Hi, welcome to TWO!
I'm not sure there's anywhere which has the abbreviations that people use, but here's a starter:
AH - Azores High. The semi-permanent area of high pressure which is supposed to stay near the Azores. It's the breaker of many a cold spell in winter!
AMO - Atlantic Multidecadal Oscillation. Over a period of decades, the North Atlantic flips between a generally warmer than average temperature profile to a colder than average profile. The cold phase is associated with increased snow episodes in winter in the UK. Currently in its warm phase, a switch to the cold phase is likely within a decade or so.
AO - Arctic Oscillation. This is the difference compared to normal pressure over the Arctic. A positive AO means pressure is lower than normal, which can bring stormy conditions with deep lows over the Atlantic. A positive AO means higher pressure than normal over the Arctic, with weaker lows and a weaker, often meandering jetstream. This can lead to HLB or MLB forming.
CAA - Cold Air Advection. This is the reverse of a plume, where cold air moves southwards from the Arctic. This is often seen when pressure rises over Greenland, for example.
ENSO - El Nino Southern Oscillation. Another term for the El Nino / La Nina cycle.
GH - Greenland High. Much in demand by folks in the north and west during winter, brings such memorable spells for the UK as the cold of December 2010.
PDO - Pacific Decadal Oscillation. The Pacific Ocean undergoes temperature switches from time to time, with a warm area in the North Pacific surrounded by colder waters along the western coast of America and Alaska (negative) swapping with a colder core surrounded by warmer waters along the same regions (positive). This indirectly affects the UK by altering the strength of the Pacific jetstream (and hence the jetstream downwind over America and the Atlantic).
FI - Fantasy Island. Usually refers to charts 240 or more hours away, but in some circumstances can be 96 hours or less. It's used when referring to charts which probably won't come off as shown.
HLB - High-Lattitude Blocking. The holy grail for cold fans is a combination of high pressure over Scandinavia, alternating with high pressure over or east of Greenland. These blocking highs impede the progress of our usual Atlantic weather systems and are responsible for our memorable cold spells of years past.
MJO - Madden–Julian Oscillation. This measures the progression of areas of tropical rainfall, measured in 8 phases (1-8). It's not directly relevant to the UK, but in certain phases (7, 8, 1) it can help reinforce any blocking that may occur in our region.
MLB - Mid-Lattitude Blocking. Usually associated with a split jetstream, this is where high pressure becomes slow-moving in the mid-lattitudes (=roughly on the lattitude of the UK). This brings warm weather in summer, cold, calm conditions in winter. It can sometimes be a precursor to HLB.
MT - Mountain Torque. This refers to the effect large mountain ranges (such as the Himalayas) have on the polar vortex in winter. If conditions are right, upper air is skewed northwards as it passes over the mountains which can cause significant warming aloft, potentially leading to an SSW event.
NAO - North Atlantic Oscillation. The difference in pressure or 500hPa heights between the Azores and Iceland. A negative NAO means pressure is lower than usual over the Azores and/or pressure is higher than usual over Iceland. This often, but not always, means weather systems are aligned to bring colder than normal conditions over the UK. Conversely, a positive NAO imples stronger than normal SW'lies, with milder weather than normal.
PNA - Pacific-North American teleconnection pattern. This refers to pressure over the Pacific and is roughly anologous to the NAO index. A positive value implies higher than normal pressure over Hawaii and lower than normal pressure near Alaska. It's associated with a strong Pacific jet. The negative phase involves lower than normal pressure over Hawaii and higher than normal pressure near Alaska, often causing a split jet and a weaker flow over the Pacific. It has an indirect effect on the UK by modifying the upstream jet pattern.
PV - Polar Vortex. The focus of attention of cold-lovers in winter, this is an upper low pressure area which is associated with deep cold Arctic air. The effects of it vary depending on location, but when it's located to the west of Greenland and is stronger than normal some exceptionally mild weather can result for the UK. Conversely, when it's weak or split into two or more chunks, MLB or HLB is more likely to occur.
SSW - Sudden Stratospheric Warming. The reversal of zonal winds in the stratosphere. This can sometimes (but not always) promote high level blocking a week or more down the line.
WAA - Warm Air Advection. This is when a plume of warm air moves northwards, such as northwards along the west coast of Greenland when pressure rises over Greenland. What goes up must come down and warm air advection usually means cold air is forced southwards further east.
Edited by user
18 January 2016 19:06:07
|
Reason: Not specified