Saturday, August 21, 2010

Residual Low Level Moisture Will Lead to Fog Development Tonight

Weak high pressure over Ontario, Canada has nudged a weak cool front just to the south of the Stateline.  Dew points on Saturday evening were still close to 70 degrees behind the front.  With light northeasterly winds, clear skies, and high dewpoints... fog will form across many areas overnight.  The fog may be dense, and as of 10 pm Saturday night DENSE FOG ADVISORIES have been issued for all of southern Wisconsin away from Lake Michigan, and for Jo Daviess, Stephenson, Carroll, and Whiteside counties in northwestern Illinois from 3 am until 10 am Sunday morning.  The fog will form and thicken overnight, and cause visibilities to drop to less than one quarter of a mile, and drivers are advised to use caution approaching fog banks, be prepared to slow down, and use the low beams.  The fog will last past daybreak, but is expected to be burned off by 10 am on Sunday morning leaving skies mostly sunny.  Drier air will work in from the northeast on Sunday, so with light winds, lots of sunshine, and lower humidity, it will turn out to be a very nice day for late August with a high in the low 80's.  High pressure will settle into Upper Michigan on Sunday night, so our region will have a clear night with comfortable temperatures.  Sunshine will be with us again on Monday with the ridge of high pressure remaining across Wisconsin and Illinois.  On Tuesday the ridge will shift off to the east as a new cool front pushes through the Stateline.  The Gulf of Mexico will be cut off, so moisture with the system will be limited, and chances of measureable precipitation will be meager.  A pleasantly cool early fall like air mass will follow in behind the front reducing high temperatures into the upper 70's on Wednesday and Thursday, and dropping overnight lows down into the 50's.  Skies are expected to be sunny with a slow warmup into next weekend.
By Meteorologist
Eric Nefstead

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