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   Easterlies - The name given to those wind belts where the winds blow from east to west (the polar easterlies, equatorial easterlies and tropical easterlies).

   Easterly Wave - A wave-like disturbance within the broad belt of tropical easterlies.  Some of these may grow into tropical depressions.

   Echo - The general term in radar for the display on the radarscope of the radio signal scattered or reflected from a target.



1982-1983 El Nino event

Note large red area off South America

indicating much warmer than normal

sea surface temperatures.


   El Nino - This term, meaning "the Child" and referring to "the Christ Child", is the name given to a major increase of the sea surface temperature over the eastern and central equatorial Pacific Ocean.

   Elephanta - In September and October at the end of the southwest monsoon, a strong southeasterly wind, named the elephanta, occurs on the Malabar Coast of India.

   Elves - Very brief doughnut-shaped illuminations which occur about 56 miles above thunderstorms and are usually associated with very powerful, positive lightning discharges.

   Elvegust - In the upper part of the Norwegian fjords, this is a cold, descending squall.

    ENSO - Acronym for El Nino-Southern Oscillation.

   Entrainment - Mixing of environmental air into an existing air current (such as a thunderstorm updraft) so that the environmental air becomes part of the air current.

   Entrance Region - The region of confluence upstream from a wind speed maximum in a jet stream where air is entering the region of maximum winds (jet max) and is accelerating.

   Etesians - In the eastern Mediterranean Sea and Aegean Sea, the prevailing north winds during the summer.

   Evaporation Fog - Fog which has formed due to evaporation of water whose temperature is warmer than that of the air.

   Evaporation Frost - Frost which is the result of cooling by evaporation due to dry winds with temperatures above freezing blowing over a moist surface.  Cooling to below freezing is then caused by latent heat loss. 

   Exit Region - The region of diffluence downstream from a jet max (wind speed maximum in a jet stream) where air is moving away from the area of maximum winds and is slowing down.

   Extratropical Cyclone - A term referring to any migratory cyclone (low) of the middle and high latitudes (outside of the tropics).



                                         Eye of Hurricane Andrew


   Eye - The fairly circular area of light winds found in the center of a tropical cyclone.   

   Eyewall - The ring of cumulonimbus clouds which surround the eye of a tropical cyclone 

   Fahrenheit - A temperature scale which has the freezing point of water at 32 degrees and the boiling point of water at 212 degrees.

   Fair - As used in weather forecasts, this term implies less than .4 sky cover of low clouds; no precipitation; no extreme visibility, wind or temperature conditions; no restrictions to visibility; and winds generally less than 11 mph.

   Fall Wind - A wind which, due to its lower temperature and greater density, gains speed as it goes down a slope.  It results from accumulated cold air either spilling over a mountain range or down a slope.

   Family of Tornadoes -Tornadoes produced in sequence by one supercell thunderstorm.

   Fata Bromosa - This name, which means "fairy fog", is sometimes seen along with a superior mirage and appears as a distant fog where, in reality, no fog exists.



Fata Morgana Mirage Badlands National Park

From the Rapid City, South Dakota NWS Office

All the mesas and other interesting objects which

appear in the hazy part of the photo are really not

there at all.

   Fata Morgana - This term, meaning "fairy Morgan" and named after King Arthur's half-sister who supposedly could create castles in the air, is a mirage which causes the appearance of castles, cities, forests, islands, or mountains where no such features exist in reality.  In many cases this type of mirage is actually caused by multiple superior images which may be magnified or even enhanced by an inferior image 



                                                  Cirrus Fibratus

   Fibratus - Clouds with a striated or hair like composition with their individual filaments plainly separated from each other.



                      Flanking Line by Michael James - photo from Flickr.  


   Flanking Line - A line of cumulus clouds usually found on the southwest edge of the most active part of a parent cumulonimbus and connected to it.

   Flash Flood - A flood which comes rapidly with little warning usually after intense rainfall.

   Flist - The name given in Scotland to a sudden shower which is accompanied by a squall.



                                             Cirrocumulus Floccus


   Floccus - Clouds which have each separate element as a tuft with a puffy (cumulus-like) or rounded appearance and whose lower part is rather ragged.

   Flood - The accumulation of water in areas not normally covered by water or the overflowing of any stream beyond its normal banks,

   Foehn - A downslope wind which is warm, dry and often gusty as it descends the lee side of the Alps due to cross-barrier flow over the mountains resulting from synoptic-scale weather patterns.



                                Foehn Wall Clouds over the Alps.


   Foehn Wall - The leeward edge of the orographic cap cloud as it is viewed from the lee side of the mountains and appearing as a wall of cloud.  It is also called a foehn bank.

   Fog - The visible mass of water droplets suspended in the atmosphere near the surface of the earth.  Fog is, in reality, a cloud with its base at the earth's surface, and, according to international definition it lowers visibility below 0.62137 mile (1 kilometer).

   46 Degree Lateral Arcs - Sometimes given the name supralateral or infralateral, depending upon whether they are mostly above or below the sun, these arcs are a halo in the form of arcs near the halo of 46 degrees.  The arcs are the result of light being refracted (bent) as it passes through the 90 degree prism ends of columnar ice crystals which have their long axis oriented horizontally.

   Fractus - A type of cloud which is usually rather small but irregular in size and shape and presents a wind-torn, shredded appearance.

   Freeze - A condition existing over a widespread area when the surface air temperature is expected to be 32 degrees Fahrenheit or lower for a significant period of time.

   Freezing - The transition of a substance from the liquid to the solid state.

   Freezing Drizzle - Drizzle which falls in the liquid state but freezes upon impact with the ground and other objects with temperatures at or below 32 degrees Fahrenheit and creates a coating of glaze.

   Freezing Fog - Fog composed of water droplets whose temperature is below 32 degrees Fahrenheit and which freeze upon impact with cold surface objects creating a coating of rime or glaze.

   Freezing Level - The lowest height in the atmosphere at which the air temperature equals 32 degrees Fahrenheit.

   Freezing Nucleus - Any particle within supercooled water which starts the growth of an ice crystal.  

   Freezing Rain - Rain which falls as liquid but then freezes upon impact with the ground and other exposed objects to form a coating of glaze.

   Front - The boundary, or transition zone between two different air masses.

   Frontal Fog - Fog which is associated with frontal zones or frontal passages.

   Frontal Inversion - A temperature inversion with temperature rising with height upon vertical ascent through a sloping front.

   Frontal Wave - A horizontal, wave-like deformation of a front which is associated with a peak of cyclonic circulation in the adjacent wind flow.  It is a very weak area of low atmospheric pressure.

   Frontogenesis - The formation of a front.

   Frontolysis - The dissipation of a front.

   Frost - The layer of ice crystals formed on exposed surfaces by direct deposition of water vapor to solid ice which occurs when temperatures fall below freezing.

   Frost Smoke - A rare fog composed of ice crystals which forms when extremely cold air at very low temperatures flows over warmer water.

   Fujita Scale - A scale developed by Dr. Theodore Fujita to classify tornadoes according to wind damage.  Originally, this scale was as follows:

   F0 - Winds less than 73 mph

   F1 - Winds 73-112 mph

   F2 - Winds 113-157 mph

   F3 - Winds 158-206 mph

   F4 - Winds 207-260 mph

   F5 - Winds 261-318 mph

However, an Enhanced Fujita Scale (EF Scale) has recently been developed which takes more factors into account.  This new scale has values assigned as follows:

   F0 - Winds 65-85 mph

   F1 - Winds 86-110 mph

   F2 - Winds 111-135 mph

   F3 - Winds 136-165 mph

   F4 - Winds 166-200 mph

   F5 - Winds above 200 mph

   Fujiwhara Effect - The tendency of two tropical cyclones which are near each other to rotate cyclonically (counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere) around each other due to mutual advection. 





   Fulgurite - A glassy tube formed when lightning strikes sandy soil.



                       Funnel near Jackson, Missouri on April 12, 2005.


   Funnel Cloud  -  A  rotating  cone-shaped  or  funnel-shaped  cloud  of condensation extending downward from a convective cloud (such as a cumulus congestus or cumulonimbus) but not in contact with the ground.

   Furiani - A violent, short-lived southwest wind followed by a gale from the south or southeast in the area of the Po River, Italy.












Copyright 2006 Ronald Hahn. All Rights Reserved