Garrett’s Blog: How Freezing Rain Develops
It’s all about the Elevated Warm Layer.
This is a great image from National Weather Service that describes how freezing rain forms. Why freezing rain instead of snow? It has everything to do with the depth of the warm layer aloft and the shallow cold air mass at the surface.
Tonight, a warm layer is moving into Arkansas around 5,000 feet above the surface, it’s about 2-3,000 feet thick and is around 46 degrees! Down at the surface, we’re looking at a shallow cold air mass. This is a function of the cold northeast winds we’ve been seeing as Arctic high pressure influences our area from the north central plains.
The east wind will keep the cold air in place at the surface while the south winds around 5,000 will move warm, moist air into the middle of the atmosphere.
As precipitation occurs higher in the atmosphere, it falls as snow… and then melts when it hits the warm layer. If the cold air is deep enough, and it has time to re-freeze; it hits the ground as sleet. If it’s too shallow it has no time to re-freeze and hits the ground as a liquid and freezes on contact with the surface.
With this storm system the shallow cold air will be in place with an unstable warm layer aloft. This could result in freezing rain if the temperatures remain below 32 which is possible given the strength of the cold east wind which continues to push the dry cold air into our area.