What does it take for you to receive a snow day?
It’s winter weather season, so now the big question is “Will it be a snow day?”
It’s not an easy question to answer, as predicting when roads will be hazardous is far more difficult than predicting winter weather — and that is difficult too. Let’s put one thing to rest though.
Research shows that snow days are good for kids — for two reasons.
First, snow transforms our world and provides an opportunity for discovery and play that only comes a few times a year.
Second, research shows that having school on a snowy day is rather unproductive due to the disruptions and excitement caused by the snow. Science clearly says: Have the snow day!
But now to predicting these special days.
Forecast difficulty
People often get irritated with meteorologists when a winter forecast goes wrong, but think about what it takes to get that winter storm forecast correct.
During the rest of the year, when a weather system comes through, it makes no difference to most people whether 0.1 inches of 0.4 inches of rain fall. It rained.
In a snowstorm, that is the difference between 1 inch or more than 4 inches.
People get mad over those differences. In addition, the weather experts need to try to figure out the type of precipitation and that can also be tricky.
Specific heat
Let’s say that the forecast ends up being perfect. The difficulty is not over. Maybe 4-6 inches of snow will come down, but how much of that will accumulate on the roads? Sometimes this is more difficult that the forecast itself.
Every material holds and releases energy (heat) differently. You know this. On a summer night, a walk on the grass is cool on your feet while a step on the sidewalk is still quite hot.
This is because every material has a different specific heat capacity. Specific heat capacity is the amount of heat (in joules) that it takes to raise 1 kg of a material 1 degree Celsius.
Concrete has a higher specific heat than grass. Grass has a lower specific heat than soil. And water has one of the highest specific heats of any substance. This is why lakes and rivers take so long to freeze even when it is super cold outside.
When it gets cold and snow starts to fall, the snow will accumulate on surfaces with low specific heat capacities first — metals, grass, trees, roofs. It takes much longer for higher specific heat surfaces to cool to the point where the snow will stick on bare soil or concrete.
Therefore, if a snowstorm comes after several days of warm weather, four inches may pile up on the grass and the roads never really accumulate any snow.
Special cases
If roads cooled in a predictable pattern, then a formula could be used to easily determine when snow would start to stick. However, there are so many variables.
Melting takes energy, so every snowflake that melts on the road takes a tiny bit of heat away. Then some of the water on the road evaporates and evaporation takes quite a bit of energy from the surface it is on. This will cool the road quicker. A ball of sleet has far more ice in it than a snowflake; therefore, it takes far more energy to melt. All that energy has to come from the road, lowering its temperature. Wind blowing across the road will cool the concrete faster than calm conditions. So many variables!
So if you are hoping for a snow day after a few days of warm weather, your best scenario is temperatures falling to well below freezing, windy conditions, and a round of sleet before the snow kicks in.
When that snow day does come, sleep in, but then get outside and have some fun. It’s good for you!
If you want to follow along while John Warner Middle School science teacher Brian Earls and I work with our students on making weekly snow day predictions, watch for our weekly Twitter posts each Sunday night at either @szydlowskim or @scienceguy65203.
Mike Szydlowski is a science teacher and zoo facilitator at Jefferson STEAM School.
TIME FOR A POP QUIZ
What is specific heat?
Put the following materials in order from lowest to highest specific heat: soil, water, grass, concrete.
Write a sentence that explains the relationship between the specific heat of a material and how long it takes to heat or cool.
If a winter storm comes after a few days of warm weather, why do you want a round of sleet to fall before the snow if you are wanting a snow day?
If you see that temperatures are going to be really cold for a few days in early winter, why is it unlikely you will be able to ice skate anytime soon?
LAST WEEK'S POP QUIZ ANSWERS
What does “bumper crop” mean?
A bumper crop refers to when an unusually large number of crops are produced.
Why does masting increase the chances of an acorn going through winter uneaten?
Masting produces more seeds on a certain year than can be eaten by predators. This leaves plenty of seeds left to become oak trees.
What happens to acorn eater populations during mast years? How about the following years?
Populations of acorn eaters will go up during mast years due to how much food was available. However, those populations will fall on the following years when less food is available.
How does masting benefit the entire ecosystem?
Masting allows the ecosystem to pulse and produce a lot of offspring but then the weaker offspring are eliminated during the off years. This produces an overall healthier ecosystem.
Why do cicadas stay underground for so long before coming up?
Many animals love to eat cicadas. If they came out in predictable and steady numbers every year, the predator populations would increase to match. By coming out only every once in a while, the predator populations will not be able to handle the big years, leaving many to survive.
This article originally appeared on Columbia Daily Tribune: Nature follows this recipe to bring you a snow day
