Arctic air masses and the hazards that come with them
If you stepped outside this morning in Central Missouri, you likely felt a sense of relief. With temperatures hovering in the 40s, it hardly feels like the precipice of a sharp turn in our weather pattern that could bring multiple hazards. This sharp change taking place over the next 24-48 hours is all being caused by a very large pressure system, known as a Continental Arctic (cA) air mass.
The air arriving this evening didn't form in the United States. It is a "source region" air mass, meaning it was formed in the Arctic Circle or Siberia, where it is almost consistently dark. This constant darkness leads to little to no heating from the sun, and this means that the deep snowpack has radiated its heat into space. This has led to the air becoming stagnant, dry, and dense.
Today, the polar jet stream buckled, opening the door for this heavy air to spill south. Because cold air is denser than warm air, this front acts like a physical plow. It is currently undercutting and lifting the lighter, warmer air we are enjoying right now. This sudden displacement is why the winds will gust to 40 mph before the temperature even drops. This is because the atmosphere is physically trying to balance the pressure difference between these two colliding air masses.
At first, the primary danger that is expected this evening is not accumulating snow, but it is rather the gusty winds paired with bands of heavier snow, leading to what is known as the threat of snow squalls. Snow squalls are a sudden, intense burst of snow paired with gusty winds that cause dangerous but brief whiteout conditions, as well as rapidly icing roads. The rapid freeze occurs due to the sharp drop in temperatures, where air temperatures at the start of the precipitation are above freezing, then quickly drop below freezing after any precipitation has hit the ground.
The danger that follows is the wind chill expected this weekend. Wind chill is important because it describes a physiological process called convective heat loss. Your body generates a thin layer of heat right above your skin, which acts as an invisible insulation suit. The strong winds accompanying this Arctic front constantly strip away the warm layer, forcing your body to burn energy rapidly to replace it. With the air being so dry, moisture also evaporates quickly from your skin, which further cools you. On Sunday, the most dangerous wind chills are expected, as temperatures will feel close to -5 degrees when walking out the door. In these conditions, it only takes 45 minutes to an hour to experience frostbite.
This cold is something to take seriously, as the specific combination of density, velocity, and dryness makes this air mass uniquely aggressive. Winterize your vehicle for ice, cover exposed skin to prevent rapid heat loss, and prepare for a weekend where the thermometer struggles to recover.
