Across the great divide (well, a divide anyway)

Between Miles 13 and 14 of the Old Glenn Highway lies the divide separating the Matanuska and Knik valleys.  It has been more defined at times but in the same place on other days.

Several posts on this blog mention that at times the temperature here at the house will be 10 to 20 degrees colder than in town just 10 miles away and today was no exception. Fifteen below at the house, just about zero in town.  The geography of that circumstance has slowly been revealing itself over the years and today a distinct border was blatantly obvious.

But first a bit of geography.  That geography of the Matanuska-Sustina Borough is first defined by two valleys, the Matanuska River Valley and the Susitna River Valley.  It has always been an irritation that people and most of the area media refer to it as the Mat-Su Valley or just "The Valley."

Having lived in the Upper Susitna Valley (that's where the East Pole is) where the residents take the distinction seriously, I have always tried to use "valleys" or the specific valley.  Since moving here, I have discovered there is a third valley, the Knik River Valley.  Each of these has distinct weather patterns.  Most often, it will be coldest in the Knik Valley but with little snow and even less wind.  To the west, the Matanuska Valley, in the middle, suffers hellacious wind storms and receives very little snow.  

What there is usually blows away in the next wind blasts.  To the west and north, the Susitna Valley often is warmer and it receives more snow.  No mountain ranges define the distinctions between the valleys  at their lower ends and most of them are on relatively the same plane.  They are more defined by drainages.

For instance you would have to work at it to define the divide between the Matanuska Valley and the Knik Valley.  I doubt there is 20 feet difference in elevation along the road between the two.  Still whatever that difference is, it creates different weather patterns.

All that is to get to the discovery recently of the actual dividing line, a line made subtlely obvious as seen in the attached photograph which I took today.  Note to the right of center (east) the hoar frost in the trees.  And then the left (west) while there is some snow on the branches there is little or no hoar frost. 

The National Snow and Ice Center defines hoar frost this way:

Hoarfrost A deposit of interlocking ice crystals (hoar crystals) formed by direct sublimation on objects, usually those of small diameter freely exposed to the air, such as tree branches, plant stems and leaf edges, wires, poles, etc., which surface is sufficiently cooled, mostly by nocturnal radiation, to cause the direct sublimation of the water vapor contained in the ambient air.

 At the divide, at least two elements could create the phenomenon of the diffence on each side of the line.  One is that it is colder to the east, which is the Knik Valley, and that most likely creates conditions more conducive to the formation of hoar frost.  The other is that it is windier to the west in the Matanuska Valley and what hoar frost does develop is whipped off the trees.

Why bother with all this.  Curiosity.  Fascination.  Perhaps a need to understand.  What's next?  Explore and find one spot with the calm of the Knik Valley the warmth of the Matanuska (when the wind isn't blowing) and the snow of the Susitna.  Perfection.