Severe storm radar signatures

1
Severe storm radar signatures

• Jim LaDue
• Warning Decision Training Branch,
• NWS
• Norman, OK

James.G.LaDue_at_noaa.gov
2
Topics

• A radar and visual view of a developing
  thunderstorm
• Radar reflectivity vs. whats observed from
  ground (hail vs. rain and storm type)
• Severe vs. nonsevere straight line winds
• Supercell storm anatomy visual vs. radar

3
Radar and visual view of a developing thunderstorm

• A scenario
• A spotter calls in to report a tower developing
  to the northwest
• How far is this tower?

4
Radar and visual view of a developing thunderstorm

• A scenario
• A spotter calls in to report a tower developing
  to the northwest

5
Radar and visual view of a developing thunderstorm

• Where does the precipitation form relative to the
  visual updraft?

Link to loop
6
Ordinary cell evolution
-10 C
0 C
TCU 7 min
7
Ordinary cell evolution
-10 C
0 C
TCU 14 min
8
Ordinary cell evolution
-10 C
0 C
TCU 21 min
9
Ordinary cell evolution
-10 C
0 C
TCU 28 min
10
Ordinary cell evolution
-10 C
0 C
TCU 35 min
11
Findings

• Use the higher slices to detect the towering
  cumulus above the boundary layer echoes
• Look for the first strong core to develop above
  the freezing layer.
• Descent of the core is rapid, less than 10
  minutes
• In this case, opaque visual core to the spotter
  appears with the reflectivity exceeding 45 dBZ

12
Visual vs radar reflectivity

• What reflectivity do you think the radar is
  detecting right of this updraft?

0026 UTC
Gene Rhoden
Jim LaDue
13
Visual vs radar reflectivity

• 50-55 dBZ
• Mostly large hail stones

0026 UTC
Gene Rhoden
Jim Leonard
Jim LaDue
14
Same Z, Different R
Z1 729 mm6/m3 (29 dBZ) R1 .22 inch/hr
Z1 729 mm6/m3 (29 dBZ) R1 .01 inch/hr
15
Visual vs. radar reflectivity30 April 2004
2131 UTC
16
Visual vs. radar reflectivity30 April 2004
2131 UTC

• Dry hail, no rain
• 55-60 dBZ
• But the radar beam is 10 kft AGL

17
Visual vs. radar reflectivity21 April 2004
0017 UTC
North of Stroud, OK
18
Visual vs. radar reflectivity21 April 2004
0022 UTC
North of Stroud, OK
19
Visual vs. radar reflectivity21 April 2004
0022 UTC

• 55-60 dBZ corresponding to heavy rain and
  golfballs

20
Three body scatter spike
21
Three body scatter spike

• The WSR-88D can directly indicate the presence of
  large hail.
• Typically associated with lots of hail and
  coated with water
• Shorter wavelength radars may see this but for
  smaller hail.

22
Visual vs. radar reflectivity09 June 2004

• Very humid airmass
• Lots of shear and low-level CAPE
• Not a lot of upper level CAPE

23
Visual vs. radar reflectivity09 June 2004
24
Warm Rain ProcessesA Recent Example
25
Cross Section through Warm-Rain Supercell
Notice the reflectivity drop off above the
freezing level.
26
Visual vs. radar reflectivity

• The ultimate consideration
• The relationship between the visual dry slot and
  the hook echo

27
What is the TVS seeing?
28
What is the TVS seeing?
1. Flanking line
1.
1.
29
What is the TVS seeing?
1. Flanking line
2.
1.
2. Dry slot and hook
2.
1.
30
What is the TVS seeing?
TVS
1. Flanking line
2.
1.
2. Dry slot and hook
TVS
TVS
2.
1.
Tornado
31
Visual vs. radar reflectivity

• Drop size distribution
• Very large hail creates translucent visual cores
  but very strong reflectivity
• Lots of small rain drops creates opaque cores
  but relatively low reflectivity
• There is no explicit relationship between
  reflectivity and what type of precipitation is
  reaching the ground

32
Visual and radar obs of strong vs. weaker
convective wind events

• Depth of the gust front is something you can
  detect by radar
• The most severe wind events accompany deep,
  vertical gust fronts
• Shallower gust fronts are accompany weaker wind
  events

33
Visual and radar obs of strong vs. weaker
convective wind events

• Case 11 August 2004 Cocoa Beach, FL

34
Visual and radar obs of strong vs. weaker
convective wind events

• Case 11 August 2004 Cocoa Beach, FL
• How deep is this gust front?

35
Visual and radar obs of strong vs. weaker
convective wind events

• Case 11 August 2004 Cocoa Beach, FL
• How deep is this gust front?

36
Visual and radar obs of strong vs. weaker
convective wind events

• Case 11 August 2004 Cocoa Beach, FL
• How deep is this gust front?

37
Visual and radar obs of strong vs. weaker
convective wind events

• Shallow squall line and gust front
• Cores well behind gust front
• Typically not as severe

38
Visual and radar obs of strong vs. weaker
convective wind events

• Case 12 August 2004 Cocoa Beach, FL
• Similar setup as the day before
• However the line is coming in from the southwest

39
Visual and radar obs of strong vs. weaker
convective wind events

• Notice the intense core is right behind the gust
  front

40
Visual and radar obs of strong vs. weaker
convective wind events

• 5 minutes later

41
Visual and radar obs of strong vs. weaker
convective wind events

• Case 11 August 2004 Cocoa Beach, FL
• How deep is this gust front?

Mid altitude convergence is strong A downburst
precursor
42
Visual and radar obs of strong vs. weaker
convective wind events

• Deep Convergence zone
• What do you think the spotters seeing?

15 kft
43
Conceptual model of a severe linear system

• Key things to note are the
• Deep convergence zone
• Gust front and severe core right next to each
  other
• LTGCG ahead of gust front indicates anvil
  spilling out over gust front

44
Supercell anatomy

• Given more cell phone images coming in real time
  from the field, lets figure out what the storm
  would look like given one image

45
Supercell anatomy

• Wheres the spotter and which way is the view?
• How far from the rotation?

4
5
3
6
8
2
7
1
46
Supercell anatomy
4
5
3
6
8
2
7
1
47
Supercell anatomy

• Where is the spotter?

4
5
3
8
7
2
1
6
48
Supercell anatomy

• Where is the spotter?

49
Supercell anatomy

• RFD dry slot

50
Supercell anatomy

• RFD

51
Supercell Anatomy

• Supercell updraft from the front side

52
Supercell anatomy
53
Supercell anatomy

• Where is the tornado threat?

54
Supercell anatomy

• Where is the tornado threat?

55
Supercell Anatomy
56
Supercell Anatomy from visual and radar findings

• Visual clear slot radar observed hook echo
• Outside the hook, inside the RFD, there is often
  no observed reflectivity
• Visual updraft occupied by weak reflectivity
• Use the convergence in velocity under the strong
  echo overhang to visualize updraft in radar
• Complimentary nature of radar and spotters
• Radar helps detect hidden mesocyclones (0137 UTC)
• Spotters help detect undetectable vortices (0157
  UTC)

57
Where are these pictures relative to the storm?
0000 UTC
A
B
C
Jim Leonard
Jim LaDue
Sam Barricklow
58
Supercell wind events

• Can produce a large number of the most damaging
  wind events without tornadoes
• Most common with HP supercells

Rear flank downdraft contains the most intense
winds but at this distance, 88D velocities
overshoot highest winds.
59
Supercell wind events
Deep convergence zone
3.4
These high wind events often have a very deep
convergence zone, extending 15 kft or more.
2.4
1.5
15 kft
0.5
60
Hail and tornado signatures

• For large hail
• Deep core gt55dBZ passing far above 20 C level
• Supercell updraft with strong BWER or WER
• Three-body scatter spike or hail spike
• For tornadoes
• Strengthening TVS in lowest slices
• Strengthening mesocyclone
• Strengthening updraft, BWER, inflow notch
• Hook development
• Having more of these together increases
  confidence
• Above all, remember the radar limitations and
  always question the algorithms

61
Stormscale rotation - mesocyclone

• Small scale rotation closely associated with an
  updraft that
• Persists for 10 minutes or more
• Vertical continuity (10 kft or more)
• Shear
• Core diameter lt 5nm and rotational velocity
  exceeding minimal thresholds
• The mesocyclone algorithm does NOT look for
  persistence and only looks for two slices for
  vertical depth criteria

62
Where to expect aspects of Mesos and TVSs
Distance from which the beam width exceeds .54 nm
No TVSs beyond here
Height of gust fronts, boundaries
63
Where to expect aspects of Mesos and TVSs
Distance from which the beam width exceeds .54 nm
No TVSs beyond here
Height of gust fronts, boundaries
64
Favorable hail clues
3.4

• Bounded Weak Echo Region (BWER)
• Intense updraft forms a hole in the reflectivity
  core.

2.4
BWER
BWERs not typically seen this far out
1.5
Typical BWER heights
0.5
65
Favorable hail clues

• Weak Echo Region (WER)
• Intense updraft also levitates a large region of
  core.
• Look for high over low reflectivities on the
  inflow side of a storm

3.4
2.4
WER
Watch out for anvil WERs. They are not updrafts.
1.5
A
WER typically from sfc to 15-20 kft.
0.5
A
B
B
66
Waiting till 2257 UTC

• The storm is still outside our CWA.
• Weve got another volume scan.

67
Favorable hail clues
3.4

• Bounded Weak Echo Region (BWER)
• Intense updraft forms a hole in the reflectivity
  core.

2.4
BWER
BWERs not typically seen this far out
1.5
Typical BWER heights
0.5
68
Where to expect aspects of Mesos and TVSs
Distance from which the beam width exceeds .54 nm
No TVSs beyond here
Height of gust fronts, boundaries
69
Lessons learned

• Spotters are especially important at long ranges
  and with compromised radar data
• Radar excels at close ranges and at dark

70
Pulse storms

• Short-lived storms
• Expect downbursts
• Potentially small hail
• Minimal flash flood threat
• Taking a radar tour

71
What will be covered

• Downdraft potential from pulse storms
• Organized wind events, bow echoes
• Hail potential
• Storm rotation and tornado potential
• Non supercell and supercell tornadoes

72
Here is a scenario

• Light winds and little shear aloft
• Hot at ground 100 F
• Cloud base of cumulus at 9000 ft
• Plenty of instability above cloud base
• Towers are building

What do you expect for the day?
73
Pulse storm downbursts
Is this the time a warning should be issued?
74
Pulse storm downbursts
As an aside
300 m
75
Pulse storm downbursts
As an aside
76
Pulse storm downbursts
The idea is to look for clues for potential
downbursts before it reaches the ground.

• Midlevel convergence
• Collapsing storm core
• Rapidly decreasing vertically integrated liquid
  (VIL)
• Height of maximum reflectivity dropping rapidly
• Bottom of elevated core rapidly drops

77
Pulse storm downbursts
Where do you think the downburst occurred?
78
Pulse storm downbursts
This time height trend of reflectivity shows the
descending core hitting the ground just after
0006 UTC.
Updraft phase
79
Pulse storm downbursts
Updraft begins to build a core aloft
2356 UTC
80
Pulse storm downbursts
0002 UTC
81
Pulse storm downbursts
Midlevel convergence signifies downdraft
commencing
0008 UTC
82
Pulse storm downbursts
0014UTC
83
Pulse storm downbursts
Downdraft impacts the ground
0019 UTC
84
Pulse storm downbursts
0024 UTC
85
Pulse storm downbursts
0029 UTC
86
Pulse storm downbursts
0037 UTC
87
Pulse storm downbursts
0042 UTC
88
Pulse storm downbursts
Storm exhausts itself
0047 UTC
89
Pulse storm downbursts

• This event shows that VIL, height of Max
  reflectivity and storm top did not give lead time
  to downburst.
• Tracking the descent of the core gave a better
  lead time
• Monitoring updraft growth might give even better
  lead time
• The stronger the elevated core, the stronger the
  initial updraft

90
Pulse storm downbursts

• mid-altitude radial convergence
• Provided 5 minutes of lead time before downburst
• Not always apparent before a downburst
• When visible, it does give leadtime

91
Monitoring the elevated core
If you have limited access to radar data, use the
Layer Maximum Reflectivity (LRM) products.
LRM max 24 33 kft
92
Pulse storm downbursts
Or use the composite reflectivity and compare
with 0.5.
Composite
0.5
93
Pulse storm downbursts
LRM layers available on NIDS
94
Intense elevated reflectivity core

• Keep in mind the height of the 0 and 20 C
  temperatures.

• Reflectivity gt 55 dBZ extending further above the
  20 C level infers an increasing chance of
  large hail.

95
Organized convective wind events

• Squall lines
• Bow echoes
• HP supercells

96
Strong squall lines
Comparing 0.5 base velocity and reflectivity,
the worst winds are pointed directly at the
radar. And the radar is close so that the
low-level winds can be sampled. Winds exceeded
100kts.
97
Strong squall lines
In other cases, the squall line is not heading
right at the radar. Where do you think the
strongest winds in this squall line will hit in
the next hour?
98
The answer
99
Strong squall lines

• There are two strikes against seeing the true
  wind magnitude.
• The true wind (blue arrow) is almost
  perpendicular to the radial (white arrow) so the
  radar doesnt see much outbound wind (red arrow).
• What is the second reason?

100
Organized wind events

• Weak squall lines
• Weak environmental shear
• Gust front pulls ahead of storm
• Storm slopes behind outflow boundary

Notice shallow gust front. Updraft quickly
slopes behind gust front.
101
Weak squall line example
Group of storms initiates in SW OK. 2200 UTC
Storms progress east and outflow races out ahead.
2318 UTC
Outflow boundary
Outflow boundary
Outflow boundary racing ahead of storms is a good
sign the squall line is weak with lower than
average wind damage potential.
102
Organized wind events

• Strong squall lines
• Strong shear
• Gust front stays with storm
• Storm remains upright

Notice deep gust front compared to previous page.
Updraft remains on top of this deep convergence
zone.
103
Strong squall lines
This squall line moved at gt 50 kt. It took the
radar 5 minutes to sample from bottom to
top. The squall line moved over 5 miles in that
period. In actuality, the leading edge is more
vertical.
At anvil level, these cores are the updrafts.
104
Strong squall lines
The storm-relative velocity shows the gust front
right at the leading edge of the core. The gust
front is vertical and deep.
Embedded circulation aloft 10 kft
105
Strong squall lines

• Mid-altitude Radial Convergence Zones
• Strong convergence in small areas from 2-5 km AGL
  implies locally strong downdraft below.

106
Strong squall lines

• Rear notches in back end of squall line
• implies a locally strong push of wind from the
  rear end of line

Rear inflow notches
107
Looking for strong squall lines with limited
radar data

• If lucky, base velocity when squall line heading
  right at radar
• If within 60 mi of the radar, look for gust front
  to remain next to core.
• Anywhere, if you have the four lowest slices,
  look for upright core along leading edge.
• Weaker squall lines do not show a solid deep,
  vertical core

108
Bow echoes
109
Bow echoes
Narrow bow echoes are typically more severe than
wide ones given everything else being equal.
110
Bow echoes

• Example of narrow bow echoes and very severe winds

111
Bow echoes
Larger bows such as this are typically associated
with lower peak winds. Winds still reached 60
mph though.
112
Bow echoes
Supercells can turn into bow echoes sometimes
resulting in the most severe wind damage
observed. The most severe winds develop to the
right of the original mesocyclone.
Example http//okfirst.ocs.ou.edu/train/casestud
ies/17aug94/17aug94.html
113
Supercell wind events

• Can produce a large number of the most damaging
  wind events without tornadoes
• Most common with HP supercells

Rear flank downdraft contains the most intense
winds but at this distance, 88D velocities
overshoot highest winds.
114
Supercell wind events
Deep convergence zone
3.4
These high wind events often have a very deep
convergence zone, extending 15 kft or more.
2.4
1.5
15 kft
0.5
115
Hail potential

• Radar cannot directly detect hail
• One big hailstone sends back the same energy as
  1000s of regular raindrops
• Either scenario could take place in a radar
  volume
• Thus we have to infer the presence of hail from
  other clues

116
Favorable hail clues

• Environmental
• Dry air aloft, moist below, large instability
• Enough wind shear for supercells
• Fairly low freezing level (wet bulb) 7500-10000
• Storm structure
• Intense reflectivity core (gt55 dBZ) above the 20
  C level
• Strong updrafts with a WER or BWER
• Storm rotation (supercells)

117
Favorable hail clues

• Intense elevated core
• Know how high your elevation slices are to your
  0 and 20 C heights at the storm location.

• Look for high reflectivity (gt55 dBZ) LRM products
  at 24 33 kft and especially the 33-60 kft
  level.

-20 C
0 C
118
Favorable hail clues
3.4

• Bounded Weak Echo Region (BWER)
• Intense updraft forms a hole in the reflectivity
  core.

2.4
BWER
BWERs not typically seen this far out
1.5
Typical BWER heights
0.5
119
Favorable hail clues

• Weak Echo Region (WER)
• Intense updraft also levitates a large region of
  core.
• Look for high over low reflectivities on the
  inflow side of a storm

3.4
2.4
WER
Watch out for anvil WERs. They are not updrafts.
1.5
A
WER typically from sfc to 15-20 kft.
0.5
A
B
B
120
Vertically Integrated Liquid

• Integrates what the radar thinks is liquid water
  in the vertical
• Not a reliable hail indicator, no set thresholds
• Does show location of the biggest storm

121
VIL
Hail is loosely associated with VIL but the
threshold changes with season and location
122
VIL density

• VIL is normalized by echo top height in meters
  and then multiplied by 1000 to yield a density of
  g/m3
• Attempts to reduce effects of different
  environments on a consistent large hail threshold

VIL 47.5 kg/m2 ET 9.1 km
VIL 70 kg/m2 ET 13.4 km
-20 C
0 C
123
VIL density

• Warning performance statistics show a VIL density
  3.28 g/m3 performs well as a large hail
  threshold in multiple CWAs.
• However

Cerniglia and Snyder, 2002 ER Tech memo
124
VIL density

• VIL density does not perform well in estimating
  severe hail size

Edwards and Thompson, 1998
125
Other ordinary cell hail considerations

• Reflectivities gt 60 dBZ indicate a high
  likelihood of hail
• Cannot discriminate hail size
• The Hail Detection Algorithm tends to
  overestimate the Probability of Severe Hail
  (POSH) in weakly sheared storms over low terrain
• Hail potential increases as the freezing level
  approaches the ground or vice versa (i.e.
  topography)

126
A word about the Hail Detection Algorithm

• Strengths
• Does well with probability of severe hail (POSH)
  with supercells.
• Shows the most intense storms
• Limitations
• Overestimates (POSH) in weak flow storms
• Subject to vertical sampling limitations

127
Vertical sampling limitations
Imagine a storm moving away from the radar that
is producing hail and is maintaining a constant
intensity.
The white line is the true height of the 50 dBZ
echo that the hail algorithm uses to figure
POSH. The blue line is what the radar sees in
VCP 21. This could mean anywhere from 0 100
error in POSH
128
Vertical sampling limitations
Imagine a storm moving away from the radar that
is producing hail and is maintaining a constant
intensity.
Fortunately the errors are better in VCP 11 Most
NWS offices use VCP 11 during severe weather
129
Example HDA case
A distant supercell with a hail spike. The
algorithm estimates gt 70 large hail with a size
of 1. Is this an underestimation, right on,
or an overestimation?
See the green triangle with a 1 hail size in it.
130
Hail algorithm results
131
Stormscale rotation

• First, a review
• Which is (cyclonic convergent, anticyclonic
  convergent, convergent, divergent)?

132
Stormscale rotation - mesocyclone

• Small scale rotation closely associated with an
  updraft that
• Persists for 10 minutes or more
• Vertical continuity (10 kft or more)
• Shear
• Core diameter lt 5nm and rotational velocity
  exceeding minimal thresholds
• The mesocyclone algorithm does NOT look for
  persistence and only looks for two slices for
  vertical depth criteria

133
mesocyclone

• Rotational velocity (max outbound max
  inbound)/2
• Use representative inbounds and outbounds, not
  the absolute maximum values

Meso diameter 3.5 nm
Vmax 50kt Vmin -22kt Rotational V 36 kt
134
A classic mesocyclone
Convergent rotation at lowest slice.
1.5
0.5
Pure rotation at higher slices.
3.4
2.4
135
Another classic supercell
J. LaDue
136
Another classic
J. LaDue
137
A diversity of mesocyclone sizes

• All of these were tornadic.
• Only the big one shows a meso hit

G. stumpf
Courtesy G. Stumpf
138
An HP supercell
Im looking for a volunteer to pick out where the
mesocyclone and HP are located
139
An HP supercell
140
An HP supercell
This was a challenging day for Central
Oklahoma. Tornadoes were common but difficult to
see.
Inflow notch suggests strong updraft
Meso is colocated next to inflow notch
141
Left and right-moving supercells

• Left movers rotate anticyclonically in the
  northern hemisphere
• Right movers rotate cyclonically in the northern
  hemisphere
• The mesocyclone algorithm does NOT detect
  anticyclonically rotating supercells

142
Left and right moving supercells

• Left-moving storms can contain
• mesoanticyclones
• BWERs
• Large hail
• Damaging winds
• but rarely do they produce tornadoes

left moving anticyclonic
Right moving cyclonic
143
Left and right moving supercells

• Left-moving storms can contain
• mesoanticyclones
• BWERs
• Large hail
• Damaging winds
• but rarely do they produce tornadoes

left moving anticyclonic
Right moving cyclonic
144
Tornado potential

• A tornado vortex signature
• Strong gate-to-gate shear
• Prefer to see this for at least two slices
• The bottom should be on the lowest slice or
  within 600 m AGL
• I prefer to see this persist for a couple scans
• But some situations will not allow me to wait.
• Due to beam spreading, my maximum TVS range is
  about 60 nm. After that, Im only seeing
  mesocyclones.

145
Tornado vortex signature

• Shear outbound inbound in adjacent gates
• Anywhere from 35 to more than 140 kts depending
  on range and severity

146
The Tornado Detection Algorithm
The TDA looks for isolated gate-to-gate shears
that are vertically correlated. If the lowest
slice with a feature is on the 0.5 slice or
within 600 m AGL, the radar calls it a (TVS)
147
The TDA algorithm

• Know when to trust it
• For this, the TDA might be taken seriously

148
The TDA algorithm

• What about on this day?

149
The TDA algorithm

• What about on this day?

• Will you believe the TDA or discount it?

150
Pros and Cons
PROS Multiple TDAs High shear in SRM Supercell
reflectivity structure Reports of damage
CONS SRM shear lacked height continuity High
SW Gust front well south of TDA Not
climatologically favored Damage could be from
high wind
151
Decision was against tornado warning

• Concerned about TDA and 0.5 shear
• but
• Environment not favorable for tornadoes
• Didnt fit climatology
• Signature lacked height continuity
• Reports were ambiguous as to cause
• so
• Readied tornado warning pending better ground
  truth or more convincing radar signature

152
Why did TDA fail?
High shear signatures due to dealias errors,
turbulence, or velocities placed in wrong trip
due to low TOVER. Damage caused by strong
outflow winds!
153
Artificial sampling from NIDS
NIDS velocity 1 km boxes
Full resolution SRM 0.2 km gates
June 13, 1998 OKC
154
Occurrence of tornado with LLDV
TVS low-level gate-to-gate velocity difference,
LLDV (m/s)
FAR green line POD red line HSS black
line Inset POD vs FAR
LLDV m/s
155
Occurrence of tornado with LLDV
TVS Maximum gate-to-gate velocity difference, MDV
(m/s)
FAR green line POD red line HSS black
line Inset POD vs FAR
MDV m/s
156
A descending TVS

• 50 of are associated with supercells
• (from Trapp et al., 1999)
• Offers greater lead time

Trapp et al., 1999
157
Nondescending Tornado Signatures

• 80 of squall lines
• 50 of supercells
• (from Trapp et al., 1999)

158
Cyclic mesocyclones

• The first mesocyclone evolves more slowly than
  succeeding mesocyclones
• Succeeding mesocyclones may also have long
  lifespans

159
Tornadoes in weak shear environments

• Favorable sounding shows
• Little CIN
• Steep low-level lapse rates

160
Tornadoes in weak shear environments

• Watch out for well defined boundaries with
  significant vertical vorticity

161
Tornadoes in weak shear environments

• Start with strong boundary with developing CU
• Boundary shear starts to roll into misocyclones

A
C
B
162
Tornadoes in weak shear environments

• CU updrafts grow
• Misocyclones A and B grow and move to the right
  while C weakens

A
C
B
163
Tornadoes in weak shear environments

• TCU continue to grow. Elevated core may form
• Misocyclone B phases with one updraft forming a
  tornado

• Misocyclone A remains unattached, only dust
  devils form

A
B
C
164
Positioning spotter scenario

• Its dark
• Theres a potentially tornadic supercell
• Which spotter is most likely going to see the
  tornado if there is one?

Kevin
Jim
165
Positioning spotter scenario

• Its a matter of luck to see a tornado at night
• The spotter needs city lights or lightning to
  silhouette the tornado
• Power flashes means the tornado is already
  hitting somebody

166
Tornado backlit by lightning

• From another storm

167
Why spotters are still needed
168
Why spotters are still needed
Because we usually dont have access to radar B
169
Why spotters are still needed
Courtesy Mike Magsig, WDTB
170
Where to expect aspects of Mesos and TVSs
Distance from which the beam width exceeds .54 nm
No TVSs beyond here
Height of gust fronts, boundaries
171
Summarizing

• For downbursts
• Look for descending core, midlevel convergence,
  especially rapid initial buildup.
• For organized wind events
• Look for solid intense, vertical core with gust
  front remaining nearby
• Small scale intense bow echoes
• MidAltitude Radial Convergence areas
• Rear flank downdrafts of intense supercells

172
Summary contd

• For large hail
• Deep core gt55dBZ passing far above 20 C level
• Supercell updraft with strong BWER or WER
• Three-body scatter spike or hail spike
• For tornadoes
• Strengthening TVS in lowest slices
• Strengthening mesocyclone
• Strengthening updraft, BWER, inflow notch
• Hook development
• Having more of these together increases
  confidence
• Above all, remember the radar limitations and
  always question the algorithms

173
resources

• General radar interpretation - OKFIRST
• http//okfirst.ocs.ou.edu/train/materials/radar.ht
  ml
• NSSL mesocyclone and tornado case study page
• http//www.nssl.noaa.gov/wrd/swat/Cases/cases_pix.
  html
• NOAA radar page
• http//weather.noaa.gov/radar/
• The Warning Decision Training Branch
• http//www.wdtb.noaa.gov/