- high pressure regions where air is stagnant (weaker pressure gradient associated with high pressure cell)
- arctic and polar plains in the northern hemisphere winter
- subtropical ocean regions in the northern hemisphere summer
- air mass will take on the temperature and moisture characteristics of the surface
- upper level winds drive air mass movement
classification convention : moistureTEMPERATURE
air masses migrating to the mid-west
| Arctic (A) | Polar (P) | Tropical (T) | ||
|---|---|---|---|---|
| coldest | cold | warm | ||
| Continental (c) | dry | cA | cP | cT |
| Maritime (m) | moist | mP | mT | |
-
surface chart on March 3, 2026 at 12z:
-
transition zone between two air masses with different characteristics
- usually temperature, but can be water vapor, wind speed, or wind direction
- development or sharpening of the difference is called "frontogenesis" -
stationary
- surface winds blow parallel to the boundary, but in opposite directions
- upper level winds blow along the front, or are very weak
- precipitation is usually not a strong feature of a stationary front, except in the summer -
warm
- views : plan and 3D
- mT (moist and warm) air is advancing, replacing mP (moist and cool) or cP (dry and cold) air
- speed is slower than the movement of a cold front, around 10 knots
- often will move in shifts or jumps
- the change in air characteristics (moisture and temperature) is slower because of the slower speed (relative to a cold front passge)
- relatively shallow slope of 1 km : 300 km
- overrunning - clouds and precipitation well in advance of the surface front
- broad area of gentle precipitation
- type of precipitation depends on the location relative to the front - rain to freeing rain to sleet to snow along a north - south axis perpendicular to the frontal boundary
-
cold
- views : plan and 3D
- occurs when cP or cA (dry and cold) air replaces mT (moist and warm) air
- significant temperature change
- significant moisture change
- wind shift
- relatively narrow band of clouds and more intense precipitation
- low pressure trough
- relatively steep frontal surface - slope is 1 km : 50 km
- steep slope is due to friction and fast movement, frontal speeds of 15 to 25 knots
- Ana-cold front and Kata-cold front
-
occluded
- views
- cold front moves faster than the warm front, so it catches the warm front
- this is known as a "cold-occlusion"
- approach is like a warm front
- passage is more like that of a cold front