Cold front will force pattern change back to Fall

Posted at 6:10 PM, Sep 28, 2014
and last updated 2014-09-28 18:27:03-04

WEST MICHIGAN – The weather has been absolutely fabulous since last weekend! Sunshine, dry conditions, and warming temperatures in to the mid/upper 70s. It certainly makes Fall a little easier to take! However, a strong cold front and low pressure system arrive on Thursday and will force a major pattern change.

Instead of the jet stream being to our north with a ridge of high pressure in control, look for the jet stream to push south of the Great Lakes by the end of this week. It’s what we call a trough. These troughs are usually characterized by cooler than normal temperatures, unsettled weather, clouds, and precipitation. In this case, I wouldn’t be surprised to see lake-effect clouds and lake-effect rain showers since the air coming in will be that cool.

Despite the clouds on Thursday, temperatures will still make the 70s, but rain and likely some thunderstorms will develop. As a low pressure system approaches Michigan from the south/west, it will strengthen and create windy conditions Thursday night in to Friday. The warmest temperatures on Friday (at this point) will occur at midnight in the 60s, then fall in to the 50s behind this system during the day. While system showers may taper off by mid-day, more showers are likely later Friday night and Saturday morning with more energy rotating through the flow as well as enhancement from Lake Michigan.

Simply put, Friday and Saturday will be raw, chilly, and at times wet days with highs confined to the 50s. Not a great week for high school homecoming parades, floats, and football games. Normal/average highs for this time of year have us in the mid/upper 60s. The attached snapshot with this story is from the GFS computer forecast model (at the surface) valid for Friday morning. All the purple, blue, and green is accumulated precipitation, so we may get a pretty good soaking as this system taps moisture from the Gulf of Mexico. In fact, thunderstorms are not out of the question! Note also the thin, gray lines around the “L” or low over the Great Lakes. The isobars packed tightly together means windy conditions. Once the system lifts through the area, the colder air will filter in and I would expect a deck of low-level strato-cumulus clouds thanks in part to Lake Michigan. Click on the image below for a larger, legible version.

I would make sure to have any outdoor work completed before Thursday. Get the complete forecast at