Practical Meteorology

Practical Meteorology is all about applying all that meteorological theory to actual weather observations and forecasts.  There were a couple things I'd forgotten.   For example, with cloud layers, anything with 5/8 (broken) coverage or greater constitutes a ceiling.  This is not true if the it is a surface based layer, such as fog or snow.  In this case, the coverage must bee 8/8 to be considered a ceiling.  

Also, there are some charts that I don't use on a daily basis, because they cover much larger areas than I need on my regular runs between Montreal and Toronto.  When doing my practice questions, I was getting questions with regards to issuing and validity times wrong, so I knew it was time to consult the AIM.  

Prognosis = Forecast
Analysis = Observation

Reference AIM MET 3.2.1 Aviation Forecasts and Charts

Significant Weather Forecast - PROG Chart

• prepared 4 times daily, based on 00Z and 12Z data
• issued 12 hours prior to validity time (00, 06, 12, 18Z)
• specific flight level range (i.e. 700 - 400 MB = FL100 - FL240; also FL250-630)
• indicate surface positions of lows, highs, and any significant weather (thunderstorms, turbulence, mountain waves, etc)
• a forecast area of turbulence implies a 50% probability of encountering turbulence somewhere within the depicted area
• jet streams are depicted when the core speed is forecast to attain 80 knots or more

Upper Level Forecast - PROG Chart

• issued 4 times daily, 12 hours before the validity times of 00, 06, 12, 18Z
• applicable FL240, FL340, FL390, FL450
• depicts forecast wind and temperatures for the chart level

Reference AIM MET 3.2.3 Weather Charts

Surface Weather Chart

• observed at 00, 06, 12, 18Z
• issued 2-3 hours after observation
• pressure patterns from surface up to 3000 ft
• surface location of fronts, precipitation, obstructions to vision

Upper Level Chart - ANAL

• observed at 00 and 12Z
• issued over 3 hours after observation
• show reported atmospheric conditions at the pressure levels, such as wind speed/direction, temperatures, moisture content
• the contours or altitude gradient can be considered as the slope of the pressure surface

Things I'd Forgotten

Over the past week, I went through 171 'General Meteorology' practice questions... I got 150 (87.7%) of them right.  So there are obviously a few things that I'd forgotten since studying for my IATRA a couple years ago.  A few examples:

Terminology

• Overrunning: condition existing when an air mass is in motion aloft above another air mass of greater density at the surface.  This process that results in expansional cooling, subsequent condensation and formation of cloud. Example: warm air ascending the surface of a warm front. 
• Altimeter Setting: station level pressure reduced to MSL assuming ISA conditions
• Land breeze: blow from land to water during the night
• Stationary front: a frontal zone separating two different air masses, neither of which is strong enough to replace the other
• Riming: the growth of a descending ice particle as it collides with nearby water droplets which then freeze onto the particle

Location of Supercooled Water Droplets:

• in unstable air: lower levels of cloud where temperatures are only a few degrees below freezing
• in stable air: amount of supercooled water increases with height when temperatures are not far below freezing

Microbusts:

• The shaft of a microburst is normally about 2.2 nm wide or less at the surface.
• Downdrafts associated with a microbust could be as strong as 6000 ft / min

Mountain Waves:

• Rotor clouds are normally centred beneath the standing lenticular cloud (i.e. below each wave crest)
• The most powerful rotor is located under the first wave crest

Upper-Air Contour Charts:

• The wind blows along the contours in the same way that the 2000 ft wind blows along the surface isobars (parallel to the height contours, with lower heights on the left)
• the closer the contours, the stronger the wind; and if the height contours are curved, then centrifugal force acts on the wind

And other random facts:

• Snow grains: imply that freezing drizzle is present aloft.
• The vertical extent of CAT associated with a jet stream will be greatest on the low pressure, cold air mass side of the jet stream core.

I'll plan to cover some of these topics in more detail soon!  It's a good thing I like Meteorology... hopefully I'll still be this enthusiastic when I come back to Radio Nav :)