# Presentation: 232728

## Severe storm radar signatures

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

- James.G.LaDue@noaa.gov

## Topics

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

## 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?

## Radar and visual view of a developing thunderstorm

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

## Radar and visual view of a developing thunderstorm

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

- Link to loop

## Ordinary cell evolution

- TCU + 7 min

- -10° C

- 0° C

## Ordinary cell evolution

- TCU + 14 min

- 0° C

- -10° C

## Ordinary cell evolution

- TCU + 21 min

- -10° C

- 0° C

## Ordinary cell evolution

- TCU + 28 min

- -10° C

- 0° C

## Ordinary cell evolution

- TCU + 35 min

- -10° C

- 0° C

## 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

## Visual vs radar reflectivity

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

- Gene Rhoden

- Jim LaDue

- 0026 UTC

## Visual vs radar reflectivity

- 50-55 dBZ
- Mostly large hail stones

- Gene Rhoden

- Jim LaDue

- 0026 UTC

- Jim Leonard

## Same Z, Different R

- Z1 = 729 mm6/m3
- (29 dBZ)
- R1 = .22 inch/hr

- Z1 = 729 mm6/m3
- (29 dBZ)
- R1 = .01 inch/hr

**Notes:**
In order to show that there is no unique relationship between Z and R, here is an example where the same Z value results from two different dropsize distributions. However, there are significantly different rainfall rates. Note that the large number of small drops generates the higher rate. 

## Visual vs. radar reflectivity30 April 2004 – 2131 UTC

## Visual vs. radar reflectivity30 April 2004 – 2131 UTC

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

## Visual vs. radar reflectivity21 April 2004 – 0017 UTC

- North of Stroud, OK

## Visual vs. radar reflectivity21 April 2004 – 0022 UTC

- North of Stroud, OK

## Visual vs. radar reflectivity21 April 2004 – 0022 UTC

- 55-60 dBZ corresponding to heavy rain and golfballs

## Three body scatter spike

## Three body scatter spike

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

## Visual vs. radar reflectivity09 June 2004

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

## Visual vs. radar reflectivity09 June 2004

## Warm Rain ProcessesA Recent Example

**Notes:**
You’ve already seen the environment for this day with the 2 soundings a couple of slides ago.  So there is a large batch of precip to the southwest of the radar, and 2 cells to the south, both exhibiting moderate rotation in the lowest levels and hook echoes from time to time. 55-60 dBZ exists, but how can you be sure there is warm rain in there?  Cut a cross section through the core (which is the turquoise dotted line) to find the following:

## Cross Section through Warm-Rain Supercell

- Notice the reflectivity drop off above the freezing level.

**Notes:**
This is an example of a warm-rain process and LEC signature on a supercell storm.  Not only were tornadoes a threat, but flash flooding as well because of intense rainrates.  Fortunately, the storm moved NE at 25 mph and significant flooding did not occur.  WDTB Instructor Jim Ladue was on this storm, verifying the complete lack of lightning and hail within this storm.

## Visual vs. radar reflectivity

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

## What is the TVS seeing?

## What is the TVS seeing?

- 1.  Flanking line

**1.**

**1.**

## What is the TVS seeing?

- 1.  Flanking line

**1.**

**1.**

- 2. Dry slot and hook

**2.**

**2.**

## What is the TVS seeing?

- 1.  Flanking line

**1.**

**1.**

- 2. Dry slot and hook

**2.**

**2.**

- TVS

- TVS

- TVS

- Tornado

## Visual vs. radar reflectivity

- Drop size distribution
- Very large hail creates translucent visual cores but very strong reflectivity
- Lot’s 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

## 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

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

- Case:  11 August 2004 Cocoa Beach, FL

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

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

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

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

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

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

## 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

## 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

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

- Notice the intense core is right behind the gust front

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

- 5 minutes later...

## 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

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

- Deep Convergence zone
- What do you think the spotter’s seeing?

- 15 kft

## 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

**Notes:**
A conceptual model of a high-end severe linear system shows the same features we've seen in the example from New York.  One is a leading edge WER and even a small linear BWER.  The updraft is upright.for several km before sloping back over the cold pool dome.  The leading gust front exhibits a steep slope and the Rear Inflow Jet behind it remains nondescending until within the heavy reflectivity core of the leading edge.  However, the gust front remains underneath the low-level updraft providing a strong initial updraft through convergence.
Depending on the line-normal upper-level storm-relative flows, some anvil material  may flow ahead of the line.  This is not a requirement for a severe linear updraft.  
The high end severe systems appear to consist of one unbroken leading edge updraft and trailing reflectivity core.  You will see little evidence of discrete cellular behavior over the leading edge of the cold pool. 

## Supercell anatomy

- Given more cell phone images coming in real time from the field, let’s figure out what the storm would look like given one image

## Supercell anatomy

- Where’s the spotter and which way is the view?
- How far from the rotation?

- 1

- 2

- 3

- 4

- 5

- 6

- 7

- 8

## Supercell anatomy

- 1

- 2

- 3

- 4

- 5

- 6

- 7

- 8

## Supercell anatomy

- Where is the spotter?

- 1

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- 8

## Supercell anatomy

- Where is the spotter?

## Supercell anatomy

- RFD dry slot

## Supercell anatomy

- RFD

## Supercell Anatomy

- Supercell updraft from the front side

## Supercell anatomy

## Supercell anatomy

- Where is the tornado threat?

## Supercell anatomy

- Where is the tornado threat?

## Supercell Anatomy

## 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)

## Where are these pictures relative to the storm?

- Sam Barricklow

- Jim Leonard

- Jim LaDue

- 0000 UTC

**A**

**B**

**C**

## 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.

## Supercell wind events

- 0.5°

- 1.5°

- 2.4°

- 3.4°

- These high wind events often have a very deep convergence zone, extending 15 kft or more.

**Deep convergence**
**zone**

- 15 kft

## Hail and tornado signatures

- For large hail
- Deep core >55dBZ 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

## 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 < 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

## Where to expect aspects of Mesos and TVSs

- No TVSs beyond here

- Height of gust fronts, boundaries

**Distance from which the beam width exceeds .54 nm**

## Where to expect aspects of Mesos and TVSs

- No TVSs beyond here

- Height of gust fronts, boundaries

**Distance from which the beam width exceeds .54 nm**

## Favorable hail clues

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

- Typical BWER heights

- 0.5°

- 1.5°

- 2.4°

- 3.4°

- BWERs not typically seen this far out

- BWER

## 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

- WER typically from sfc to 15-20 kft.

- 0.5°

- 1.5°

- 2.4°

- 3.4°

- WER

**B**

**A**

**A**

**B**

- Watch out for anvil WERs.  They are not updrafts.

## Waiting till 2257 UTC

- The storm is still outside our CWA.
- We’ve got another volume scan.

## Favorable hail clues

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

- Typical BWER heights

- 0.5°

- 1.5°

- 2.4°

- 3.4°

- BWERs not typically seen this far out

- BWER

## Where to expect aspects of Mesos and TVSs

- No TVSs beyond here

- Height of gust fronts, boundaries

**Distance from which the beam width exceeds .54 nm**

## Lessons learned

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

## Pulse storms

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

## 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

## 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?

## Pulse storm downbursts

- Is this the time a warning should be issued?

## Pulse storm downbursts

- As an aside

- 300 m

## Pulse storm downbursts

- As an aside

## 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

## Pulse storm downbursts

- Where do you think the downburst occurred?

## Pulse storm downbursts

- This time height trend of reflectivity shows the descending core hitting the ground just after 0006 UTC.

- Updraft
- phase

## Pulse storm downbursts

- 2356 UTC

- Updraft begins to build a core aloft

## Pulse storm downbursts

- 0002 UTC

## Pulse storm downbursts

- 0008 UTC

- Midlevel convergence signifies downdraft commencing

## Pulse storm downbursts

- 0014UTC

## Pulse storm downbursts

- 0019 UTC

- Downdraft impacts the ground

## Pulse storm downbursts

- 0024 UTC

## Pulse storm downbursts

- 0029 UTC

## Pulse storm downbursts

- 0037 UTC

## Pulse storm downbursts

- 0042 UTC

## Pulse storm downbursts

- 0047 UTC

- Storm exhausts itself

## 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

## 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

## Monitoring the elevated core

- If you have limited access to radar data, use the Layer Maximum Reflectivity (LRM) products.

- LRM max
- 24 – 33 kft

## Pulse storm downbursts

- Or use the composite reflectivity and compare with 0.5°.

- 0.5

- Composite

## Pulse storm downbursts

- LRM layers available on NIDS

## Intense elevated reflectivity core

- Keep in mind the height of the 0° and –20° C temperatures.

- Reflectivity > 55 dBZ extending further above the  –20° C level infers an increasing chance of large hail.

## Organized convective wind events

- Squall lines
- Bow echoes
- HP supercells

## 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.

## 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?

## The answer

## 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 doesn’t see much outbound wind (**red arrow**).
- What is the second reason?

## 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.

## 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.

## 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.

## Strong squall lines

- This squall line moved at > 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.

## 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

## Strong squall lines

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

## 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

## 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

## Bow echoes

## Bow echoes

- Narrow bow echoes are typically more severe than wide ones given everything else being equal.

## Bow echoes

- Example of narrow bow echoes and very severe winds

## Bow echoes

- Larger bows such as this are typically associated with lower peak winds.
- Winds still reached 60 mph though.

## 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/casestudies/17aug94/17aug94.html

## 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.

## Supercell wind events

- 0.5°

- 1.5°

- 2.4°

- 3.4°

- These high wind events often have a very deep convergence zone, extending 15 kft or more.

**Deep convergence**
**zone**

- 15 kft

## 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

## 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 (>55 dBZ) above the –20 C level
- Strong updrafts with a WER or BWER
- Storm rotation (supercells)

## 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 (>55 dBZ) LRM products at 24 – 33 kft and especially the 33-60 kft level.

- -20 C

-   0 C

## Favorable hail clues

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

- Typical BWER heights

- 0.5°

- 1.5°

- 2.4°

- 3.4°

- BWERs not typically seen this far out

- BWER

## 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

- WER typically from sfc to 15-20 kft.

- 0.5°

- 1.5°

- 2.4°

- 3.4°

- WER

**B**

**A**

**A**

**B**

- Watch out for anvil WERs.  They are not updrafts.

## 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’

## VIL

- Hail is loosely associated with VIL but the threshold changes with season and location

## 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

- -20 C

-   0 C

- VIL = 47.5 kg/m2
- ET  = 9.1 km

- VIL = 70 kg/m2
- ET  = 13.4 km

## 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

## VIL density

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

- Edwards and Thompson, 1998

## Other ordinary cell hail considerations

- Reflectivities > 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)

## 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

## Vertical sampling limitations

- 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

- Imagine a storm moving away from the radar that is producing hail and is maintaining a constant intensity.

## Vertical sampling limitations

- Fortunately the errors are better in VCP 11
- Most NWS offices use VCP 11 during severe weather

- Imagine a storm moving away from the radar that is producing hail and is maintaining a constant intensity.

## Example HDA case

- A distant supercell with a hail spike.
- The algorithm estimates > 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.

## Hail algorithm results

## Stormscale rotation

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

## 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 < 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

## mesocyclone

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

- Vmax = 50kt
- Vmin  = -22kt
- Rotational V = 36 kt

- Meso diameter = 3.5 nm

## A classic mesocyclone

- 0.5°

- 1.5°

- 3.4°

- 2.4°

- Convergent rotation at lowest slice.

- Pure rotation at higher slices.

## Another classic supercell

- J. LaDue

## Another classic

- J. LaDue

## A diversity of mesocyclone sizes

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

- G. stumpf

- Courtesy G. Stumpf

## An HP supercell

- I’m looking for a volunteer to pick out where the mesocyclone and HP are located

## An HP supercell

## 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

## 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

## Left and right moving supercells

- Right moving cyclonic

- left moving anticyclonic

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

## Left and right moving supercells

- Right moving cyclonic

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

- left moving anticyclonic

## 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, I’m only seeing mesocyclones.

## Tornado vortex signature

- Shear = |outbound + inbound| in adjacent gates
- Anywhere from 35 to more than 140 kts depending on range and severity

## 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)

## The TDA algorithm

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

## The TDA algorithm

- What about on this day?

## The TDA algorithm

- What about on this day?

- Will you believe the TDA or discount it?

## 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

## Decision was against tornado warning

- Concerned about TDA and 0.5 shear
-                              *but...*
- Environment not favorable for tornadoes
- Didn’t 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

## 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!

## Artificial sampling from NIDS

- NIDS velocity
- 1 km boxes

- Full resolution
- SRM 0.2 km gates

- June 13, 1998 OKC

## 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

## 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

## A descending TVS

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

- Trapp et al., 1999

## Nondescending Tornado Signatures

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

## Cyclic mesocyclones

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

## Tornadoes in weak shear environments

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

## Tornadoes in weak shear environments

- Watch out for well defined boundaries with significant vertical vorticity

## Tornadoes in weak shear environments

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

- A

- B

- C

## Tornadoes in weak shear environments

- A

- B

- C

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

## Tornadoes in weak shear environments

- A

- B

- C

- 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

## Positioning spotter scenario

- It’s dark
- There’s a potentially tornadic supercell
- Which spotter is most likely going to see the tornado if there is one?

- Kevin

- Jim

## Positioning spotter scenario

- It’s 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

## Tornado backlit by lightning

- From another storm

## Why spotters are still needed

## Why spotters are still needed

- Because we usually don’t have access to radar B

## Why spotters are still needed

- Courtesy Mike Magsig,
- WDTB

## Where to expect aspects of Mesos and TVSs

- No TVSs beyond here

- Height of gust fronts, boundaries

**Distance from which the beam width exceeds .54 nm**

## 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

## Summary contd

- For large hail
- Deep core >55dBZ 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

## resources

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