Q&A : We answer all of your cold weather questions

There have been a lot of ups and downs when it comes to the temperatures in Central Florida this season.

Of course in some states, having temperatures in the lower 50s and 60s right now would mean shedding the extra coat and enjoying an early spring. But for us in Florida it’s more like this:

For a state that rarely sees weather that prevents people from donning their flip flops, we thought it would be a good idea to go over some commonly asked cold weather questions.

Let’s begin.

Back to Basics: The right tire pressure

Why does my tire pressure light come on when it’s cold?

This is a big one. It happens every now and then. It’s a cold morning, you’re bundled up, running late for work and all of a sudden your tire light comes on when you start your car to add insult to injury. No need to panic! More often than not your tires are giving you a science lesson.

Just like us, air molecules move slower when it’s cold. They want to be warm and cozy so when it gets cold, the molecules huddle together. This lowers the pressure in the tire. When the air is warm, the molecules move faster and away from each other increasing the pressure in the tire. Tires lose or gain 1-2 pounds per square inch for every ten-degree change in temperature. You aren’t losing this air, it’s just taking up less volume within your tire. Once you are driving for a while, the molecules will move a little faster and warm up, increasing the tire pressure. This may cause your light to go off on its own. Once the weather warms up again, the issue should resolve itself. It is important to pay attention to the tire pressure because it is dangerous to drive on a low tire. Low tire pressure can also lead to lower fuel economy and a shorter overall lifespan of the tire.

How does frost form?

Speaking of being late, frost on your windshield can add extra time to your morning routine, especially if you’re not prepared for it. Frost forms on clear, calm and cold nights typically on cars, grass, plants and other objects close to the ground. Frost develops from objects radiating their heat into the atmosphere at night. If there is enough moisture available, frost develops. Some surfaces, like the rooftop of a car, radiate their heat faster and therefore can develop frost more quickly than other objects that don’t cool as fast.

Frost can form in two ways. The first is depositional frost when the dewpoint is below freezing. The dewpoint is the temperature at which dew forms. The dewpoint becomes the frost point when that number becomes 32 degrees or lower. Once the temperature of the object reaches the frost point, frost will develop.

In this case, water vapor, water in a gas form, goes directly to a solid-state. The liquid phase of water is bypassed. You can tell this type of frost developed because it forms crystal patterns on the surface it formed on.

The second way to get frost is when dew forms on an above-freezing object and then freezes as the temperature of that object falls below freezing. The dew forms when the object cools to the dew point, which is above freezing initially. The object will continue to cool under clear skies and calm winds. If the temperature of the object falls below freezing, the dew will freeze.

Frost only develops when temperatures at the surface are at 32 degrees or below. Sometimes, however, frost will develop when the temperature reading is in the upper 30s. This happens because the official temperature is taken six feet off of the ground. Cold air is dense and hangs out right on the ground, below where the official temperature is taken. The air a few feet below where the temperature is actually being recorded can be several degrees colder than what the official temperature six feet above is recording.

Frost can significantly damage or kill plants and crops. Covering your plants or bringing them indoors all together can prevent damage.

The National Weather Service issues a frost advisory when widespread frost is likely to highlight that action needs to be taken to save plants and crops.

What is a freeze?

A freeze occurs when the temperature falls to 32 or lower. A hard freeze is when the temperature falls to 28 degrees or lower. Plants and crops can be damaged or killed if action isn’t taken. Exposed outdoor pipes can also freeze or burst if the time spent below freezing is significant for an overnight period.

The National Weather Service issues freeze and hard freeze watches when temperatures could dip below their respective thresholds within the next 36 hours. Warnings are then issued when those thresholds are expected to be met.

What is wind chill?

Floridians are much more familiar with the heat index in the summer, how it feels when you factor in humidity than the wind chill. The wind chill is similar in the sense that it is an apparent temperature, perceived by humans when other factors come into play.

Wind chill is a real and important temperature and not something to make a cold day appear even colder.

The wind chill is the combination of wind speed and temperature. The wind chill gets lower when either the wind speed increases or the temperature drops. This temperature is important because frostbite and hypothermia can set in faster when the wind chill gets more intense. The wind works to blow away body heat that would otherwise hang out right around your skin. When that heat is blown away, you get colder faster. The stronger the wind, the more heat is stripped away from your body, and therefore the colder you feel.

Wind chill is calculated with this formula. Wind chill = 35.74 +.6215T-35.75v^.16+.4275TV^.16.

“T” equals temperature. “V” equals wind speed.

The National Weather Service issues a wind chill advisory when you should start thinking about limiting your time outdoors to prevent frostbite or hypothermia. A wind chill warning is issued when it becomes life-threatening to be outside for an extended period of time.

Thresholds are different depending upon what part of the country you live in. It takes a much colder wind chill for an advisory or warning to be issued in the northern states than it does in Florida since they are used to the cold weather and better prepared to handle it.

About the Author:

Jonathan Kegges joined the News 6 team in June 2019 as the Weekend Morning Meteorologist. Jonathan comes from Roanoke, Virginia where he covered three EF-3 tornadoes and deadly flooding brought on by Hurricanes Florence and Michael.