The surface meteorological chart above depicts the current surface conditions at chosen sights across North America. This map, updated shortly after each hour, illustrates the present weather patterns and the location of storm systems over the continental United States.
The hourly observations (updated every hour) contain information about surface temperature and dew point temperature in degrees Fahrenheit, sea level pressure, wind speed and direction, cloud cover and type of weather conditions occurring at each surface station during the last hour. The hourly observations link provides detailed information on how to decode and interpret the numbers and symbols at each station. The blue contours called isobars and depict areas of High and Low pressure.
In the background, infrared satellite data shows the cloud patterns over North America. The brightness of the cloud images is inversely proportional to the temperature of cloud tops, therefore the deep clouds with high (and thus cold) cloud tops typically indicating areas of intense rain and/or hail associated with deep convection appear brightest on this image. However high cirrus clouds will often also appear very bright, but these clouds do not produce precipitation. One can attempt to relate the areas of cloudiness to the pressure pattern and the areas of precipitation depicted by the radar data (previous panel). Clouds and precipitation tend to be associated with low pressure systems also known as midlatitude cyclones.
Midlatitude cyclones can be identified as a minimum in the pressure field, and an area of cyclonic circulation of the surface flow. These storm systems are typically characterized by cloud cover in the vicinity of the low pressure center, relatively warm and moist flow with a southerly component ahead of the cold front and colder and drier airmass behind it, as well as areas of precipitation associated with both warm and cold fronts.