Examining Yesterday’s Lack Of Severe Weather

June 27, 2018 0 Comments

It was in the forecast, but it didn’t pan out. Such is the life of a forecaster sometimes. I will say that no one hates missing a forecast more than me, but anytime we can get severe weather out of the forecast I am happy.

To best understand the weather scenario yesterday, I want to explain a comparisonĀ I like to use during our editorial news meetings. Severe weather (and many other kinds of weather) are like baking a cake – all of the ingredients need to come together in the right way in order to get the proper outcome. If you use half of the correct amount of flour, or too much butter and eggs, your cake will turn out different than what you are hoping for.

While we had some ingredients in place yesterday, they didn’t come together in the right way.

In order to get severe thunderstorms, you need to have the right combination of these four things:

  • Moisture
  • Lift – the ability to get air to rise.
  • Instability – the ability to have air continue to rise.
  • Wind Shear – the change of wind direction and/or speed with height.

The moisture and lift were there, but our weather earlier in the day affected what happened during the afternoon and evening. This was when the best combination of ingredients looked like it was going to come together.

In the morning hours into the early part of the afternoon, a line of showers moved toward us from the west. Here is what the satellite/radar looked like in the morning.

You can see how the line of showers dissipated before it moved in, but we saw lots of debris clouds which kept our temperatures lower and as a result lowered our instability.

There were severe storms to our north and south, however. Here’s a look at those storms yesterday evening.

Another map that explains this is by looking at the wind shear. Locally, wind shear did not pan out as high as some of our computer models had predicted, but there were higher areas of shear to our north and south. This is a map of a severe weather parameter called helicity. This can be defined as the ability for a thunderstorm updraft to rotate. This is important for tornado development.

You can see areas of higher helicity to our north and south, highlighted by the areas circled by blue circles. Note the area of extremely high helicity in eastern Missouri, which correlates to the complex of storms that moved through there.

The closest warning to us yesterday was just to our north along I-80 where a Tornado Warning was issued for parts of Henry and Bureau Counties.

There were multiple reports of funnel clouds and tornadoes across Illinois. Here is a look at central and northern Illinois. There were confirmed tornadoes outside of Champaign and Chicago.

So to recap, the severe weather potential was there yesterday, but all of our ingredients didn’t come together in the right way to produce severe weather. The moisture and lift were there, but cloud cover from earlier in the day limited our instability, and wind shear was lower locally than expected, but also high in other areas nearby.

Sometimes severe weather looks like a good bet, but it requires a lot to go right to get it. This is why it didn’t pan out yesterday, but maybe we won’t be as lucky next time.

-Chief Meteorologist Brian Walder

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