Nebulosus: A layer of cloud (such as stratus) with no clear markings; A thin layer of clouds without distinctive characteristics. Applies mainly to cirrostratus and stratus.

Negative Feedback Mechanism: As used in climatic change, any effect that is opposite of the initial change and tends to offset it.

Nephoscope: A device for measuring the direction and angular velocity of clouds.

Neutercane: A term invented here in the good old USA to describe subtropical cyclones with a radius of much less than 100nm giving hurricane force winds. The thermal structure of its core is warmer than a sub-tropical cyclone and cooler than a hurricane.

Newton: A unit of force in physics. The force that accelerates a mass of 1kg by 1m per second per second.

NEXRAD: An acronym for Next Generation Weather Radar. It is also known as WSR 88D.

Nimbostratus (Ns): A combination of nimbus (rain) and stratus (flattened layer). A deep layer of thick, grey, formless rain cloud; A gray, often dark, cloud layer whose appearance is usually rendered diffuse by falling rain or snow, nimbostratus usually covers the entire sky and is thick enough to blot out the sun. Ragged clouds or shreds of clouds, called scuds, frequently occur below the main layer, indicating imminent wind and precipitation. The rain or snow produced by nimbostratus is steady and persistent, unlike the showers produced by some cumulus clouds. Nimbostratus is often classified as a low-altitude cloud, but it can appear at middle altitudes during a rainstorm.

Nitrogen Oxides (NOX): Gases that form when nitrogen in the air reacts with oxygen.

Noctilucent Cloud: Thin but sometimes brilliant clouds occasionally seen towards the north in summer from latitudes of 50 degrees or more when the Sun is not far below the horizon. These clouds are at heights of 80-85km and seem to move at 100-300 knots!

Nocturnal Inversion: See Radiation inversion.

Normal Lapse Rate: The average drop in temperature with increasing height in the troposphere; about 6.5°C per kilometer.

Normand's Theorem: On an aerological diagram, the dry adiabatic through the dry bulb temperature, the saturated adiabatic through the wet bulb temperature and the saturated mixing ratio line through the dew point all meet at a point. From this, one may derive an approximate condensation level by taking the difference between the surface temperature and dew point (in °C) and multiplying by 400 to get a height in feet, e.g. temp. 20°C, dew point 10°C, cloud base approximately 4,000 feet.

Northeaster (Nor'easter): A name given to a strong, steady wind from the northeast that is accompanied by rain and inclement weather. It often develops when a storm system moves northeastward along the coast of North America.

Northern Lights: See Aurora.

Nowcasting: Short-term weather forecasts varying from minutes up to a few hours.

Numerical Weather Prediction (NWP): The latest weather observations are converted into numbers which are then processed by computer which solves the equations of motion and physical equations of state. The numerical answers are then converted back into charts, graphs, tables and typed forecasts.