Definition
A numerical weather prediction model run by the National Weather Service that produces short-range forecasts (out to about 84 hours) over North America at a higher resolution than larger global models. The NAM is one of several computer models whose output is used to generate the Significant Weather Prognostic Charts and other aviation forecast products.
Plain English
A weather forecasting computer model that focuses on North America. It looks at the atmosphere in finer detail than worldwide models, so it picks up smaller-scale weather features that matter for the next few days.
Context Anchor
Seen in aviation weather study and forecast discussions, especially when learning how significant weather prognostic charts are produced.
Derivation
Mesoscale comes from the Greek mesos meaning 'middle' and the English 'scale.' In meteorology, mesoscale refers to mid-sized weather features — things like thunderstorm complexes, sea breezes, and frontal bands — that are larger than a single storm but smaller than a continent. Calling the model 'mesoscale' tells you it is tuned to resolve those mid-sized features.
Why Pilots Care
Gives pilots a reliable picture of developing weather hazards along their route so they can choose safer altitudes and alternate airports.
Intuition Check
Do not read “model” as a small physical copy of something. Here, a model means a computer simulation that predicts future weather.
Example Sentence 1
The forecaster compared output from the NAM model and the GFS model before issuing the prognostic chart.
Example Sentence 2
Before departure the pilot checked the latest NAM model output on the prognostic chart for icing potential.