East Wind Season Is Over

March 9, 2011

I’ve been putting together graphics for a winter recap AMS meeting and noticed this.   It probably confirms what a lot of you “east county” folks noticed:

We didn’t get nearly as much east wind this winter compared to the last two.  Most likely no complaining about that!  Last winter we had 77 days (November-February) with peak easterly gusts over 25 mph; this year only 40.  That’s a significant decrease.  Also, for a second winter we avoided any unusually high/damaging wind like we saw in January 2009.  The numbers here represent November through February.

The easterly Gorge wind disappears rapidly in March, and actually reverses to a dominate westerly wind by the time April rolls around.  The main reason is that “inversion season” ends; cold air doesn’t sit around long east of the Cascades in the lower elevations because of the increasing sun angle.  The Dalles, Pasco, Hermiston; all those folks see average high temperature rise above Portland’s by late month.  So far fewer periods of high pressure locked in eastside like we see in Winter.  The east wind is driven by that pressure differential across the Cascades.  In fact west wind becomes more common in the 2nd half of the month.  The 2nd (minor) cause of the wind reversal  is that we don’t get as many strong low pressure systems moving up against the West Coast, helping to pull that air through the Gorge.

Of course we will still get gusty east wind at times through the Spring, but for no longer than 12-24 hours at a time; either when a strong low approaches the coast, or more likely high pressure eastside along with it’s sunny/warm weather.  

 Chief Meteorologist Mark Nelsen