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Metro Detroit weather: Next winter storm approaches

How can you plan for days ahead?

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DETROIT – After a dry Friday afternoon, snow will quickly develop and spread eastward through the early evening, and steadily increase. Snow will fall most of the night.

Temperatures will rise through the night, and be in the mid- to upper 20s (-2 to -3 degrees Celsius) by dawn, with a southeast wind at eight to 13 mph.

Here's what I expect for snow totals, and this includes whatever we get Saturday night:

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The Friday night snow is what I consider to be the first part of a two-part impact from this storm. I think there’s actually going to be a lull from the precipitation in the morning, with perhaps just a bit of light snow or sleet, but nothing major.

Part two of the storm will be the next batch of moisture moving in for the afternoon, and this one will bring a mix of snow, sleet, freezing rain and possibly even some rain to the far south. This second push won’t have as much moisture to work with, so precipitation amounts during the afternoon should be light.

Ever wonder how we can have literally four different types of precipitation across the area at the same time? It’s all because of temperatures aloft.

In this first graphic below, notice the wedge of above-freezing air that has moved in aloft from left to right. What’s really important to note is the thickness of that warm layer and how it changes.

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When the air is above freezing from the ground all the way up to the cloud, as it is on the far left of the graphic below, then we get all rain. Keep that thick layer of warm air aloft, but drop the surface temperature below freezing, and what falls from the cloud remains a liquid, which then freezes on contact with the surface. That’s called freezing rain.

Now narrow that warm air wedge even further, and a raindrop falling from the cloud (or a snowflake that melts into a drop) falls into that thicker below-freezing layer, and freezes into a little ball of ice. That’s called sleet (or ice pellets).

Finally, if the air column above us is all (or virtually all) below freezing, then snowflakes fall from the cloud and reach the ground in that state.

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Highs Saturday will depend on  where you are. Those of you south of I-94 or I-696 may sneak just above freezing, while those of you north of I-94 or I-696 will probably stay at or just below freezing.

Saturday’s sunrise is at 7:57 a.m., and Saturday’s sunset is at 5:03 p.m.

A cold front approaching Saturday evening will change everything to all snow showers, but I don’t expect much accumulation -- probably an inch or less for most. My bigger concern Saturday night is that lows will drop precipitously behind the front, so wet surfaces (not salted, just wet from melting) could quickly freeze into icy surfaces. Be careful if you’ll be out late Saturday night. Overnight lows will be in the mid-teens (-10 degrees Celsius).

To help you plan, here’s a series of maps showing the timetable for this weekend’s weather events:

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It will be mostly cloudy to partly cloudy Sunday, with temperatures barely rising -- perhaps into the upper teens (-7 degrees Celsius).

Sunday night will become mostly clear, with near 0 degrees (-18 degrees Celsius) in and near Detroit, and below 0 in the suburbs.

Christmas week travel weather

There are no changes from Thursday's forecast for the week ahead, which is a huge travel week for many of you or your families.

Monday, Tuesday and Wednesday all look dry for travel around the state, with mostly sunny or partly cloudy skies. After that bone-chilling start Monday morning, highs rise into the mid-teens (-10 degrees Celsius), then into the mid-20s (-4 degrees Celsius) Tuesday and into the low 30s (0-1 degrees Celsius) Wednesday.

Thursday’s weather system still appears weak, with possibly some snow showers. Highs will be in the upper 20s (-2 degrees Celsius).

Friday looks partly cloudy, as does Christmas Eve. Christmas Day might bring a weak weather system with some festive light snow. I’ll keep you posted if this changes.

But one of the best parts of this forecast is that we should have "normal" winter temperatures Christmas week and weekend, so that pretty much assures us of our White Christmas (which I told you a week ago would be the case), and also means that temperatures will be perfect for the children (and parents) to head out and play in the snow.


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