As we progress into the heart of winter, we often characterize its presence with the cold and frigid temperatures that embark on the Willamette Valley, where temperatures dip below the freezing mark.
Students and staff struggle to stay warm as they scrape the ice off of their cars and all attention is focused to the news stations as the word "snow" makes an appearance in the forecast for our area.
A cold front can advance into the Northwest, displacing warmer air, and bring a rise in atompsheric pressure, moisture, and cooler temperatures, as it sucks in Arctic air from the north and precipitation as another front comes in off of the Pacific. We then have the making for a snow event.
Unfortunately, we don’t see snowfall all that often in McMinnville; it may occur a couple of times a year, if even that. Sure we can look at a map and infer that McMinnville has a higher degree of latitude than Boston, for example, and so then we ask ourselves, "Why don’t we experience the cold and harsh winters like they do?"
The reason is simple. We have the Pacific Ocean just west of us. As the Jet Stream travels from West to East, warm marine air runs right over the coastal mountains and right into the Willamette Valley; almost like a soft and fuzzy blanket, bringing us moderate temperatures and what our area is famous for- RAIN.
When the Jet Stream has an occasional shift and fluctuates the wind currents, a colder air mass will push the warmer air out of our region and create a cold front as it makes its way down from the north.
Another scenario is that cold winds may generate in the Columbia Gorge and flow west, dispersing a blast of cold winter air into the Willamette Valley.
This occurs when a pressure gradient emerges in the Cascades, creating a difference in pressure between the east and west, which can then stir up those gusty east winds which then tear through the greater Portland-Metro region. Combine one of these two occurrences with a precipitated weather front, and we have the making for a possible snow day. But more likely than not, we seem to get either cold weather with no precipitation or vice versa.
Just remember: the weather outside is always changing, so keep up-to-date with the weather by looking at satellite images, dew points, barometric pressure readings, Doppler radars, and then you’ll be able to gain an accurate understanding of why the weather is doing what it is.