Metro Detroit weather: Finally a break from the snow

Plus: The Space Station flies overhead this evening

By Paul Gross - Meteorologist
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Detroit (WDIV)

DETROIT - So much to talk about this afternoon, so little time.  First, Mother Nature showed us yesterday just how complicated weather forecasting can be.  We meteorologists spend a lot of time dealing with thermodynamics when forecasting either severe summer storms or wintertime wintry mixes.  In the case of Sunday, the wintry mix we got (instead of all snow that we expected on Friday) was a surprise.  Here’s a quick explanation about how our various types of precipitation develop:

If the atmosphere is below freezing from the clouds all the way to the ground, then we only get snow falling from those clouds.  But now let’s introduce a wedge of above freezing air aloft.  If there’s just a narrow wedge of that warmer air, then the snow falls, melts, but then re-freezes into little ice balls, which is called sleet.  Some of us got that on Sunday…perhaps you heard the pinging on your windows.  Now let’s widen that above freezing layer a bit…the snowflakes melt, but don’t have time to refreeze, so they reach the surface as raindrops falling into below freezing air, which then freeze into a layer of ice on the surface.  Some of us got that on Sunday, too (and that caused a lot of trouble at Metro Airport).  Obviously, if it’s above freezing from the clouds to the ground, then we only get rain - unless the actual surface temperature is still below freezing, then you can still get a thin glaze of ice until the surface itself warms above freezing.

On Friday, as Ben Bailey and I were mulling over the computer models and working on the Sunday part of the forecast, we looked at projected vertical cross-sections of the atmosphere, and none of them projected that above freezing layer aloft making it up into our area.  This was a point of discussion for us.  Some models brought it up to Toledo, so it was a close call for southern Lenawee and Monroe Counties.  Obviously, as the weekend progressed, it became apparent that a wintry mix was going to affect at least part of our area.  This hopefully gives you a little insight into this aspect of our forecast process, and helps you to understand what happened Sunday.

Many of us got eight-to-twelve inches of snow in the Friday to Sunday timeframe, and that puts Metro Airport at 20.8 inches for this month, and 52.5 inches for the season…well above average for both.  In fact, here we are in mid-February, and we’re already only 2.6 inches from a top-ten snowiest February, and only 11.3 inches away from a top-ten snowiest winter!  By the way, five of Detroit’s top-ten all-time snowiest winters have occurred since the 2004-2005 winter and, yes, climate change has something to do with that.

Today we finally got a break.  That sunshine sure looked and felt great, and if we can keep the clear skies into the evening hours, we’ll be able to see the International Space Station fly overhead.  This time, it’ll be at a kid-friendly school-night time!  Just face a little left of west at 6:48 p.m. and look relatively low in the sky, and you’ll see a bright “star” fade into view, and fly a slow steady path to your left across the southern part of sky (by the way, there are no blinking lights – it’s a steady, light).  There’s plenty of time to see it:  it’ll take four minutes to travel to the southeast, where it’ll fade from view.  We never get tired of seeing this and, every time, we think about those astronauts on board and all of the scientific research they are doing.  I’d love it if NASA someday sends an invite to be the first science journalist to travel to and report from the International Space Station!

Some high, thin clouds will move in overnight, with bitter cold low temperatures around 7 degrees (-14 degrees Celsius) in our Urban Heat Island closer to Detroit, and colder in rural areas.  Fortunately, calm air means no wind, which means no wind chill.  Two concerns, however linger about the tonight forecast.  First, today’s sunshine and near-freezing temperatures caused melting, and wet pavement will freeze and become icy once the sun gets lower in the sky.  Watch out for areas of ice if you’ll be heading out tonight or Tuesday morning.  The second concern is a little less certain.  While the air above us is very dry, the melting that occurred this afternoon may have raised the humidity just above the surface.  The clear skies and light wind means that temperatures will fall close to the dewpoint temperature and, when that happens, fog can develop.  One of our high-resolution computer models is actually showing some fog development tonight, but some other models aren’t.  Our concern is that if any patches of dense fog develop in the well-below freezing temperatures, then this is called freezing fog, and can deposit a thin layer of ice (“black ice”) onto surfaces.  There’s no guarantee that we’ll see any fog but, if you do, then please be aware that some of that invisible ice could await you on unsalted paved surfaces.

Tuesday looks like we’ll start with some sunshine, then clouds will thicken by afternoon.  Highs once again should reach the upper 20s to near 30 degrees (-2 to -1 degree Celsius).  East wind at 4 to 8 mph.

Tuesday’s sunrise is at 7:32 a.m., and Tuesday’s sunset is at 6:03 p.m.

Mostly cloudy for at least the first half of Tuesday night, then some computer models actually bring in some clearing after midnight.  Lows in the low 20s (-6 degrees Celsius) will be much warmer than how we started the day on Tuesday.

Wednesday should feature some sunshine once again, but clouds will increase during the afternoon. There’s the slight chance for a scattered, light rain shower late in the day, but the better chance appears to be Wednesday night.  Highs Wednesday will soar into the low to mid 40s (6 degrees Celsius), with lows Wednesday night remaining above freezing and only dropping into the upper 30s (3 to 4 degrees Celsius).

Mostly cloudy with a small shower chance on Thursday…the best chances appear to be very early in the morning and very late in the day.  Highs in the mid 40s (7 degrees Celsius).

Rain shower chances increase Thursday night ahead of an approaching cold front, with lows dropping below freezing and possibly creating some icy patches if wet surfaces don’t dry up before that temp drops.  If the front comes through early enough, we could even mix in a few snowflakes late Thursday night.

Breezy and colder on Friday with a scattered, light snow shower possible in the morning, followed by developing sunshine.  Highs in the upper 20s (-2 to -1 degree Celsius).

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