Weather Pattern Repeats…Wet Period Ahead

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Thank you for stopping by the Weather Watch 12 Blog.  In today’s entry we will discuss the current weather pattern, and also look ahead to potentially a wet second half of April.

When I started at WISN back in December I have been providing long range forecasts exclusively in our blog.  The long range forecasts that I make are based based on the LRC, which is a weather pattern theory that I learned about while working in Kansas City.  If you are new to the blog or just need a quick refresher…

Here is what the theory states:

  • A unique weather pattern sets up every year between October 1st and November 10th
  • 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/spring/early summer-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.

As I have mentioned many times, this year’s cycling weather pattern is on roughly a 60-62 day cycle.  Since we are dealing with large scale weather features, ridges and troughs, the best way to see the pattern is by looking at the middle of the atmosphere.  This middle of the atmosphere is known as the 500mb level. 

Let’s look back to October…or 3 cycles ago to show where we are in the pattern.  Below is the archived 500mb map from October 17.  I labeled 3 key features on the map.  A large trough in the East, a trough off the Pacific Northwest coast, and a ridge in the Great Basin.

Now let’s fast forward 3 cycle periods to where we are about to be in the pattern.  Below is the 500mb forecast map from the 6Z GFS for this coming Saturday, April 17.  The features are labeled 1-3, and correspond to the map above so that you can make comparisons.

The features are again all present, the ridge that was over the Great Basin, is now shifted further east, mainly because the trough in the East is not as strong as it was back in mid-October.

Now that we have compared the pattern, and know where the pattern is currently at…what can be expected for the second half of April?

Back in late March I issued the long range forecast for April and May.  In discussing April I said the pattern would be active, and that Milwaukee would very likely see over 4.00″ of precipitation.  We are now 13 days into the month, and precipitation has been recorded on 8 of the days, totaling 2.05″ at Milwaukee-Mitchell. 

In the April forecast that I said the final 8-9 days of April would be wet, with some areas picking up 2″ of rain in this timeframe.  What did I base this on?

Let’s look back at the previous 3 cycles that correspond to roughly April 20-29 here in Milwaukee.

October 20-28

  • Rain recorded on all days but 1
  • Rain total in this period: 2.85″

December 20-28

  • Rain or snow recorded on all days
  • Precipitation in this period: 1.70″
  • Snow total: 6.8″

February 20-28

  • Rain or snow recorded on all days but 1
  • Precipitation total during period: 0.34″
  • Snow total: 5.4″

Now that we have looked back, translating this forward will mean a wet period beginning around April 20 and lasting for just over a week.  This wet period should push the April rain total for Milwaukee to over 4.00″ for the month…and possibly over 5.00″ in spots.

If you have questions about the LRC or how I use it to make long range forecasts please leave your thoughts in the comments section of the blog.  Remember, this is a fully interactive blog and I would love to answer any questions you may have!

For the latest weather updates please join us on Facebook at WeatherWatch 12  And make sure to watch WISN 12 News for your 7 day forecast!

Have a great day!

Jeremy Nelson


2 Responses

  1. I like it. Pushing the envelope in using surface trends. While your forecast is possible, I would warn readers that using the surface data to forecast based on past trends can be tricky.

    Jeremy has noted it is easiest to look in the middle of the atmosphere because of the ability to see large scale features and shifts. Look at this last 10 days…a shift of the Great Basin ridge into the Plains states changed the complexity of the surface output. If you had looked at other locations in the Plains, the surface trends may not line up to past cycles. Also, seasonal differences abound at the surface. When considering surface friction and other atmospheric dynamics, surface trending can be a slippery slope.

    That said, there are locations near the larger features that surface trends tend to repeat. I think Jeremy was able to pick one out.

    Interesting trend indeed.

    • I didn’t touch on temps because during the Spring a big driver or lack of our temperatures is Lake Michigan. Just look at how it is keeping our area cool today with the east/southeast wind. Also, watch on Wednesday when highs soar into the 70s in areas, and then locations impacted by a southeast wind may only warm into the upper 50s or 50s. I am confident in the wet period ahead since the larger features seem to have a memory and want to fall into the same long term long wave trough over and over again.


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