Weather / Meteorology Flashcards
What are ways to get weather forecasts?
Internet Coastguard broadcasts Local radio stations Marina notice boards NAVTEX receiver for passages
In the Northern Hemisphere, which direction do low pressure systems revolve?
Anticlockwise
In the Northern Hemisphere, which direction do high pressure systems revolve?
Clockwise
The deeper and faster moving the depression indicates
The worse the weather is likely to be.
From where do low pressure systems approach the UK?
The Atlantic
The closer isobars are on the chart indicate what about the wind?
The stronger the wind is.
Which angle does the wind blow along the isobars of low pressure system - inward or outward?
Slighting inwards.
Which angle does the wind blow along the isobars of high pressure system - inward or outward?
Slightly outwards
When a low pressure system is moving in, what kind of clouds would you see in the sky up to 12 hours ahead?
High, thin, wispy clouds against a blue sky.
As a low pressure system (depression) approaches, how will clouds appear?
lower, thicker, and darker
What kind of winds are produced by high pressure systems?
Light winds
If average wind speed is expected to be F8 or more, or gusts 43-51 knots
Gale Warning
If average wind is expected to be F6 or F7
Strong Wind Warnings “Yachtsman’s Gale”
Within 6 hours of time of issue of warning
Imminent
Within 6-12 hours of time of issue of warning
Soon
More than 12 hours from time of issue of warning
Later
Good visibility in miles
> 5 miles
Moderate visibility in miles
2 < x < 5 miles
Poor visibility in miles
<2 miles
Wind changing in an anticlockwise direction (e.g., NW to SW)
Backing
Wind changing in a clockwise direction (e.g., NE to SE)
Veering
Term meaning No significant precipitation
Fair
Wave height for a Smooth sea state
0.2-0.5m
Wave height for a Slight sea state
0.5-1.25m
Wave height for a Moderate sea state
1.25-2.5m
Wave height for a Rough sea state
2.5-4.0m
Wave height for a very rough sea state
4.0-6.0m
Wind in knots for Beaufort Scale 1
light airs 1-3 knots
Wind in knots for Beaufort Scale 2
light breeze 4-6 knots
Wind in knots for Beaufort Scale 3
gentle breeze 7-10 knots
Wind in knots for Beaufort Scale 4
moderate breeze 11-16 knots
Wind in knots for Beaufort Scale 5
fresh breeze 17-21 knots
Wind in knots for Beaufort Scale 6
strong breeze 21-27 knots
Wind in knots for Beaufort Scale 7
Near gale 28-33 knots
Wind in knots for Beaufort Scale 8
Gale 34-40 knots
Wind in knots for Beaufort Scale 9
Severe gale 41-47 knots
Wind in knots for Beaufort Scale 10
Storm 48-55 knots
What is a Sea Breeze?
Land warms at a faster rate than the sea, heating the air above it. This rises and is replaced by cooler air from the sea. Warm air moves from land to sea and cooler air from sea back to land. Resulting wind can be up to force 4.
What is a land breeze?
Far weaker than a sea breeze. Warm air from sea rises to moves to land. Cooler air from land moves back to sea. Occurs on clear nights.
What are some physical things you can look at to determine wind speed?
Look for trees and flags tossing about Fast moving clouds Boats further down river heeling over
Besides wind strength, what 4 factors will determine how rough conditions are
- The fetch, or how far the wind has been blowing over the sea. 2. Direction and strength of tidal stream 3. Swell 4. Depth of water
Will sea fog burn off as the sun comes up?
No, it may actually get worse.
What do you call it when wind changes in an anticlockwise direction (e.g., NW to SW)?
Backing
What do you call it when wind changes in an clockwise direction (e.g., NE to SE)?
Veering
What 5 factors determine how rough conditions will be?
- Wind strength
- The fetch
- Direction and strength of tide
- Swell
- Depth of water
What is land fog?
Forms on long, clear nights when the heat has radiated from the ground. The air is in contact with the ground is cooled and water vapour condenses to form fog. Can be patchy and low-lying. Sun will burn it off.
What is sea fog?
Formed when warm moist air (usually from the SW in the UK) blows over cold sea and the moisture condenses to form fog. Most common in spring along the cost and in summer out to sea where water is deep and never particularly warm. Can form when it’s quite windy and will not burn off.
Is visibility good or poor behind a cold front?
Good
What kind of weather should you expect directly behind a cold front?
Isolated squally showers with good visibility
What kind of weather should you expect directly in front of a warm front?
Heavy rain with poor visibility
What kind of cloud is this?
Cirrostratus (Height of base: 20,000 - 40,000 ft)
Usually generated at the forefront of frontal weather systems, the movements of cirrostratus can be used to predict what the weather will do in the next 24 hours.
Cirrostratus tend to be sheet-like and cover the whole sky. You can usually tend to see the sun or moon through them. Their pressence usually indicates moist weather within the next 12 - 24 hours.
There are two main ‘species’ of cirrostratus:
Cirrostratus fibratus - similar to cirrus, but with more consistency. Wispy strands all tightly knitted together, making for more of an animal fur look
Cirrostratus nebulosus - a uniform veil-like layer covering the sky. Sometimes almost unnoticeable, cirrostratus nebulosus is featureless, composed entirely of ice
Though cirrostratus itself does not produce precipitation, it can indicate whether or not precipitation is likely. If cirrostratus nebulosus exists in the sky it is likely that an incoming warm front will bring persistent rain within a day. If cirrostratus fibratus is spotted, stratus may proceed it, bringing only light drizzle.
What kind of cloud is this?
Cirrus
Cirrus clouds are white wispy clouds that stretch across the sky. By all accounts, cirrus clouds indicate fair weather in the immediate future. However, they can also be an indication of a change in weather patterns within the next 24 hours (most likely a change of pressure fronts).
By watching their movement and the direction in which the streaks are pointed, you can get a sense of which direction the weather front is moving.
They often form in advance of a warm front, where the air masses meet at high levels, indicating a change in the weather is on the way.
Technically these clouds produce precipitation but it never reaches the ground. Instead, it re-evaporates, creating virga clouds.
What kind of cloud is this?
Cumulus (Height of base: 1,200 - 6,500 ft)
Cumulus clouds are detached, individual, cauliflower-shaped clouds usually spotted in fair weather conditions. The tops of these clouds are mostly brilliant white tufts when lit by the Sun, although their base is usually relatively dark.
Mostly, cumulus indicates fair weather, often popping up on bright sunny days. Though if conditions allow, cumulus can grow into towering cumulus congestus or cumulonimbus clouds, which can produce showers.
What kind of cloud is this?
Cumulonimbus (Height of base: 1,100 - 6,500 ft)
Thunderstorm clouds. The King of Clouds.
Cumulonimbus clouds are menacing looking multi-level clouds, extending high into the sky in towers or plumes. More commonly known as thunderclouds, cumulonimbus is the only cloud type that can produce hail, thunder and lighting. The base of the cloud is often flat, with a very dark wall-like feature hanging underneath, and may only lie a few hundred feet above the Earth’s surface.
Cumulonimbus clouds are associated with extreme weather such as heavy torrential downpours, hail storms, lightning and even tornadoes. Individual cumulonimbus cells will usually dissipate within an hour once showers start falling, making for short-lived, heavy rain. However, multicell or supercell storms contain many cumulonimbus clouds and the intense rainfall may last much longer.
What kind of cloud is this?
Stratus (Height of base: 0 - 1,200 ft)
Definition: Gray, featureless low-altitude layer cloud capable of ground contact
Description & Characteristics. When you think of a cloudy, dreary day, you might have stratus clouds on your mind. Stratus clouds are blanket clouds that sit low to the ground, and on occasion, come in contact with the ground, better known as fog. If you live in a city with tall buildings, you might know stratus clouds by their ability to obscure the tops of buildings.
Stratus clouds form in calm, stable conditions when gentle breezes raise cool, moist air over colder land or ocean surfaces. These clouds can exist in a variety of thicknesses and are sometimes opaque enough to darken days, allowing for little light to pass through.
Stratus is usually accompanied by little to no rainfall but if it is thick enough, it can produce light drizzle. This drizzle can also fall in the form of light snow if cold enough.
What kind of cloud is this?
Nimbostratus clouds (Height of base: 2,000 - 10,000 ft)
Nimbostratus clouds are dark, grey, featureless layers of cloud, thick enough to block out the Sun. Producing persistent rain, these clouds are often associated with frontal systems provided by mid-latitude cyclones. These are probably the least picturesque of all the main cloud types.
These mid-level clouds are often accompanied by continuous moderate rain or snow and appear to cover most of the sky. Nimbostratus will often bring precipitation which may last for several hours until the associated front passes over.
If there is hail, thunder or lightning present it is a cumulonimbus cloud rather than nimbostratus.
What kind of cloud is this?
Altostratus (Height of base: 6,500 - 20,000 ft)
Altostratus layers are often composed of both water and ice and usually form when a layer of cirrostratus descends from a higher level.
Altostratus clouds often form ahead of a warm or occluded front. As the front passes, the altostratus layer deepens and bulks out to become nimbostratus, which produces rain or snow. As a result, sighting it can usually indicate a change in the weather is on the way.
What kind of cloud is this?
Cirrocumulus clouds tend to be large groupings of white streaks that are sometimes seemingly neatly aligned. In most climates these mean fair weather for the near future.
However, in the tropics, these clouds may indicate an approaching tropical storm or hurricane (depending on the season).
What is an occluded front and how is it depicted on an isobar chart?
Cold fronts tend to move faster than warm fronts and over time they can catch up with each other and create an ‘occluded’ front.
This is shown as a purple line with a purple semi-circle and triangle next to each other.
The air trapped between a warm and cold front is called a ‘warm sector’ and we often see low cloud and patchy light rain associated with this type of air.
How is a warm front depicted on an isobar chart?
A warm front is shown with a red line and red semi-circles.
The way in which the semi-circles point shows the direction in which the front is moving.
How is a cold front depicted on an isobar chart?
A cold front will have a blue line and blue triangles. The way in which the triangles point shows the direction in which the front is moving.
What is a trough and how is it depicted on an isobar chart?
Black lines that have no semi-circles or triangles are called ‘troughs’ and mark areas where the air is particularly unstable. This means that the air is quite turbulent or moving around a lot, especially when we have, for example, warm air beneath cold air that wants to rise. We tend to see showers associated with this type of air, therefore they don’t mark any sort of boundary in the same way that a front does.
Condition favoring fog formation is
Moisture laden air
Temperature Behind a cold front is
Lower than in front of it
Air pressure behind a cold front is
Higher than in front of it
Majority of weather systems in the US come from
Westerly direction
Best source of marine boating weather is
National weather service
Northern hemisphere winds flow around into a low in what direction
Counterclockwise
Warm air
Rises
Warm moist air compared to dry cool air is
Lighter
Back to surface wind-turn 45 degrees to your right - low pressure area is
To your left
High pressure air mass is characterized by
Cool dry air
Fastest moving fronts are usually
Cold fronts
A hurricane is a tropical storm with sustained winds
64 knots or greater
A tropical cyclone is
Low pressure area over warm tropical waters
Clouds from which rain is falling are called
Nimbus
Main problem in thunderstorms tornadoes etc
Wind
Which of the following provides the most serious threat to boaters
Wind
The height of wind created waves depends on
How long wind is blowing, extent of the fetch, strength of the wind
Fog occurs most often near a
Warm front
Fronts are named for the kind of air that is
Behind them
Thunderstorms form ahead of
Cold fronts
On a colored weather map warm fronts are
Red
Weather is caused by
Heat
Thunderstorms are produced by
Cumulonimbus clouds
Clouds in front of a warm front are
Stratus and cirrus
A particularly dangerous phenomenon that can occur several miles away from a thunderstorm and a squall line is a
microburst
What is Meteorology?
Study of Weather
What happens to air when you heat it?
It becomes less dense and rises
What happens to air when it is cooled?
It becomes denser and falls
True or False? Moist air is more buoyant than dry air
True
What happens in the water cycle?
Evaporation Condensation Precipitation
Name four types of clouds?
Cirrus Stratus Cumulus Nimbus
True or False? The darker and thicker looking the clouds the worse the weather is likely to be
True
What are the two types of Weather Systems?
High Pressure and Low Pressure
What are the two units of measurements used?
Millibars (mb) and HectoPascals (hPa)
What is a barometer used to measure?
Air pressure
What kind of weather would you expect to find in the Northern Hemisphere with high air pressure?
Light winds that rotate clockwise Surface wind blows outwards No rain Clear skies Stability Pleasant Weather
What kind of weather would you expect to find in the Northern Hemisphere with low air pressure?
Strong, gusty wind that rotates anti-clockwise Surface wind blows inwards Rain Cloud Instability Unpleasant weather
True or False? General direction of movement is from East to West
False - general direction of movement is from west to East, not always though
What are the charts that show the weather called?
Synoptic charts
What does it mean if isobars are really close together?
Strong wind
How can you identify cold fronts on the chart?
Blue spikes
How can you identify warm fronts on the chart?
Red semi-circles
What are the three types of barometer?
Original liquid barometer Aneroid barometer Electronic barometer
What is a front?
Where warm and cool masses meet
What is a depression?
An area of low pressure
How do you convert wind speed of knots to the Beaufort Wind Scale?
Add 5 then divide by 5
What does imminent gale warning mean?
Within 6 hours from forecast time
What is poor visibility?
1000m - 2M
What are some sources of Weather Forecasts?
Internet Coastguard VHF Public Radio and TV GSM Telephone Met Office Navtex HF and MF Radio Barometer
What is a Dew Point?
The temperature to which air must be cooled for water to turn from water vapour into liquid water
