Weather Forecasting
Learning Objectives
In order to properly forecast the weather the meteorologist needs data.
Thousands of weather stations all over the world collect surface measurements at 0000, 0600,120 and 1800 GMT daily.
Upper atmosphere data is collected using aircraft or radiosondes at 0000 and 1200 GMT daily.
Both the surface and the upper air data is sent to the World Meteorological Center in Washington DC and the National Meteorological Center in Maryland. The data is then used to prepare weather maps and "canned" forecasts.
Television and radio use either the prepared forecast or they can use the weather maps to prepare their own.
Types of Forecasts:
Persistence Forecast: forecast based on the continuation of the current weather conditions. It is short term and not accurate.
Steady State or Trend Forecast: forecast is based on the patterns of movement of weather systems. For example: if a front is moving W-E at 10 mph then this forecast would predict the weather in an area based on the continuation of that movement. This type of forecast can be unreliable.
Analogue or Weather Type Forecast: using patterns in the weather that have occurred in the past to make a prediction. For example; the last few times when a low pressure moved up the coast it intensified into a Northeaster therefore the low pressure currently moving up the coast will turn into a Northeaster.
Climatological Forecast: this is a vague long range forecast based on long standing climate trends. For example...it will be hot (mid 80's to 90's) and humid on August 23, 2000
Numerical Forecasts: most forecasts are numerical forecasts, very accurate. This forecast takes data gathered at the surface and in the upper atmosphere and puts it into numerical models. The models use 6-8 mathematical equations to show how temp, humidity and other atmospheric conditions will change over time. The models look at 18 layers of the atmosphere and using the collected data as a starting point predict 12 24, 36 and 48 hour into the future.
There are several models from which to choose. Each model emphasizes different pieces of data. A meteorologist will use the model most accurate for his area and will often modify or fine tune a prediction based on experience and local conditions. For example: a meteorologist living in Hampton Roads will use a model that emphasizes the role that surface water plays in weather. A meteorologist in the western part of the state may want to emphasize how topography controls weather.
It is important that the meteorologist takes into account local factors such as topography, bodies of water, forests etc. (anything that could have an affect on weather systems.)
Weather Lingo:
Partly Cloudy/ partly Sunny:there is no difference between these two. Clouds should be covering 30-70% of the sky.
Cloudy: clods should be covering 90% of the sky.
Fair: clouds cover less than 40% of the sky.
Slight Chance of Precipitation: there is a 10-20% chance of precipitation.
Chance of Precipitation: there is a 30-50% chance of precipitation.
Occasional Precipitation: there is a greater than 50% probability of precipitation but it will affect less than half of an area.
