Looking for a Snow Day
By Jillian Smoker, Grade 7
As winter approaches, many people anxiously await for a snow day, full of snow forts, snowball fights, sledding, and more. But sometimes, these snow days just won't come. This is because there are many conditions that there has to be for snow to occur.
Conditions For Snow
First of all, there needs to be enough moisture in the air so clouds can form and produce snow. This means, the more moisture there is, the heavier the snowfall will be. Even though snow is possible just at the below freezing point, it is more often to occur in the 0º F - 10º F range. The next thing you need for snow is a front, which happens when two different types of air clash with each other. This front is necessary for clouds by forcing the air up into the atmosphere. Last of all, atmospheric instability is needed to help air rise quicker so snow can form quicker. The less stable the atmosphere is, the heavier snowfall there will be and the more narrow the band of snow will be.
How Snowflakes Form
A snowflake forms when a cold drop of water freezes around a dust or pollen particle and it turns into an ice crystal. This ice crystal's inside order of water molecules (which are V-shaped) allows it to be patterned and always form a six-armed snowflake. The shape of the ice crystal's six arms depends on where it drops in the atmosphere, which is why not one snowflake is alike.
Different Types of Snow
The two main types of snow are wet snow and dry snow. Dry snow happens when the snowflakes fall through dry, cool air, making them small, powdery, and unable to stick together. This is the kind of snow that would blow easily in the wind and come in flurries. When it is slightly warmer than 32º F, wet snow can form when the edges on a snowflake melt, making it able to stick to other snowflakes. Snowmen and snowballs are the easiest to make with this kind of snow.
Snow for West Chester
In Philadelphia, snow usually appears from as early as November and as late as January. For West Chester in particular, the most snow usually comes in February with an average of 7.5 inches of snow. The latest that snow can come is usually in April.
Citations:
https://www.weather.gov/fsd/news_bandedsnowfall_20151121
https://www.currentresults.com/Weather/Pennsylvania/Places/philadelphia-snowfall-totals-snow-accumulation-averages.php
https://www.noaa.gov/stories/how-do-snowflakes-form-science-behind-snow
https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/snow/how-does-snow-form
https://weatherspark.com/y/22733/Average-Weather-in-West-Chester-Pennsylvania-United-States-Year-Round