April & May Long Range Forecast

***Watch WISN 12 News for the latest on the weekend rain chances***

Thank for stopping by the Weather Watch 12 blog. Each day we strive to give you weather information that you will find no where else in Southeast Wisconsin. In today’s entry I will discuss the weather pattern for the next two months and also provide temperature and precipitation forecasts thru the end of May. This is a lengthy entry…but worth your time.

Since arriving 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. For a great example of this theory and how it relates to our current warm-up in Milwaukee…just check the blog entry from Tuesday.

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. So what does this mean for the month of April?

To get a good idea of what to expect during April let’s look back to the previous cycles of October, December, and February. That is roughly 60, 120, & 180 days…or 3 cycle periods. Typically when showing the LRC I use 500mb maps since this is where the long term long wave ridges and trough reside. In this entry I will focus on doing surface comparisons since we have 3 cycle periods to look back on. The data used is for Milwaukee.

Let’s begin by talking about a few things that stand out regarding the weather pattern in October, December, and February.

Precipitation

  • October & December above average precipitation totals. February below average precipitation, BUT above average snowfall.
  • ‘Signature’ storms in each month around the 7-9 timeframe & 20-25 timeframe.
  • Final 8-9 days of each month were wet.

Temperatures

  • Departure from average monthly temperatures October(-3.1)  December(+0.2)  February(+2.1)
  • Average to above average temperatures each month from roughly 17-25.

To summarize the 3 months, they had above average precipitation or snow. Temperatuers were cool in October, and then pretty close to average in December and February.

Now a quick glimpse at November, January, and March.

Precipitation

  • All 3 months at least 0.90″ below average or more.
  • Active periods were short.

Temperatures

  • Departure from average monthly temperatures November(+6.4) January (+1.7) March (+4.0)
  • Common warmer periods from roughly 17-24 of the month.

The surface comparisons above show a pattern, but another way to see the pattern is by looking at the Arctic Oscillation(AO). If you are wondering what the AO is…here is a great description.

The Arctic Oscillation

The Arctic Oscillation refers to opposing atmospheric pressure patterns in northern middle and high latitudes.

The oscillation exhibits a “negative phase” with relatively high pressure over the polar region and low pressure at midlatitudes (about 45 degrees North), and a “positive phase” in which the pattern is reversed. In the positive phase, higher pressure at midlatitudes drives ocean storms farther north, and changes in the circulation pattern bring wetter weather to Alaska, Scotland and Scandinavia, as well as drier conditions to the western United States and the Mediterranean. In the positive phase, frigid winter air does not extend as far into the middle of North America as it would during the negative phase of the oscillation. This keeps much of the United States east of the Rocky Mountains warmer than normal, but leaves Greenland and Newfoundland colder than usual. Weather patterns in the negative phase are in general “opposite” to those of the positive phase.

The chart below shows the AO over the past 90 days…the red lind at the very end is a forecast which we can ignoe for right now. Notice the AO was at its lowest point from December into early January, and then again in February. These were wetter months and also had temps close to average in Milwaukee. While the positive or higher points on the chart below occurred in January and March. These two months were over 1.23″ below average for precipitation and also warmer months.

Now that we have identified the patterns…what can be expected for April & May?

April Forecast

Precipitation: Above average…likely over 4.00″

Temperatures: Close to average.

Notes: Outside of the first few warm days in April, a cooler and more active weather pattern will set up. A storm around the 7-9 should once again occur. The last 8-9 days of April could bring 1″-2″ of precipitation to the area. We will also likely see some snow during the month. Quick shots of cool/cold air will likely push lows to 32 or lower at various times all month long. If you are looking to get an early start on planting this year…I would hold off for a while.

May Forecast

Precipitation: Below Average

Tempeatures: Above Average

Notes: If the trends continue this should be a warm month with below average precipitation. A warmer period may occur around the 17-24 of the month, and then a bigger warm-up the last day or two of the month that will extend into early June. This would be great news because Memorial Day is th 31st! I think a day of 85 degrees or warmer is likely sometime in May.

Thank you for reading the outlook and pattern that I am expecting over the next 2 months. If you have questions about the weather pattern, the April & May forecast, or just have some thoughts…please post them to the comments section of the blog.

Have a great day!

Jeremy Nelson

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4 Responses

  1. Snow in April. Hopefully it won’t be a lot. Let it rain instead. I am looking forward to hoping on the lawn mower for the first time this year.

    • Bryan,

      The grass is ‘greening’ up pretty quick. The rain this weekend will likely help out. We didn’t see much moisture in March…a pretty dry month.

      Jeremy

  2. I’d think the suggestion of snow is a bit of a stretch, but…

    2007… March 25 – high 79, March 26 – high 80
    April 11 – 7 inches of snow

    2009… March 17 – high 75
    March 28, 29 – 5 inches of snow

    The weather doesn’t play by the rules in Wisconsin.

    • I’d say we see more snow in April than we did in March. It wouldn’t take much…only 0.8″ this month.

      Jeremy

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