Vince_Condella's Blog

When we step outside and feel the wind in our face, that is only one component of the global wind system.  What really matters is the wind aloft, not near the ground.  I'm speaking of the jet stream, a fast river of wind found above 25,000 feet.  It represents the boundary between warm and cold air masses, and this time of year it begins to snake south across the central United States.  That's when the ski resorts in the western U.S. get happy.

During the summer months, most of the lower 48 United States are under the influence of a warm air mass.  Cold air is trapped well to the north across northern Canada and the Arctic region.  So the jet stream remains well north of the U.S. - Canada border. 

However, now the colder air is beginning to creep south of the U.S. - Canada border as daylight hours get shorter and the Sun angle gets lower in the sky.  Here comes the jet stream, too, and with it low-pressure systems bringing rain and snow.

Tonight (Tuesday) we are getting a steady dose of rain as a surface low-pressure center located over Missouri rides northeast with the jet stream, tapping Gulf of Mexico moisture.  The long range computer models, however, are indicating an even bigger change this weekend.  A huge dip in the jet stream over the Rockies will allow cold air to spill south from Canada and produce areas of snow showers in Colorado, Wyoming, and Montana.

Meanwhile, the upper winds will pass north of Wisconsin this weekend as a huge ridge of high pressure builds over the eastern half of the country.  With the upper air winds north of us, cold air is pushed north of us and mild air moves in from the south.  Good news for us: a lot of sun and warmth this weekend.

So the upper air wind pattern produces cold air in the Rockies, warm air east of the Mississippi.  At least for this weekend.  But the jet stream is always on the move, meandering and changing shape.  Soon it will be our turn to be located under one of those dips in the jet stream and a shot of cold air.

For now, though, we'll enjoy the warmth and sunshine for the second half of this week!