Post #5: Larger Weather Patterns

There are several different factors to the weather systems that dictate the climate in Portland. One of the most prominent is the fact that the ocean is just to the west of the city. This allows maritime polar air masses to come from the west. These air masses are characterized by a cooler temperature and lots of moisture. These air masses dictate much of the climate of Portland as can be seen through the discussion following.

Looking at the below picture showing wind direction, it can be seen that 37% of the time the wind blows from the west. The wind that blows from the east can also be a result of the sea breeze effect, meaning that wind will change directions at night.

Average Time in Percentages of Wind Direction

 Mid-latitude cyclones can form above the ocean and come into Portland. These storms do not generally result in massive hurricanes, rather they bring condensation and cloud cover. They can be quite large in area. This makes it possible for the same storm to move in from the west and "remain" over the city for a few days at a time. The chance of rain on any given day based on averages can be seen in the graph below.

Chance of Rain During the Day

As can be seen, the chance of precipitation rarely falls below 20%. While this isn't a great indicator, it does offer a picture of how the precipitation the area receives ranges over the months of a year. Perhaps a better indicator of climate is to compare what kind of precipitation an area receives. This can be noted by the image below which shows the type of precipitation Portland receives.

Precipitation Type Percentages

Looking at this figure, it can be noted how prominent rain is in the precipitation Portland receives. This indicates a relatively mild climate where the temperatures rarely drop below freezing.

Images from:
WeatherSpark. "Average Weather for Portland, Oregon, USA." Weatherspark.com. 2012. Web. 7 April, 2014. http://weatherspark.com/averages/31237/Portland-Oregon-United-States