Weather Brief: Medium and Long Range Weather Discussion

  • La-Nina likely to persist through the summer
  • Chilly weather next 1-2 weeks overall
  • Next month expected to be warm overall

Medium Range Forecast

Heading into the early part of May, it looks like the ensembles are thinking overall we will see below normal temperatures over the Great Lakes and Mid-Atlantic. This is likely a continuation of the weather pattern we have seen this past week. There will be some warm days mixed in, but persistent short-wave lengths across the Northern Hemisphere and North Atlantic blocking and also a block in the Western Canada/Alaska region, forcing colder air into Central Canada and the E US.

The North American Ensemble Forecast System pretty much says the same thing. Colder over the northeast into early May.

CDC Temperature outlook heading into early May confirms our suspicions of colder weather for much of the E US. For early May, that means temps likely in the 60s.

Long Range

The month of May will probably see near-normal conditions overall. A cold start will be followed by a warm period mid-month. Seems the ensembles and forecast system thinks we can actually turn quite warm in the back half of the month. We will see if that does happen but I think overall we are headed for a cool start, followed by neutral temps, and finishing the month off above normal.

The precipitation forecast is pretty normal for climatology this time of year. May is a rainy month in our area and it will likely stay that way this year.

MJO Forecasts

Taking a quick peak at the tropics, low frequency forcing will shift out of the dateline and back into the Continental Maritime. I think this lends credence to some of the rumors of La-Nina maintaining through the summer.

This will make it difficult to get a robust MJO wave to cross the Pacific. Again, sometimes we need a nice tropical wavetrain to get some monsoon rains and feed the plants. There will always be sub-seasonal variance, so for now we take it for what its worth but the forecast is generally not in our favor in the long term. Typically, monsoon rainfalls occur when the MJO is more strongly in phases 6-7-8.


Confidence is increasing in a multi-year La-Nina event. This one has origins from late 2020. The models indicate that we will stay in La-Nina mode at least through the summer months. Typically this is warm and dry for our region, but multi-year events aren’t common and tend to do their own thing. It is likely that the summer will be pretty hot overall. Both of the graphs below are just different ensemble model forecasts. Negative numbers indicate La-Nina.

We have seen some renewed sub-surface warming in the western Pacific, but this has to make its way east or it just reinforces the La-Nina SST pattern. The subsurface warmth has yet to make a significant influence in the actual SST pattern, which remains typical of a La-Nina pattern.

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