High vs. Low High pressure areas are generally larger and move slower than low pressure. The winds are generally weaker than those around a low pressure, especially in the center. High pressure does not necessarily mean warm weather, a 'cold anticyclone' has cold air near the ground. These cold anticyclones are common in Siberia and Canada.

If cold air is moving toward warm air, then it is a “cold front”. Definition: a warm-cold air boundary with the colder air replacing the warmer. A typical cold front plows into warmer, lighter air forming towering clouds, rain, and often thunderstorms.

Air Movement- Cold Front

Symbol for Cold Front The weather map symbol for a cold front is a blue line with triangles pointing the direction the cold air is moving. As a cold front moves into an area, the heavier, cool air pushes under the lighter, warm air it's replacing. The warm air cools as it rises. If the rising air is humid enough, water vapor in it will condense into clouds and maybe precipitation.

Weather Associated with Cold Fronts In the summer, an arriving cold front can trigger thunderstorms- sometimes severe with large hail, dangerous winds, and even tornadoes!

Warm Front If warm air is moving toward cold air, it is a “warm front”. Definition: boundary where a warm air mass replaces a cool air mass. Warmer tropical air is forced over the cooler polar air. Heavier, denser cold air retreats slowly as warm air rises over cold air, bringing widespread clouds and precipitation.

Air Movement- Warm Front

Symbol for Warm Front The weather map symbol for a warm front is a red line with half-circles on it. The circles on the red line point in the direction the warm air is moving. As the warm air advances northward it rides over the cold air ahead of it, which is heavier. Sometimes the cold air slows the warm front down and can lead to several days of wet weather.

Weather Associated with Warm Fronts When a warm front passes through, the air becomes noticeably warmer and more humid than it was before. As the warm air rises over the cold air the water vapor in it condenses into clouds that can produce rain, snow, or sleet. A slow-moving warm front can mean hours, if not days, of cloudy, wet weather before the warm air finally arrives.

Stationary Front When a warm or cold front stops moving, it becomes a stationary front. Once this boundary resumes its forward motion, it once again becomes a warm front or cold front. A stationary front is represented by alternating blue and red lines with blue triangles pointing towards the warmer air and red semicircles pointing towards the colder air.

Occluded Front When a cold and warm front merge into one front, it is known as an occluded front, or occlusion. The warm air mass becomes trapped between two colder air masses, one from the west and one from the east, and is forced up. Occluded means "closed in." A large area of bad weather accompanies the occluded front. Warm front weather will be followed by cold front weather in all occlusions.

Predicting the Weather Weather forecasting takes time and research. Here are just a few tips on scientific weather forecasting … Watch for a steadily falling barometer with winds from the east/northeast.  This usually indicates the arrival of a storm from the south or southwest within 24 hours. Expect fair weather if the barometric pressure is steady and winds are coming from the southwest to northwest. Look for the presence of cirrocumulus clouds that are in patches or in widespread layers. This is usually a sign of an advancing, large, unstable weather system. Watch for the formation of cumulonimbus clouds early in the day. As they become more active, the likelihood of severe weather increases. Expect nice weather the following day if the night sky is clear.

Cirrocumulus

cumulonimbus

Weather Maps Blue book page 71

Ocean Currents The patterns of ocean surface currents are determined by the force and direction of the winds and by land masses that act as barriers.

Ocean Currents Surface currents are cause by winds, and they have circulation similar to those in the atmosphere. For example, surface currents in the tropics are set in motion by the trade winds that drive the ocean water before them. Density Currents formed by the movement of more dense seawater toward an area of less dense seawater. Temperature and salinity affect the density of seawater. Ocean currents traveling away from the equator are warm-water currents Ocean currents traveling toward the equator are cold- water currents.

Ocean Currents Examples of warm currents: Examples of cold currents: Gulf Stream Alaska Brazil Norwegian Agulhas Mozambique Kuroshio (Japan current) East Australia Examples of cold currents: California current Peru current Canary East Greenland Labrador Benguela West Australia Oyashio

How Do Hurricanes Form? Hurricanes need four conditions to form: low air pressure warm temperatures moist ocean air tropics winds (near the equator). It starts as a tropical wave, a westward-moving area of low air pressure. As the warm, moist air over the ocean rises cold air from above replaces it producing strong gusty winds, heavy rain, and thunderclouds (tropical disturbance). As the air pressure drops and there are winds up to 38 mph, it is a tropical depression. When the cyclonic winds speeds from 39 to 73 mph, it is a tropical storm. The storm becomes a hurricane when there are winds of 73 mph or more.

El Nino Weather La Nina Weather El Nino and La Nina   What are El Nino and La Nina? El Nino - (El Nee-nyo) is the warming of water in the Pacific Ocean. La Nina - (Lah Nee-Nyah) is the cooling of water in the Pacific Ocean. El Nino Weather La Nina Weather Rain and flooding along the Pacific coast Warm water disrupts food chain of fish, birds, and sea mammals Tornadoes and thunderstorms in southern US Fewer than normal hurricanes in the Atlantic Snow and rain on the west coast Unusually cold weather in Alaska Unusually warm weather in the rest of the USA Drought in the southwest Higher than normal number of hurricanes in the Atlantic