Lec 9 Adjusted: Weather Forecasting

Numerical Weather Prediction (NWP)

The routine daily forecasting of weather by computers using mathematical equations (atmospheric models) that describe how weather elements change over time.

Atmospheric Model

A mathematical model consisting of equations that provide approximations of the atmosphere's behavior under certain assumptions, used in NWP.

Prognostic Chart (Prog)

A "machine-made" forecast chart representing the predicted state of the atmosphere at a specified future time, showing isobars, contours, and pressure systems.

Limitations of NWP

1. Idealization of the real atmosphere, 2. Inaccurate boundary predictions in non-global models, 3. Sparse data availability in some regions, 4. Computational constraints of model resolution, 5. Unpredictable atmospheric chaos.

Ensemble Forecasting

A method that runs multiple forecasts from a single model, each with slightly different initial conditions, to reflect measurement errors and generate a range of possible outcomes.

Persistence Forecasting

A simple method that predicts future weather will be the same as the present weather. It is most accurate for very short time periods.

Steady-State (Trend) Forecasting

A method based on the principle that surface weather systems will continue moving in the same direction and at the same speed as they have been.

Analogue Forecasting

A method that predicts weather by finding past weather chart patterns that strongly resemble current conditions (pattern recognition).

Statistical Forecasting (Model Output Statistics - MOS)

A method that uses statistical relationships between historical NWP model outputs and observed weather to make forecasts for specific situations.

Probability of Precipitation (PoP)

A numerical forecast expressing the chance of measurable rain, calculated as PoP = Certainty x Areal Coverage. It does not indicate intensity or duration.

Climatological Forecasting

A forecast based solely on the historical climate (averages) of a particular region.

Lead Time

The amount of time between the issuance of a forecast and the occurrence of the predicted event. Types range from very short-range (

Forecast Accuracy

A measure of quality pertaining to how closely the actual weather agrees with the forecast for a specific time and place.

Forecast Skill

A measure of quality that compares a forecast's accuracy to simple reference forecasts like persistence (current conditions) or climatology (normal conditions).

Observation (Forecasting Step)

The first step in forecasting, involving the simultaneous measurement of weather elements worldwide via surface stations, upper-air soundings, satellites, and radar.

Sounding

A two-dimensional vertical profile of temperature, dew point, and winds, used to calculate indices for predicting phenomena like thunderstorms.

Station Model

A symbolic representation showing the weather conditions at a specific observation station on a weather map, including temperature, pressure, wind, clouds, and present weather.

Weather Data Analysis (Forecasting Step)

The step where processed data from surface maps, upper-air charts, and NWP models are analyzed to locate and delineate weather systems like highs, lows, and fronts.

Tropical Cyclone Wind Signal (TCWS)

A warning system that indicates expected wind threats from an approaching tropical cyclone, ranging from TCWS #1 (lowest) to TCWS #5 (highest).

Heavy Rainfall Warning System

A warning system for long-duration, widespread rain events (e.g., from monsoons or cyclones) with levels: Advisory (possible flooding), Alert (alarming flooding), Warning (serious flooding).

Thunderstorm Warning System

A warning system for short-duration rainfall events with levels: Watch (chance of development), Warning (thunderstorm is threatening).

Flood Advisory System

A system for monitoring and warning about river flooding, with levels from Monitoring to Severe Flood Warning, based on telemetered water level data or rainfall forecasts.