The 300mb map defines the jet stream position. The 500mb map illustrates the positions of and troughs and ridges, which may indicate areas of stormy or fair weather. The 850mb map can be used to indicate the presence or absence of moisture available for precipitation. Model Forecasts Computer models use current weather conditions to project how conditions will change in the coming hours and days. The model output must be interpreted, since few normal surface features are drawn on the maps.
Many models are available, each with different strengths and weaknesses.
These are good to use as a guide but be careful about relying on them only. Satellite Imagery Satellite observations display existing cloud conditions. Water vapor shows the percentage of water vapor existing through the atmosphere. Radar Imagery Radar imagery displays areas where precipitation is occurring in liquid or solid form. This is not a forecast product, but rather a depiction of current conditions.