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Snow Close, Yet Snow Far

by Matt Zaffino

Bio | Email | Follow: @Zaffino

Posted on December 27, 2007 at 9:00 PM

Updated Wednesday, Nov 4 at 2:47 PM

Unless you live above 500 to 700 ft, this snow forecast was a big fat bust. As I said in last night's blog, I was not real impressed with the potential for an all-out valley white-out. The computer guidance up to last night was pretty much saying snow, but a couple things needed to happen:

We needed really heavy precipitation rates! When that happens, melting snow cools the air and lowers the snow level. I've seen it happen here, but its rare, and difficult to forecast. We only needed cool a layer of air about 500 to 1,000 ft thick.

We needed a source of cold air! The east wind eventually picked up a bit in east Multnomah County, but the temperatures in and east of the Gorge were just too warm. We also had too much south wind.

If the low level air had been dry we would've had a better chance of seeing snow reach the valley floor because of evaporative cooling. Like the melting I described above, evaporation cools the air, even more effeciently than melting. But the air mass was saturated so there was no substantial evaporation to cool the air.

There was some decent snowfall in Clark County, and elevations above 500 ft.

Ridgefield, WA (100 ft) 3" Wow!
La Center, WA (650 ft) 6"
Clark County, WA (1400 ft) 7"
NW Portland (1200 ft) 4"
Cascade Locks 4"

So that's that one. I'm sure we'll have a few more chances of valley snow before spring.

Matt Zaffino
KGW Chief Meteorologist