Download Warm Fronts - UMD | Atmospheric and Oceanic Science

Extratropical Cyclones
AOSC 200
Tim Canty
Class Web Site: http://www.atmos.umd.edu/~tcanty/aosc200
Topics for today:
Fronts
Cyclogenesis
Lecture 19
Nov 3 2016
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
1
Today’s Weather Map
http://www.hpc.ncep.noaa.gov/html/sfc2.shtml
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
2
Today’s Forecast
http://www.hpc.ncep.noaa.gov/national_forecast/natfcst.php
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
3
Fronts
Front: transition between two air masses
The upward extension of the front is called the
“Frontal Zone”
Fig 8.13:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
4
Fronts
Fig 8.14:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
5
Fronts
Warm air flows over cold air mass… why?
Fig 9-11 Meteorology: Understanding the Atmosphere
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
6
Cold Fronts
Fig 8.15:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
7
Cold Fronts
Represented as blue triangles pointing toward warm air
Travels ~25 knots
Warm air forced up, cools, releases latent heat, leads to storms
Fig 8.17:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
8
Cold Fronts
As cold front moves through,
temps. hold steady then drop
Fig 9-13 Meteorology: Understanding the Atmosphere
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
9
Cold Fronts
As cold front moves through,
temps. hold steady then drop
Pressure drops then rises after
front passes
Fig 9-13 Meteorology: Understanding the Atmosphere
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
10
Cold Fronts
As cold front moves through,
temps. hold steady then drop
Pressure drops then rises after
front passes
Precipitation forms along
leading edge of front, “squall
line”
Fig 9-13 Meteorology: Understanding the Atmosphere
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
11
Cold Fronts
As cold front moves through,
temps. hold steady then drop
Pressure drops then rises after
front passes
Precipitation forms along
leading edge of front, “squall
line”
Winds shift from southwest to
northwest
Cold fronts generally move to
the south, southeast, or east
Fig 9-13 Meteorology: Understanding the Atmosphere
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
12
Cold Fronts
Table 8.2: Essentials of Meteorology
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
13
Warm Fronts
Fig 8.19:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
14
Warm Fronts
Represented as red semi-circles pointing toward cold air
Travels ~10 knots
Warm air slides over cold air and slowly cools.
Clouds form starting with cirrus, then various layers of stratus
Fig 8.20:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
15
Warm Fronts
As warm front moves through, temperature keep rising
then level off
Fig 8.20:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
16
Warm Fronts
Pressure drops, levels off, then rises again
Fig 8.20:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
17
Warm Fronts
Cloud coverage changes from high cirrus clouds to mid
and then low level stratus clouds.
This happens ahead of the front.
Fig 8.20:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
18
Warm Fronts
Fig 8.19:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
19
Warm Fronts
Winds change from south or southeast to south or southwest
Fig 8.20:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
20
Warm Fronts
Table 8.3: Essentials of Meteorology
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
21
Stationary Fronts
Represented as red semi-circles and blue triangles
Front doesn’t move
Winds blow along front but in opposite directions
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
22
Occluded Fronts (cold type occlusion)
cP
mP
Cold front moves faster than warm front, may catch warm front
Warm air is forced up over both cold/very cold air masses
May have mix of clouds similar to both cold and warm fronts
Fig 8.22:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
23
Occluded Fronts (cold type occlusion)
cP
mP
Cold front moves faster than warm front, may catch warm front
Warm air is forced up over both cold/very cold air masses
May have mix of clouds similar to both cold and warm fronts
Fig 8.22:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
24
Occluded Fronts (cold type occlusion)
cP
mP
Cold front moves faster than warm front, may catch warm front
Warm air is forced up over both cold/very cold air masses
May have mix of clouds similar to both cold and warm fronts
Fig 8.22:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
25
Occluded Fronts (warm type occlusion)
mP
cP
Cold front moves faster than warm front, may catch warm front
Cool air is forced up over cold air mass
May have mix of clouds similar to both cold and warm fronts
Fig 8.22:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
26
Occluded Fronts (warm type occlusion)
mP
cP
Cold front moves faster than warm front, may catch warm front
Cool air is forced up over cold air mass
May have mix of clouds similar to both cold and warm fronts
Fig 8.22:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
27
Occluded Fronts
Table8.4:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
28
Warm type occluded Front
Fig 8.23:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
29
Mid-latitude cyclones
Cold, warm, and occluded fronts
are often part of a larger system
called the mid-latitude or extratropical cyclone
Fig 8.24:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
30
Cyclone Model
1920’s: Bjerknes described the evolution of cyclones
Begins as a frontal wave along stationary front separating
cP air from mT air – birth stage
Table 10-1 Meteorology: Understanding the Atmosphere
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
31
Cyclone Model
1920’s: Bjerknes described the evolution of cyclones
Open wave develops strong cold and warm fronts,
precipitations falls along broad area – young adult stage
Table 10-1 Meteorology: Understanding the Atmosphere
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
32
Cyclone Model
1920’s: Bjerknes described the evolution of cyclones
Occluded front develops, pressure reaches minimum,
winds reach maximum, – mature stage
Table 10-1 Meteorology: Understanding the Atmosphere
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
33
Cyclone Model
1920’s: Bjerknes described the evolution of cyclones
Cut-off cyclone develops, pressure rises, clouds and
precipitation dissipates – death stage /
Table 10-1 Meteorology: Understanding the Atmosphere
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
34
Cyclone Model
1920’s: Bjerknes described the evolution of cyclones
Cut-off cyclone develops, pressure rises, clouds and
precipitation dissipates – death stage /
Cyclogenesis needs: temperature gradients,
strong jet stream, and surface boundary
(mountain, coastline near warm ocean)
Table 10-1 Meteorology: Understanding the Atmosphere
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
35
Cyclone Model
Fig 8.25:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
36
Regions of Cyclogenesis
Fig 8.28:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
37
Regions of Cyclogenesis
Lee side lows
Alberta Clippers:
Form on lee side of Canadian Rockies. Fast moving and
somewhat dry
Colorado Low:
Form on lee side of U.S. Rockies. In the right spot for very
cold polar air to interact with warm, moist Gulf air. Can have a
mix of precipitation. Thunderstorms along the southern edge of
front, lots of snow NW of the center of low pressure
Can sometimes form near Oklahoma Panhandle or in Texas
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
38
Regions of Cyclogenesis
East Coast Lows
Gulf Low:
Form along southern coast. Cold land and warm ocean
means good probability of precipitation
Hatteras Low (Nor’easter):
Form along eastern coast. Warm gulf stream water provides
warm air and moisture that interacts with cold air on land.
If the pressure of a Hatteras Low drops by 24mb in 24 hrs, it’s
considered a “bomb”
Can produce hurricane strength winds, flooding, heavy snow.
Can last for days!!!
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
39
Nor’easters
Fig 8.U1:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
40
Cyclogenesis in 3-D
Surface high pressure directed to southeast by jet stream
Surface low pressure directed northeast by jet stream
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
41
Cyclogenesis in 3-D
Fig 8.32:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
42
Cyclogenesis in 3-D
Fig 8.32:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
43
Cyclogenesis in 3-D
Fig 8.32:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
44
Cyclogenesis in 3-D
Fig 8.33:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
45
Cyclogenesis in 3-D
Fig 8.33:
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Essentials of Meteorology
46
Rossby Waves
Zonal Flow: Jet stream moves from west to east
without meandering around much
Fig 7-15 Meteorology: Understanding the Atmosphere
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
47
Rossby Waves
Meridional Flow: Jet stream wanders around a lot
as the wind moves from west to east
Sometimes happens when a large pacific storm
hits the jet stream
Fig 7-15 Meteorology: Understanding the Atmosphere
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
48
Rossby Waves
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
49
Lecture Recap
• Fronts
• cold
• warm
• stationary
• occluded
• cold type
• warm type
• Cyclogenesis
• frontal wave
• open wave
• occluded cyclone
• cut off cyclone
• comma cloud, dry slot,
comma tail
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
50