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Insider Blog: Why there’s such a deep layer of ice on the ground after this storm

Your intuition probably tells you that it takes longer to stop on ice than it does dry pavement, but let's break it down by numbers.

It can take you an extra 200 feet to stop your vehicle on an ice surface compared to a clear roadway. That equates to about 10 more seconds, or 4 times the recommended three car lengths.

This is relevant information given the icy accumulation that's been hiding under the top layer of snow since yesterday.

Here is the order of our changeover from rain to snow. A fairly deep warm layer was slow to completely erode Thursday morning, meaning we had extended periods of freezing rain and sleet before we made the complete switchover to snow.

Some communities in mid-Missouri reported half an inch to an inch of sleet before snow started to fall. This means we had a significant time frame where we had both a warm melting layer aloft, and a deep enough layer below freezing here at the surface for it to at least partially refreeze. I say partially, because we saw it eventually freeze into a solid mass of ice, meaning there must have been a liquid element to it.

It may also have melted a bit initially after falling on a surface that hadn't yet cooled to 32 degrees. Any salt treatment on the roads may have also have contributed to initial melting, making for a wet and slushy sleet layer.

However it happened, temperatures were rapidly dropping on Thursday, allowing for this slushy layer to freeze into a thick sheet of ice as snow fell on top of it. Crews were then able to plow the snow, but not the thick layer of ice below, making roads still treacherous Thursday night after the snow had stopped. Now, we'll have to watch out for hard to see black ice as freezing temperatures return. Now that road salt and sun are working together, main roads are clearing, but tonight, refreezing is possible on these roadways.

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John Ross


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