Transcript Nearpod Weather part 3 File

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.
Cold Front
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:
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Gulf Stream
Alaska
Brazil
Norwegian
Agulhas
Mozambique
Kuroshio (Japan current)
East Australia
• Examples of cold currents:
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California current
Peru current
Canary
East Greenland
Labrador
Benguela
West Australia
Oyashio
How Do Hurricanes Form?
Hurricanes need four conditions to
form:
1. low air pressure
2. warm temperatures
3. moist ocean air
4. 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 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