S190 Unit 6 & 7 Critical Fire Weather Factors & Alignment

Front

List Critical Fire Weather factors

Back

• Drought

• Unstable air 

• Dry Lightning

• Strong & Shifting Winds

• Warm Temperatures

• Low Relative Humidity

These factors, combined with receptive fuels, may result in extreme fire behavior.

Front

Critical relative humidity (RH) on the East Coast?

Back

• 40-10%

Generally here in NJ below 30% becomes a heads up situation that leads to the issuance of Critical Fire Weather statements, especially in combindation with wind.

Remember low RH leads to lower fuel moisture and increased spotting potential.

Front

Why is instability of the atmosphere a Critical Fire Weather

Back

Unstable air enhances upward motion, promoting vertical growth and increasing oxygen availability. This creates conditions favorable for fire whirls, gusty winds, plume-dominated fires, and dry lightning.

Ustable Air Enhanced upward motion leads to: - Vertical growth - More oxygen

Front

What does this diagram show?

Back

The diagram demonstrates how unstable air contributes to enhanced upward motion, vertical growth, and increased oxygen, which can lead to fire whirls, gusty winds, plume-dominated fires, and dry lightning.

Front

Describe the impact of drought

Back

Drought conditions can significantly impact fire weather by reducing moisture content and affecting fuel loading.

However, drought is not always a critical factor in fire behavior.

Front

What is a Hudson High?

Back

The Hudson Bay High is a high-pressure system that moves southeast, bringing a dry cold front on its leading edge. This system can produce extremely low relative humidity and is associated with extreme fire behavior.

Front

What was the Bass River Fire?

Back

The Bass River Fire occurred on July 22, 1977, characterized by extreme fire behavior and resulted in four firefighter fatalities. Key contributing factors included strong northwest winds at 20 mi/h, unusually low relative humidity (27%), unstable air, drought conditions, and a post-cold frontal passage. The fire was influenced by the southeast quadrant of the Hudson Bay High.

Front

What is the symbol for cold fronts

Back

The blue line with triangles represents the leading edge of a relatively cold or cooler air mass.

Front

In what direction is the cold front moving.

What direction of winds are ahead of a cold front.

What direction of winds are behind the cold front.

Back

East - South East. The triangles point in the direction the frontal boundary is moving

Ahead East-NorthEast

Behind SouthEast

Remember winds are named where they come from!

Front

What happens to temperature and humidity after a cold front passes

Back

Temperatures will become cooler and Relative Humidity will decrease