Frost advisories have been issued for all of mid-Missouri this evening. This is as temperatures are expected to drop close to freezing, especially in rural areas.
If you have gotten your gardens going, it's important to take proper precautions for sensitive vegetation!
Here's a look at how frost forms.
During the day, the sun heats the earth-- the soil, the grass, the trees... everything around us. The ground has the capacity to store that heat throughout the day, but when the sun goes down, that heat will slowly be released back into the atmosphere.
When the heat is released from these surface they cool! (Wow, thanks captain obvious!)
But a pretty important thing also happens due to this cooling. An important property of the atmosphere is that as temperature cools, the likely hood of water vapor (a gas) to condense into water droplets (liquid). This happens when the temperatures drops to the dew point. Tonight, our dew point is forecast to be around 31*F.
As temperature approaches that dew point point, water vapor will condense into water droplets-- and because temperatures will fall close to freezing, those droplets will freeze onto surfaces!
So what's behind this nonsense cold? Yep. It's that thing again. The polar vortex. It's not just a December through February occurence. It can swing down from the arctic in the month of May. This cold snap is a perfect example.
This system will also be responsible for bringing the cold air which will bring accumulating snow to the northeast and bring a rare round of May lake effect snow to upstate New York!