Download Tim Canty - University of Maryland

Thunderstorms
AOSC 200
Tim Canty
Class Web Site: http://www.atmos.umd.edu/~tcanty/aosc200
Topics for today:
Thunderstorms
Lecture 21
Nov 10, 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
Forecasting (Surface Map)
Fig 9.14:
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
2
Forecasting (500 mb Map)
Fig 9.15:
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
3
Forecasting (Future Surface)
Fig 9.16:
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
Actual weather (+1 day)
Fig 9.17:
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
5
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
6
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
7
Friday’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
8
Saturday’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
9
Forecast Range
Nowcasting
A description of current weather parameters
and 0-2 hours description of forecasted
weather parameters
Very short-range weather
forecasting
Up to 12
parameters
Short-range weather forecasting
Beyond 12 hours and up to
description of weather parameters
hours
description
of
72
weather
hours
Beyond 72 hours and up to 240 hours
Medium-range weather forecasting description of weather parameters
Extended-range weather
forecasting
Beyond 10 days and up to 30 days description
of weather parameters, usually averaged and
expressed as a departure from climate values
for that period.
Long-range forecasting
From 30 days up to two years
http://www.wmo.int/pages/prog/www/DPS/GDPS-Supplement5-AppI-4.html
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
Ensemble Forecasts
Ensemble forecasts:
Run model numerous times for slightly different
initial conditions
Perform statistical analysis of all the model runs
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
Ensemble Forecasts
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
Forecast Errors
Fig 13-25 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
13
Thunderstorms
Thunderstorms: single cloud (“cell”) or cluster of clouds
that produce lightning, thunder, rain, and sometime
tornadoes and hail
Largest storms (supercells) form over southern central
plains in US
Generally need warm, moist air (mT)
Fig 11-2 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
14
Thunderstorm Locations
Thunderstorms need convection of warm, moist air
Most likely to occur around ITCZ
Fig 11-3 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
15
Thunderstorm Locations
In the US: most likely to occur in Florida and portions of Southwest
Why?
Fig 11-4 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
16
Thunderstorm Locations
Strong sea breezes bring moist air
over land.
Increases convection and often leads
to thunderstorm development
http://www.meted.ucar.edu/fire/s591/climatology/other/land_sea.htm
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
17
Thunderstorm Locations
Moist marine air mixes with warm land air during convection
http://www.meted.ucar.edu/fire/s591/climatology/other/land_sea.htm
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
18
Sea-level pressure in Summer
Low pressure systems form over land in N.H. summer: Thermal Lows
ITCZ has moved northward
Similar pattern develops in S.H during summer
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
19
Sea-level pressure in Summer
Combination of thermal low and “spin up” of cylcones to the east of the
Rocky’s provides moisture and energy to generate strong convection
Low pressure systems form over land in N.H. summer: Thermal Lows
ITCZ has moved northward
Similar pattern develops in S.H during summer
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
20
What affects thunderstorm growth?
• Lifting mechanism: thunderstorms can’t grow unless
something causes the air to rise in the first place
• Environmental temperature
• Moisture
• Wind speed and direction at all levels
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
What affects thunderstorm growth?
• Lifting mechanism: thunderstorms can’t grow unless
something causes the air to rise in the first place
• Environmental temperature: determines stability of
atmosphere
• Moisture
• Wind speed and direction at all levels
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
What affects thunderstorm growth?
• Lifting mechanism: thunderstorms can’t grow unless
something causes the air to rise in the first place
• Environmental temperature: determines stability of
atmosphere
• Moisture
• Wind speed and direction at all levels: wind shear helps
increase duration of thunderstorm
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
23
Types of Thunderstorms
• Single cell
• Multicell
• Squall line
• Mesoscale Convective Complex
• Supercell
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
24
Single Cell (Air-mass thunderstorm)
Cumulus stage: needs source of warm, moist air
Water condenses and cloud spreads out in all directions
Dry air entrained in from all sides – promotes growth of droplets
Precipitation begins to form
Fig
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
10-2 Essentials of Meteorology
25
Single Cell (Air-mass thunderstorm)
Mature stage: lightning, rain, and small hail
Updrafts increase – promotes further droplet growth (see Ch 5)
Precipitation falls and evaporates, cooling air beneath cloud. Downdraft
begins and increases in strength
Downdraft hits ground and interacts with updraft
Fig
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
10-2 Essentials of Meteorology
26
Single Cell (Air-mass thunderstorm)
Dissipating stage: updraft weakens, downdraft dominates
Source of moisture and energy shuts down, storm weakens
Cloud begins to disappear as dry air entrained into cloud, evaporates
droplets
Often develop in mT air masses, last ~ 1 hour
Fig
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
10-2 Essentials of Meteorology
27
Heat Bursts
Fig 12-11 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
28
Heat Bursts
Fig 12-11 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
29
Heat Bursts
Fig 12-11 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
30
Heat Bursts
Descending air heats adiabatically
leading to hot, dry air at the surface
Fig 12-11 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
31
Multicell Thunderstorms
Wind shear keeps the downdraft from interfering with updraft
Strong down draft aids the updraft (gust front)
Increased updraft aids in formation of new cells
Fig
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
10-5 Essentials of Meteorology
32
Multicell Thunderstorms
Wind shear keeps the downdraft from interfering with updraft
Strong down draft aids the updraft (gust front)
Increased updraft aids in formation of new cells
Fig
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
10-4 Essentials of Meteorology
33
Gust Front
Cold air (downdraft) hits the
grounds and spread out.
Acts like a cold front and
forces up warmer air
Warm air rises, condenses
and can form a shelf cloud
Fig
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
10-6 Essentials of Meteorology
34
Multicell Thunderstorms: Squall Lines
Pre-frontal squall lines may form ahead of an advancing cold front as
the air aloft forms waves downwind from the cold front
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
Multicell Thunderstorms: Squall Lines
Rising air from wave
aids lifting from surface
Pre-frontal squall lines may form ahead of an advancing cold front as
the air aloft forms waves downwind from the cold front
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
36
Derechos
Line of storms (squall line) forms along cold front
Updraft brings in warm, humid air
Downdraft spreads cool air along the surface
http://earthsky.org/earth/what-you-need-to-know-about-derechos
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
37
Derechos
Cold air spreads out along the front, creating bow shape
This causes more storms to develop and spread out along the front
These storms strengthen updraft, lead to “upshear tilting”
Draws in upper level winds from behind the cloud: “rear inflow jet”
http://earthsky.org/earth/what-you-need-to-know-about-derechos
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
Derechos
Fast, upper level winds drawn down and reach surface
Increase speed of gust front moves storms forward , spread out along front
http://earthsky.org/earth/what-you-need-to-know-about-derechos
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
Multicell Thunderstorms: Mesoscale Convective Complex
Composed of multiple single-cell
storms in different stages of
development
Individual thunderstorms supports
formation of other convective
cells
To last a long time, good supply of
moist air near surface is needed
Fig 11-14 Meteorology: Understanding the Atmosphere
40
Copyright © 2016 University of Maryland
This material may not be reproduced or redistributed, in whole or in part, without written permission from Tim Canty
Lecture Recap
• Thunderstorms
• conditions
• stability
• single cell
• heat burst
• multicell
• gust front
• shelf cloud
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