Not So Ideal Weather Using ‘Ideal’ High School Chemistry

I hope my reference to High School Chemistry didn’t conjure up painful memories from your past; a la exploding graduated cylinders, or brutal Bunsen burner burns.

If not, please read on with an open mind.chemistry_book

Very basic chemistry explains why the Willamette Valley has been cold, foggy, gloomy and literally unhealthy for those with certain respiratory conditions.

So here comes the ‘hard’ part. Take a deep breath as I now present to you a very simple equation fundamental to science. Does the Ideal Gas Law ring a bell? All of the gasses we deal with in our atmosphere can be described using this handy equation.

P = ρRT

The simple relationship says. The pressure of any gas (P) is equal to the density of the gas (ρ) times the gas constant (R) times the temperature of the gas (T)

Okay, if you’ve made it this far the rest is easy.

Using simple algebra we can easily  rewrite this equation as such:

ρ=P/RT

Since the gas constant (R) doesn’t change – (duh it’s a constant) we can easily rearrange this to read:

ρ ≈P/T

This is an elegant little expression. It can be read like this: The density (basically the weight) of a gas (our air) is inversely proportionate to it’s temperature. Since our air pressure hasn’t changed much, it’s easy to see that the colder our air is (T), the denser it is as well (ρ). 

This relationship represents  the cornerstone of our weather lately.

The cold dense air is heavy and is resting right on top of us  in the lowest parts of the Valley. Since there are no buoyant forces to make this air rise, all of the dust, ash and other particles are trapped in this shallow dense air. We call this stagnant air. The longer this stagnant air sticks around, the more pollutants it adds. It’s kind of like adding a bit more salt to your soup day after day.

It’s unfortunate, because we have a giant ridge of high pressure aloft which would ordinarily give us unseasonably warm, sunny weather. Look at the temperatures on the mountain lately. 53 at Mt. Hood meadows today, 60s in the Coast Range. The low January sun angle isn’t strong enough to warm this layer up so it becomes less dense and lifts away. There is also little evidence of a major pressure change (AKA wind) to help move the gloom.

So here’s the real kicker: we may have to wait for rain to make us sunny again. How the heck can rain make it sunny you may ask?

Well, rain would mean an area of low pressure would move above us, it would also cool the atmosphere from above thus restoring the atmosphere back to equilibrium. A state where the temperature decreases with height, or the exact opposite of an inversion.

A Groundhog Preview

Will Punxsutawney Phil see his shadow tomorrow? Shadow or no shadow we are looking at a very springlike forecast as we begin the month of February.
A very weak disturbance moved through the district overnight and brought a little rain and mountain snow to the region. Skies have cleared out mostly and all I expect for the remainder of the day is an isolated sprinkle or flurry in the highest terrain.
Temperatures will top off into the low 50s in many spots with increasing amounts of sunshine. Due to the clear skies nighttime lows will dip to near freezing and even below in the outlying areas. Some frost and freezing fog are possible for the Thursday morning commute so drive with caution.
Long term models keep us mostly sunny and dry all the way through the weekend with cold nights and bright sunny days with highs in the upper 40s to lower 50s. An east wind will develop which should limit much of the AM fog.
Have a great day, Meteorologist Matt Brode
Follow me on twitter @mattbrode

A Little Rain Followed by Spring?

If you liked the weather on Monday, today should be nearly a carbon copy. Mostly cloudy skies today with some occasional sun-breaks. Overall temperatures should remain in the upper 40s, and I think we see less widespread 50s. Clouds lower and thicken overnight as a pretty weak rain maker approaches the area.
Rain should begin sometime after midnight in the valleys and continue through the morning commute on Wednesday. By Wednesday afternoon the rain is gone and we see the clouds begin to decay.
Due to the moisture, we may see some fog early Thursday morning, but breezy east winds will develop and sun will return to the region for most of the period through the weekend – and possibly even beyond.
Have a terrific Tuesday,
Matt Brode
Follow me on twitter: @mattbrode