ASK THE METEOROLOGIST
“Why don’t we have tornadoes in Oregon; is it based on weather patterns, jet stream or topography? Which state has the most tornadoes and which the least?”
Derek Cole, Medford
One of the main reasons we don’t see a lot of severe weather across the Pacific Northwest is the lack of very humid air. Sure, we get rain …but the summer months tend bring in much drier air than the winter months. Moisture content is very low and this supports dry thunderstorms as opposed to classic thunderstorms like the Midwest.
The main reason for this is the cold ocean temperatures along the West Coast. The Pacific Current runs from north to south down the coastline (bringing in cold water from the Gulf of Alaska). When looking at the Great Plains, moisture is very abundant and comes from a very humid source — the Gulf of Mexico.
In addition to the lack of moisture, the topography does comes into play. Tornadoes and severe weather tend to develop more-so over flat terrain. The flat terrain allows temperatures to warm considerably into the afternoons and allows moisture to come in and settle near the surface. This is not always the case with mountains and valleys.
When areas of low pressure trek across the country during the spring and summer, cold air meets very warm air. Cold air is brought in from the storm system, and warm air already exists from the sun and the Gulf of Mexico. This clashing of air forces warm air (less dense) to rise. Rising air is what’s needed to initiate thunderstorms.
The most tornadoes from 2013 was in Illinois, however much of the Plains down into Texas had more than 60 tornadoes last year (per state). Less than 10 per state were recorded across the New England states and the West.