Common Weather Terms

ACE Index: Accumulated Cyclone Energy Index.  The measure of total seasonal activity used by NOAA.  It is a wind energy index that is defined as the squares of the maximum sustained surface wind speed, in knots, measured every 6 hours for all named storms while they are at least tropical storm strength. The ACE index is combined with the seasonal total number of named storms, hurricanes, and major hurricanes to categorize a hurricane season as being above normal, near normal, or below normal. The 1950-2000 seasonal average for ACE in the Atlantic Basin is 96.

AGW: Anthropogenic Global Warming- Refers to human induced global warming. Commonly referenced when discussing current climate change 

AMM- Atlantic Meridional Mode- The dominant source of coupled ocean-atmosphere variability in the Atlantic.

AMO: Atlantic Multidecadal Oscillation: A multidecadal pattern in the Atlantic Ocean in the Northern Hemisphere, which is mainly identified through variations in sea surface temperatures. The AMO is significant because there is a correlation between its state and temperatures and precipitation in the Northern Hemisphere. The AMO impacts Atlantic hurricane activity. There tends to be more hurricanes when the AMO is in a warm phase as has been the case since 1995. and was before from the 1930s to 1960s.

AO: Arctic Oscillation- The AO refers to opposing pressure patterns in the middle and high latitudes of the Northern Hemisphere. The negative phase is represented by high pressure over the polar region and lower pressure at the mid-latitudes. The opposite occurs during the positive phase. The AO plays a role in weather patterns as it affects the track of storms, and the location of cold air. When the AO index is negative, there tends to be high pressure at the pole and weaker zonal winds, so more cold air is able to drop down into the mid-latitudes. 

CAD: Cold Air Damming- The phenomenon in which a low-level cold air mass is trapped topographically. This is often observed in winter with arctic air masses east of the Appalachians. East - northeast winds pile up cold air on the east side of the mountains cause pressures to rise and nose south. Damming is observed from New England as far south as Georgia.

CAPE: Convective Available Potential Energy- The amount of energy a parcel of air would have if lifted a specific distance vertically in the atmosphere. CAPE is a measure of atmospheric instability, and is useful in predicting severe weather.

CFSR- Climate Forecast System Reanalysis- Data developed by NOAA’s NCEP. The CSFR was designed and executed as a global, high resolution, coupled atmosphere-ocean-land-sea ice system to provide the best estimate of the state of these coupled domains over the 31-year period of 1979-2009.

CONUS: The contiguous United States or mainland United States are the 48 U.S. states on the continent of North America that are south of Canada and north of Mexico, plus the District of Columbia.

EPAC/WPAC: As the Pacific straddles the 180th meridian, the West Pacific (WPAC or western Pacific, near Asia) is in the Eastern Hemisphere, while the East Pacific (EPAC or eastern Pacific, near the Americas) is in the Western Hemisphere.

ENSO: El Nino-Southern Oscillation- A see-saw pattern in surface pressures and ocean temperatures that occurs in the tropical Pacific Ocean. The warm oceanic phase is known as El Nino, and cold phase is called La Nina and includes high air pressure and colder ocean temperatures in the Eastern Pacific.  ENSO affects the location of the Jet Stream in the Pacific and North America and, in turn, storm tracks.  The state of ENSO affects global precipitation and temperature patterns and understanding the state of ENSO aids in snowfall, severe weather, and tropical cyclone forecasting.

By convention we use the NINO 34 (5N-5S 170W to 120 W) departure from normal SSTs as the measure for ENSO with departure from normal>0.5C for three consecutive months as threshold. Other measures include MEI and SOI.

EPO: Eastern Pacific Oscillation - A dipole pattern similar to the NAO in the Atlantic, but located in the eastern Pacific.  There is a tendency for heights/pressures/temperatures to be higher to the north and lower to the south in the negative phase and lower to the north and higher to the south in the positive phase.  The negative phase corresponds to widespread cooling over central and eastern North America and the positive phase to warming.

IPCC AR5: The Fifth Assessment Report (AR5) of the United Nations Intergovernmental Panel on Climate Change (IPCC), will be the fifth in a series of such reports. The IPCC was established by the World Meteorological Organization (WMO) and the United Nations Environment Program (UNEP) to assess scientific, technical and socio-economic information concerning climate change, its potential effects and options for adaptation and mitigation.

The Fifth Assessment Report is now underway and is expected to be finalized in 2014.

MEI: Multivariate ENSO Index- The MEI is used to monitor ENSO and is based on six variables observed over the tropical Pacific. These variables include sea-level pressure, zonal and meridional components of surface wind, sea surface temperature, surface air temperature, and total cloudiness in the sky. 

METAR: METAR is a format for reporting weather information. A METAR weather report is predominantly used by pilots in fulfillment of a part of a pre-flight weather briefing, and by meteorologists, who use aggregated METAR information to assist in weather forecasting. Raw METAR is the most popular format in the world for the transmission of weather data. It is highly standardized through International Civil Aviation Organization (ICAO), which allows it to be understood throughout most of the world.

MJO: Madden Julian Oscillation- An eastward tracking wave extending to high levels of the atmosphere which can enhance and then suppress vertical motion in the atmosphere, and which thus results in enhanced and then suppressed cloudiness and rainfall. The MJO cycles typically last 30 to 60 days. The MJO index has 8 different stages, and the stage of the MJO can affect temperature patterns in the United States and affect the frequency can be used to forecast enhanced periods of tropical activity in both the Pacific and Atlantic.

MSLP: Mean sea level pressure (MSLP) is the pressure at sea level or (when measured at a given elevation on land) the station pressure reduced to sea level assuming an isothermal layer at the station temperature.

NAO: North Atlantic Oscillation- One of the most commonly looked at teleconnection patterns for weather forecasting. The value of the NAO is determined by the differences in pressures over the high latitudes and central latitudes of the North Atlantic. The positive phase of the NAO is characterized by a low difference in pressure between the two regions, a below average pressure over the high latitudes, and an above average pressure over the central latitudes. The opposite occurs during the negative phase. The NAO is significant in forecasting because its state affects the intensity and location of the jet stream and storm track in the North Atlantic. As a result, significant changes in temperature and precipitation occur in Europe and North America based on the NAO.

NCDC: NOAA’s National Climatic Data Center maintains the world's largest climate data archive. The Center's mission is to preserve these data and make them available to the public, business, industry, government, and researchers.

NRL: Naval Research Labs is the corporate research laboratory for the Navy and Marine Corps and conducts a broad program of scientific research, technology and advanced development. NRL has served the Navy and the nation for over 85 years and continues to meet the complex technological challenges of today's world.

NWP: Numerical Weather Prediction uses mathematical models of the atmosphere and oceans to predict the weather based on current weather conditions.

PDO: Pacific Decadal Oscillation- a pattern of variability of climate that occurs in the Northern Hemisphere in the Pacific. Each stage generally lasts around 20 to 30 years. The cold phase features cooler ocean temperatures in the Eastern Pacific and warmer ocean temperatures in the western part of the Pacific. The opposite occurs during the warm phase. The PDO is often referenced in discussions of climate change since its state can significantly affect the global temperature and the occurrence of some types of weather events. It affects the favored ENSO state – the cold PDO favoring more frequent, stronger and longer lasting: La Niñas and the warm phase more frequent, stronger and longer lasting El Niños. 

PNA: The Pacific-North America (PNA) pattern is one of the most prominent modes of low-frequency variability in the Northern Hemisphere extratropics. The PNA pattern reflects a quadripole pattern of 500 millibar height anomalies, with anomalies of similar sign located south of the Aleutian Islands and over the southeastern United States. Anomalies with sign opposite to the Aleutian center are located in the vicinity of Hawaii, and over the intermountain region of North America (central Canada) during the winter and fall.

PVA: Positive Vorticity Advection, or PVA, is the result of more cyclonic values of vorticity advecting into lower values of vorticity. It is more generally referred to as "Cyclonic Vorticity Advection" (CVA). In the Northern Hemisphere, CVA produces divergence as a result of how there is a loss of cyclonic vorticity. Coriolis vorticity in this situation is ignored because it acts about the same on all the air flowing through the base of the trough. The divergence with CVA is significant because it creates forced lift in the atmosphere. This forced lift, in the presence of conditions favorable for atmospheric convection, can cause clouds or precipitation.

RTMA: Reatl Time Mesocale Analysis The National Weather Service (NWS) weather forecast offices (WFOs) produce and send digital forecasts to various users. These forecasts of hydrometeorological variables, such as temperature and precipitation, contribute to the generation of the NWS National Digital Forecast Database (NDFD). RTMA is a gridded analysis of the hydrometeorological variables that matches the NDFD spatial resolution.

SMFR- Stepped Frequency Microwave Radiometer: Remote sensing technology used to determine surface winds speeds derived from the sea foam created by winds at the ocean surface The technology provides a continuous measurement of surface winds.The instrument is attached to the wing of each aircraft in the fleet that flies through hurricanes, including the USAFR 53^rd WRS and NOAA Hurricane Hunters.

SOI: Southern Oscillation Index- The SOI is computed from normalized surface level pressure anomalies at Tahiti and Darwin Australia. Negative values of the SOI indicate a relatively small difference in pressure between Tahiti and Darwin, and is indicative of El Nino conditions. During a La Nina episodes the SOI is usually positive. During weaker ENSO events the SOI can oscillate positive and negative in response to the passage of the MJO waves.. 

THC: Thermohaline Circulation- A large scale serpentine circulation that traverses all the oceans. The portion in the Atlantic Basin plays a key role in the climate. The water sinks in southern ocean and the North Atlantic, the rate of which is  influenced by fluctuations in temperature and salinity. The circulation increases in speed when the water sinks more rapidly (when it cools and becomes more saline through evaporation). A strong (fast) THC usually correlates to the AMO being in its warm phase, which is typically when more Atlantic hurricanes occur and when more arctic ice melts. The hemispheric temperatures reflects the AMO as well as the propensity for drought in the US. Warm AMO periods (last 25-35 years) lead to warmer hemispheric temperatures and more frequent drought. .The conveyor belt surfaces again in the Indian and Pacific Ocean where it affects the ocean gyres and temperature anomalies there as well. 

WPO: Western Pacific Oscillation- The WPO pattern is a primary mode of low-frequency variability over the North Pacific in all months.  During winter and spring, the pattern consists of a north-south dipole of anomalies, with one center located over th Kamchatka Peninsula and another broad center of opposite sign covering portions of southeastern Asia and the wester subtropical North Pacific.  The positive phase of hte WP pattern is associated with above-average temperatures over the lower latitudes of the western North Pacific in both winter and spring, and with below-average temperatures over eastern Siberia in all seasons.  It is also associated with above-average precipitation in all seasons over the high latitudes of the North Pacific, and below-average precipitation across the central North Pacific especially during the winter and spring.

 

Weather Models:

CFSv2: The Climate Forecasting System version 2 - Climate forecast system was developed at the Environmental Modeling Center at NCEP. It is a fully coupled model representing the interaction between the Earth's oceans, land and atmosphere. It became operational at NCEP in March 2011.

ECMWF: European Center for Mid-range Weather Forecasts: ECMWF model is run every 12 hours, and produces a deterministic and ensemble forecast for global weather over the next 10 days. The model produces output for every 24 hour interval. The ECMWF model is often regarded as one of the best in the world due to its accuracy in mid range forecasting 

GFDL: Geophysical Fluid Dynamics Laboratory model- Includes specific intensity forecasts for hurricanes.

GFS: Global Forecasting System A global numerical weather prediction model run by the National Centers for Environmental Prediction (NCEP). The model is run four times per day and forecasts out to 384 hours (16 days). Data is output every 6 hours for the first 180 hours of the forecast. After that, data is output every 12 hours and the model resolution decreases.

NAM: North American Mesoscale Model-A numerical weather prediction model that is run by NCEP. The NAM is run every 6 hours, and its forecasts go out to 84 hours. This model is used for short-term forecasting because its resolution is higher than the resolution of the global models.

NOGAPS: Navy Operational Global Atmospheric Prediction System- The Navy’s global operational weather model. The model has also been adapted for tropical weather prediction.

 

RAP: The Rapid Refresh (RAP) model is an operational NCEP hourly updating operational weather prediction system covering North Americacomprised primarily of (1) a numerical forecast model and (2) An analysis/assimilation system to initialize that model.

 

RUC: Rapid Update Cycle-an operational weather prediction model run by NCEP. The RUC is run every hour and contains numerical forecasts out to 18 hours. The RUC Model is used for short range or near-term forecasting. The model analyzes current weather data and determines a short term forecast based on the analysis.

UKMET: United Kingdom Meteorological Office model

WRF: The Weather Research and Forecasting Model (WRF) is a next-generation mesoscale numerical weather prediction system designed to serve both operational forecasting and atmospheric research needs. WRF is suitable for a broad spectrum of applications across scales ranging from meters to thousands of kilometers.

WW3: Wave Watch III- The third generation ocean wave model produced by NOAA and NCEP. The WW3 is the wave model used by NCEP, NOAA, the NWS, and many other forecasting organizations for wave forecasting.

  

 

Common Abbreviations:

ACC- Anomaly Correlation Coefficient

CAA: Cold Air Advection

DFN: Departure from normal

NHC: National Hurricane Center

NCEP: National Center for Environmental Prediction

NHC:  National Hurricane Center

HPC: Hydrometeorological Prediction Center

IPCC: Intergovernmental Panel on Climate Change

ITCZ: Intertropical Convergence Zone

PV- Potential Vorticity

PVU- Potential Vorticity Unit

SPC: Storm Prediction Center- Part of the National Weather Service. Responsible for providing hazardous weather forecasts including tornado and severe weather watches for the United States.

SST: Sea Surface Temperature

TCHP: Tropical Cyclone Heat Potential

TPC: Tropical Prediction Center

WAA: Warm Air Advection