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Cascades snow forecast, special on storm energy

Hello skiers,

Yes, its going to snow in the Cascades.

A weather system is coming in later today (Saturday night) into Sunday. The snow will be falling in the Cascades late tonight but mainly Sunday as the cooler air rushes in. Not a lot of snow, but the snow level will drop to 3,500 to 4,500 ft. Expect 1-2, but up to 4-6 in some spots on the mid to upper slopes (see map below). As a convergence zone develops Stevens and the Summit, may get heavy snow for a short period of time. Some of this new snow will eventually melt or evaporate away in the days ahead. However, some of the new snow will stay put in the shade and north facing slopes upper slopes.

BTW, snow doesnt really evaporate, but sublimates from a frozen solid to a gas (invisible water vapor). Snow (frozen water) can change phase straight to water vapor without melting, while a dry wind can accelerate the process.

Water is the most amazing thing, especially when it changes phases from liquid to vapor, then to a frozen form. ((See far below: Pacific storms, hurricanes and the Columbus Day storm of 1962.))

There is no snow right now on the slopes, so we are starting from dirt, except maybe some at Whistler in the alpine above the Roundhouse. Tonight and Sundays storm is cool coming from the northwest, which is often what we see in La Nina years. There is another storm coming in late Tuesday with 1-4. All models point to a continuing active pattern, so we are on our way but in just a small way right now. Its early to get overly excited, but the snow stoke is building.

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The Energy of Storms.

The storms coming off the Pacific, which plow into the NW and produce our powder days, are driven by the energy of a great global atmospheric conflict. Warm, moist air moving northward from the torrid tropics collides with cold, dry air plunging south from the frigid polar regions during the fall and winter. It is this grand collision of contrasting air types which creates the energy and drives the storms producing the unsettled winter weather in our mid-latitudes. Our north Pacific storms are some of the largest and most powerful storms on earth and in the end have a cold core overtaking the tropical influx of air from the south.

However, the energy which produces and drives hurricanes is a different animal. Hurricanes have warm cores and work like a heat engine. The energy of a hurricane is almost magical, a creation of pure physics.

Hurricanes are driven by a property of water called latent heat - specifically latent heat of condensation. It is heat released when condensation occurs and can be powerful in a warm environment like the tropics. Latent, of course, means it is hidden - this is where the magic takes place. Here is how it happens.

The ultimate mover of weather is heat from the sun. The earth, from north to south and over the ocean or land absorbs and reflects the warmth from the sun differently. In the tropics the sun warms the ocean. Once the ocean temperature hits about 80 degrees or warmer the stage is set for a hurricane. BTW, that 80 degree threshold is why we will never have a hurricane our offshore waters are in the 50s .

Back to our story. The tropical sun warms the ocean. Then the warm air above the ocean more easily evaporates the warm surface ocean water. What happens is the liquid ocean water is evaporated by the suns energy into invisible water vapor. This phase change from liquid to gas (water vapor) takes the suns heat energy and "hides" it. The evaporation process captures that sun heat energy and stores it into the water vapor. Then the warm air rises, without further heating the air. But that hidden warmth within the water vapor will reappear.

Here is the magic - why water is so fascinating. As the water vapor rises it cools. The cooling will bring the water vapor to a point of saturation, back to a visible liquid state (condensation) - a cloud, which is water droplets! Remember that warmth which was stored when the liquid evaporates that hidden heat is released when condensation occurs - forcing more vigorous rising air currents, further producing more clouds and thunderstorms. Once those smaller storms are organized into a rotating cluster of connected thunderstorms the genesis of a hurricane is born.

Given the right conditions, its a chain reaction that wont stop. A perfect heat engine of continuous evaporation and condensation of water, storing and releasing heat as fuel. The only thing which will stop a hurricane once it gets going is cooler ocean waters, moving over land both which disrupt the heat engine. Also, if the hurricane moves into strong upper air currents which can shear it apart.

Most, if not all of these hurricane killers can occur as hurricanes move northward. But then, even more magic can happen.

A warm core hurricane moving far enough north can morph into a cold core mid-latitude storm. The hurricane is the warmth and moisture from the tropics, moving north to collide and mix with cold air from the north as the high latitude chill dives southward to transforms the hurricane into a cold core Pacific storm.

This is not uncommon. This time of year, we see typhoons (hurricanes) move northwestward off Asia to near the Aleutians and make this transformation into a Pacific storm, then days later pummel the Pacific NW with rain or dissipate in the Gulf of Alaska.

The famous NW Columbus Day storm of 1962 had its origins in a typhoon by the name of Freda in the western Pacific many days before landfall in the NW. The Columbus Day Storm hit the NW with winds as high as (reported) 179 mph and is considered the greatest storm (not a hurricane or tornado) to hit the US in the 20th century.

To be perfectly clear, the Columbus Day storm did not have hurricane attributes by the time it hit Washington and Oregon. The storm had transformed and re-formed into a Pacific storm losing its warm core and acquiring a cold core. It was a rare storm with extreme lowering central pressure; 958 mb, and would have been equlavant to a Cat 3 hurricane at that low pressure. The ideal maximum wind storm track favored the greatest wind speeds for Oregon and Washington and we sure got them. It was all about the destructive wind, with insignificant rainfall.

Most people here in the NW, dont realize northern California was also hammered but with major and all-time record rainfall and rare major fall flooding for NorCal. The storm even delayed the World Series at Candlestick (SF vs NY). There was an atmospheric river (Pineapple Express) attached to our Columbus Day storm aimed at California which caused the heavy rain. Sacramento had 3.77 / 24hrs, Oakland 4.52 /24hrs.

What a day that was! The Columbus Day storm of 1962 shows we have some of the strongest storms on the planet and they can happen fairly early in the season.

Larry Schick - meteorologist
Grand Poobah of Powder

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