Weather Forecasting Basics Introduction

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Questions and Answers

What is the primary purpose of weather forecasts?

To provide entertainment during storms

To predict climate changes over years

To determine seasonal weather patterns

To save lives, property, and crops (correct)

What type of information do weather balloons collect?

Pollutant levels in the air

Ocean temperatures and currents

Atmospheric conditions at various altitudes (correct)

Ground temperature only

Which method uses computers and mathematical equations for daily weather forecasts?

Traditional weather observation

Numerical weather prediction (correct)

Doppler radar analysis

Satellite imaging

What is a prognostic chart in the context of weather forecasting?

A chart representing the atmosphere at a specified future time Signup and view all the answers

How often does one standard NWS model produce weather depictions?

Every hour Signup and view all the answers

Which of the following is true about Doppler radar data?

It provides information on precipitation types and storm warnings. Signup and view all the answers

What is a critical tool for transitioning from large scale to small scale forecasts?

Super-computers Signup and view all the answers

How far into the future can some weather models forecast?

Up to 16 days Signup and view all the answers

What does a 40% chance of rain indicate about measurable rainfall in a specific location?

Rain will occur during 4 out of 10 instances with the same conditions. Signup and view all the answers

Which forecasting model primarily uses Doppler radar and pattern recognition?

Very short range forecasting Signup and view all the answers

What is the primary purpose of the Climate Prediction Center?

To create seasonal forecasts based on global weather changes. Signup and view all the answers

What differentiates a weather watch from a weather warning?

A warning indicates actual hazardous weather, while a watch indicates potential hazardous conditions. Signup and view all the answers

Which time range of forecasting extends from 3 to 8 days into the future?

Medium range Signup and view all the answers

What is the main characteristic of long-range forecasting?

It uses computer modeling for extended outlooks. Signup and view all the answers

What does skilled weather forecasting aim to achieve compared to persistence and climatology?

It prioritizes accuracy over random guessing. Signup and view all the answers

Which type of forecasts is often considered to be more accurate for large-scale weather events?

Several days in advance for large-scale weather events. Signup and view all the answers

What does ensemble forecasting primarily focus on?

Comparing different models for common predictions. Signup and view all the answers

Which forecasting technique relies on the assumption that future weather will mirror current conditions?

Persistence forecast Signup and view all the answers

In the context of probability forecasting, what does the forecaster base their predictions on?

Prior 30 years of data. Signup and view all the answers

What is a characteristic feature of observational forecasting?

It is based on visible weather signs in the sky. Signup and view all the answers

What does a trend forecast suggest about surface weather systems?

They will operate the same way they have been moving. Signup and view all the answers

What is often referred to as a 'spaghetti plot' in forecasting?

A visual representation of ensemble forecasts. Signup and view all the answers

What type of forecast groups weather patterns based on their similarities?

Weather type forecast Signup and view all the answers

How is the chance of rain typically defined in weather forecasting?

The percentage of coverage of area expected to see rain. Signup and view all the answers

Study Notes

Weather

Meteorology: Unit 4

Air Masses & Fronts

Air Mass: A large body of air with similar temperature and moisture at a given altitude.
Source Region: The area where an air mass originates (often polar or tropical). Mid-latitudes are where air masses clash, producing weather activity.

Air Mass Classifications

Humidity:
Maritime (moist)
Continental (dry)
Temperature:
Polar (cold)
Tropical (warm)

Air Masses of North America

cP and cA: Produce extreme cold winter weather.
Lake Effect Snow: Occurs when extremely cold air moves across a warm body of water (like the Great Lakes), creating snowstorms.
mP: Responsible for cold, damp weather along the NE coast of N. America and for cold, rainy winter weather along the west coast of N. America.
mT: Responsible for hot, muggy weather found in the eastern US in summer.
cT: Responsible for heat waves in the western half of the US in summer.

Fronts

Front: A transition zone between two air masses of different densities. Often associated with temperature and humidity differences.
4 Types:
Cold Front
Warm Front
Stationary Front
Occluded Front

Locating Fronts on a Surface Map

Sharp temp. change: Over relatively short distances.
Changes in moisture: Content (shown by dew point).
Shifts in wind direction.
Pressure & pressure changes.
Clouds & precipitation patterns.

Cold Front

Stable air replaces unstable air.
Drawn with a solid blue line with blue triangles showing the direction of movement.
Often has rain and strong thunderstorms along the leading edge.
Air behind cools quickly.
Tend to move toward S, SE, or E.
Occasionally, special conditions create a 'back door' cold front, moving from the east.
Cold air damming can occur when a cold front stalls at the Appalachian Mts.

Warm Front

Warm, unstable air replaces colder air.
Drawn with a solid red line with red half-circles (semi-circles) along the front showing the direction of movement.
Moves much slower than cold fronts (~½ speed).
Associated with light rain and more gradual changes than a cold front.

Stationary Front

Essentially no movement.
Red semi-circles point towards colder air.
Blue triangles point towards warmer air.
The line marks the boundary where cold, dense air meets warmer air.
Often the transition to either a warm front or cold front.

Occluded Front

Forms when a cold front catches up to and overtakes a warm front.
Shown by a purple line with alternating cold front triangles and warm front half circles.
On the same side of the line.
Pointing in the direction the front is traveling.
Air behind the front is colder and drier than air ahead of it.
Can have heavy precipitation where the cold front overtakes the warm front.

Mid-Latitude Cyclones

Fluid boundary where warm tropical air masses meet cold polar air masses. Known as the polar front.
Ridges and troughs move and change ("stretchy") with different air masses.
Meeting of contrasting air masses (polar and tropical) leads to mid-latitude weather systems.

Cyclogenesis

Generation of depressions and formation of cyclones.
The Norwegian Model (1910s-1920s): Depressions form from waves that develop along a polar front.
Stages:
1. A segment of the polar front is a stationary front. High pressure on both sides. Warm air below, blowing from the west and cold air above, blowing from the east. Wind shear creates cyclonic wind.
2. A low-pressure system forms at the point of rotation (central pressure), the junction of the two fronts. The stationary front begins moving, with the warm front to the east and the cold front to the west. Precipitation begins to form.
3. Cold air displaces warm air upward, creating precipitation ahead of the warm front and a "kink" in the pressure system. The pressure difference is greater as the faster moving front (cold) moves toward the warm front (slower).
4. The cold front moves faster than the warm front, the warm sector shrinks in size and central pressure drops. The system becomes a mature cyclone and has an increased likelihood of intense thunderstorms and widespread rain.
5. The cold and warm fronts merge, forming an occluded front at the point of central pressure (the "triple point"). The system begins to dissipate as frontal air moves away.

Convergence and Divergence

Convergence: The piling up of air in a region when it slows down.
Divergence: The spreading out of air in a region when it speeds up.
Both occur all along the polar front.
On surface maps, convergence is depicted with converging arrows, and divergence with diverging arrows.

Conditions for Cyclogenesis

Ventilation/air flow
Sharp contrast between temperatures of opposing air masses
Jet stream plays a role (and can shift or change patterns).
Sharp contrast between opposing air masses is crucial for cyclogenesis. Areas like the Hatteras and Colorado lows offer these contrasting conditions.
Hatteras Low: Warm gulf water creates warm, moist air below the stationary front. This often creates Nor'easters.
Colorado Low: Forms on the leeward side of the Rockies. Provides mP air and continental air (P or T).

Special Cyclonic Storms

Bomb Cyclone: When the central pressure falls by more than 24 mb in 24 hours.
March 26, 2014: Example of a bomb cyclone where rapid cloud development and heavy rain occurred.

Weather Forecasting Methods

Numerical Weather Prediction (NWP): Routine daily forecasting using computers and mathematical equations. Using atmospheric conditions from current measurements.
Models: Used because atmospheric conditions are always changing and based on temperature information.
Forecast Types:
Short range (12-72 hours, 3 days). Doppler radar and surface weather maps & recognition.
Medium range (3-8 days). Statistical forecasts and charts
Long range (8+ days). Computer modeling and "outlooks," overview of expected conditions.
Climate prediction (forecasting for seasons.)

Weather Observations

Data from land-based stations (temperature, dew point, wind, pressure) with over 10,000 stations.
Ships and buoys
Airports gather data every hour.
Weather balloons.
Satellites (visible and infrared images)
Doppler radar (information on rain, snow, sleet, & hail)
Various warnings.
Computer models used to create analyses (and forecasts)
Large to small patterns and analyses.

Forecasting Techniques

Persistence: Predicting weather will be the same as current conditions.
Trend: Predicting the continuation of existing conditions.
Pattern recognition: Using similarities in past events to anticipate future outcomes.
Statistical: Making predictions based on numerical data analysis.
Probability: Based on prior data for the likelihood of a specific event (like a white Christmas).
Weather type: Grouping patterns (such as when a jet stream dips down).
Climatological forecasts: Made months in advance and based on typical patterns for an area.

What is a Chance of Rain?

Percentage of area coverage that will experience rain.
Percentage of time rain falls in a given period.
Confidence level of the forecaster's prediction.
(Random) number a dog might pick based on its food bowl

Time Range of Forecasts

Very short range: Up to 6 hours. Data from Doppler radar, pattern recognition, experience. Forecasters distinguish between Watch (conditions favor hazardous weather) and Warning (hazard is occurring).
Short Range: 12 to 72 hours (3 days). Uses Doppler radar & surface maps.
Medium range: 3 to 8 days into the future. Uses statistical forecasts.
Long range: Beyond 8 days, up to 16 days. More of an overview, using computer models to project conditions.
Climate: Seasonal forecasts, often from teleconnections like El Niño and La Niña.

Accuracy and Skill in Weather Forecasting

A bias for fair weather exists, making a simple forecast for fair weather half the time already statistically average.
Skilled forecasters improve predictions beyond persistence and climatology.

Determining Movement of Weather Systems

Mid-latitude cyclones and fronts move in the same direction and speed as the past six hours.
Low-pressure areas move parallel to isobars of warm air, toward the greatest pressure drop.
High-pressure areas move toward the greatest pressure rise.

Studying That Suits You

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Description

Test your knowledge about fundamental concepts in weather forecasting. This quiz covers topics such as weather balloons, Doppler radar, and forecasting methods. Explore how various tools and models are used to predict weather and understand the science behind it.