Dry December continues, but inversion is breaking up

Dec 16, 2011

A drought in December? It's been record dry this month, so far, says KPLU weather-meister Cliff Mass. In the meantime, we'll get a few showers, and possibly a glorious Saturday.

The off-shore pressure "ridge" is still there, keeping all the storms away from the Northwest. But, it's weakening, and the "inversion" -- which led to stagnant air, burn-bans, and so much fog -- appears to be breaking up.

For today, you may have noticed temperatures have warmed up, possibly reaching the 50's by late afternoon. And Saturday, while there might be some morning clouds, Mass is forecasting some sunshine by afternoon.

Then, by Saturday evening, some light rain arrives and persists into Sunday.

Next week, Mass sees more of this pattern ... a little rain, a lot of clouds, an occasional sun-break. But no storms anywhere in sight.

Have your feet been especially cold this past week?

It could be because the air temperature, especially when it's cool and dry, is quite a bit lower at ground-level compared to eye level. And the official temperature is always measured at head-level (technically, at two meters or approximately six feet).

"Any time the temperature gets to 35 or 36 on these cold clear -- or nearly clear -- nights, the surface could be at freezing," says Mass.

Mass tested this with his own hand-held infra-red radiometer, and blogged about it in detail. At his house in north Seattle, while the temperature at two meters was 30 degrees, his sidewalk was just 27. And his grass lawn? A mere 25 degrees.

"The surface is like a refrigerator coil. It's very good at radiating infrared energy to space," he says

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The weekly KPLU feature "Weather with Cliff Mass" airs every Friday at 9 a.m. immediately following BirdNote, and repeats twice on Friday afternoons during All Things Considered. The feature is hosted by KPLU’s Health and Science reporter Keith Seinfeld. Cliff Mass is a University of Washington Professor of Atmospheric Sciences and renowned Seattle weather prognosticator. You can also listen to a podcast of this and previous "Weather with Cliff Mass" shows.