EMSC":1hy4r6ep said:
I'm sure Jspin has all the details.
I may not have all the details, but following our winter weather (and Powderfreak's discussions) closely has allowed me to get a good idea of what is going on. Most of what has been said here is on the right track, and Admin’s post is spot on in describing some of our best understanding of how the Northern Greens appear to capture so much snowfall. One clarification I’ll make to Admin’s post is with regard to Lake Champlain freezing over. I’d say the seasons are definitely in the minority in which the lake freezes over entirely (somehow I think I’ve heard a number like 1/3 of winters, but I’ll try to check on that). With that said, Lake Champlain is not all that big compared to the Great Lakes, and even if it doesn’t freeze over every year, it get’s pretty well covered with ice in a typical season.
With regard to the whole lake effect issue, I’ll try to clear up the confusion somewhat – it turns out that all these moisture sources that people have heard about (Lake Champlain, St. Lawrence Seaway, The Great Lakes) aren’t necessarily out of the picture for the Greens.
First off, I’ll point out that yes, you can get lake effect snow off Lake Champlain.
I’ve been in it, I’ve watched it on radar, and I’ve seen the accumulations. However, as stated, the east-west fetch of Lake Champlain is far too small to really produce much lake effect. The only way you get lake effect off Lake Champlain is when you have winds in the N or NNW directions (as Admin said), then the fetch is long enough. Thus, this full blown lake effect off Champlain will only affect places to the S, SE, and right along the E shore of the lake. Middlebury got hit with lake effect off Champlain in November last year, and
a good discussion developed on Easternuswx.com, led by some of the Middlebury guys reporting on it. Lake effect was also streaming off the Finger Lakes at the same time. Unfortunately, I don’t seem to have a radar image of that episode in my web archives, but I should have captured one. We’ll have to see if Powderfreak has any images. The radar showed the beautiful streamers coming off Lake Champlain and the Finger Lakes, even the Weather Channel featured the radar as I recall. Check out that link to the discussion, and you can hear about some of the finer points of lake effect from some of the locals and experts.
Powderfreak also posted the BTV NWS warning from that event.
So, what about the Green Mountains and actual lake effect from Champlain? The folks who have seen people talking about this are not crazy. With a NNW wind,
the fetch off the lake can run right into the MRG/Sugarbush/App Gap region, and they get snow out of it. All these references you see in the lake effect warnings that mention Addison County - the MRG/Sugarbush/App Gap region is right along the east side of Addison County – you will see this region mentioned by NZucker in the discussion link above. We’re usually talking in the 6-inch range tops for the MRG/’bush area out of these types of events from what I’ve seen, but one could get a nice little surprise powder morning out of it.
So what about the Great Lakes and the St. Lawrence? Well, occasionally you will see streamers from Lakes Ontario/Erie spread all the way across and hit the Greens, but that’s a LONG way for lake effect snow, and the results are usually a few inches in the Killington area, but not so much “directly” in the Northern Greens from what I’ve seen, so that doesn’t explain it. As admin said, the distance from the Great Lakes to the Greens is just too far for major lake effect. However, the lakes may play an important role in our snowfall, and this is where the St. Lawrence may come in as well (what people have heard about the St. Lawrence affecting out snowfall may not be out of this world either). It seems like the area north of the Adirondacks, north/northeast of the Great Lakes, west/on of the St. Lawrence, and northwest of Lake Champlain is an area that has the ability to pool moisture (with the potential for all these moisture sources to contribute – even the tiny ones a little bit). I only know about this region because Powderfreak speaks about it, but with the right wind, this pool of moisture smashes into the wall of the Northern Greens, and with the orographic effect that Admin specifically talked about in his post (which nicely explains the gradient one sees from Jay Peak southward) lots of snow falls. Sometimes moisture wraps all the way around from the Atlantic with storms up to our northeast, and that contributes to this pool as well. So, for the very small moisture sources like the St. Lawrence and Lake Champlain, perhaps they are not contributing like the Atlantic or the Great Lakes, but they’re not going to hurt, and they may be doing their tiny fractional part in the overall effect (as long as they are not frozen). Any moisture source is going to help a little to keep the atmosphere saturated, so that may be part of what people are hearing about effects from these smaller bodies of water. I’ll try to get Powderfreak in here for his expert input, because he is certainly one, if not THE world’s expert on this specific phenomenon for the Northern Greens due to his meteorological knowledge and observations from the area.
J.Spin