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MID-LATITUDE CYCLONES

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Presentation on theme: "MID-LATITUDE CYCLONES"— Presentation transcript:

1 MID-LATITUDE CYCLONES
Dr. Sam Miller Weather & Climate – MTDI 1200OL Plymouth State University 1

2 Ahrens, Ch. 8

3 Mid-Latitude Cyclones

4 Mid-Latitude Cyclone (MLC)
A cyclonic storm that most often forms along a frontal boundary in the middle latitudes 30 – 60 °N/S Region of low pressure Counterclockwise in the Northern Hemisphere Synoptic scale: 1,000 – 5,000 miles across Period: 2 – 10 days Produces large areas of clouds and precipitation

5 Why are MLCs important? Bring a variety of significant weather
Can produce snow storms, tornadoes, hail, strong winds, rain storms, ice storms, etc. Transport warm air from subtropical regions Transport cold air from the polar regions Transport warm air from the surface to the upper atmosphere Redistribute moisture

6 Cyclogenesis

7 Cyclogenesis Means origin or intensification of a cyclone
Part of the life cycle of a midlatitude cyclone For MLCs, this involves a linkage between fronts and low pressure areas near the Earth’s surface, and the Polar Jet near the tropopause.

8 Divergence occurs downwind of an upper-level trough and upwind of an upper-level ridge
ALOFT H

9 UPWARD VERTICAL MOTION
DIVERGENCE ALOFT POLAR JET UPWARD VERTICAL MOTION (CHIMNEY) L LOW-LEVEL CONVERGENCE SOUTHWEST NORTHEAST

10 Chimney SURFACE

11

12 Cyclogenesis The MLC’s surface low forms directly below the area of upper-level divergence For the surface low to continue intensifying the upper-level trough and low must continue to position themselves such that the low is right under the area of upper-level divergence, and, The upper divergence must be stronger than the low-level convergence

13 Cyclogenesis Surface low will try to remain beneath area of upper-level divergence East of the upper-level trough Follows flow of Polar Jet Stream The MLC begins dying when the upper-level low or trough moves directly overhead the surface low Surface low no longer positioned below the area of upper-level divergence

14 Life Cycle

15 Polar Front Theory Theory to describe life cycle of a midlatitude cyclone formation and development For cyclogenesis of an MLC to occur, it needs Boundary between warm and cold airmasses at the surface THE POLAR FRONT POLAR FRONT CAUSES POLAR JET STREAM Curvature of the Polar Jet Stream AN UPPER-LEVEL TROUGH PROVIDES DIVERGENCE ALOFT STAGES

16 (a) Initial Stage Front separates cP and mT air masses
Manifested as stationary front Wind flow is parallel to front in opposite directions Low-level convergence at the front Beginning of cyclonic wind flow

17 (b) Frontal Wave Wavelike kink develops
With sufficient divergence aloft, surface low develops Boundary between airmasses is deformed by rotation: Cold front and warm fronts develop Overunning creates precipitation mostly north of warm front

18 (c) Growing Wave System moves with mid-level wind
500 mb Steers the storm Central pressure drops Isobars encircle low and wind speeds increase Precipitation forms along cold front Warm sector develops

19 (d) Mature Wave System moves eastward and strengthens
Warm sector decreases in size as cold front begins overtaking warm front Widespread precipitation Comma cloud can be identified on satellite images

20 (e) Occlusion Cold front overtakes warm front
Storm is at its most intense Can’t intensify anymore Clouds and precipitation cover large area Comma cloud develops dry slot

21

22 (f) Dissipation (The End)
Low separates from fronts Cut off from divergence aloft Low-level convergence begins filling low Cold air encircles the surface low No supply of energy storm dies

23 (a) Initial Stage (b) Frontal Wave (c) Growing Wave (d) Mature Wave (e) Occlusion (f) The End

24 North American MLCs

25 North American MLCs Midlatitude Cyclones affecting the CONUS have distinct formation regions Some more common in Winter when Polar Jet is “low zonal” – Large waves; flow has large north-south excursions Systems are strong and slow moving Some more common in Summer when Polar Jet is “high zonal” – Small waves; jet is mostly straight from west to east Systems are weaker and relatively fast moving

26 L L L L L L NORTH AMERICAN MLCs GULF OF ALASKA LOW ALBERTA CLIPPER
GREAT LAKES LOW L L HATTERAS LOW COLORADO/ WEST TEXAS LOW L GULF OF MEXICO LOW

27 ALBERTA CLIPPER L L L L L L

28 GREAT LAKES LOW L L L L L L

29 COLORADO/WEST TEXAS LOW

30 GULF OF MEXICO LOW L L L L L L

31 CAPE HATTERAS LOW L L L L L L

32 GULF OF ALASKA LOW L L L L L L

33 North American MLCs Alberta Clipper Great Lakes Low
Move out of Canadian Rockies very fast in the middle of the winter – often follows Hatteras Low by about 24 hrs Great Lakes Low Often forms from same upper-air feature as Gulf of Alaska Low Colorado/West Texas Low Form on the lee side of the Rockies in CO, OK, WY, or TX Gulf of Mexico Low Form over the Gulf of Mexico Affect the East Coast Cape Hatteras Low Affect East Coast Produce Nor’easters in New England Alaska Low Form over the Gulf of Alaska Affect Pacific Northwest GENERALLY DO NOT REACH NEW ENGLAND

34 North American MLCs Alberta Clipper Great Lakes Low
Move out of Canadian Rockies very fast in the middle of the winter Great Lakes Low Often forms from same upper-air feature as Gulf of Alaska Low Colorado/West Texas Low Form on the lee side of the Rockies in CO, OK, WY, or TX Gulf of Mexico Low Form over the Gulf of Mexico Affect the East Coast Cape Hatteras Low Affect East Coast Produce Nor’easters in New England Alaska Low Form over the Gulf of Alaska Affect Pacific Northwest GENERALLY DO NOT REACH NEW ENGLAND

35 North American MLCs Alberta Clipper Great Lakes Low
Move out of Canadian Rockies very fast in the middle of the winter Great Lakes Low Often forms from same upper-air feature as Gulf of Alaska Low Colorado/West Texas Low Form on the lee side of the Rockies in CO, OK, WY, or TX Gulf of Mexico Low Form over the Gulf of Mexico Affect the East Coast Cape Hatteras Low Affect East Coast Produce Nor’easters in New England Alaska Low Form over the Gulf of Alaska Affect Pacific Northwest GENERALLY DO NOT REACH NEW ENGLAND

36 North American MLCs Alberta Clipper Great Lakes Low
Move out of Canadian Rockies very fast in the middle of the winter Great Lakes Low Often forms from same upper-air feature as Gulf of Alaska Low Colorado/West Texas Low Form on the lee side of the Rockies in CO, OK, WY, or TX Gulf of Mexico Low Form over the Gulf of Mexico Affect the East Coast Cape Hatteras Low Affect East Coast Produce Nor’easters in New England Alaska Low Form over the Gulf of Alaska Affect Pacific Northwest GENERALLY DO NOT REACH NEW ENGLAND

37 North American MLCs Alberta Clipper Great Lakes Low
Move out of Canadian Rockies very fast in the middle of the winter Great Lakes Low Often forms from same upper-air feature as Gulf of Alaska Low Colorado/West Texas Low Form on the lee side of the Rockies in CO, OK, WY, or TX Gulf of Mexico Low Form over the Gulf of Mexico Affect the East Coast Cape Hatteras Low Affect East Coast Produce Nor’easters in New England Alaska Low Form over the Gulf of Alaska Affect Pacific Northwest GENERALLY DO NOT REACH NEW ENGLAND

38 North American MLCs Alberta Clipper Great Lakes Low
Move out of Canadian Rockies very fast in the middle of the winter Great Lakes Low Often forms from same upper-air feature as Gulf of Alaska Low Colorado/West Texas Low Form on the lee side of the Rockies in CO, OK, WY, or TX Gulf of Mexico Low Form over the Gulf of Mexico Affect the East Coast Cape Hatteras Low Affect East Coast Produce Nor’easters in New England Alaska Low Form over the Gulf of Alaska Affect Pacific Northwest GENERALLY DO NOT REACH NEW ENGLAND

39 Nor’easters Known by meteorologists as “coastal” storms
Intense MLC offshore of the northeastern US Produce strong NE winds along the coast Normally develop off the coast of North Carolina and move northward along the coast Hatteras low moving northward along coast

40 Nor’easters Frequently very intense in the Gulf of Maine
Associated with Heavy snows in the NE, heavy rains further south, strong winds, high waves, etc.

41

42

43

44

45 Context

46 Are cyclonic storms unique to the Earth?
Context Are cyclonic storms unique to the Earth?

47

48 Mars

49 Are cyclonic storms unique to the Earth?
Context Are cyclonic storms unique to the Earth? No.

50 Review

51 Overview of MLC Cyclogenesis Definition Scale and period
Importance to midlatitude weather Cyclogenesis Role of Polar Front, Polar Jet, Divergence aloft and low-level convergence Meteorological “bomb” Conditions necessary for continued intensification

52 Stages of Life Cycle North American MLC’s Initial Frontal Wave
Growing Wave Mature Wave Occlusion The End North American MLC’s Alberta Clipper Great Lakes Low Colorado/West Texas Low Gulf of Mexico Low Cape Hatteras Low Alaska Low

53 Additional Graphics Sources

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