- Air Masses
- Air masses are explained quite well in the Lab introduction, therefore I will not spend much time with them here. The main idea to keep in mind is that air masses are defined by WHERE THEY ORIGINATE and not where they currently are. Therefore, WIND DIRECTION is the best variable to determine which air mass is located in the region being considered.
- Station Model
- Station models are explained quite well in the Lab introduction, therefore I will not spend much time with them here. Common mistakes are not rounding wind speed to the nearest 5 kt and/or cloud cover to the nearest 25%. Also, units are NEVER placed around the station circle.
- Fronts
- A weather front is a boundary between two distinct air masses. That means that on one side of a front the following weather variables should be quite different than those on the other side of the front: wind direction, dewpoint temperature, air temperature.
- WIND DIRECTION IS THE MOST IMPORTANT VARIABLE WHEN LOCATING A WEATHER FRONT! Since wind direction will relate to the air mass, wind direction will shift dramatically when a front passes. For example, the winds in the warm air ahead of a cold front will be southerly, but the winds in the cooler air behind the cold front will normally be from the northwest.
- Question #11 in the lab is a good example of the various shifts of weather variables with frontal passage.
- Clouds are good indicators of weather fronts. Since cold fronts lift warm, humid air vertically, the clouds along a cold front tend to be vertically developed (cumuloform). These clouds tend to produce showers and thunderstorms of short duration (minutes or hours). Since warm air rides over cold air ahead of a warm front, clouds are more horizontally developed (stratiform). These clouds tend to produce steady precipitation (many hours or a few days).
Helpful Links:
Lifting Along Frontal Boundaries
Cold Front Clouds/Precip Animation
Warm Front Clouds/Precip Animation
Penn State Weather Tutorial
Surface Station Model Decoding
Current US Station Model Plots - Print to practice finding air masses and fronts
