air masses an air mass is a large section of the troposphere with uniform temperature and moisture...
TRANSCRIPT
Air MassesAir Masses
• An air mass is a large section of the troposphere with uniform temperature and moisture in the horizontal.
Moisture Content• Formed over water: Maritime• Formed over land: Continental
Temperature• Cold air mass: Arctic• Cool air mass: Polar • Warm air mass: Tropical
Maritime Arctic – mAMaritime Polar – mPMaritime Tropical – mT
Continental Arctic – cAContinental Polar – cPContinental Tropical - cT
Areas of Air Mass FormationAreas of Air Mass Formation• Air mass type is determined by the area
over which the air has stagnated.
(Or mA)
Air Mass Movement and Air Mass Movement and ModificationModification
• Air masses can move from their formation zone by advection (wind) and be modified by temperature or water content.
• The transition takes place slowly and it can take days to weeks before the entire air mass is transformed.
Air Masses of CanadaAir Masses of Canada• Continental Arctic: cA
– not in summer; low water content; warmed from below, strong winds produce turbulence; heap clouds and snow showers; rarely in B.C. except as a cold-air invasion
• (Continental Polar: cP) not according to Air Command Weather Manual
• Maritime Arctic: mA– starts as cA that spends some time over the northern Pacific ocean; moist and unstable
at high altitudes; stratocumulus and cumulus; pe/sn/-shra; Summer: northern lakes affect air mass
• Maritime Polar: mP– more time spent over Pacific ocean; warmer in lower levels; more stable than mA;
orographic lifting makes rain west of mountains and dry east of mountains; Summer: Tsra/Cb
• Maritime Tropical: mT– very warm and moist; Gulf of Mexico, Caribbean & south of 30°N; Winter: rarely at
surface N of Great lakes, but present at high altitudes; unstable when Frontal lift; sn/ra/zr/icing and turbulence; FOG (east coast); Summer: shra/tsra
FRONTS vs AIR MASSESFRONTS vs AIR MASSES(ARTIC FRONT)
(Maritime Front)
(POLAR FRONT)
Winter: mT moves far south and Canada generally only sees Continental arctic front and maritime arctic front.Summer: cA moves far north (or disappears) and we only see Maritime Arctic front or Maritime Polar front
Pg 6-7
cA mA mP mT
TROPOPAUSE
POLARPOLAR FRONTSFRONTS
The transition zone between two air masses is called a front.
FrontsFronts• Named by the movement of the cold air:
– Cold Front: that portion of the front where the cold air is advancing
– Warm Front: that portion of the front where the cold air is retreating
– Stationary Front: the cold air is neither advancing nor retreating.
– Occluded Fronts and Trowals: trough of warm air aloft.
Fronts found around a cold Fronts found around a cold airmassairmass
Formation of FrontsFormation of Fronts
• Fronts are always located in troughs of low pressure between two different air masses.
1.
2. 3.
Speed of FrontsSpeed of Fronts
• The speed of the front is equal to the component of the geostrophic wind (parallel to isobars) in the cold air mass that is perpendicular to the front.
25 kts
15 kts
20 kts
10 kts
FRONTSFRONTS
Cold FrontsCold Fronts• Has a relatively
steep frontal slope• Tends to lift the
warm air up (like a wedge)
• Clouds are of the vertical development category. Cu, TCu, Acc, Cb
• Showery precipitation is likely near the front.
The Cold FrontThe Cold Front
• Factors:• moisture of the warm air mass• stability of the warm air mass
• speed and steepness of the frontal surface• Wind: veers, some gusts
• Temperature: drops• Visibility: improves after passage
• Pressure: approaching front, pressure will drop, then rise after passage
• Turbulence: usually associated with Cb’s• Severe Cb’s can spawn tornados and hail
• Precipitation: showery in character, usually a narrow band 50 n.m.
Cold Warm
Warm FrontsWarm Fronts• Has a relatively
shallow frontal slope.
• Warm air overruns the cold air mass (moves up slope)
• Clouds gradually change from Ci, to Cs, to As, to St and Ns as the front approaches.
• Continuous precipitation is likely within 400 miles of the front.
Warm air massis stable
Embedded ThunderstormsEmbedded Thunderstorms• If the warm air mass is moist and unstable
thunderstorms can form within the normal clouds associated with the warm front.
Warm air massis unstable
Embedded Cb
The Warm FrontThe Warm Front
• Factors: Moisture Degree of overrunning Stability
• Wind: Veers• Frontal Slope: 1 in 150 to 1 in 200• Temperature: gradual rise• Visibility: low ceiling and low visibility; fog• Pressure: drop, then rise• Turbulence: usually little• Precipitation: steady precipitation• CI, CS, AS, NS
ColdWarm
Winter Warm Front = Freezing Rain!Winter Warm Front = Freezing Rain!
KaBoom
If you encounter ice pellets, the freezing rain is above you and ahead of you in the direction of the front.
Frontal SlopesFrontal Slopes• The slope of a warm front is approximately 1:200
(meaning it rises 1 foot vertically for every 200 feet horizontally)
• The slope of a cold front is between 1:50 to 1:100 depening on the speed of the front.
• A very fast moving cold front may have a vertical slope in the lower thousand feet causing severe weather due to rapid uplifting of the warm airmass.
Warm FrontNormalCold Front
Fast movingCold Front
WIND SHEAR @ WARM FRONTWIND SHEAR @ WARM FRONT
Airplanes in flight will cross the front in advance of a warm front and behind a cold front (when the fronts are depicted at their surface positions).
Frontogenesis and FrontolysisFrontogenesis and Frontolysis
Frontogenesis – The formation or strengthening of a front
Frontolysis – The dissipation or weakening of a front
Little graves!
7-16 Frontogenesis and 7-18 Frontolysis7-16 Frontogenesis and 7-18 Frontolysis
1 2
3 4
5 6
FRONTAL WAVEFRONTAL WAVE
Cold sector upper wind
FRONTAL WAVEFRONTAL WAVE
Warm sector surface wind
Cold sector surface wind
Warm sector upper wind
Warm sector high level windTROW
AL /
(OCCLUSION)
TROWALS chap.8-12TROWALS chap.8-12
Colder
Colder
Colder
Cold
Cold
Cold
Warm
Warm
Warm
OCCLUSION or Occluded Front
Frontal PassageFrontal Passage
• Temperature: Temperature will tend to rise after a warm front passes and fall after a cold front passes. (there are always exceptions to these rules).
• Dew point: Will rise after warm front passes and fall after cold front passes.
• Visibilities: visibility often improves with the passage of a cold front.
Warm Front PassageWarm Front Passage(Pressure and Winds)
1008
1004
1000
996
992
Winds: 170/20Pressure: 1010 mbWinds: 170/20Pressure: 1001 mbWinds: 230/22Pressure: 995 mbWinds: 270/25Pressure: 998 mb
Pressure: falls as the front approaches and rises after it passes
Winds: always veer after the front passes
Cold Front PassageCold Front PassagePressure and Winds
1008
1004
1000
996
994
Winds: 270/25Pressure: 1009 mbWinds: 270/25Pressure: 1002 mbWinds: 340/25G35Pressure: 995 mb
Winds: 020/25Pressure: 1000 mb
Pressure: falls as the front approaches and rises after it passes
Winds: always veer after the front passes
(Gusty winds when the front passes)
JET JET STREAMSTREAM
Pg 12-11
Pg 12-13
Jet StreamsJet Streams• Rapidly flowing streams of air embedded
within the main airflow.
• Usually thousands of miles long, a few hundred miles wide, and a few thousand feet thick.
• Minimum wind speed to qualify as a Jet is 60 knots.
Jet Streams and FrontsJet Streams and Fronts• Jet Streams roughly follow frontal waves.
• Temperatures to the north of a jet stream will be colder. (and warmer to the south)
JETSTREAM
Jet Stream Turbulence (CAT)Jet Stream Turbulence (CAT)
• Looking at the jet from west to east (looking downwind), this shows the most turbulent areas.
Low Level Nocturnal JetLow Level Nocturnal Jet
40-65 KNOTS
Pg 11-13
Summer, often over the prairies on clear night. Sheet of wind 700 to 2000 agl begins about dusk and peaks in early morning. Wind shear is major problem. Speeds excessive for isobar spacing.