The correct answers are a, b, and d.

Feedback:
Prior to sunrise, there is strong down valley flow and flow on the slopes is strongly downslope. As the sun comes up, the flow on the east facing slope begins to switch from downslope to upslope. The down valley flow decreases in strength and ends by mid-morning. The winds on the west facing slope remain in shadow, so changes in the flow on that slope are slower to occur. As the sun hits the valley floor in the morning, smoke trapped in the valley begins to lift and quickly mixes out. As the sun rises, the temperature starts to increase and the humidity, which is highest just before sunrise, starts to decrease.

As the sun rises, smoke begins lifting out of the valley.

The Fire Behavior Analyst (FBAN) explains how the expected weather conditions could affect fire spread and growth.

FBAN:
The result of the increased temperature and decreased humidity is increased fire activity. The smoke will lift as the inversion breaks and the fire will be better ventilated, allowing it to grow. The spread of the fire is affected by both the natural tendency for it to move up slope and the direction of the wind. Therefore, the initial downslope winds will act against the slope effect and the fire will creep along the slope. Once the sun comes up and the winds switch to direction, the fire spread will increase upslope as the upslope winds strengthen.

Slope winds flow developing after sunrise.

Based on expected changes in weather conditions and the FBAN's analysis of the expected fire behavior, the Incident Commander has decided to move fire fighting resources:

Incident Commander:
In anticipation of sunrise, we are going to concentrate the crews along the rear and flanks of the fire so that they are out of the way when the winds shift and the fire starts increasing its upslope progression.

Fire fighter location as winds and fire move upslope.

The correct answers are a and c.

Feedback:
The wind will continue to move upslope and strengthen, and an upvalley component will begin to develop. The resulting flow will have a cross slope component. The temperature will increase to near the warmest of the day and the relative humidity will drop to near its minimum value.

Upvalley flow begins to develop in the afternoon.

The Fire Behavior Analyst (FBAN) explains how the expected weather conditions could affect fire spread and growth.

FBAN: –
Upslope winds act with the natural tendency of the fire to move up a slope and increase the spread of the fire. The spread rate is related to the wind speed, so as the upslope flow strengthens, the fire moves more quickly. Also, as the inversion lifts, the fire will grow vertically. We are concerned about the fire moving into the trees up the valley. The fire could then move into the tree crowns and result in extreme crown fire behavior. The higher temperatures and lower relative humidity will also aid in the fire spread by preheating and drying fuels. The mid to late afternoon is normally when the most active fire behavior occurs.

Fire behavior becomes more active in the afternoon.

Based on expected changes in weather conditions and the FBAN's analysis of the expected fire behavior, the Incident Commander has decided how to best place fire fighting resources:

Incident Commander:
We'd really like to work on the upvalley flank of the fire to keep it from moving into the trees. However, if the winds will start to push the fire up the valley, we will have to move those resources and concentrate our efforts on the down valley flank. We can't put our fire fighters in danger.

View of the fire in late afternoon.

The correct answers are a, b and d.

Feedback:
In the late afternoon, the highest temperatures, strongest upslope and upvalley winds and lowest humidities will be present. As the sun goes down, the slope winds will turn downslope, and the upvalley wind will decrease and cease. As the downslope winds increase in strength, a downvalley component of the wind begins to form. As the valley cools overnight, the temperature near the fire will drop and the relative humidity will increase. As the temperature drops in the valley, a radiation inversion will develop, initially near the valley floor.

Downslope and later downvalley winds develop overnight.

The Fire Behavior Analyst (FBAN) explains how the expected weather conditions could affect fire spread and growth.

FBAN:
The mid to late afternoon often sees the most active fire behavior. With the high temperatures and low relative humidities, fuels are preheated and dried. Also, the upslope and upvalley flow cause relatively fast spread up and along the slope. As the sun goes down and the upslope and upvalley winds decrease, the upslope spread of the fire will begin to slow. The cooler temperatures and higher relative humidity will reduce the fire activity as fuels react to the cooler, more moist conditions. As the downslope winds develop, the upslope fire spread will continue to decrease and the downvalley component of the winds can cause a change in the direction of spread. However, both downslope and downvalley winds act against the natural tendency for fire to move uphill, and the fire spread in general should be distinctly slower than seen in the afternoon hours. The inversion (the region where the temperature increases with height) that forms in the valley will have the effect of decreasing fire behavior beneath it. In this area, great progress can be made in fighting the fire. Meanwhile, the portion along the slope near the top of the inversion is known as the thermal belt, where the relative humidity will continue to be lower and more active fire behavior can be observed.

Based on expected changes in weather conditions and the FBAN's analysis of the expected fire behavior, the Incident Commander has decided how to best place fire fighting resources:

Incident Commander:
Nighttime hours are when we often make the most progress on fighting the fire. I plan to concentrate on the upvalley flank of the fire and try to create some good fire breaks in anticipation of what will happen tomorrow when the wind shifts again. Near the top of the inversion, I'll alert the fire fighters that fire behavior may be more active in that region. We also need to be careful under the inversion, as smoky conditions can affect the fire fighters.

Late afternoon conditions.