Changes in the Wind: Observing the Jet Stream and Weather Fronts

My runs and bike rides this past week have been rather cold and wet.  The warm air I had been enjoying was replaced by moister, cooler breezes.  This change made me think about the jet streams, or rivers of air in the atmosphere that run between cold and warm air masses, and weather fronts.

Jet Stream Types

There are two primary jet streams in each hemisphere.  The polar jet stream type is found in latitudes of 50 to 60 degrees north and south of the equator.  Subtropical jet streams are found in latitudes 20 to 30 degrees north and south of the equator.  Since I live in Pennsylvania, the polar jet stream affects the weather in my area.  The polar jet stream is more forceful and is associated with chillier air swept down from the Arctic region.  As the jet stream dips further down into the United States, it pulls more Arctic air with it.

Illustration of the Jet Stream

Illustration of the Jet Stream

Source: http://www.climate.gov/news-features/event-tracker/us-temperature-extremes-and-polar-jet-stream

Jet Stream Influences

Jet streams are influenced by the seasons, air temperature, and locations of high and low pressure systems in the atmosphere.  In my area, it is spring and the air temperatures had been in the upper 60° F range, but dropped to the low 40° F range for a few days.  The change in temperature ushered in moisture in the form of rain that lasted three days.  From the weather map in my local paper, I learned a low pressure system had moved into the area.

Weather Map

Weather Map

Source: Pittsburgh Post Gazette, Wednesday, April 22, 2015.

Pressure Systems

High pressure systems carry with them air that slowly descends.  During the descending process, the air becomes warmer, which inhibits cloud formation.  This is why most high pressure systems are associated with more pleasant weather conditions.   There may be circumstances where high pressure systems do not bring good weather, but these cases are not the norm.

On sunny, clear blue sky days, high pressure dominates.  This helps make flowers bloom and plants grow.

Daffodils in bloom Lisa A. Wisniewski

Daffodils in bloom
Lisa A. Wisniewski

In order for the air to rise back up over different altitudes, it must cool.  As the air cools, the humidity within it condenses.  Depending on the amount of condensing that occurs, rain, snow, or other condensation (also known as precipitation) may fall.  This is why low pressure systems are typically associated with cloudy, stormy, or more inclement weather.

Cloud formation Lisa A. Wisniewski

Cloud formation
Lisa A. Wisniewski

Changes Just Like the Weather

Fortunately, jet streams and weather fronts move through areas.  Though some fronts may stall, or stay in an area for a few days, they do not stay forever.  A quick look at the weather map this morning shows high pressure moving into my area once again.  The signal for this to me was the sunrise yesterday and today’s clearer skies.  Hopefully, this front will stay a while and allow me to experience more enjoyable runs and bike rides for the next few days.

Sunrise April 25, 2015 Lisa A. Wisniewski

Sunrise April 25, 2015
Lisa A. Wisniewski

Resources and Related Links

Cloud formation – http://www.srh.noaa.gov/srh/jetstream/clouds/cloudwise/learn.html

Condensation – https://water.usgs.gov/edu/watercyclecondensation.html

High and low pressure fronts- http://usatoday30.usatoday.com/weather/tg/whighlow/whighlow.htm

Jet stream – http://www.livescience.com/27825-jet-stream.html

Polar jet stream – http://www.climate.gov/news-features/event-tracker/us-temperature-extremes-and-polar-jet-stream

Subtropical jet stream – http://www.britannica.com/EBchecked/topic/571160/subtropical-jet-stream

Weather fronts – http://www.livescience.com/39004-weather-fronts-definition-facts.html

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