Warm front
Moves slower (usually 10-25MPH)
Contain warm air that often has a high humidity
Bring Low celings
Poor visibility and Rain
Generally less intense
Cold Front
Cold front moves faster (25 to 30MPH)
Stays close to the surface, snowplow sliding under the warmer air and forces the less dense air up
Rapidly ascending air causes the temperture to decrease and forces the creation of clouds
Stationary front
Two air masses that are relatively equal
Weather is typically a mixture that can be found in both warm and Cold fronts
Occluded Front
Fast moving cold front catches up with a slow moving warm front
Warm front weather prevails but is immediately followed by cold front weather
Cold Occluded Front
Fast moving cold front is colder then the air ahead of the slow moving warm front
The cold air replaces the cool air and forces the warm front up into the atmosphere
Creates a mixture of weather found in both warm and cold fronts
Warm occluded Front
Air ahead of warm front is colder than the air of the cold front
The cold front rides up and over the warm front
The air is forced aloft by the warm front occlusion is unstable, the weather is more severe then the weather found in a cold front occlusion
Embedded thunderstorms, rain, and fog are likley to occur
Radiation Fog
On clear nights with little to no wind
It occurs when ground cools rapidly due to terrestrial radiation and the surrounding air reaches its dew-point
Advection Fog
Warm, moist air moves over a cold surface
Wind is required to form advection fog
Above a wind speed of 15kts, the fog usually lifts and forms low stratus clouds
Upslope Fog
Moist stable air is forced up sloping land features like a mountain range
Also requires wind
May not go away in the morning and can presist for days
Steam Fog
When Cold, Dry air moves over warm water
As the water evaporates it rises and resembles smoke
common over bodies of water during coldest times of year
Ice Fog
Occurs in cold weather when temperature is much below freezing and water vapor forms directly into ice crystals
Precipitation Fog
When Raindrops fall and evaporate into cooler air, increasing its humidity until it becomes saturated and fog forms
Microburst
Degrades performance, producing strong turbulence and hazardous wind direction changes
5-15 minutes can produce downdrafts of 6,000 feet per minute and headwind losses of 30-90 knots
High pressure system
Downward, outward and clockwise
Low pressure system
Upward, inward and counterclockwise
Sigmets
Issued for:
1. Severe Icing not associated with thunderstorms
2. Severe or extreme turbulence or clear air turbulence (CAT) not associated with thunderstorms
3. Dust or Sandstorms that lower surface or inflight visibilities to below 3 miles
4. Volcanic Ash
Valid for 4 hours, unless it is a hurricane in which case it is valid for 6 hours
Convective Sigmets
Issued for:
1. Severe thunderstorms with surface winds greater then 50 knots
2. Hail at the surface greater then or equal to 3/4 inch in diameter
3. Tornadoes
4. Embedded thunderstorms
5. Line of thunderstorms
6. thunderstorms with heavy or greater precipitation that affects 40 percent or more of a 3,000 square mile or greater region
Issued 55 min past the hour, valid for 2 hours
