National Weather Service
Lincoln, IL
Outline
• Thunderstorm
Basics & Severe
Weather
• Weather Safety
• Soundings & SPC
Analysis Products
• Radar
Interpretation
• Case Studies
2
THUNDERSTORM
BASICS
Important Ingredients
Photo by Roger Look
1. Lift
2. Moisture
ALL
T-storms
3. Instability
4. Wind Shear
Strong or
Severe
T-storms
Lifting the Air...
1) Lows, Fronts, Wind
Shift Lines
2) Other
Thunderstorms
3) Jet Stream
4) Heating the Ground
The air needs to be moist...
Sources
1) Gulf of Mexico
2) Local
Vegetation
The air needs
to keep moving...
Instability
• Air forced up (updrafts)
will continue to rise
• Air forced down (downdrafts)
will continue to sink
The air needs
to keep moving...
Instability
• Air forced up (updrafts)
will continue to rise
• Air forced down (downdrafts)
will continue to sink
The atmosphere is
like a balloon
As the Hot Air Balloon is
heated, it rises (unstable air)
When the heat is shut
off, it sinks (stable air)
The wind can
make a BIG difference...
Wind Shear is:
Directional Shear
1) Wind direction
changing vertically
(Directional Shear)
AND / OR
2) Wind speed
changing vertically
(Speed Shear)
Speed Shear
The wind can
make a difference...
With Strong Wind Shear:
•
Storms are more
organized
•
Storms are longer
lived
•
Rotation can develop
in a storm
Directional Shear
Speed Shear
Updrafts and Downdrafts:
• It is IMPORTANT to identify
the Updraft and Downdraft
– Updraft / Inflow
• Warm, moist air
feeds storm
• Usually where most
tornadoes form
– Downdraft / Outflow
• Cool, rainy air spreads out
• High wind gusts
• Heavy rain / Hail
Photo by
Mark Sefried
SEVERE STORM
FEATURES
Severe Storm Features
Seen at long distances from the storm ≈ 15-30 miles or more
OVERSHOOTING
TOP:
• VERY strong updraft
• If the top persists,
the storm is
strengthening
• If it collapses, severe
weather is imminent
Looking Northeast – more than 15 miles away
STORM TOWER:
Sharp, bulging edges & tilted
updraft because of wind shear
ANVIL:
• Solid, sharp edges,
spreading back toward
the west
Severe Storm Features
Seen at distances of ≈ 10 to 20 miles
Photo by Jarrod Cook
Looking WNW - more than 10 miles away
Flanking line on western side of storm
Produced 1.00” Hail, Wind Damage, & Heavy Rain
Sharp Anvil spreading back toward the
west
Flanking Line: Indicates the storm will
intensify, or sustain itself for quite some time
Severe Storm Features
Seen at close distances from the storm ≈ 5 miles or less
Rain-Free Base
and Wall Cloud:
Indicates a strong updraft
– rain & hail can not
penetrate it
There is a higher potential
for a tornado with a
rotating wall cloud
Photo by Brian Morganti
Looking northwest – less than 5 miles away
Comparison:
Severe Storm vs. Weak Storm
• Anvil and overshooting top
• No anvil
• Stronger updraft &
instability
• Weaker updraft &
• Stronger wind shear
• Sharp edges in tower
instability
• Weaker wind shear
• Fuzzy edges in tower
SEVERE
THUNDERSTORM
TYPES
Photo by Mark Sefried
Multicell Cluster Storms
Characteristics
• Most common type
of thunderstorm in
Illinois
• Form near fronts &
boundaries from
nearby storms
Looking Southeast
Photo by Paul Hadfield
• Severe weather:
– Heavy Rain / Hail
– Downburst Winds
– Weak Tornadoes
Moderate to Strong Updrafts
Weak to Moderate Wind Shear
Multicell Cluster Storms
Spotter View
Storm B
Storm C
Storm A
Multicell Cluster Storms
Spotter View
Storm C
Storm B
Storm A
Multicell Cluster Storms
Spotter View
Storm C
Storm B
Storm A
Multicell Cluster Storms
Spotter View
Storm C
Storm D
Storm B
Storm E
Time Span (First to last image) ≈ 40 minutes
• New storms form on the W or SW side of the cluster
• Dissipating storms weaken on E or NE side of the cluster
• Clusters, usually last an hour or two
Multicell Cluster Storms
Radar View
Weakening
thunderstorms
Strongest
thunderstorms
New, developing
thunderstorms
Squall Lines
Characteristics
• Long line of
separate storms
– Usually develop
ahead of a cold front
• Squall lines are
usually oriented
in a N-S or NE-SW
direction
Moderate to Strong Updrafts
Moderate to Strong Wind Shear
Squall Lines
Characteristics
• Long line of
separate storms
– Usually develop
ahead of a cold front
• Squall lines are
usually oriented
in a N-S or NE-SW
direction
• Multiple downdrafts
merge to produce
a “Gust Front”
Moderate to Strong Updrafts
Moderate to Strong Wind Shear
Squall Lines
Characteristics
• Severe Weather:
– Potential for high
winds / damage
– Occasional
Tornadoes
– Heavy Rain
– Hail
(up to golf ball sized)
Heavy Rain
Tornado
and Hail
Wind
Damage
Squall Lines
Visual Clues
Shelf Cloud
• Long cloud at the
front of the squall line
Squall Lines
Visual Clues
Shelf Cloud
80 mph winds
Widespread wind damage
• Long cloud at the
front of the squall line
– Where the Warm
Updraft and Cool
Downdraft meet
– Shelf clouds that
are low hanging
with a “wavy” look
aloft, often produce
the highest winds
Updraft
Downdraft
A dark grey or greenish color
indicates heavy rain / hail
Squall Lines
Radar View
• Tornadoes
favored at the
front of the line
Apr 19, 2011
70-85 mph
wind
Favored area for
Tornadoes
– Look for kinks
in the line
– End or break in
the line
70-100 mph
wind
Favored area for intense
wind
• High Wind
– Anywhere
along the
leading edge
of the line
Favored area for
Tornadoes
Supercells
Characteristics
• Highly organized storms
• Pose a HIGH threat
to life & property
• Updrafts rotate
– Rotating “Updraft” is
called a “MESOCYCLONE”
or “MESO”…this only
occurs in supercells
– Rotation caused
by “wind shear” in
the atmosphere
Photo by Kyndi Hanson
near Peoria, 6/5/10
Looking NNW
Strong Updrafts
Strong Wind Shear
(Directional & Speed Shear)
Supercells
Characteristics
• Severe Weather:
– Tornadoes
• Higher potential for
strong or violent tornadoes
– High winds / wind damage
• Two downdrafts – one near heavy
rain, other in rear of the storm
• Wind up to 100 mph possible
– Large Hail & Heavy Rain:
updraft / downdraft interface
• Hail bigger than a golf ball
• Flash Flooding
Supercells
Visual Clues
Rotating Updraft (Mesocyclone)
1. Wind shear causes a
“rolling” motion
Images courtesy of National Geographic
Supercells
Visual Clues
Rotating Updraft (Mesocyclone)
1. Wind shear causes a
“rolling” motion
2. A strong updraft pulls this
“rolling” air upward
Images courtesy of National Geographic
Supercells
Visual Clues
Rotating Updraft (Mesocyclone)
1. Wind shear causes a
“rolling” motion
2. A strong updraft pulls this
“rolling” air upward
3. The result is a rotating,
tilted updraft – or a
Mesocyclone
Images courtesy of National Geographic
Supercells
Visual Clues
Rotating Updraft (Mesocyclone)
Photo by Don Bell
Peoria, IL 6/5/10
Classic Supercell
HP Supercell
Spiral bands and striations in updraft
tower are clues that the updraft is rotating
Supercells
Visual Clues
Wall Cloud
• Persistent lowering near
the updraft
(the rain-free base)
• Usually long lived – the
key is rotation
• Upward motion often
present
• May contain a “tail
cloud” which points
toward the rainy area
(forward flank downdraft)
Supercells
• Supercell Variations:
– Classic
• Many are in this category
• Potential for long-track
tornadoes
– High Precipitation (HP)
• Rain and hail often surrounds
the updraft
• Rotation is usually hidden by
the heavy precipitation
• Very DANGEROUS to spot
Classic Supercells
Side View
Image courtesy of National Geographic
Upper Level Winds &
Direction of Storm
Tilted
Updraft
Front Flank
Downdraft
Rear Flank Downdraft
Classic Supercells
Top View
Important Point
• Safest spotting
position is on the
southern flank of
the storm, with the
inflow at your
back
Safest Spotting
Location
Classic Supercells
Radar View
Important Points
• The Hook Echo is
the meso – not
necessarily a
tornado
• The precipitation
shield “leans”
in the direction of
the storm movement
• The Rear Flank
Downdraft has
VERY gusty winds
Hook Echo
Rear Flank
Downdraft
Tornado Life Cycle
Classic Supercells
1. Developing Stage
Photo by Mike Umsheid
Watch for:
1. A “clearing” area near the wall cloud & developing funnel
(called the Rear Flank Downdraft – RFD – or “Clear Slot”)
Tornado Life Cycle
Classic Supercells
1. Developing Stage
Photo by Eric Sebens
Photo by Mike Umsheid
Watch for:
1. A “clearing” area near the wall cloud & developing funnel
(called the Rear Flank Downdraft – RFD – or “Clear Slot”)
2. Rotation and dust whirl at the ground and a connection to
wall cloud or funnel
Tornado Life Cycle
Classic Supercells
2. Mature Stage – Potentially the most dangerous
stage of a tornado
Photos by Jarrod Cook
Tornado Life Cycle
Classic Supercells
2. Mature Stage – Potentially the most dangerous
stage of a tornado
Photos by Jarrod Cook
Photo by Mike Umsheid
Watch for: Debris with the tornado which may hide
the fact that it is still in contact with the ground
Tornado Life Cycle
Classic Supercells
3. Dissipating (Rope) Stage
Photo by Mike Umsheid
Tornado Life Cycle
Classic Supercells
3. Dissipating (Rope) Stage
Photo by Jarrod Cook
Photo by Mike Umsheid
Watch for: Another tornado to develop a few miles
or so downstream of the dissipating one
Tornado Life Cycle
“Cyclic” Supercells
• Favored area:
Downstream of a
dissipating tornado
Old tornado
New tornado
forming
• The new wall cloud
and funnel cloud
will be the dominant
Looking East
Photo by Scott Blair
part of the storm
• Watch this area very carefully for a
NEW tornado to develop
Photo courtesy of Dan Robinson
West of Jacksonville, IL
2/20/14
HP Supercells
Side View
Looking WNW
Tilted
Updraft
Mesocyclone
RFD & Rear Precipitation Shield
HP Supercells
Side View
Looking WNW
Tilted
Updraft
Mesocyclone
RFD & Rear Precipitation Shield
HP Supercells
Top View
Important Points
• Wall cloud and
tornado are often
obscured by rain
• Often has a
“kidney bean”
shape early on
• Safest place to
spot is on the
south flank
Safest Spotting
Location
HP Supercells
Radar View
Important Points
• The meso and tornado are
“usually” located at the
front of the storm in the
“notch”
…but not ALWAYS…
Mesocyclone
HP Supercells
Radar View
Important Points
• The meso and tornado are
“usually” located at the
front of the storm in the
“notch”
…but not ALWAYS…
At times, the presence of a
meso / tornado can be
VERY difficult to see
using just the reflectivity
BE CAREFUL with
HP Supercells!!
11/17/13
Near Gifford, IL
MesocycloneLocation ?
HP Supercells
Radar View
Important Points
• The meso and tornado are
“usually” located at the
front of the storm in the
“notch”
11/17/13
Near Gifford, IL
MesocycloneLocation ?
…but not ALWAYS…
At times, the presence of a
meso / tornado can be
VERY difficult to see
using just the reflectivity
BE CAREFUL with
HP Supercells!!
Mesocyclone is still back
here
“NON-SUPERCELL”
TORNADOES &
OTHER ROTATIONS
Non-Supercell Tornadoes
“Landspouts”
• No “organized”
large scale rotation
– No wall cloud
– No rotation on radar
Creative Commons Sam Fakhreddine
Non-Supercell Tornadoes
“Landspouts”
• No “organized”
large scale rotation
– No wall cloud
– No rotation on radar
• Can be nearly
transparent at times
• Often form near an
E-W front OR on the
southwest end of
multicell clusters
Creative Commons Sam Fakhreddine
Non-Supercell Tornadoes
“Landspouts”
• Winds on either side
of a front come from
opposite directions causing
a “horizontal rolling”
Non-Supercell Tornadoes
“Landspouts”
• Winds on either side
of a front come from
opposite directions causing
a “horizontal rolling”
Non-Supercell Tornadoes
“Landspouts”
• Winds on either side
of a front come from
opposite directions causing
a “horizontal rolling”
• An updraft in the
developing cloud
strengthens
Non-Supercell Tornadoes
“Landspouts”
• Winds on either side
of a front come from
opposite directions causing
a “horizontal rolling”
• An updraft in the
developing cloud
strengthens
• The updraft stretches the
horizontally rolling air in
the vertical…
Non-Supercell Tornadoes
“Landspouts”
• Winds on either side
of a front come from
opposite directions causing
a “horizontal rolling”
• An updraft in the
developing cloud
strengthens
• The updraft stretches the
horizontally rolling air in
the vertical…
Non-Supercell Tornadoes
“Landspouts”
• Winds on either side
of a front come from
opposite directions causing
a “horizontal rolling”
• An updraft in the
developing cloud
strengthens
• The updraft stretches the
horizontally rolling air in
the vertical…
…which causes the
landspout tornado to
form
Other Rotations
Gustnado
• Small short-lived rotations
along a gust front
• Does not reach up to cloud,
no rotation in cloud OR on
radar
• Look for rotation at the
ground not just dust
• Can cause minor damage,
mainly from the wind gust
• Report a “Gustnado” not a tornado, when
you see them
SEVERE STORM
SPOTTER SAFETY
MAIN Objective – Stay Safe
1) Personal safety is THE
TOP PRIORITY
2) The NWS does NOT
encourage spotters to
chase storms
3) Some spotters MAY be
mobile, most will not
– ALL need to be ALERT to
rapidly changing conditions
that could impact your safety!
4) Adhere to the concept
of “ACES”
Awareness
•
Constantly monitor your
surroundings, and the
risks around you
–
–
–
–
Know the roads and the
area you are spotting in
Be alert for areas with
damage or flooding
Be mindful of safety zones
& escape routes
Monitor the weather
conditions at all times –
in ALL directions
Awareness – Stay Informed
www.weather.gov/Lincoln
Top News
of the
Day
Watches/
Warnings
and
Outlooks
pages
Awareness – Stay Informed
www.weather.gov/Lincoln
Weather Safety
• Daily Weather Story
• Go to SKYWARN/Spotter
Training section for additional
resources & links to download
• Graphical Short
Term Forecast
(During Severe
Weather Events)
Communications
Useful Items for Spotters
• Communication Device
(cell phone or radio)
•
•
•
•
•
Safe shelter nearby
GPS or local maps
Binoculars
Weather radio
Smart Phone or
Laptop to monitor
weather conditions
• Camera
(still and/or video)
Communications
REPORTING
• WHO you are
– A trained spotter
• WHAT you have witnessed
– The specific weather event
• WHEN the event occurred
– NOT the time you are reporting,
but when the event happened
• WHERE the event occurred
NOT JUST YOUR LOCATION
– Use well known roads, which
could be found on any map
Escape Routes
• VERY IMPORTANT when
you need to get away from
danger
• Have clear paths allowing
you to reach safety
BEFORE the threat arrives
• ALL Spotters:
• A secure, indoor shelter that
will be unlocked at all times
• Mobile spotters:
• Adequate roads or paths for
you to move to a secure shelter
Escape Routes: Safe Zones
Tips for Mobile Spotters
• Keep options open for escape
routes; a 4-way intersection is best
• Avoid operating in the roadway
“Hot Zone”
– Park well off the roadway, with hazard
lights on: parking lots are safer
– Don’t park near trees, electrical poles
& lines, or signs
– Limit time outside the vehicle:
lightning is a MAJOR hazard
• Never have your back to moving traffic
• Wear a reflective vest; it will make you
more visible
HOT
ZONE
HOT
ZONE
Escape Routes: Safe Zones
Tips for Mobile Spotters
• Never spot alone
• Don’t get trapped on a dead end road
• Be aware of traffic congestion AND
construction areas
– Avoid underpasses which are dangerous!
• Know your position with respect to
the storm movement
• Remain alert for emergency
vehicles & pedestrians
• Never drive through the core
of the storm (Heavy rain & hail)
Night Spotting...
Spotting at night is
very dangerous!
This should only be
done from a safe
shelter
Mobile spotters
should only attempt
this if they have
communications with
someone who knows their
position and if a safe shelter is nearby
Photo by Alan Broerse
Lightning Safety
Safe Locations
• Secure building with
windows & doors closed
• A hard topped vehicle
with the windows closed
– This is safe because you
are enclosed in the metal
frame of the vehicle – NOT
because of the tires!!
When you see lightning
OR hear thunder – Go
to a safe location
IMMEDIATELY!!
Lightning Safety
Intense lightning can
occur many miles
away from the storm –
in areas with NO rain!
Don’t return
outdoors too soon!
Stay in your safe
shelter at least
30 minutes AFTER
the last rumble of
thunder.
High Wind Safety
• Mobile Spotters
Get indoors, if you
can safely!
Slow down and find
a safe place to pull
off, away from trees
and power lines
High Wind Safety
• Mobile Spotters
Get indoors, if you
can safely!
Slow down and find
a safe place to pull
off, away from trees
and power lines
• Other Spotters
Stay away from
windows and doors
Be alert for falling
trees or tree limbs
Photo by Steve Hardesty
Hail Safety
• Mobile Spotters
Driving in hail is
hazardous. STOP
driving & safely
pull over if you get
caught in large hail
Large hail can
damage car
windows,
and injure you
Hail Safety
• Mobile Spotters
Driving in hail is
hazardous. STOP
driving & safely
pull over if you get
caught in large hail
Large hail can
damage car
windows,
and injure you
• Other Spotters
Stay away from
windows & doors
Flood Safety
• Flooded roads are
dangerous for ALL
types of vehicles
• Most deaths from
flooding occur in
vehicles
• It only takes 18” – 24”
of water to cause an
auto to float or to push
it off of the road
• Most flash floods occur at NIGHT in Illinois, making
it difficult to see the depth of water on a roadway
Flood Safety
Never cross a
water covered
road OR bridge
in a vehicle
• Turn around,
and take another
route
Photo from
Peoria Journal-Star
4/22/13
Photo by Steve Davis
Galesburg Register-Mail
5/28/13
Flood Safety
Never cross a
water covered
road OR bridge
in a vehicle
• Turn around,
and take another
route
Photo from
Peoria Journal-Star
4/22/13
Never walk into a
flooded area
Photo by Steve Davis
Galesburg Register-Mail
5/28/13
Flooding: Road Impacts
Photo from Woodford Co EMA 4/18/13
Tornado Safety
• Whether indoors or
outdoors: Flying &
falling debris is the
biggest hazard, resulting
in injuries & fatalities
Tornado Safety
– Get in: A sturdy shelter
– Get down: A basement
or underground shelter
is the best. If none is
available, get to the
lowest level near the
center of the building.
– Cover up: Minimizes
your risk of injury from
falling debris
Tornado Safety
Mobile Spotters
• Never try to outrun a
tornado in a vehicle,
especially in heavy
traffic
– Park your car and get
into a sturdy structure
– Don’t take shelter under
bridges or overpasses
• LAST RESORT:
If no shelter is nearby,
lie flat in a ditch to
protect yourself
Upper Air
Sounding
Interpretation
88
Nov 17, 2013 - 6 AM Sounding
Dew Point
Plot (black)
Temperature
Plot (red)
89
Nov 17, 2013 - 6 AM Sounding
Trajectory
of Rising
Air (yellow)
90
Nov 17, 2013 - 6 AM Sounding
LI – Lifted Index
Negative values
indicate instability
CAPE –
Convectively
Available Potential
Energy
Values above 1,500
= strong instability
CIN – Convective
Inhibition
Indicates “capping”.
Values less than
100 can be
overcome easier91
CAPE Limitations
These two
soundings
have the
same CAPE
value.
Which one
would most
likely
produce the
strongest
storms?
92
Nov 17, 2013 - 6 AM Sounding
Wind
Plots
93
Nov 17, 2013 - 6 AM Sounding
STM – Storm
Motion
Movement of
storms. Direction
moving FROM
and speed in
knots.
HEL – Helicity
Infers rotation
storms may
encounter.
Values > 250
threat of
tornadoes.
94
VERTICAL WIND PROFILES
95
Storm Prediction
Center (SPC)
Analysis
Products
96
www.spc.noaa.gov
97
SPC Mesoanalysis Page
Select a
sector
from the
choices
above the
map…or
on the map
itself.
98
SPC Mesoanalysis Sector
Choose from the various images within the sector
99
Observations
Summary
of:
Convective
Outlook
Watches
Warnings
Radar
100
Thermodynamic Fields
1. SBCAPE
Potential energy
available to sfc
air being lifted
MDT – 1,000
STG > 1,500
2. CIN - amount of
capping
< 50 support for
supercells
50-100
moderate
support
101
>100 poor
support
Thermodynamic Fields
1. SB Lifted
Index & CIN
Lifted Index
when raising
air from the
surface
2. LI < -2 and
CIN 0 – 50
High prob of
t-storms
102
Thermodynamic Fields
1. LCL Height
The lower the
LCL Height,
the more
support there
is for supercell
tornadoes
2. Values:
> 1250
tornadoes
less likely
103
200 – 1000
strong tornado
support
Wind Shear
1. 0-6 KM Shear
Vector
The amount of
wind shear in
the lowest
20,000 ft
2. Values:
> 35-40 Kts
favorable for
supercells
104
Wind Shear
1. Effective
Shear
Can help to
assess storm
type
2. Values:
10-25 kts –
single cells
25-40 kts –
multicells and
bows
105
> 40 kts supercells
Wind Shear
1. 0 – 1 KM SR
Helicity
Amount of
rotation
potential in
lower levels
(below
3,000 ft)
2. Values:
> 100 - threat
of tornadoes
from
supercells
106
Composite Indices
1. Supercell
Composite
Takes into
account CAPE,
Helicity, & Bulk
Shear
2. Values:
2 – 11
a moderate
likelihood of
supercells
107
>11 is a high
likelihood of
supercells
Composite Indices
1. Sig Tor
Parameter w/
CIN
Shear, Helicity,
CAPE/CIN, &
LCL Height
2. Values:
< 1 = Non
tornadic
supercells
108
> 1 = Significant
Tornadoes
possible
(EF2-EF5)
Composite Indices
1. Craven/Brooks
Sig Svr
0 – 6 KM Shear
and MLCAPE
2. Values:
Likelihood of
2”+ Hail, 65 kt +
wind, EF2 +
tornadoes…
5-20 = Low
20-40= Mod.
> 40 = High
109
Interpreting
Doppler Radar
Imagery
110
The Radar Beam
Due to the physical nature of the radar
beam and the curvature of the earth, the
radar beam gets WIDER and HIGHER the
farther it travels.
o
Beam Diameter
center of 0.5
beam height (ARL)
10 nm
1000 feet
600 feet
50 nm
1 mile
4400 feet
100 nm
2 miles
12500 feet
150 nm
3 miles
25000 feet
Range
111
Radar Limitations
Radar Horizon
B
A
Radar
Radar beam cannot see lower portion of storm “B”
112
112
Radar Limitations
Beam width vs. range
Radar
Beam
Width
Distance from radar:
Radar beam width:
113
60
120
180 miles
1
2
3 miles
Radar Limitations
Distance vs. effective resolution
Radar
A
B
Aspect Ratio Problem
View from above
114
C
beam width
Radar Limitations
Storm Distance – 100 mi
Beam Height – 12,000 ft
Beam Width – 1.7 miles
Copyright Johnathon Garner
A
Radar reflectivity
B
Radar velocity
115
Beam height & width vs. effective resolution
Radar Limitations
Beam width vs. effective
resolution
Storm 20 miles from radar
Same storm 80 miles from radar
Base Reflectivity
A portion of the radar beam reflects off of
particles/objects and is returned to the
antenna.
The position of the “target” (raindrop, hailstone,
etc…) is determined by the difference between
the time the energy is sent and when it returns to
the antenna.
The intensity is determined by comparing the
amount of energy returned to that which was
originally transmitted.
117
Base Reflectivity…cont’d
Applications
 Detects precipitation and boundaries
 Valuable for analyzing storm structure
 Sensitive enough to detect clouds,
birds, insects, bats, smoke from fires,
and even dust
 Is the most widely used radar product
118
Examples
119
Examples
120
Composite Reflectivity
A derived product from base reflectivity. It
displays the HIGHEST reflectivity of ALL the
radar angles at a point on the surface.
Applications

Designed for quickly determining the highest
reflectivity core of a storm (i.e. the updraft)

DO NOT use for identification of low level
features, such as boundaries or hook echoes

Used for many “mosaic” images
121
Composite Reflectivity
122
Base Reflectivity
123
Composite Reflectivity
124
Base Reflectivity
125
OUTFLOW BOUNDARY
Outflow boundary – A surface “front” formed
by the spreading of thunderstorm cooled air
 Outflow boundaries can intersect with each other or with
thunderstorms to rapidly produce new storms or make
existing storms stronger
 Can persist for several minutes to more than a day
A GUST FRONT is a type of outflow boundary


126
Surge of strong or damaging winds at leading edge
Also associated with wind shift, large temperature
drop, heavy rain and shelf clouds/roll clouds
Outflow boundary
127
128
1 hour after the outflow
boundary moved ahead of the
thunderstorms, the convection
dissipated.
Base Velocity
A base product that uses the principles of the
Doppler effect to produce velocity images.
Applications
 Estimates the wind speed AND direction
 Valuable for evaluating significant storm
structure features and boundaries
 Data used as input for derived products that
infer storm rotation, or a vertical profile of
upper level wind
130
Doppler Effect
A target moving AWAY
from the radar returns
energy at a LOWER
frequency
A target moving TOWARD
the radar returns energy at
a HIGHER frequency
A STATIONARY target
returns energy at the
SAME frequency
131
Base Velocity - Interpretation
WARM colors (red/yellow shades) and “+”
values
imply wind direction AWAY
from the radar.
COOL colors (blue/green shades) and “-”
values
imply wind direction
TOWARD the radar.
132
PURPLE or RF indicates range folding,
which implies that a wind speed/direction
can not be determined.
Base Velocity
133
Base Reflectivity
6/4/99 Squall Line
Several reports of golfball sized
hail and wind gusts to 70 mph
19 weak tornadoes (F0 - F1)
Numerous reports of crop damage,
damage due to falling tree limbs
134
0 fatalities
3 injuries
Storm Relative Velocity
A derived image that uses the base velocity
product with the average storm motion
subtracted out
Applications

Used to estimate the wind speed AND
direction relative to the storms themselves,
at various elevations in the atmosphere.

Very valuable for interpreting rotation within a
storm and its 3-D velocity structure.
135
Storm Relative Velocity
136
Base Reflectivity
137
SR Velocity - Guidelines
Rotation (mesocyclone) at the lowest
elevation angle does NOT always mean
a tornado is present!
 Approximately 10 % of all mesos
are associated with a tornado
…HOWEVER…
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 Nearly 90% of all mesocyclones are
associated with severe weather (includes
large hail, damaging wind OR tornadoes)
SR Velocity - Guidelines
When warning decisions are made,
several things are considered:
 Radar Data
 Spotter Reports
 Environment
 Knowledge & expertise of the
forecaster
139
Tornadoes and Doppler radar
Supercell tornadoes – a mid level (and
sometimes low level) mesocyclone can usually
be detected.
Landspouts & Gustnadoes – difficult to detect
 Rotation low in the atmosphere
 Diameter of circulation is very small
 Move slowly
140
 Located in areas where there is little or no
precipitation on radar
Case Study
Classic Supercell
(Cyclic)
11/17/13
Pekin Tornado - 1044 AM CST
8 minutes before tornado touched down
Pekin Tornado - 1049 AM CST
3 minutes before tornado touched down
Pekin Tornado - 1049 AM CST
Photo by Jeannie Howell
3 minutes
before
tornado
touched
down
Pekin Tornado - 1053 AM CST
Tornado on ground in Pekin for 3 minutes
East Peoria/WashingtonTornado
1058 AM CST
Tornado about to redevelop in East Peoria
East Peoria/WashingtonTornado
≈ 1100 AM CST
Tornado between East Peoria & Washington
East Peoria/WashingtonTornado
1103 AM CST
Tornado about 3 minutes from Washington
East Peoria/WashingtonTornado
1107 AM CST
Tornado leaving Washington & debris signature evident
East Peoria/WashingtonTornado
1107 AM CST
Dual-Pol
Tornadic
Debris
Signature
(ZDR & CC)
East Peoria/WashingtonTornado
1112 AM CST
Tornado entering Woodford County & debris signature still evident
East Peoria/WashingtonTornado
1117 AM CST
Tornado continuing across Woodford County &
debris signature still evident
East Peoria/WashingtonTornado
1122 AM CST
Tornado continuing across Woodford County &
debris signature still evident
Case Study
HP Supercell
11/17/13
Gifford Tornado - 1242 PM CST
Three minutes before tornado touched down.
Development of Gifford HP
Supercell Tornado
3 minutes before tornado…
Mesocyclone
Rain area to southwest
wall cloud
11/17/13 southwest of Gifford, IL
All Photos Courtesy of Jessie Starkey
Gifford Tornado - 1246 PM CST
Tornado touched down at 1245 PM.
Circulation has rapidly intensified.
Development of Gifford HP
Supercell Tornado
touchdown…
3Tornado
minutes before
tornado…
12:45 pm
Mesocyclone
Rain area to southwest
wall cloud
11/17/13 southwest of Gifford, IL
All Photos Courtesy of Jessie Starkey
Development of Gifford HP
Supercell Tornado
12:46 pm
11/17/13 southwest of Gifford, IL
All Photos Courtesy of Jessie Starkey
Development of Gifford HP
Supercell Tornado
12:47 pm
11/17/13 southwest of Gifford, IL
All Photos Courtesy of Jessie Starkey
Development of Gifford HP
Supercell Tornado
12:48 pm
11/17/13 southwest of Gifford, IL
All Photos Courtesy of Jessie Starkey
Development of Gifford HP
Supercell Tornado
12:49 pm
11/17/13 southwest of Gifford, IL
All Photos Courtesy of Jessie Starkey
Gifford Tornado - 1251 PM CTS
Tornado has intensified to EF3.
Transition to HP Supercell.
Tornado is rain wrapped.
Development of Gifford HP
Supercell Tornado
12:46
Tornado
touchdown…
12:47
12:48
minutes before
tornado…
12:493pm
12:50
pm
12:45 pm
Tornado is becoming
wrapped in rain from Mesocyclone
the southwest
Rain area to southwest
wall cloud
11/17/13 southwest of Gifford, IL
All Photos Courtesy of Jessie Starkey
Gifford Tornado - 1251 PM CST
Dual-Pol
Tornadic
Debris
Signature
(ZDR & CC)
Gifford Tornado - 1256 PM CST
EF3 tornado at Gifford.
Circulation has tightened further.
Gifford Tornado - 1256 PM CST
Dual-Pol
Tornadic
Debris
Signature
(ZDR & CC)