Big upper low will produce sharply cooler temps

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WEST MICHIGAN — Remember the dull gray, cloudy, cold, fall-like, showery day with high winds and waves on Thursday? Don’t shoot the messenger, but there are more days like that coming over the next few.

While Friday and Saturday were gorgeous…and frankly some of the best last really good days of summer and beach weather, a strong cold front will sweep through Michigan on Sunday afternoon. That front will likely generate a few showers and thunderstorms, some of which may be severe. The primary threat would be damaging straight line winds, but the breezy conditions and strong wind field may also create an isolated tornado or some large hail.

Once the front sweeps through sharply cooler air will filter in the next several days as temperatures run about ten degrees below normal. In fact, the surface system that passes through the state on Sunday and slowly occludes (or dies) will morph itself into a strong upper level low pressure system. This cold pool of air aloft will generate instability (like last Thursday) and park itself over the Great Lakes through at least early next Thursday. Expect partly sunny to mostly cloudy skies each day with a few isolated instability showers possible during the heat of the day with some energy pivoting around the upper low. We’ll also see breezy conditions Sunday and downright windy conditions on Monday with westerly winds at about 15 – 25 mph. That means small craft advisories for boaters and a high beach hazard risk BOTH days for swimmers. Like last Thursday, this will produce rip currents, structural currents, longshore currents, and high wave action. Swimming is NOT advised!

Once we kick the upper low and trough out of the region later Thursday and Friday, temperatures will warm to the upper 70s to near 80 with a bit more sunshine expected. The thumbnail attached to this story is from one of our computer forecast models and is valid for Monday morning. It is a snapshot at about 18,000 feet above the surface, or the 500 millibar level for you weather geeks. This level clearly shows us the trough/ridge pattern across the United States. Note the big upper level low and trough coming in to the Great Lakes, while the western half of the nation remains under a ridge (of high pressure) and continues to bake with 90s and triple digit heat.

Take a look (below) at that same upper level map (18,000 feet) from our computer forecast model valid next Thursday morning. You can see the upper low and trough are finally just starting to lift out of the Great Lakes!

GFS

It’s important to note that regions underneath these troughs and upper lows are typically characterized by cloudy, cooler, showery weather that is more unsettled. It’s the opposite of a ridge of high pressure. Get the complete West Michigan forecast at www.fox17online.com/weather.

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