During the summer months, storm patterns and tracks shift farther northward. By mid-summer, the threat for severe storms weakens and shifts to the central and northern plains states and the upper Midwest.
The impact of the longer duration of daylight is to warm the atmosphere enough to cause the jet stream pattern northward. As you may recall from our IQ Weather lessons, the jet stream is a main ingredient for strong storm formation.
When the jet stream drifts farther north and weakens during the summer months, severe weather becomes less frequent.
As the end of summer approaches, and the overall atmosphere begins to cool, the jet stream will typically begin to drift back southward slowly. That sets up a second min-severe weather season in the autumn.
Summertime is also the early part of the hurricane season! As of today, we have had 5 named storms so far. The peak of hurricane season is in September, and hurricane season does not end until the last day of November. As you...
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: