Raymarine c97 - Glossary of Weather Terms

25.10Glossaryofweatherterms
TermDenition
ColdfrontTheboundarybetweentwodifferentairmasseswherecoldairpusheswarmairoutofthewayandbrings
colderweather.
CycloneAlargeareaoflowatmosphericpressure,characterizedbyinwardspirallingwinds.A“low”alsocalleda
“depression”.AlsothenameusedforahurricaneintheIndianOceanandWesternPacic.
Depression
Anareaoflowpressure.Alsocalledacyclone.
Dryline
Aregionwherethereisastronggradientindewpointtemperatures.Itisoftenfoundinaregionwhere
strongthunderstormsdevelop.
Forecast
Somethingthattellsuswhattheweatherisprobablygoingtobelike.
Front
Theboundarybetweentwomassesofairwithdifferenttemperatures(i.e.amassofcoldairandamassof
warmair).
High
Alsoknownasan'anticyclone'anareaofhighatmosphericpressurewithasystemofwindsrotating
outwards.Thisusuallymeansdryweather.Itistheoppositeofa'low'.
HighPressure
AmassofairthatpressesdownstronglyonthesurfaceoftheEarthbecauseitisbeingcooledandis
thereforemoredense.
Hurricane
Aviolent,spirallingstormthatformsovertheAtlanticOcean,withwindsover120kph.Suchstormsusually
havealifespanofseveraldays.Alsoknownasatyphoonortropicalcyclone.Thereare5levelsofhurricane:
•Category1—Winds74–95mph(64–82ktor119–153km/hr).Stormsurgegenerally4–5ftabovenormal.
Norealdamagetobuildingstructures.Damageprimarilytounanchoredmobilehomes,shrubbery,and
trees.Somedamagetopoorlyconstructedsigns.Also,somecoastalroadoodingandminorpierdamage.
•Category2—Winds96–110mph(83–95ktor154–177km/hr).Stormsurgegenerally6–8feetabove
normal.Someroongmaterial,door,andwindowdamageofbuildings.Considerabledamagetoshrubbery
andtreeswithsometreesblowndown.Considerabledamagetomobilehomes,poorlyconstructedsigns,
andpiers.Coastalandlowlyingescaperoutesood2–4hoursbeforearrivalofthehurricanecentreSmall
craftinunprotectedanchoragesbreakmoorings.
•Category3—Winds111–130mph(96–113ktor178–209km/hr).Stormsurgegenerally9–12ftabove
normal.Somestructuraldamagetosmallresidencesandutilitybuildingswithaminoramountofcurtain
wallfailures.Damagetoshrubberyandtreeswithfoliageblownofftreesandlargetreesblowndown.
Mobilehomesandpoorlyconstructedsignsaredestroyed.Lowlyingescaperoutesarecutbyrisingwater
3–5hoursbeforearrivalofthecentreofthehurricane.Floodingnearthecoastdestroyssmallerstructures
withlargerstructuresdamagedbybatteringfromoatingdebris.Terraincontinuouslylowerthan5ftabove
meansealevelmaybeoodedinland8miles(13km)ormore.Evacuationoflowlyingresidenceswith
severalblocksoftheshorelinemayberequired.
•Category4—Winds131–155mph(114–135ktor210–249km/hr).Stormsurgegenerally13–18
ftabovenormal.Moreextensivecurtainwallfailureswithsomecompleteroofstructurefailureson
smallresidences.Shrubs,trees,andallsignsareblowndown.Completedestructionofmobilehomes.
Extensivedamagetodoorsandwindows.Lowlyingescaperoutesmaybecutbyrisingwater3–5hours
beforearrivalofthecentreofthehurricane.Majordamagetoloweroorsofstructuresneartheshore.
Terrainlowerthan10ftabovesealevelmaybeoodedrequiringmassiveevacuationofresidential
areasasfarinlandas6miles(10km).
•Category5—Windsgreaterthan155mph(135ktor249km/hr).Stormsurgegenerallygreaterthan18ft
abovenormal.Completerooffailureonmanyresidencesandindustrialbuildings.Somecompletebuilding
failureswithsmallutilitybuildingsblownoveroraway.Allshrubs,trees,andsignsblowndown.Complete
destructionofmobilehomes.Severeandextensivewindowanddoordamage.Lowlyingescaperoutes
arecutbyrisingwater3–5hoursbeforearrivalofthecentreofthehurricane.Majordamagetoloweroors
ofallstructureslocatedlessthan15ftabovesealevelandwithin500yardsoftheshoreline.Massive
evacuationofresidentialareasonlowgroundwithin5–10miles(8–16km)oftheshorelinemayberequired.
IsobarAlineonaweathermaplinkingareaswithequalairpressure.
Lightning
Dischargeofstaticelectricityintheatmosphere,usuallybetweenthegroundandastormcloud.
Low
Alsocalleda'depression'thisregionoflowpressurecanmeanwetweather.
LowPressure
AmassofairthatpressesdownonlyweaklyonthesurfaceoftheEarth’ssurfaceasitiswarmedand
itthereforelessdense.
MillibarAunitusedtomeasureatmosphericpressure.
OccludedFrontAnareawherewarmairispushedupwardsasacoldfrontovertakesawarmfrontandpushesunderneathit.
Weatherapplication(NorthAmericaonly)
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