Our first lake effect event....(10-22-13)

<B>(1:30 pm Tuesday October 22nd)</B> Colder air is moving into central New York this afternoon and that will set the stage for an early season lake effect event with some snow possible for parts of the region.
Things are coming into better focus now in terms of our early season lake effect event for parts of central New York.  There are actually two events and here is the condensed version of what happens.  One round of lake effect could bring a couple slushy inches of snow to the Tug Hill tonight (Tuesday night) and a more meaningful round Wednesday night and Thursday in the same areas with the potential for 6 or more inches to the highest elevations along with thunder and lightning. The areas in the potential bullseye would be southeast Jefferson, Northeast Oswego and central Lewis counties. For the hills south of Syracuse there is even a chance for a coating of snow on Thursday night.

If you’re interested in more of the nuts and bolts of what’s going on,read on.

First, as I write this Tuesday morning, a cold front is moving through central New York.  This front will bring the first shot of cold air into the region.  Since this will be the first important lake effect event of the season, it seems like a good time to remind you of some of the basic mechanisms of lake effect.  The arrival of the cold air is the first ingredient.  When we try to gauge lake effect potential we look at the difference between the lake temperature and the temperature at 5,000 feet, or what we call in meteorology the ‘Delta T’ or change in temperature.  The key number to remember is that we need a ‘Delta T’ of roughly 13 C to get the updrafts in the atmosphere going to cause lake effect. Right now, the average lake temperature is about 60 F or 15 c and the air coming over the lake will approach -5c.  By tonight that ‘Delta T’ number rises to 20 C!  

That is cause for some concern for tonight but wind will also start to play a role. Winds in the lower atmosphere start this afternoon out of the southwest then transition into the west and west-northwest overnight.  That is going to put any lake effect rain and snow on the move.  That is why we are only calling for a couple of inches over the Tug Hill tonight.

Something else will happen Wednesday that may temporarily disrupt the wind flow.  A strong disturbance in the jet stream winds aloft will pass to our south then spin up low pressure down at ground level off the East Coast.  

By Wednesday night and continuing into Thursday the winds turn back into the west and remain that way for an extended period of time.  This is the time frame where a more significant snow could fall over the Tug Hill.  The set up is impressive looking as not only do we have the favorable wind flow coming over the full length of Lake Ontario but we will also have some moisture feeding off bands coming from the Upper Great Lakes.  This tends to enhance the lake effect off Lake Ontario. Here is a computer forecast map that shows this:

One other thing I want to mention about this image is has the lake effect band stretching from southern Oswego county down toward Utica. I watched a couple minor lake effect events and I noticed this particular model had a tendency to push the lake effect a bit too far south.  That may be the same case come the end of this week. Also, those ‘Delta Ts” I mentioned above will be huge; on the order of 20 to 21c at times.  That means the clouds should grow deeply into the atmosphere.  During a typical mid winter lake effect event clouds can grow to 10,000 feet or greater.  In this case, the clouds could top off at 20,000 feet.  That will fuel not only the heavier precipitation but also thunder and lightning.

It is worth mentioning at this point that because we are dealing with such an early season event that temperatures are going to be borderline.  Lower elevations as you come off the Tug like in Sandy Creek and Pulaski may see rain/snow mix during this time as temperatures would be in the upper 30s and lower 40s.

I there is the possibility of some snow in the higher elevations south of Syracuse.  That would have to happen later Thursday night and early Friday.  The low level winds will turn into the northwest by this time plus we will be dealing with our coolest temperatures at this time (at least mid 30s over higher elevations and possibly colder)

I did hear some chatter from the national Weather Service that the set up for this early season lake effect is similar to an event that happened at the end of October 2006. I searched their website and found this map of snow totals that occurred back then:

That red area up over the Tug Hill is where 6” or more fell with a high total of 11” in Highmarket in Lewis county.  The take away from this map is that yes, there will be some lake effect snow over the next couple of days but odds are any significant accumulation is going to be over a relatively small area up in elevation.

Stayed tuned as we will have more updates as the next couple of days progress.

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