Friday, December 9, 2011

Visible satellite over the midwest with lake effect snow

Today we have an interesting and somewhat busy visible satellite image over the midwestern United States.  Here's what the view was at 11:15 AM PST.  I've labeled some of the more salient features.  You can click the image to get a bigger view.

The first thing that stands out (to me, at least) is the large swath of snow covering a wide band from eastern Nebraska up through northwestern Iowa, southeastern Minnesota and into northern Wisconsin.  Snow and clouds tend to both be bright and white, so the only real way to know that what we're looking at is snow is to watch an animation.  Here's a link to an animated version of this map (warning, it's a very large image animation, so it may take a while to load and you'll have to scroll around on the image to find the area you want to look at.)

You can tell that swath is snow because it's not moving while clouds will actually move with the flow.  Many places to the southeast of that snow area are still waiting to see their first snow of the year.  In fact, just today the first measurable snowfall of the year fell in much of the Chicago area, though it's not much and it's difficult to pick out any sort of snow cover on the satellite image.  Today's snowfall totals near Chicago are at this link.

The jet stream (strong winds aloft) is marked by a band of cirrus clouds, visible in the above image as the cloud band from Indiana up through northern Ohio and over the eastern Great Lakes.  This location compares favorably with this morning's analysis of the upper-level winds over the area.  You can see the tail end of the jet streak over the northeastern US matches up with this cloud band's location.

Of course, this means that much of the western Great Lakes are on the poleward side of the jet stream--this places them in some pretty cold air.  In fact, there's a lot of cold air streaming from the west-northwest across the western Great Lakes this morning.  This is a great setup for the Lake Effect to really kick in.  As cold air streams out over warmer water, it makes the air rather unstable (cold air above and warm air below).  As a result, many bands of cumulus clouds often form.  Some of these can become dense enough to support snow falling out of them, and we then get Lake-Effect Snow.  I wrote a previous blog post about this mechanism and you can find that here.

You can see that, with cold winds out of the west-northwest, there are indeed bands of cumulus clouds that are developing out over the lakes and on the eastern shores of the lakes (downwind).  They are particularly notable over western Michigan, northern Lake Huron and parts of the upper peninsula of Michigan.

There are also some lake effect bands also developing over eastern Lake Erie and Lake Ontario, but they're just covered up by that cirrus deck above so we can't see them.  We can see them on radar, though.  Here's the latest radar image out of Buffalo, NY:
You can see a nice band of precipitation coming right through Buffalo and parallel to the main axis of Lake Erie.  That's got to be a strong lake effect band.  Light snow mixed with rain is being reported at Buffalo.  However, most of eastern Lakes Erie and Ontario are under lake effect snow advisories or warnings.  The dark teal color in the image below represents a lake effect snow warning while the lighter teal color represents lake effect snow advisory. The light green is just a short term forecast statement.

So, fun things happening in the weather over the eastern US for now.  However, it looks like this weekend will probably be cold, but rather quiet.

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