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WEATHER - PowerPoint PPT Presentation

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WEATHER. Adapted from Skračić ,T., „ Waypoint ”. Glossary :

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AdaptedfromSkračić,T., „Waypoint”



weatherconditions, high / lowpressure, windbelts, localpatterns, barometer, weathersystems, anticyclone, depression, clockwise, anti-clockwise / counter-clockwise, moveeastward / westward, upward / downward, at sealevel, onshorewind, down-slopewind, saturatedair, fog, dew, deadcalm, breeze, gale, storm, hurricane, seacondition, ripples, waves, crests, spray, foam, impairedvisibility,climate, hinterland, mainland, coastalarea, maestral (NW), tramontana (N), burin (NE), bura (NE), levant (E), jugo (SE), lebić (S-SW), pulent(SW-W), calm / roughsea, gust, thunder, coastal radio station, harbourmaster’s office.


RadiantenergyfromthesunheatstheEarth's surfaceunevenlysothattheatmosphereis warmerin some placesthaninothers; sincewarmair is lessdensethancoldair, itrises.

  • Cold airsinks to replaceitandvariationsaboveandbelowaveragepressureoccurresultinginregionsofrelativelyhighandlowpressure.
  • Air alwaysmovesfrom a regionofhighpressureto one oflowerpressure – but notdirectlybecausethemovement is deflectedbytherotationoftheEarth. Theflowofair is felt as windwheneverthere is a differenceinatmosphericpressurebetweentwolocalities; itsstrengthis determinedbythe rate of change inpressurebetweenthetwocentres.


  • pressure is one ofthesailor's principleindicationsofimpendingchanges to windandweatherinhisarea. In general, whenthebarometer is steady, or risingsteadily, thisindicatesfairweather. Ifit is fallingslowly, thisindicatesrain, possiblywind. Whenthebarometeris fallingor risingrapidly, thisindicatesstrongwind – probablyrain.
highs and lows
  • Anticyclonesanddepressions (highsandlows) are thetwomainweathersystemsofthemiddlelatitudes. Inthenorthernhemisphere, ananticyclone is a systemwherewindsblowin a clockwisedirectionaroundareasofhighpressure. Thestrongestwindsblowroundtheouterextremitiesoftheareaandgraduallydiminishinstrengthtowardthe centre wherethey are light or non- existent. Anticyclones are fairweathersystemswithmoderatewindsandreasonablyclearskies. They are generallyslowmoving, sometimesremainingstationary for severaldays. Depressionsandtheirassociatedfronts are largely
  • responsible for unsettledweather, strongwindsandheavyrainfall. A depression is anareaoflowpressurearoundwhichthewindsblowinananti-clockwisedirectioninthenorthernhemisphere. Theyvarygreatlyinsizeandintensityandcanmoverapidlyinanydirection but most usuallyeastward.
local winds
  • Wind is movingaircreatedby temperature differences. Localwindsinvariousforms are a modification to the general weatherpatternbut stemfromthe same basiccause. Seabreezesdevelopincoastalareawhenconvectionovertheland on a warmsunnydaycausesstrongupwardcurrentsofair. Therisingairis replacedbyaninflowofairfromovertheseawhichcreatesanonshorewind.
at night
At night
  • At nighttheprocess is reversedandthelandbreezeoccurs. TheEarthcoolsquicklyaftersunsetwhilethesearetainsits temperature andsoair is drawnofftheland to replacethewarmairrisingfromoverthesea.
katabatic wind
  • Inareaswherethecoastline is more dramaticandcloudlessskiesat nightresultinradiationcoolingoftheland, a strong, down-slopewindcandevelop as airincontactwiththegroundbecomeschilledandflowsrapidlydownthehillside.
fog and sea fog
  • Fogcanform at any time ofyear. Itoccurswhenwarmmoistair is cooledsufficiently to becomesaturatedandcondenseintowatervapour. Seafog (advection) occurswhenwarmmoistairflowsover a relativelycoldseasurfaceandthe temperature oftheairincontactwiththissurface is lowered. Ifthesea temperature is belowthedewpoint temperature oftheairandcoolingcontinuesuntiltheair is saturated, condensationwilltake place andformmist or fog.