N is for…

Nimbostratus:

Nimbostratus in action

Grey cloud layer, (from Latin nimbus or rainy cloud and stratus or spread out) often very dark and associated with continuous rain or snow.

Nowcasting:
The detailed description of current (localised) weather, together with forecasts for the following 2 or 3 hours, usually relying on remote sensing such as satellite imagery and weather radar.

Numerical Weather Prediction:
The practice of using mathematical equations, applied to measurements of initial weather conditions to produce a weather forecast. Powerful computers are widely used in this way to produce localised, short term forecast as well as global, long range predictions.

Never trust a Northerly!
A phrase constantly kept in mind by BBC weather forecasters in the North of England when deciding what to "go for", especially during the winter months.