© 2019 Terry Swails

THANK THE TROPICAL PACIFIC....

February 10, 2017

 

I like to look at the tropical Pacific for clues to the long range weather pattern. One of the more telling drivers to look at is the MJO (Madden Julien Oscillation). There are 8 phases of the MJO and research finds that each has a temperature correlation here in the Midwest. These variables change from month to month. Tracking the forecast oscillations through the phases of a given month is usually a good indicator of what's to come in terms of temperature departures.

 

Currently, we're just coming out of phase 6 (which we've been in for over a week) into phases 7 and 8. Here's the temperature anomalies those phases correlate to. The dotted green line is the daily forecast, in this case from the EURO through February 23rd. The red arrow directs you to the departures for that phase in February. 

 

 

What's pretty obvious here is that temperatures in phases 6, 7, and 8 in February have proven to be near to above normal across the Midwest. Occasionally you will find a day or two where that's not the case but on average it's what's likely to occur.

 

The ensemble forecasts from the EURO EPS (an average of 51 members) are in good agreement and what you would expect with the MJO in the above phases. Here's what they are showing for temperatures the next 15 days in Cedar Rapids, Minneapolis, Chicago, and St. Louis.

Aside from the blatant warmth, these MJO phases correlate to dry conditions as well. Sure enough the models agree. The EURO has this for total precipitation the next 10 days.

The GFS has this for the same 10 day period. Dryness reigns!

 

One area I will pay attention to the next few days is the tropical Pacific between Darwin Australia and Tahiti. It's in this region where the SOI (Southern Oscillation Index) is measured. The last couple weeks the SOI has been in positive territory and today the index was lower but still positive at +.05.

The SOI is essentially the basis for the MJO. When the SOI is positive, temperatures here in the Midwest have a tendency to be mild. Notice below the last time we had a 2-3 week period of negative SOI values was late November through mid-December. It's no coincidence that was the last time the weather was consistently cold and snowy over my local area.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

So, when the SOI goes into negative territory it's generally a sign that pressures are rising in Australia, indicating energy is traversing east out of that part of the Pacific. In 6-10 days that has a response over the North American continent. The larger the negative departure, the more energetic the pattern is likely to become here at home.

 

Here are the pressure anomalies currently in place in the region around Australia towards Tahiti where the SOI is measured. Low heights (or pressure) in blue indicates low pressure and positive SOI values.

By February 17th notice the change. The blues are replaced by browns indicating higher than normal pressures in the western source region of the SOI. 

If this happens it should equate to negative SOI values. The question for me is how low do they go and how long does the trend last? If it's brief, chances are positive values return and we continue on with our mild ways with only a short interruption. In other words, more of the same.

 

If winter is going to make any sort of comeback in the Midwest this year that SOI needs to tank and stay negative for an extended period of time. Keep an eye on that index. Roll weather...TS 

 

   

 

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