National Weather Service United States Department of Commerce

The Challenges and Complexities of Weather Forecasting, by Mark Bloomer

Weather forecasting is a complex and often challenging skill that involves observing and processing vast amounts of data. Weather systems can range from small, short lived thunderstorms only a few miles in diameter that last a couple hours to large scale rain and snow storms up to a thousand miles in diameter and lasting for days.

Forecasting ultimately is a three step process. These include:

1) Observing

2) Forecasting

3) Communicating.

When a forecaster comes on duty, their first order of business is to become familiar with what is currently happening in the weather. This includes looking at satellite imagery, surface data, precipitation reports, and getting a briefing from other forecasters on duty. The next order of business is to project weather changes into the future to derive a forecast. Short range forecasting, looking a few hours into the future, typically depends on closely observing how weather systems are currently evolving and tracking, and projecting their movement into the future based on what is understood about dynamics of the atmosphere. Forecasts out beyond a day rely more on numerical weather modeling. Numerical forecast models compile data from surface observations, weather balloons and satellite imagery to create a computer generated simulation of the weather into the future. The model simulations use dynamic equations that express how the atmosphere will respond to changes in temperature, pressure and humidity over time. Forecasters deal with many forecast models that are run several times a day and must decide which ones to rely on based on how well they seem to be handling current weather, how realistic their output is, and how consistent the forecast models are being from one run to the next. The forecaster may even decide that no model can be relied on at that time.

Once the forecasters have created a forecast that they are reasonably confident in, their next role is to deliver that forecast in a way that people can understand and appropriately respond to. The mission of the National Weather Service is to communicate forecasts in a way that helps save lives and protect property. When the potential exists for a weather event that may impact our forecast area, a weather watch will be issued such as a winter storm watch, a high wind watch or a thunderstorm watch. When a watch is issued, those who may be impacted are advised to stay closely tuned to updated forecasts for potential warnings. A weather warning means the warned event is expected and people in the affected area should prepare. National Weather Service warnings often include “call to action” statements which alert the public on how to prepare for the expected weather.

Following a significant weather event, forecasters will call weather spotters throughout their forecast area to ascertain the impact of a weather event on the area. They will gather information on how much rain or snow fell, and if any damage occurred due to weather. By reviewing the impact of an event, forecasters can learn how well their forecast verified as well as what may have happened that was unexpected, and thereby be able to improve on future forecasts.