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A Mid Winter Forecast Snapshot

Each year I like to look at comparisons of snow cover across the U.S., the ocean temperature anomalies, and the upper air flow to find good ways to correlate these three seemingly unrelated factors in our winter weather.

The best way to do this is to take a snapshot of all three conditions on the same date for separate years. That way you are comparing apples to apples.

This winter we have a developing strong La Nina…cold water across the equatorial Pacific…with a stripe of warmer water extending across the northern Pacific Ocean…pointing to the NW coast of the U.S.

Take a look at the ocean temperature anomalies, snow cover and upper air flow for this year:

 

Now, go back to 2016, which was a snowier winter. Here are the three maps for that winter, which was dominated by an El Nino…warmer than normal water in the equatorial Pacific:

 

If we go back yet another 5 years to 2011, another La Nina winter, you can see the three maps:

 

By comparing the 3 you can see some interesting features develop.

  1. Snow cover by mid-winter during an El Nino year is typically a bit more robust than in a La Nina. That may seem to be counter-intuitive as you would expect cold water to produce more snow. But an El Nino over Pacific actually infuses the air with moisture, as you have learned in you IQ Weather course.
  2. The position of the warm water across the north Pacific determines the anchor location and strength of the upper-level flow. Notice that during both of the La Nina year, the Pacific vortex was anchored farther west in the north Pacific Ocean. This is quite important as it affects the flow pattern of weather systems as they approach the west coast…they tend to be weaker and easily split apart.
  3. During the El Nino year, notice the anchor position of the Pacific vortex is farther east and much stronger. That helped to bring powerful storms ashore along the west coast of the United States, and provided more frequent opportunities for storms that produced snowfall. And, you can see a much more snowy looking snow cover map with the El Nino year!

 As we have stressed throughout the IQ Weather course, the oceans play a huge role in determining the weather patterns around the globe. This is just one example of how that happens….and how we take that knowledge and use it to forecast weather.

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