understanding local diurnal winds

Understanding Local Diurnal Winds

• Sea Breezes and Land Breezes dependent on the differences in heating and cooling between land and water.

• Upslope and downslope winds forced by the differences in heating and cooling between terrain and lowlands.

Sea and Land Breezes

Sea Breeze

Return Flow

Return Flow

Land Breeze Circulation

Sea Breeze Facts

• Builds up in coastal regions during the day

• Best developed in late spring and summer when sun is strongest.

• Can cool the coast by 5-15F, sometimes more.

• Tends to suppress clouds over water, but enhance over land.

• Starts at the coast and extends landward and seeward, 20-50 km

Sea Breeze Front: sharp leading edge of cooler air

Can See the Influence of Sea and Land Breezes on Clouds

Washington Coast Sea Breeze Front

Colliding Sea Breezes Can Produce Strong Upward Motion

Fig. 7-7, p. 176

Sea Breeze Winds Along the Southern Oregon Coast

• Gusts frequently reach 30-35 knots during the summer during the afternoon.

• Very painful to stay on the beach!

• Strong pressure gradient normal to the coast between the warm land areas and the cold upwelling water.

2-minute average July-August winds along the Northwest coast.

Southern Oregon Coast Near Brookings

SummerDiurnalWinds

The Sound BreezeViewed Using Ferry Data

Picture take in Sequim looking NStrong Regional Sea Breeze Winds During the Summer

Land Breezes Tend to Be Weak in the Northwest

• Why? Because the land rarely cools down more than the water.

• Local minimum temperatures generally in the low to mid-50s…similar to the temperature of the Sound and the Pacific Ocean.

• But it can happen in winter during unusually cold periods.

Land Breeze example during a cold period.

Slope Winds

Slope WindsUpslope Flow on Heated Slopes

Downslope Flow on Cooled Slopes

Low temperatures are generally cooler in low spots on cold, cloud-free nights.

Eastern Washington Slope flows

Fig. 7-11, p. 178

Fig. 7-11, p. 178

Warm WarmL L

Valley breeze

Cool H HCool

Mountain breeze

Editable Text

Fig. 7-12, p. 179