Jeff Renner's Top 10 Weather Questions

1. Why is there such a big difference in the weather between Western Washington and Eastern Washington?

The Cascades usually prevent the moist ocean air, which dominates weather in Western Washington, from reaching Eastern Washington. Moist air changes temperature more slowly than dry air, which keeps average summer temperatures in Western Washington in the low-mid 70s. It also keeps winter temperatures from plunging into a deep freeze very often. Eastern Washington summer temperatures average in the mid-upper 80s. The drier air east of the Cascades can heat up or cool down rapidly, resulting in greater extremes in temperature throughout the year.

2. Is Puget Sound really the wettest area in the country?

Not at all. Seattle, for example, is well down the list of major cities when it come to yearly rainfall, trailing even Boston, Miami and Atlanta. Seattle averages 38 inches of rain each year, while Boston averages 44 inches, Atlanta 48 inches and Miami 57 inches.

3. What are the wettest and driest days of the year?

The driest day in the Seattle area has historically been August 4, when it has rained only six times in the past century. The wettest day? November 19, when it's rained 74 times over the past 98 years!

4. Why are some areas, such as Bellingham and Enumclaw, so much windier than others?

Wind is the result of air moving from high pressure areas into low. The bigger the difference in pressure between two places, the faster the wind moves. When this air is forced through a narrow gap such as a mountain pass, it speeds up evens more. That's why areas such as Bellingham and Enumclaw, which are near mountain passes or river valleys, often record the highest wind speeds in Western Washington.

5. What exactly is high pressure? What about low pressure?

High pressure is an area of sinking air. As it sinks, the air warms and tends to evaporate moisture, and that's why we often associate clearing skies with high pressure. Low pressure is an area of rising air that cools, causing the water vapor to condense into cloud droplets, raindrops or snowflakes.

6. What's the difference between "rain" and "rain showers" in the forecast?

Meteorologists forecast "rain" when they expect the wide, flat stratus clouds that produce rainfall over large areas. When puffy cumulus clouds are expected, meteorologists forecast "rain showers" because these clouds may cause rainfall over your house, while your neighbor across the street might remain dry.

7. Why does the weather vary so much from one spot in Western Washington to another?

Fly across Washington State and you'll find few flat areas. This state, particularly the western half, is covered with mountains and hills. Air rising up a hill or mountain cools, which in turn tends to create or enlarge clouds and increase their ability to produce rain or snow. Conversely, air sinking down the back side of a hill or mountain gets warmer, which tends to destroy or reduce clouds and their ability to produce rain or snow. For that reason, changes in the wind direction and the presence of hills and mountains make a big difference in local weather.

8. Is weather tougher to forecast in Western Washington than other places?

Yes. Western Washington is considered one of the most difficult places to forecast weather for several reasons. Most storms approach us from over the Pacific Ocean, where there are few weather observation stations. Our region's many mountains and hills also produce weather that differs a lot over short distances.

9. When does Western Washington usually get its first snowfall?

December 3 marks Western Washington's average first day of snowfall. We have a 13% chance of having a "White Christmas."

10. When does the first killing frost usually arrive in Western Washington?

The earliest killing frost officially recorded in the Seattle area was on October 16, 1946. The average data for the first killing frost is November 2. However, rural areas, especially sheltered valleys, will often experience an earlier killing frost.

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