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Analysis of reflectivity echo
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Rainfall Estimation Limitations
Brightband
Contamination
Radar Centered Arch of Higher
Rainfall Accumulations on prouduct.
Overestimate
rainfall
But rare to
affect convectiveflash flooding
events
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Rainfall Estimation Limitations
Inaccurate Z/R relationship due to
estimation of drop size distributions
Same Reflectivity,
Vastly Different
Rainrates
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Mixed shape
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Mixed shape
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Anticipating Dominant Warm Rain
Process Convection
Assess the environment
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Ft. Collins Flood (07/28/97)
12z and 00z Denver U/A soundings
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Efficiencyschematic
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Precipitation in
Flash Floods Enhanced Intensity
Precipitation efficiency
Tropical, maritime
connection Deep, above-freezing
layer
Low-level jet, rapid
moisture replenishment Low-level focus (terrain
and boundary)
http://www.comet.ucar.edu/class/FLOAT_2001/index.htm
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Flash flood threat from weakly
sheared cells
Warm cloud depth
increases collision
coalescenceresulting in
excessive rainfall
rates
Storm top may not
be high
W R i P
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Warm Rain Processes
Radar Signatures
Kansas Turnpike Flash Flood Aug 30, 2003
LEC
C S ti th h W
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Cross Section through Warm-
Rain Supercell
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0.5
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V shape notch
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Hook shape echo
The hook echo is always located the right
rear of the main echo movement.
The hook echo is always associated with
meso-cyclone and hailstorm.
When the meso-cyclone is detected using
lowest ( 0.5 elevation angle ) , a tornado
may occur.
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200252708:55 gmt)
2.4deg
3.4deg1.5deg
0.5deg
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Same supercell at max BWER
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Same supercell at max BWER
detection range Large BWER
is barely
visible @ 78
nm or only148 km
-20
C
Wide lower topped supercell
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Wide, lower topped supercell
updraft
Front-flankupdraft
Very wideupdraft
Prolific 5.5 cmhail and 45 m/swinds
-20
C
BWER = 5mi max size
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The Weak Echo Region
WERs are ellipticalin shape
Is that the shape ofthe updraft?
7.3 km AGL 45
dBZ
reflectivity
contour
10 km
O i i f th W k E h R i
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Origin of the Weak Echo Region
Quarter Panel Display
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Quarter Panel Display6/18/1992
Severe sheared updraft intensity
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Severe sheared updraft intensity BWER detection
BWER (Bounded Weak Echo Region)
0.5
1.5
2.4
3.4
BWERs
difficult
to detect
this far
out
Typical
BWER topnear the
-20to -25o
C level
-20C
Needs a
connection to
the low-level
WER
Classic severe updraft
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Classic severe updraft
signature case
Right-rearupdraft
Typical width
Produced a fewrecord sized
hailstones
BWER = 2mi max size
-20
C
Classic severe updraft
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Classic severe updraftsignature case
Velocity
-20
C
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Example
>45 dBZ echo
to 7300 m AGL
hookWER
BWER
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Radar Characteristic of Severe
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StormsIn a Sheared Environment
Strong low-level reflectivity gradients.
Displaced low-level Echo Core.
Occasionally concaved echo open to inflow. Mid-level sloping echo overhang: WER*.
Strong upper mid-level echo core over low-level reflectivity gradient/concavity.
Echo top above mid-level echo core. * Sometimes BWER
After Lemon, 1980.
Remember these 6 characteristics!!
On updraft flank:
Summary: Severe updraft
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Summary: Severe updraftsignatures
severe updraft signatures common to allstorms in order of most severe first
BWER
WER
Intense and deep reflectivity core relative to the
20C level
Storm top displaced over WER
Deep convergence zone*
Supercell Visual Appearance
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p pp
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The gust front
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2013/11/4
2 69
SA
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2013/11/4
2 70
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( f ) ( )
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13: 42 (left ) 13: 51 (right )
Li l i d lti ll t
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Linearly-organized multicell storms
W kl ti ll li
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Weakly convective squall line
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S t i l
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Some terminology
Squall line: multicell convection organizedinto laterally-aligned cells that may or maynot be interacting
Bow echo: a squall line with a bow-shaped morphology
Gust front- leading edge of downdraft-driven convective storm outflow
T i l ( td)
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Terminology (contd)
Mesoscale Convective System(MCS)A multicell convective complex
Most often includes a radar-observed linear
organization in its mature phase May be relatively disorganized
In its largest, longest-lived formsbecomes a Mesoscale ConvectiveComplex (MCC)
A satellite view of an MCS
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A satellite view of an MCC
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MCS schematic cross section
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MCS schematic cross-section
Morphology and Evolution
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Morphology and Evolution
Role of air flows in complex multicell system
3 distinct modes (TS, LS, and PS)
Parker and Johnson (2000)
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Bow Echoes
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From Fujita, 1978, the morphology of the typical
Bow Echo.
Echo is bowed towards the direction of the echo movement.
A bow echo is often associated with strong surface winds at the
leading of the bow echo.
Bow Echoes Important 3-D features
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Development of Cyclonic bookend vortex
Affects strength of RIJ
Can be an area of increased downdrafts (non-supercell and
supercell tornadoes)
p
Elevated RIJs
Line-end vortices
RINs Strong reflectivity
gradient
Weak Echo Regions
Displaced echo top
Supercell transition
Bow Echoes
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Bow Echoes
Rear-Inflow Notch (RIN) May indicate a descending RIJ
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Bow Echoes
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Supercell transition to Bows
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Can you apply the Lemon
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technique here?
Yes, accountingfor storm motion, a
WER and BWER
can be detected
-20
C
WERand
BWER
along
leading
edge
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Summary: Severe updraft
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signatures
severe updraft signatures common to allstorms in order of most severe first
BWER
WER Storm top displaced over WER
Deep convergence zone
Intense reflectivity core, and deep relative to the20C level
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Volumetric Radar Data
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AZ/RAN 272o/172 km
3 km (10 kft)
9.1 km (30 kft) 12.2 km (40 kf
6.1 km (20 kft
Volumetric Radar Data
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AZ/RAN 293o/67 km
Ground-Relative Wind ProductionM h i
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Mechanisms
Much more than a simple downburst
HL
+5mb
-2mb
roun - e a ve n ro uc onMechanisms
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Mechanisms
Most likely area for XDW is on outflow flank oflow-level mesocyclone and in the precip-filled
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The Gust front
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(CR 37)
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(CR 37)
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(STI 58)
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(HI 59)
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(HSR 33)
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(ET 41)
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(V 27)
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(VWP 48)
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1(OHP 78)
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3(THP 79)
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(VIL 57)
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(SW 30)
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()
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( )
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2005614
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08:43(gmt) 08:55(gmt) 09:08(gmt)
2002527
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