This glossary, is meant to briefly define scientific terms (in ABC order), that may not be familiar to many who read my blog. More terms will be added here.

AO (Artic Oscillation): The positive phase (+AO) has the polar vortex near the north pole and supports warmer than normal temperatures for much of North America.. The negative phase (-AO) has ridge over the north pole, displace polar vortex into lower latitudes. This phase supports colder than normal temperatures for most of North America.

CAA (Cold-Air Advection):  The wind flow of colder air into a region of warmer air. The warmer airmass is replaced by the colder airmass.

CAPE (Convective Available Potential Energy): The amount of positive buoyancy a lifted parcel has and an indicator of instability in the atmosphere. This is convective parameter primarily used to forecast severe weather or thunderstorms.

EPO (Eastern Pacific Oscilation) The positive phase (+EPO) has trough over parts of Alaska, Western Canada, or the NE Pacific Ocean. The negative phase (-EPO) has a ridge over those same regions. The +EPO typically supports warmer than normal temperatures for much of CONUS.

Frontogenesis – An increase in the horizontal thermal gradient with time.

Frontoloysis – An decrease in the horizontal thermal gradient with time. (The oppposite of frontogenesis)

Isentropic Lifting:  Thermodynamic lifting caused by warmer air overriding cold air.

Lapse rate: The rate the temperature changes with height. A faster decrease of temperature change with height, results in steeper lapse rate and a more unstable atmosphere.

NAO ( North Atlantic Oscilation)  The positive phase (+NAO) has a low pressure or trough over Greenland and supports more warm weather in the East. The negative phase (-NAO) typically has blocking ridge over Greenland and supports more cold and snowstorms during the wintertime.

However, they are different types of -NAO patterns, that don’t have a blocking ridge right over Greenland. They commonly referred to the below:

West-Based -NAO: Has a blocking ridge more over the Davis Strait/Baffin Island. This favors more snowstorms for Mid-Atlantic or Southeast US.

East-Based -NAO: Has a blocking ridge near or over Iceland. This favors more winter storms for the Northeast US or New England.

50/50 Low: This term nicknamed by meteorologist Dave Tolleris, for an a closed 500mb low near 50N 50W position or New Foundland. This low is cold air source and helps buckle the flow along the east coast.

PNA (Pacific/North American Pattern) The positive phase (+PNA) has ridge over Western North America and trough over Eastern North America. Supporting colder than normal temperatures over the Eastern US. The negative phase (-PNA) typically has trough over the Western US and a Ridge over Eastern US.  Supporting warmer than normal temperatures over Eastern US.

Polar Vortex:An upper-level cyclonic circulation with a cold, dense airmass, located near the north and south poles. It is stronger during the winter and weaker the during the summer. Sometimes during the winter, a piece of the polar vortex, will drop south and bring very cold weather to the CONUS.

Pressure Gradient – The rate that pressure changes with distance. A strong pressure gradient, has a large difference between lower and higher pressures, over a short distance.

Thermal Gradient – The rate that temperature changes with distance. A strong thermal gradient, has a large difference between lower and higher temperatures, over a short distance. Thermal gradients often form cold or warm fronts.

WAA (Warm-Air Advection) The wind flow of warmer air into region of colder air. Cold air is more dense. Warmer air rides over colder air first.