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Fall Pattern Stays Locked In This Week

Posted at 6:25 PM, Oct 20, 2013

WEST MICHIGAN — So this cooler, unsettled, fall pattern will remain locked in to the Great Lakes this week. After all, it is mid/late October, so perhaps not so unusual. However, normal/average highs for this time of year have us at/around 60 degrees. We’ll mainly see highs only in the upper 40s/low 50s this week.

The attached snapshot shows several things…but mainly the reason why we have the cooler, unsettled pattern. The upper level winds around 30,000 feet known as our jet stream has dipped south over the Great Lakes and will remain there the entire week. We call that a trough. Weather underneath these troughs are mainly characterized by a cool, wet pattern. Conversely, when the jet stream lifts north we call that a ridge…characterized by high pressure with mainly dry, warm, settled weather. (The west coast is seeing that now)

The snapshot is actually from one of our forecast models (valid Tuesday morning) and is what the atmosphere would look like at about 18,000 feet. This altitude does a nice job for the meteorologist at showing the trough/ridge pattern. So a quick glance through the week at these maps at 18,000 feet (or 500 millibars for you weather geeks and pilots) immediately tell us where our weather is heading. Unfortunately, the trough never really lifts out at all this week.

We’ll continue to see lake-effect and lake enhanced clouds and precipitation this week from colder air coming over the warmer Lake Michigan waters. In fact, don’t be surprised to see some snowflakes mixing in from time to time (especially at night) as temps drop in the P.M. hours. Since the ground is still very warm, I don’t anticipate anything except on grassy areas and cold metal surfaces like cars.

Get the complete West Michigan forecast at www.fox17online.com/weather.