Weather Maps Flashcards
The meteo society of Canada publishes two types of weather charts. What are they?
Surface and Upper Level charts
What is another name for Upper Level Charts?
Constant Pressure Chart
What are the two types of surface charts?
- Surface analysis charts (give actual information observed at a specific time
- Surface prognostic charts (give forecasted information)
On surface charts how are winds indicated?
An arrow shaft indicating degrees true in tens of degrees and velocity
How is the wind velocity indicated on a wind arrow on a surface chart?
- Half feathers: 5KTS
- Full feathers: 10KTS
- Pennants (triangle): 50KTS
How high up are pressure patterns drawn on a surface analysis chart?
Surface to 3000AGL
What kind of weather is included in a surface anylysis chart?
Any weather visible from the surface up to any altitude is included.
But only pressure levels up to 3000ftAGL
What is important to rememeber about surface analysis charts?
The info in them can be a few hours old as it can take up to 3 hours for the map to be drawn
Information in these charts is based on information taken at 00Z, 06Z, 12Z, and 18Z
The good thing about these charts is they allow you to see how weather has been developing over time.
Station Surface Analysis Chart legend
Example of Station Surface Analysis
Example of Surface Analysis Chart
When are Upper Level charts issued?
00Z and 12Z
What are the two types of Upper Level Charts?
Analysis and Prognostic
What kind of weather do the Upper Level Analysis charts show?
Reported conditions aloft for wind speed and direction, temperature, moisture, frontal systems, and pressure systems
Are usually around 3 hours old by the time they are pusblished (same as surface analysis charts)
Fronts not included in these charts unless they extend up to the pressure level o that chart
What are the four Upper Level Analysis charts?
250mb
500mb
700mb
850mb
What are the two Prognostic Upper Level Charts?
Significan Weather
Significant Weather, High Level
Why are upper level charts often refered to as constant pressure charts?
Because they are based on levels of constant pressure. Since you will always have your altimeter set to 29.92 in the areas these charts cover (Standard Pressure Region), we are no longer seeing the pressure at the surface and instead the H’s and L’s will show us areas where our true altitude will be higher or lower than indicated.
The GFA uses Sea Level Pressure
The H’s and L’s on Upper Level charts are not depicting areas of high and low pressure…what are they depicting?
The height of specific pressure markers. In the picture, 700mb of pressure would be found at different altitudes based on the temperature of the air in different regions. In a colder region, reaching 700mb of atmospheric pressure may happen as early as 8000ft of altitude. In very hot regions, it may take you all the way to 11000ft to reach 700mb of pressure.
So the H’s and L’s represent areas where that map marker (250, 500, 750, 800) is higher or lower.
The lines on upper level charts are not called isobars, they are called _______
Contours. Upper level charts are more like topographical hiking maps. The contrours show the heights of the atmosphere. The closer together the contours, the stronger the winds.
What is a decameter?
10 meters. Altitudes on upper level charts are given in decameters instead of feet for some reason
How do you convert decameters into feet?
Times the decameter number by 10 then times the answer by 3.
150 dM X 10 = 1500 x 3 = 4500
This isnt perfect, in fact its way off, the actual conversion of 150dM turns out to be closer to 5000ft but this is what they told us to use.
What are the average altitudes for the most frequently used constant pressure levels?
In Standard Altimeter regions, your true altitude will be constantly changing but why does this not matter?
Because everyone else also has their altimeter set to 29.92 so their altitudes change as well.
How far apart are contour lines spaced apart?
6 decameters except on the 250mb chart where they are 12 decameters apart
What are SIG WX charts?
Upper Prognostic weather charts
One is for the 700-400mb level. The other is for FL250 to FL630
What does xxx on a hi-level SIG WX chart mean?
The cloud base or weather is below the height of the chart
Upper level weather charts are issued ____ daily.
Two times daily at 0000Z and 1200Z
OCNL means…?
between 25% and 50% of the time
Surface Prognostic Charts are forecasts issued __ and __ hours before validity time
48 and 36
