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.

Advertisements

Weather Advantage – The Mountains

Check Out This Graphic

ECMWF HEIGHTS

 It shows a massive ridge of high pressure over the entire Pacific northwest. A set-up means unseasonably warm and sunny conditions right? Not so fast.

The weather pattern we’ve been experiencing lately has been characterized by cold, saturated and foggy conditions. In order for this ‘gloom’ to go away we need this air mass to lift. Air that is able to lift is called unstable air. It happens when the air above us is cooler, which is generally the case.

But happening now is very mild air above us. In fact, this morning at 7000′ in The Cascades we are reporting temperatures in the upper 40s, while the Valleys are just above freezing. This creates a stable air mass – or air that is more difficult to lift.

Without geeking out too much, the set-up for the next several days favors the mountains. Our cold Valley air is dense, (cold air weighs more than warm air) and due to the weight and gravity, this air stays in the lowest locations and is locked in place due to the stability.

So this means people hitting the slopes will be enjoying spring-like skiing and coming off the slopes with sun tans.

In the Valley, we get to deal with air-stagnation, poor air-quality and cool temperatures despite the giant ridge overhead.

If we can get enough of an east wind, we could clear out and see sunshine and mild temperatures, but as of now it looks like this won’t happen. Our only hope is some late day sun to heat the air and give it some instability. But in the dead of winter with such a low sun angle I wouldn’t be too optimistic.

So, advantage – the Mountains.

Snow, Snizzle, What Is it Falling From The Sky Today?

A lot of people across the region are reporting some light snow on their lawns  this morning. A very cold and damp air mass is changing drizzle into ‘snizzle’.
Monday 'snizzle' covers the side of the road in SE Portland.
Typically in a setup like this, we get an inversion – meaning that the air aloft (above the ground) is warmer. This allows the cold air to sink to the lowest elevations. Cold air actually weighs more than warm air. We call this stable air.

An airmass is considered unstable, when lifted air continues to rise on its own because it’s warmer than the air above. Think about the old adage: warm air rises.

Since the air today above the surface is cooler, the surface air is rising, cooling and condensing out this moisture in the form of snizzle and sometimes light snow.

Science aside, as we make our way through the later half of today and especially all week-long, the air above will warm-up. This means that we return to a ‘typical’ set-up where the coldest air will remain along the valley floors with a lot of fog.

Air in the mountains and along the coast will be warmer and much sunnier.

Another shot – albeit a slight one for Valley snow

If you are a snow lover and hoping to see some more Valley snow, I have some good news and some bad news.

It’s been feeling very springlike lately with highs in the mid 50s. Now that’s warm for January standards; but enough of that, if one thing is certain, it’s that much colder air is moving in.

Rain will get going late tonight and through much of Wednesday. As the rain moves through a potent cold front also moves through. But as every north-westerner knows, how much moisture is available as the coldest air moves-in?

So here’s the good news: any precipitation that falls overnight on Wednesday and into Thursday should be in the form of snow. This means that all of us have a chance to see snow flying.

The bad news: it appears as though the brunt of the precipitation is in the form of rain when temperatures are too warm, so sticking snows are unlikely along the Valley floor.

Here is the latest 72 hour forecast from our in house RPM model.SnowCast_72hr

So it doesn’t look too promising for Valley snow to accumulate. But keep in mind, if any moisture hangs on for a longer period of time and the cold air (which can be pulled down quickly by intense precipitation rates) sets in, we may have to adjust our forecasts.

Right now I’d say anyone, even along the Valley floor, could see at least a dusting.

Most Of Oregon Had A White Christmas and A Dry 2013?

Unless you live along the Coast or in the Willamette Valley, chances are good you had a white Christmas.
From the Coast Range to the Gorge, to the Cascades and points east –

snow was in the air. Check out some of these snow totals. Christmas2012

Back in Portland Christmas was a wet day with cool temperatures in the upper 30s to lower 40s.
The front that brought the rain and snow is lifting out and behind it is cool showery weather.

So weatherwise, prepare for scattered showers for the remainder of the night with temperatures falling slowly into the upper 30s. If you are headed out to a movie, grab an umbrella and the rain gear, but overall the heaviest rain has ended.

Tomorrow some scattered showers will roll-in as the next weather maker moves to our south. Highs will be in the mid 40s.

Get ready for this breaking news: Thursday through next year – that’s right I said next year – should be mainly dry! Morning fog, followed by partly sunny skies is the forecast from Friday and beyond – courtesy of a dry east wind.

On A Final And Personal Note,although I was unable to be with my family today, I am grateful that we will all celebrate tomorrow in San Diego. Working with my wife Kacey is always fun, and my in-laws near Dallas, Texas had a wonderful Christmas surprise – A White Christmas. They sent me this beautiful picture which I showed on the 6pm news tonight. Dallas

Merry Christmas to all, and all a goodnight,

Weekends Rule in August

Have you noticed a peculiar weekend weather trend this August?

I have, and decided to crunch some numbers. We are nearing the halfway point of August and the weekends have been unusually hot. Lets look at the supporting evidence.

Below are the high temperatures for the first two weekends in August at PDX:

 August 4th: High: 102

Sunday August 5th: High 94

Saturday August 11th: High 87 degrees

Sunday August 12th: High 94 degrees

Contrast the weekend days to weekdays (Monday – Friday): The average high for these weekdays are 81 degrees – or 13.3 degrees cooler.

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

First Snow, Now Floods

After a snowy, cold start to our work-week mother nature has delivered a fire hose of moisture. Heavy rains and massive snow melt due to warmer temperatures have rivers and streams on the rise.
Here are some areas flooding right now:
South Yamhill River at McMinnville Pudding River at Aurora Clackamas River at Estacada Clackamas River at Oregon City Johnson Creek at Sycamore
Meanwhile the central Willamette Valley has seen the worst flooding from Salem and Turner.
As always, turn around if you see flooded intersections and roadways.
The other story over the past couple of days is the tremendous amount of snowfall in the Cascades. Here are some 48 hour snow totals:
Ski Bowl 25″ Timberline Lodge 21″ Mt. Hood Meadows 44″
a warm front slowly lifts through the region today, the heaviest rains will taper off by late afternoon. This will give the smaller rivers and creeks some time to subside, however, another storm will move through the region Friday with more rain expected.
Stay with us here at KOIN Local 6 for updates.
Matt Brode