Metro Detroit weather: Powerful weekend storm looms after warm Friday

Temperatures could approach 50 degrees

By Paul Gross - Meteorologist

DETROIT - Temperatures Thursday rose generally to between 35 and 40 degrees (2 to 4 degrees Celsius), but 10 to 20 mph west winds with higher gusts knocked wind chills down much colder. Still, the sunshine sure looked great.

Some mid and high level clouds will cross the area overnight, but don’t worry, it’ll be a dry night. Temperatures will drop into the low 20s (-6 degrees Celsius) by dawn. West wind will eventually become northwest, and lighten up to 2 to 5 mph.

Any lingering mid and high clouds first thing Friday morning will move off, leaving us mostly sunny for the balance of the day. The sunshine, combined with a light and variable wind, will make for the perfect winter day, as temperatures once again rise into the upper 30s to near 40 degrees (4 degrees Celsius). In fact, those of us with bare ground and no snow cover could even reach the low 40s (5 degrees Celsius).

Friday’s sunrise is at 7:20 a.m., and Friday’s sunset is at 6:14 p.m.

Mostly clear Friday evening, then clouds start increasing later at night. Lows in the mid 20s (-4 to -3 degrees Celsius).

Weekend storm update

Everything remains on track with our weekend storm, and today’s computer models only suggest minor changes.

Saturday will not only start dry, but perhaps even with some filtered sunshine. Clouds will increase, and showers are possible by late afternoon. With a bit of luck, we could get through most of the daylight hours dry.

Afternoon temperatures in the low to mid 40s (6 degrees Celsius) will not be the high for the day, as temperatures will rise higher Saturday evening, perhaps even approaching 50 degrees (10 degrees Celsius) around or a little after midnight. Wind during the day will blow from the east at 5 to 10 mph.

Here is a series of maps showing you the storm’s progression during the day Saturday:

Showers will increase Saturday evening, with some thunderstorms possible. As mentioned above, temperatures will rise through the evening and then level off after midnight. It will also start becoming windier as the powerful cold front approaches, with the east wind eventually becoming south at 20 to 30 mph.

Here’s how the weather pattern will shape up Saturday night:

Notice on the above maps those skinny yellow lines. Those are called isobars. They are lines of constant pressure. One of the primary laws of meteorology is that the faster the pressure changes, the faster the wind blows.

So, as the low deepens, the pressure changes faster as you go from the low outward -- and there must be a corresponding increase in wind speed. This basic meteorology will play out big time for us.

First, when the cold front passes through, any shower ahead of the front could potentially have strong wind gusts, and by the way, this low will deepen so quickly that you’ll hear meteorologists all around the country calling it a “bomb.”

This is a real meteorological term and, no, it’s not something recently made up to hype storms. There are actual criteria in terms of how much the pressure drops in twenty-four hours, and this storm likely will satisfy that criteria.

But the main wind event will be post frontal on Sunday.

Once that cold front passes by, the pressure will start rising very rapidly. Adding to the wind potential is that the wind direction from the surface aloft will be the same, and that wind aloft will be quite strong, blowing potentially at 65 to 80 mph just one mile aloft.

Putting all of this together gives us high confidence that surface wind gusts from the west on Sunday will approach or exceed 50 mph. The National Weather Service will most certainly issue a Wind Advisory, with a High Wind Warning definitely in play. Be ready for scattered power outages around town.

Precipitation-wise, we’ll start Sunday with scattered rain showers, but they will quickly change over to snow showers. Temperatures will fall all day, from low 40s (6 degrees Celsius) at daybreak to the mid 30s (2 degrees Celsius) by late afternoon.

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