Flight Plan

My flight plan....to encourage, mentor, guide those pining for the sky. I'm also here to virtually open the flight deck door for those who want to take a peek at the many aspects of aviation.....enjoy!

...and welcome aboard!...


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Friday, March 19, 2010

Mountain Meteorology- Metman Morris

Captain Doug near the top of Blackcomb (Whistler, B.C)

Mountain Meteorology

There's synoptic meteorology and then there's localized meteorology. Weathermen and pilots are always analysing weather - well at least I do. I'm back home from three days of skiing, but here's some meteorological facts to ponder.

From another post, I already alluded to lapse rates - the rate at which temperature changes with height. There's the dry 3C/1000 feet, wet (moist) 1.5C/1000 feet and the normal lapse rate 1.98 C/1000 feet. Of course we pilots round it off to 2C/1000 feet. Anyone know what the term is when temperature increases with height? (Answer: inversion). Anyone know how many types of inversions there are: (Three: nocturnal, frontal and subsidence).

By knowing the temperature and dew point one could figure out the cloud base assuming a dry lapse rate and then switch to 'wet' at the clous base to figure out the freezing level. They ask this stuff of the commercial pilot exams. The second day of skiing saw moderate rain at the base of the hill turning quickly to snow by the second chairlift. By the third chairlift one was into blizzard like conditions. Another meteorological trend - winds increase with height.

As well, visibility can go from unlimited (15 statute miles is considered unlimited due to the curvature of the earth but you'll see places like Calgary, Alberta report 40 sm because they can the Rockies) to near zero visibility in fog (cloud forming along the hill). The big term for this is "orogrpahic lift." Prior to the revolution in weather reporting i.e. pre-METAR, zero visibility was reported as WO X OF. (indefinite ceiling at zero feet, obscured with zero visibility). Now I think it translates into O Sm VV OO (Zero statute miles and vertical visibility zero hundred feet). You may hear the term WO X OF from the senior pilots.

On a side note, I skied during the Paralympics and one event was downhill racing for the blind or partially blind. So when I skied into poor visibility I thought about these skiers. They follow a "lead" skier and communicate through headsets. Can you imagine going full tilt down a hill skiing IFR?

So I mentioned about temperature, rain/snow boundary, freezing levels, visibility and now pressure.

The highest point on these twin mountains is 7349 feet A.S.L. The typical cabin pressure of an airliner is 6000 to 8000 feet above sea level. One could feel the effect of pressure. A little weaker, light headed and sometimes headaches. Can you imagine what happens when you add a bit of alcohol? This happens daily on flights. I liken passenger flying to "wining and dining in the Swiss Alps."

The peak's height is below the 700 mb chart which represents conditions at 10,000 feet but is higher than the 850 mb chart at 5000 feet. The CN Tower is 1815 feet. Whistler/Blackcomb has 5133 feet of vertical (from the top to the base). Three CN Towers!

Why am I comparing the two? Well to give some appreciation of pressure differential, a well developed low pressure system is abut 980 millibars. A solid high pressure system would have a reading of say, 1040 mbs (millibars). The difference between the two is 60 mbs, enough to cause gale force winds and lots of weather. One millibar roughly translates into 30 feet in altitude. So the height of the CN tower translates into 60 mb. Thus the difference from the base of the tower to its top is enough to drive most storms. Food for thought.

Hear ends my meteorological lesson.

On a humorous note. Here's one comic from Farside regarding mountain flying. Let's hope everyone has a GPWS (Ground Proximity Warning System) on board.

Say what's a mountain goat doing up here?

Say...what's a mountain goat doing way up here in a cloud bank?


Tim said...

Looks like you're having fun!


From the Flight Deck said...

Hi Tim. Overall it was fun, but I had to slow down quite a bit because of my wife, younger son and daughter. That proved to be a little exasperating. They did let me ski on my own. I didn't fall once in three days. That only proves one thing. I skied like a little old lady. :)