Those beautiful days of 70 and 80 degree temperatures back in late Summer and early Fall are getting smaller and smaller in the rear view mirror, as we drive further into the cold weather months.
We’re in that time of year where our concerns turn to scary terms like “The Polar Vortex” and “Arctic Outbreak”. These sound like great names of Hollywood action adventure movies! But let’s take a look at how our atmosphere works and why we may be headed to a frigid period in the latter half of December with the possibility of a visit by the dreaded “Polar Vortex”.
So, the temperature difference between the warm equatorial regions and the polar regions results in a tremendous gradient in the density of air between these two regions. This gradient in air mass density creates strong changes in pressure from the beautiful, palm tree laden, tropical locales and the inhospitable, frigid polar regions. Because of our counter clockwise rotating planet, the air at higher altitudes (~20-40 thousand feet) is dragged along in counter clockwise fashion around the globe and flows at maximum speeds in those belts of strong pressure gradients between the chilly poles and the much warmer equator.
Our wonderful atmosphere is always in the process of balancing out the tremendous difference in temperature from the areas that get a minimum of solar energy at the north and south pole, and the area that receives maximum radiant energy along the equator.
Earth’s rotation, differences in atmospheric temperature at the surface and aloft, and a property of physics called the conservation of angular momentum, create movements of air toward the poles in the upper levels of the atmosphere and motion in the opposite direction, toward the equator, in the lower levels of the atmosphere. This circulation pattern is our atmosphere’s never-ending attempt to correct for the imbalance in radiant energy at the poles and the equator. Much of this movement of air around the globe is arranged in tight belts of high-speed wind flow that meteorologist call the jet stream.
What is the Polar Vortex?
The Polar Vortex is a special, high altitude jet stream that encircles the poles at around 60° north and south latitude. This ribbon of fast moving air is usually stable in terms of its position near the arctic circle; which means the vortex is usually more circular in shape as it wraps around the poles. However, this channel of high speed upper level wind flow can weaken and slow down when air occasionally becomes warmer than normal at these high altitudes around 50-100 thousand feet above ground level. This process is called stratospheric warming and causes the polar vortex to drift away from its typical location centered on the poles. Or, the vortex can sufficiently weaken to where it splits into two vortices.
When this happens, the polar vortex can drop further south into Canada; creating a massive trough of cold air across the United States. This configuration may remain in place for many days, funneling extremely cold air southward out of the Arctic into the mid latitudes. These are the incredibly cold periods that can occur in the winter months that are referred to as “Arctic Outbreaks”. In recent times the frightening term “Polar Vortex”, has gained popularity when referring to these record breaking, cold waves.
How will the Polar Vortex effect us in the Four States?
Cold weather fans will be very happy to know that medium range computer models are advertising a weather pattern just prior to Christmas that features a brief period of the dreaded “Polar Vortex”. It appears that from around December 15th to December 24th, the Four States area will experience temperatures that are below, to well below normal as a large area of low pressure descends through the center of the nation; funneling modified Arctic air all the way to the Gulf Coast.
And, to throw a little excitement into the mix, there is a chance for some snow in the days leading up to Christmas, in this cold pattern. Model forecasts show two low pressure systems that will traverse the Plains and midwestern states, and each of these systems may produce some accumulating snow in the area, just before Christmas. And, if this pattern takes just a little longer to develop and ends up slowing down just a bit; you never know….we may have a chance at a White Christmas. We’ll just have to wait and see what the atmosphere has in store for us!