Is The Pattern Set?

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Thank you for stopping by the Weather Watch 12 Blog!  If you follow the blog you have read about a weather pattern theory that I use called the LRC.  We are currently in a very exciting time of year, as the weather pattern is about to become set, and will begin cycling for the next 9 months or so!

If you are new to the blog, or just need a quick refresher, here is what the LRC states:

• A unique weather pattern sets up every year between October 1^st and November 10^th
• The weather pattern cycles, repeats, and continues through winter, spring and into summer.  Identifying the cycle length helps tremendously when making long range weather predictions.
• Long term long-wave troughs and ridges become established and also repeat at regular times within the cycle.  These dominant repeating features are a clue to where storm systems will reach peak strength, and where they will be their weakest.
• The LRC is a winter-long pattern!  There is a pattern! It isn’t just one long-wave trough, storm system, or ridge. It is a sequence of troughs and ridges that are cycling across the Northern Hemisphere.

To put this in very simple terms, the weather pattern that occurs in October and November repeats thru the Winter, Spring, and into the Summer. The cycle length will vary each year. I’ve seen cycles lengths of 40-46 days, 48-52 days, and 60-62 days.

One of the big questions is whether the pattern sets up before October 1, or if the pattern before this date is just a combination of the old and new patterns.  The easiest way to show if the cycle is repeating, or what the possible cycle length may be, is to do a simple map to map comparison.  Since we are looking for long term longwave ridges and troughs, the best map to look at is the 500mb(middle of the atmosphere) chart.

The first time that the cycle length is identified each year is a very exciting time.  Once the cycle length is determined, a long range forecast for the winter can be made.  It also allows us to make general forecasts to time out specific storms weeks in advance.  Since this is a large scale pattern, detailed snow forecasts(like 6″-12″) for individual storms cannot be made weeks in advance.

So now the big question…what is the cycle length this year?  I don’t want to go on record yet, because I would like to see about 2 more weeks of the pattern.  But looking back to late September, the 500mb maps are beginning to line up and show signs of a repeating cycle.

Let me show you an example.  Below is the 500mb analysis from today’s 12Z NAM computer model.  Notice the ridge in the West, and the large upper level low over the South.

 

Now let’s compare this to the September 27 500mb archieved map.  This shows a large ridge in the West, and also an upper level low over the South.

These maps are about 37 days apart.  Could this be the new cycle length?  Lots of questions still need to be answered, but over the next 2 weeks I will keep a close eye on the features that move across the United States, and then compare them to what occurred in early October!  What do you think about the 2 maps above?

Finally, I want to touch on the cold air that is going to move across the Great Lakes on Thursday and Friday.  This will likely be the coldest air so far this season, and also bring the first sizeable lake effect snows to areas favored by north or northwest winds.

Below is a snowfall forecast from our in house high resolution computer model.  Notice that parts of the U.P. of Michigan, and also northern Indiana could be looking at 4″-6″+ of snow by early Saturday! 

Here in southeast Wisconsin we likely miss out on the snowflakes, but our time may not be that far away!  We’ll keep watching the pattern, and look for the complete winter forecast later this month!

Have a great day!

Jeremy Nelson