A blizzard is a severe winter storm defined by three conditions: sustained or frequent wind gusts of 35 miles per hour or greater, falling or blowing snow that reduces visibility, and visibility reduced to one-quarter mile or less for a period of three hours or longer. The unique combination of heavy snow and high winds makes blizzards exceptionally dangerous, paralyzing travel and creating life-threatening conditions. Specialized monitoring technology is necessary to track these powerful storms and provide the public with the advance notice required for safety and preparedness.
Satellite Systems for Storm Tracking
Meteorologists begin tracking blizzards using Geostationary Operational Environmental Satellites (GOES) and Polar-orbiting Satellites, which provide a global view of developing storm systems. Geostationary satellites orbit at approximately 22,300 miles, moving at the same rate as the Earth’s rotation, allowing them to remain over a fixed point on the equator. This stationary perspective enables continuous, near-real-time imaging of cloud patterns and storm movement, which is useful for short-term forecasting.
Polar-orbiting satellites travel in a lower, north-to-south path, passing over the poles multiple times a day. Their closer proximity to Earth, around 512 miles up, allows them to collect high-resolution data invaluable for longer-term predictions. These satellites measure atmospheric temperature and water vapor at various layers, providing detailed vertical profiles of the atmosphere.
The data collected from both types of satellites are analyzed using different spectral bands, including visible, infrared, and microwave. Infrared sensors measure the temperature of cloud tops, with colder temperatures indicating higher cloud development associated with heavier snowfall. Microwave sensors penetrate upper cloud layers, allowing forecasters to estimate precipitation intensity and the overall moisture content within the storm system.
Ground-Level Measurements
As a blizzard approaches, ground-based technology provides the localized data necessary for immediate warnings. The Next Generation Weather Radar (NEXRAD) system uses Doppler radar technology to detect precipitation and wind velocity. This radar transmits microwave pulses and measures the frequency shift of energy returned from snowflakes and ice crystals to determine their motion.
Modern radar uses dual-polarization technology, sending out horizontal and vertical energy pulses to analyze the shape and size of precipitation particles. This capability allows meteorologists to distinguish between rain, sleet, and snow, accurately forecasting snowfall rates and accumulation. The radar’s velocity data also helps identify areas of intense wind gusts and the potential for blowing snow.
Automated Surface Observing Systems (ASOS) and Automated Weather Observing Systems (AWOS) are networks of automated stations providing continuous, surface-level weather reports. These systems measure air temperature, dew point, atmospheric pressure, and wind speed and direction. For a blizzard, horizontal visibility is important, as sensors use light-scattering technology to determine how far a person can see.
ASOS stations issue special reports when parameters, such as a rapid drop in visibility below one-quarter mile, are met, confirming a blizzard event is underway. The combination of surface wind speed and low visibility measurements from these stations forms the basis for localized blizzard warnings.
Vertical Atmospheric Data Collection
To understand the three-dimensional structure of an approaching blizzard, meteorologists rely on data collected through the vertical column of the atmosphere. Radiosondes, commonly known as weather balloons, are launched twice daily worldwide to gather atmospheric profiles. These instrument packages transmit data on pressure, temperature, and relative humidity as they ascend through the troposphere and into the stratosphere.
Wind speed and direction at various altitudes are derived by tracking the radiosonde’s position using GPS technology. This vertical profile data helps identify atmospheric features, such as temperature inversion layers or pockets of warm air aloft. The presence of warm air dictates whether precipitation falls as snow, sleet, or freezing rain, significantly impacting the storm’s severity.
Supplemental tools like wind profilers use Doppler radar principles directed vertically to provide near-continuous measurements of wind speed and direction. While radiosondes offer a snapshot in time, wind profilers offer temporal resolution that helps forecasters monitor changes in wind shear and momentum transfer. Understanding the vertical wind profile helps predict how much upper-level wind energy will mix down to the surface, contributing to the sustained high winds defining a blizzard.
Numerical Weather Prediction
The vast amounts of data collected from satellites, ground systems, and vertical soundings are fed into sophisticated Numerical Weather Prediction (NWP) models. These models are complex computer programs that use the fundamental equations of physics and fluid dynamics to simulate the future state of the atmosphere. Supercomputers process trillions of calculations and integrate the massive global datasets into a cohesive forecast.
Data assimilation involves combining the latest observations with a previous short-range forecast to create the most accurate starting point for the model run. Models like the Global Forecast System (GFS) and the North American Mesoscale (NAM) model then project the storm’s evolution. These models simulate the path, intensity, and timing of the blizzard, predicting crucial factors like the storm’s track and the location of the heaviest snowfall.
Forecasters analyze the output from multiple NWP models, often running ensemble forecasts that introduce slight variations to gauge the certainty of a prediction. If multiple model runs converge on a similar outcome, confidence in the blizzard forecast increases. This computational stage transforms raw observational data into actionable predictions, allowing meteorologists to issue forecasts and warnings days in advance.