The lake-effect rain machine will be active Tuesday, particularly in the morning. Not
only have the chilly north winds that greet Chicago morning commuters traveled the
length of Lake Michigan, the atmospheric setup also features a temperature decline
between the lake surface and a mile aloft of 30-degrees. That's a much steeper drop
than normal. A decrease of just 20 degrees is enough to encourage air to rise and cool
producing lake clouds -- so Tuesday's elevated decrease goes even further in
encouraging the comparatively mild air hugging the lake surface to ascend and cool --
a prerequisite for cloud and shower formation.
The lake setup breaks down Tuesday afternoon and chilly temperatures Tuesday night
threaten frost away from the lake. Monday's 55-degree high is the chilliest of the fall
season to date. It's also the coolest since May 28.
ATMOSPHERIC STIRRINGS OVER GREENLAND AND NORTH ATLANTIC SIGNAL
NEW CHILL HERE NEXT WEEK
Buckling of jet stream is to set up northwest flow aloft over the Midwest.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune
