Lake Effect Snow - A Primer For the UP Snowbelt
byon 01-08-2013 at 03:17 AM (490 Views)
This is a blog that should have been completed 2 years ago. I've had questions on how Lake Effect Snow (LES) affects my area and I think (maybe) that I know enough now to answer that question to a bunch of semi-mets.
LES is a phenomenon that requires 3 key ingredients - a cold atmosphere, a warm and large body of water and the correct wind field to produce snow showers over land. I know that sounds simplistic but it really is that simple for us.
Anyone who studies weather has seen something like this image:
It gets the point across pretty easy. Cold air from the north interacts with a warmer body of water, causing vapor to rise into cloud formation. As the vapor collects, the clouds hit the other side where the land is colder again, forming frozen precipitation and causing it to fall. It's just that easy here sometimes.
Lets break everything apart for our region.
Cold air mass
The above 850mb chart shows what temperatures need to be at that level in order for LES to form. To be perfectly honest, Lake Superior is 10C in November and December, when LES is a bit more rare. As a kid I can remember big snowstorms in November but that usually involved a major storm system, not LES.
Anyway, air temperatures for the 850mb need to be somewhere around -11C to -15C for us to get what we would call "significant" snow. Sure, warmer air will produce LES but my people don't consider it significant precipitation. Also, inversion heights need to be around 4000ft for any hope of good snow. That is enough to drop a inch or two but not enough to cause any serious problems. 7000ft? Now you are talking about some better height, which should easily drop 2-3 inches in a couple hours.
I haven't even mentioned the fact that LES can happen in dry or moist air. Obviously dry air inhibits snowfall greatly. I've been in many a storm where moisture values in the 50's and 60's drop a inch in 10 minutes.
This is, by far, the reason I break my back shoveling at work and not so much at home. Anything that faces the southern side of Lake Superior is going to get hit with snow at some point during the winter. Which areas see the most? A favorite saying for luckless hunters is "If it's brown, it's down". Take a look at the map and imagine that exact saying for snow.
The Keweenau Peninsula sees the most. It shouldn't be that surprising since it is surrounded by water on 3 sides and rises very fast from the lake. LES still has plenty of time to rise from opposite shores and dump in this area. And winds (that topic comes up soon) can come from almost any direction to impact the area. INTERESTING NOTE: very rarely will you be able to pick up LES on a radar signature for the area. The Huron Mountain range in northern Marquette County obscure any decent chance of a return signature. I've only seen major storms show up on the radar there.
The Keweenau Peninsula
The Iron Hills of NW Marquette County are a favorite for heavy snow (I happen to work in them). Negaunee and Ishpeming see quite a bit of snow from LES. Marquette is at a average altitude of 660 feet. Negaunee? 1370! Ishpeming? 1410. So not only is Marquette warmer being next to the lake, the snow also has more distance to fall, taking the moisture out of it along the way. I can tell you that my house has hardly any snow, yet my work in Negaunee really needs to get the snow piles hauled away.
Alger County, specifically Munising, MI, get more than their fair share of snow. The Keweenau manages to block some of the LES that can hit Marquette. No such luck for Munising, as there is no land mass to get in the way. Munising, though at only 614 feet, has many high hills surrounding it, allowing the hills to put a stop to momentum, dumping additional snow on the town.
Finally, the far Western and Eastern sides of the UP also get their share. The western side is more hilly but sees less snow since the lake narrows on that end, not allowing as much of the vapor to get up in the air. The eastern side sees snow but does not have the high hills that the central and western sides have.
The above shows the classic pattern for LES in the UP. Cold 850mb temps coming out of the NW hit the Lake, inversion to 5-7k, snow on the other end. The classic NW breeze will manage to give snow to most everyone along the lakeshore. As the idiot caption on the next image will show, NW winds make for some pretty pictures.
NW winds are favored for most of the year. The Keweenau will see snow from the W, NW, N, NE and E winds, which makes it one hell of a place for snow. If 390 inches suits your fancy. Marquette and Munising areas will get them from the NW, N and NE. The far west from NW and N winds. No matter what, the UP will see snow. Earlier this year a NW LES storm hit. The skies cleared and MODIS was able to get a great shot of where the snow fell.
So what has happened this year? Barely anything, for sure.
The usual NW snows have not shown. The eastern UP has seen more in the way of snow but is still under for the year. My yard still shows grass through the snow. Most areas have enough snow cover for snowmobiles but retailers are hurting for business. The lower lakes depend on Lake Superior snowmelt for their water levels and they aren't going to get it if this keeps going.
However...I do recall the 2001-02 winter. We barely saw any snow until mid-January, then everything changed. Over the next 2 months we got 250 inches and saw the sun for only two days. Anything can happen..........