I made this a couple days before Exam 3 for CU Boulder's ATOC 1050 to help me cram all this junk into my head and spit it out on a piece of paper. I do not have a good understanding of these concepts and mainly just copied material from slides. This is unorganized and probably incomplete but does aggregate everything seen on lecture slides since Exam 2. If you stumble across this as a student, please don't use this as the only way to study. Take some practice tests, dude.
- CU Boulder ATOC 1050 Exam 3 Study Document
- Preface
- Table of Contents
- Air Mass
- Source Regions
- Classifying Air Masses
- Air Mass Modification
- Properties of Air Masses
- Lake Effect Snow
- Fronts
- Polar-Front Theory (Norwegian Cyclone Model)
- Regions for Mid-Latitude Cyclones
- Cyclone Formation
- Convergence and Divergence
- Upper Level Convergence and Divergence
- Weather Forecast
- Weather Alerts
- Weather Forecasting Tools
- Weather Reporting
- Computer Forecasting
- Other Forecasting Methods
- Determining the Movement of Weather Systems
- Thunderstorms
- Types of Thunderstorms
- Lightning and Thunder
- Lightning Formation
- Tornadoes
- Tornado Life Cycle
- Tornado Formation
- Tornado Forecasting
- Useful Pictures
- Immense body of air
- 1600km (994mi) or more across, several km thick
- Homogeneous physical properties
- Extensive, physically uniform area
- Dominated by stationary/slow-moving anticyclones with extensive areas of calm/light winds
Air Masses are named based on latitude and nature of surface of source region
- Arctic (A)
- Polar (P)
- Tropical (T)
- Maritime (m)
- Continental (c)
| cA | continental | arctic |
| cP | continental | polar |
| cT | continental | tropical |
| mT | maritime | tropical |
| mP | maritime | polar |
As air masses move, the air mass affects the location and the location affects the air mass in the following ways:
- Temperature
- Moisture
- Stability (energy exchange, mechanical lifting)
| Class | Characteristics | Source Region | Weather |
|---|---|---|---|
| cP, cA | cold, dry, stable | N. Canada & Alaska | cold dry air, lake effect snow |
| mP | cold, moist, conditionally unstable | N. Pacific & N. Atlantic Oceans | rain/snow |
| mT | warm/hot, moist, unstable | sub-tropical Pacific and Atlantic Oceans, Gulf of Mexico | humid w/ precipitation |
| cT | warm/hot, dry, unstable | northern Mexico | clear skies, hot, no precipitation |
Produced when a cold air mass moves across a long expanse of warmer water. The lower layer of air picks up water vapor from the lake and rises through the colder air above. Snow is then deposited downwind.
Boundary surfaces that separate air masses of different densities
- Nearly stationary boundary
- Airflow on both sides is parallel to the line of the front
- Weather: clear/cloudy skies with possible light rain
- Cold dense air wedges under warm air, forcing the warm air upward
- Moist, unstable warm air condenses and creates cumulus clouds
- Upper level westerly winds create cirrostratus and cirrus clouds out in front
- Thunderstorms, heavy rain, strong winds
- As it passes, temperature drops, winds shift from southwesterly to northwesterly, pressure rises, and precipitation stops
- Leading edge of the front is steep and shallow
- Slopes upward over the cold air at the surface
- Slope is approximately 1:50
- Move quickly with a speed of approximately 25+ knots
- Weather: narrow band of precipitation along the cold front with potentially severe thunderstorms directly along the front
A line of active showers and thunderstorms that develop parallel to and often ahead of an advancing cold front
Cold fronts that move in from the east/northeast (rather than south, southeast, or east). Usually move out of Canada and into the northeastern United States
- Warm, moist air replaces cold, dry air
- Slope is approximately 1:300
- Average speed is approximately 10 knots
- In front, light and variable surface winds, cold temperatures, and high cirrus clouds overhead
- Moves slowly, takes a day or two to pass
- Cirrus clouds gradually thicken into cirrostratus clouds, then altocumulus and altostratus clousd
- Chance of light precipitations with nimbostratus clouds overhead
- Winds become brisk and southeasterly, atmospheric pressure slowly decreases
- Precipitation warms (snow to rain)
- Fog may form at the surface
- After front passes, temperatures increase, dew point increases, winds shift from southeast to south or southwest, atmospheric pressure stops falling, precipitation stops, and most of clouds clear (some stratocumulus will remain)
The rising of warm air over cold
Form when a cold front catches up to a warm front
The air behind the cold front is colder than the air head of the warm front
The air behind the cold front is not as cold as the air ahead of the warm front
The majority of weather in the mid-latitudes (Florida to Alaska) is generated by mid-latitude cyclones. The Norwegians were the first to develop an atmospheric model that could predict the development of mid-latitude cyclones.
Wave cyclones develop along the polar front where there is a large temperature gradient.
- Stationary front: separates cold polar air from warm sub-tropical air
- Frontal wave: the initial king that forms on the polar front
- Open wave: fully developed cyclone, warm sector
- Mature: pressure drops, winds increase, cold front inches closer to warm front
- Advance occlusion: the cold front has caught up to the warm front, leaving cold air at the surface
- Dissipation: without a surface temperature gradient, the cyclone loses energy and gradually dies out
The warm air mass located between the cold and warm fronts
There are regions named for where mid-latitude cyclones form
As westerly winds blow over a mountain range, the air expands vertically on the downwind (lee) side, which can intensify any pre-existing areas of low pressure
East coast mid-latitude cyclone that develops or intensifies off the east coast of N. America in the fall, winter, or spring. They produce strong winds and heavy rain, snow, and sleet
High pressure at surface associated with surface divergence, with convergence aloft to maintain surface high pressure.
Low pressure at surface associated with surface convergence, with divergence aloft to maintain surface low pressure.
Atmospheric condition that exists when winds cause a horizontal net inflow of air into a specified region. Adds mass to a column of air.
Causes:
- Winds directed towards each other
- When faster winds approach slower winds
Atmospheric condition that exists when winds cause a horizontal net outflow of air into a specified region. Removes mass from a column of air.
Causes
- Winds directed away from each other
- When slower winds approach faster winds
If isobars (or geopotential height contours) have even spacing, the winds will be faster in the region of an upper-level ridge rather than in a region of an upper-level trough
Tends to occur on the west side of an upper level trough (or the east side of an upper level ridge). Occurs when faster winds approach slower winds.
Tends to occur on the east side of an upper level trough (or the west side of an upper level ridge). Occurs when slower winds approach faster winds.
A scientific estimate of the weather conditions at some future time. Includes the following metrics:
- Temperature
- Humidity
- Cloudiness
- Precipitation
- Wind speed
- Wind direction
Issued to inform the public of less hazardous conditions caused by wind, dust, fog, snow, sleet, or freezing rain
Indicates that atmospheric conditions favor hazardous weather occuring over a particular region during a specified time period
Indicates that hazardous weather is either imminent or actually occuring within the specified forecast area
A light instrument carried by a balloon to take temp, humidity, and pressure measurements vertically throughout the atmosphere
Determines the velocity of falling precipitation either toward or away from the radar unit by taking into account the doppler shift
Satellite images are useful for forecasting, especially over the ocean and polar regions
Circle the earth in a north-south direction
Placed in an orbit over the equator. Remain at a fixed point above the Earth, traveling at the same rate that the Earth rotates.
Obtained by detecting radiation emitted by objects, which gives information about the temperature of the object
Measures how much water vapor is in the air by detecting the wavelength emitted by water vapor
Give a picture of the weather at a given point in time
A chart that shows how one or more weather variables has changed at a station over a given time period
From radiosondes, shows 2D vertical profile of temp, dew point, and winds
How to read:
- Isobars: horizontal blue lines of equal pressure
- Isotherms: vertical blue lines of equal temperature
- Temperature curve: thick black line on the right
- Dew point temperature curve: thick black line on the left
- Wind observations: Shown by wind barbs on the right side
- Dry adiabat: Green lines
- Moist adiabat: Purple lines
Technique used to forecast weather using numerical models designed to represent atmospheric processes
Machine-generated maps of predicted future weather conditions
A process for forecasting that corrects for model tendencies
A technique used for forecasting that produces multiple forecasts using the same model with slightly different initial conditions
Based on the tendency of weather to remain unchanged for several hours or days
Uses the average weather statistics measured over many years
Based on the assumption that weather repeats itself, involves pattern recognition
Based on the speed and direction of features such as fronts, cyclones, clouds, and precipitation; see nowcasting
Made routinely of weather elements based on the past performance of computer models, use MOS
Provides the probability that something will happen (i.e. a "white Christmas")
A weather forecast that is good for a few hours
A weather forecast that is good from about 6 hours to a few days (usually up to 3 days)
A weather forecast that is good from about 3-8 days
A weather forecast that extends beyond 8 days
Provides 30 and 90-day outlooks. Not typical forecasts, but instead provide info on whether a region will be drier/wetter than normal or colder/warmer than normal
- For short time intervals, mid-latitude cyclonic storms and fronts tend to move in the same direction and at approximately the same speed as they did during the previous six hours
- Low-pressure areas tend to move in a direction that parallels the isobars in the warm air (the warm sector) ahead of the cold front
- Lows tend to move toward the region of greatest surface pressure drop, whereas highs tend to move toward the region of greatest surface pressure rise
- Surface pressure systems tend to move in the same direction as the wind at the 500mb level. The speed at which surface systems move is about half the speed of the winds at this level
A storm that generates lightning and thunder. Usually produces gusty winds, heavy rain, and hail. They are convective storms that form in rising air.
| Year | Day | Second | Current |
|---|---|---|---|
| >16 million thunderstorms | 45 thousand thunderstorms | 100 lightning strikes | 2 thousand thunderstorms |
- Updraft: the rising motion which creates clouds and precipitation
- Downdraft: the sinking motion created by falling precipitation
- Gust front: the surface boundary that separates the advancing cooler air from the surrounding warmer air at the surface
The rate of change in wind speed and/or wind direction with height. Its impact on the orientation of the updraft is the key difference between the different types of thunderstorms
| Type | VWS | Updraft Orientation | Downdraft Location | Duration | Instability | Strength |
|---|---|---|---|---|---|---|
| Air-Mass | weak | vertical | falls into and extinguishes the updraft | 15-30 mins | moderate | weak |
| Severe | strong | tilted | falls next to the updraft | 30+ mins | strong | strong |
| Supercell | strong | tilted and rotating | falls next to the updraft; often a second downdraft forms | many hours | very strong | strongest |
- Moist, unstable, rising air creates cumulus clouds
- Water vapor condenses into liquid or solid cloud particles, releasing large quantities of latent heat, keeping the rising air inside the cloud warmer than the air surrounding it
- No precipitation yet, the updrafts keep the water up in the cloud
- Falling precipitation creates a downdraft
- Downdraft causes entrainment, which brings drier air into the cloud
- Entrainment causes evaporation, which cools the air and enhances the downdraft
- Both an updraft and a downdraft exist at this stage
- Where the cold downdraft reaches the surface, the air spreads out horizontally in all directions creating the gust front
- Begins about 15-30 mins after the Mature Stage starts
- Downdraft overpowers updraft, curring off the source of warm rising air to fuel the thunderstorm
A thunderstorm that contains at least one of the following criteria:
- Winds in excess of 58 mph
- Hailstones larger than 1 inch in diameter
- Produces a tornado
A thunderstorm that is 12-30 mi in diameter
A discharge of electricity, a gian spark, which occurs in mature thunderstorms. It can heat up the air around it to 54,000 deg F.
Locations:
- Within a cloud
- Cloud to cloud
- Cloud to surrounding air
- Cloud to ground
An imbalance of positive and negative charges causes lightning. Some cloud physicists believe this occurs through cloud droplet crystallization.
The extreme heat from lightning causes the air to expand explosively, thus initiating a shock wave that becomes a booming sound that travels outward in all directions
- The electrical potential gradient becomes large enough to overcome the air's insulating properties and a flow of electrons called the stepped leader rushes towards the surface
- As electrons approach the ground, a region of positive charge moves up into the air through any conducting object
- When the downward flow of electrons meets the upward surge of positive charge, a strong eletrical current called the return stroke carries positive charge upward into the cloud
A single lightning flash consists of many return strokes.
A rapidly rotating column of air extending down from a cumulus cloud that is a small area of intense low pressure with a circulation that reaches the ground. The central pressure of a tornado can be 10% lower than the surrounding pressure. The friction at the surface causes winds to rush towards the center where it is forced vertically.
- Tornado Alley: Texas to Nebraska
- Dixie Alley: Mississippi and Alabama
- Ideal Conditions: warm, humid surface air is overlain by cooler, drier air aloft (conditionally unstable conditions) combined with strong vertical wind shear
Refers to a visible funnel that does not reach the ground
Some tornadoes consist of a single vortex, but more commonly smaller suction vortices are contained within the larger cell. These are referred to as multiple vortex tornadoes.
A scale that uses the damage caused by the tornado to estimate the tornado wind speeds
Dust swirling upward from the surface marks the tornado's circulation on the ground and a short funnel often extends downards from the thunderstorm's base
Damage is usually the most severe as the funnel reaches its greatest width and is almost vertical
The tornado stretches into the shape of a rope and dissipates
Tornadoes are commonly associated with a supercell thunderstorm.
- The wind shear causes the air near the surface to rotate about a horizontal axis
- The strong updraft within the developing thunderstorm tilts the rotating tube upward and draws it into the storm
- The rotating shaft in the updraft lowers the pressure and enhances rising motion (adds more fuel to the storm)
- The updraft, counterclockwise swirling precipitation, and the surrounding air create the rear flank downdraft
- The formation of the rear flank downdraft seems to play an important role in the formation of tornadoes
- The relatively cold air of the downdrafts wrap around the rotating column
- This causes the bottom of the column to rise slower than the top of the column, resulting in vertical stretching of the column, resulting in a faster spinning column (like a figure skater)
- This rapidly rotating column is known as a tornado vortex
- Doppler Radar: can determine rainfall intensities, and multiple doller systems can determine the motion of a storm system
- Bounded weak echo region (BWER): the region free of precipitation because the updraft is so strong taht precipitation cannot fall through it
- Hook echo: the precipitation that gets wrapped around the rotating updraft
