenish so often this summer. Daytime heating encourages air near the surface of the earth to warm, rendering it buoyant. This heated air then ascends and cools prompting the thunderstorm development we've been observing much of the afternoon. It's a situation likely to spawn additional (though scattered) thunderstorms over at least sections of the Chicago area into evening. The thunderstorm development is being further enhanced by the convergence of ground level winds along inland-moving easterly winds off Lake Michigan. The cooling these winds promote across the counties closest to the lake has been--and is likely to continue--inhibiting thunderstorm development by stabilizing the air. Only sprinkles or light showers--remanants of the west and north suburban thunderstorms---are able to make it into these lakeside counties.
Indications are areas west and north of the Chicago--including DeKalb, Kane, McHenry, Boone, Ogle and Lee Counties will be affected from time to time by these thunderstorm clusters--any of which may spawn some cold air funnels and produce hail and some downpours.
We'll have more on WGN News at 5:30 pm and 9PM tonight--and also a look at a surge of warmth Friday which appears poised to bring us July's warmest temperatures to date. That warmth may be followed by vigorous if not some possibly severe thunderstorms later Friday night into a portion of Saturday.
Tom Skilling
