Meteorology – Jet Streams Fronts and Air MassesConnecting the Weather

• Air Masses• Fronts• Jet Stream• Quiz

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Meteorology – Jet Streams Fronts and Air MassesAir Masses

A mass of air takes on Temperature and Moisture from where the source of air originates.

Source Region - Land or Sea

Amount of Time over the Source region

Modification as the Air Mass moves away from the source.

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Meteorology – Jet Streams Fronts and Air MassesAir Mass Classification and humidity

Artic – Polar Ice Cap in Winter

Polar – Forms 40’ to 60’, Summer up to 80’

Tropical – Forms from high pressure cells, Summer over large continents

Equatorial – Region between Sub tropical Highs

Humidity depends on source

Maritime – Forms over Water – more humid

Continental – Originates over Land – less humid

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Meteorology – Jet Streams Fronts and Air Masses

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Air masses affecting the UK are either Polar or Tropical with Artic air mass in winter

Meteorology – Jet Streams Fronts and Air MassesWhat happens as an Air Mass moves from Cold to Warm?

Air becomes heated in the Lower Levels

To pilot this gives you..Unstable AirWarmer AirLow Humidity

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What happens as an Air Mass moves from Warm to Cold?

To pilot this gives you..More stable airColder in lower levelsIncreased Humidity

Meteorology – Jet Streams Fronts and Air MassesAir Masses

Polar MaritimeSource – Greenland & Iceland

Conditions at SourceColdStableHigh Humidity

As Air Mass moves South East becomes Unstable resulting inCu and Cb over LandHeavy Showers, Rain, HailModerate to severe IcingGood Visibility

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Meteorology – Jet Streams Fronts and Air MassesAir Masses

Tropical MaritimeSource – Azores

Conditions at SourceWarmSlight InstabilityModerate Humidity

As Air Mass moves North East Air cools from belowAdvection FogSt & Sc by daySt at nightPoor Visibility

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Meteorology – Jet Streams Fronts and Air MassesAir Masses – Tropical continental

Source – North Africa

Conditions at SourceWarmStableLow Humidity

As Air Mass moves North it cools from below becomes more stable, Humidity stays low.

Hot & Dry weatherPoor Visibility due to Haze

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Meteorology – Jet Streams Fronts and Air MassesAir masses, Arctic Maritime, Winter only

Source – Artic Circle

Conditions at SourceColdStableLow Humidity

As Air Mass moves South it is heated from below becomes VERY unstable,

ColdMoist - PrecipitationHeavy SnowCu & Cb CloudsUnstablePossible Thunderstorms

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Meteorology – Jet Streams Fronts and Air MassesAir Masses, Polar continental, Winter only

Source – Siberia & North Europe

Conditions at SourceColdStableLow Humidity

As Air Mass moves over cold land of Europe it stays cold and stableColdVery DryNo PrecipitationPossible Thunderstorms along east coast if Air Mass has moved over North Sea

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Meteorology – Jet Streams Fronts and Air Masses

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Meteorology – Jet Streams Fronts and Air Masses

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Coffee!!!!!

Meteorology – Jet Streams Fronts and Air MassesWhen Air Masses meet we call them… Fronts

A front is a zone of transition between two contrasting air massesThe three types of front areColdWarmOccluded

The interaction of two air masses at the frontal surface frequently gives rise to a great deal of frontal cloud and weather.

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Meteorology – Jet Streams Fronts and Air MassesFronts

Typical cross section through a frontal system

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Meteorology – Jet Streams Fronts and Air MassesWarm front

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Meteorology – Jet Streams Fronts and Air MassesWarm Front Weather

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Wind veers & increases slightlyTemperature / Dewpoint rise.Pressure steadiesPrecipitation changes from RA to DZ or DZRA.Cloud changes from NS to ST or SC.

Meteorology – Jet Streams Fronts and Air MassesCold Front

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Meteorology – Jet Streams Fronts and Air MassesCold Front Weather

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Pressure rises rapidlyWind veers and decreases slightlyTemp / Dew point fall.Visibility improvesIntermittent Rain Heavy Showers begin from NS / Embd Cb

Meteorology – Jet Streams Fronts and Air Masses

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Meteorology – Jet Streams Fronts and Air MassesWarm Occlusion

• Air Masses• Fronts• Jet Stream• Quiz

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Less cold air over-rides colder air ahead.

Meteorology – Jet Streams Fronts and Air MassesCold Occlusion

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Colder air under-cuts less cold air ahead

Meteorology – Jet Streams Fronts and Air Masses

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Meteorology – Jet Streams Fronts and Air MassesJet Streams

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A jet stream is an river of high velocity air with velocities of 60 – 250kt, on rare occasions 300kt flowing generally west to eastIt is a wind belt in created by thermal wind in a boundary zone between warm and cooler air i.e. a frontal zone. It usually separates the colder and warmer air.

Meteorology – Jet Streams Fronts and Air MassesJet Streams

Max wind speed in a Jet Stream is found on the warm side of the frontal zone at an altitude just above than of the cold tropopause and below that of the warm tropopause and the direction usually agrees with that of the front.

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Meteorology – Jet Streams Fronts and Air MassesConnecting the Weather

Interpretation of Wx infoTips for en route Wx interpretation and cross referencing Met chartsExample: F215 shows vis 999 ocnl SHRA 4km vbis cloud 2500 ocnl 1500METAR 9999 BKN 2500 SHRA ; TAF 9999 BKN 2500 PROB30 TEMPO 5000 +SHRAAIRMET Says cold front with gusting winds passing early in day, isolated heavy showers laterConclusion, flight can go ahead, choose alternate carefully and proceed with caution.

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Meteorology – Jet Streams Fronts and Air MassesQuizDefine CAVOKMore than 10k vis, no cloud below 5000ft or MSA, no CuNim in vicinitySHSNRA VV003Heavy showers of snow or rain, vertical visibility 300ftAn airmet says Cold Sector. Conditions?Colder dryer air, good vis, scattered cumulusMETAR : EGLF 031450Z 02012KT 6000 BKN017 04/00 Q1034. Flyable?YesMETAR : EGLF 031450Z 02012KT 9000 OVC005 04/04 Q1004. Flyable?NoTAF says PROB30 TSRA BKN 020 flyable?Yes with cautionPROB50 Exists?No, any more than PROB40 is BCMG or TEMPO

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Met Office websiteForm 214-215TAFs, METARs, AIRMETOther sites, XCweather.co.uk, avbrief.co.uk, sky demon

Meteorology – Why it’s a bad idea to bypass proper Met planning

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