Your intuition is probably telling you that it takes longer to stop on ice than on dry pavement, but let’s break it down into numbers.
It may take you an extra 200 feet to stop your vehicle on an icy surface compared to a clear road. That equates to about 10 seconds longer, or 4 times the three recommended car lengths.
This is relevant information considering the accumulation of ice that has been hiding under the top layer of snow since yesterday.
Here is the order of our transition from rain to snow. A fairly deep warm layer took a while to fully erode Thursday morning, which meant we had long spells of freezing rain and ice pellets before transitioning completely to snow.
Some communities in central Missouri reported half an inch to an inch of sleet before snow began to fall. That means we had a significant period of time where we had both a hot melt layer aloft and a layer deep enough below freezing here at the surface that it at least partially refreezed. I say partially, because we finally saw it freeze into a solid mass of ice, which means there must have been a liquid element.
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 also have contributed to the initial melting, creating a wet, melting layer of sleet.
Either way, temperatures dropped quickly on Thursday, allowing that layer of slush to freeze into a thick layer of ice as snow fell on it. Crews were then able to clear the snow, but not the thick layer of ice below, making the roads still treacherous on Thursday evening after the snow stopped. Now, we’ll have to watch out for hard-to-see black ice when freezing temperatures return. Now that the road salt and the sun are working together, the main roads are clearing, but tonight refreezing is possible on these roads.