How to Use Aviation Observation Maps
Observation Weather Maps
Both US flight rules and upper air analysis maps are shown the lastest observation.
US Flight Rules
Visual Flight Rules (VFR) - the pilot has the responsibility for seeing and avoiding other aircrft, towers, mountains, etc.
* Marginal Visual Flight Rules (MVFR) - conditions between VFR and IFR. Generally defined as visibility between 3 and 5 miles, and ceilings between 1,000 and 3,000 feet.
* Instrument Flight Rules (IFR) - the pilot may be in clouds, flying solely by instruments, and therefore unable to see other aircraft. The controller takes the responsibility for aircraft separation.
* Low Instrument Flight Rules (LIFR) - ceiling below 500 feet AGL and/or visibility less than one mile.
Upper Air Analysis
Wind Barb - the symbol in white which indicates both the wind direction and speed. It points in the direction "from" which the wind is blowing. Each short barb represents 5 knots, each long barb 10 knots. A long barb and a short barb is 15 knots.
Temperature - the number in the upper left in degrees Celsius.
Dew Point Temperature - the number in the lower left in degrees Celsius.
Pressure - the number in the upper right which represents the last three digits of the observed pressure reading in millibars (mb).
Here is an example:
Forecast Weather Maps
Forecast model maps are derived from the Global Forecast System(GFS) by NCEP. Flight levels are in Feet(x100).
Shows winds at different flight levels. Jet streams can be identified through these maps.
Shows temperatures at different flight levels.
Shows instablity of the air at different flight levels in terms of the Richardson number(Ri). It is a measure of the ratio of the work done against gravity by the vertical motions in the waves to the kinetic energy available in the shear flow. In general, the smaller the value the less stable the flow with respect to shear instability. The most commonly accepted value for the onset of shear instability is 0.25. Once turbulence is established within a shear layer, energetical considerations indicate that it should be sustained so long as the value is less than 1. Freezing Level Shows freezing level in height (feetx1000).
How to is by weatherunderground.com