Forecasting Convective Mode and Severity

1
Forecasting Convective Mode and Severity

• Mark F. BrittNational Weather ServiceSt. Louis,
  MO

2
Why Am I Here?

• A Basic Review of Severe Thunderstorm
  Forecasting.
• Examine moisture return,instability, and shear
  calculations.
• Examine how the amount and distribution of
  instability, vertical shear, and forcing interact
  to determine cell type, convective mode (linear
  or discrete), and coverage.
• Determine what type(s) of severe weather to
  expect for a given environment.

3
Using Numbers

• There are NO magic numbers or thresholds. They
  are merely guidelines.
• Best to look where several key parameters overlap
  instead of depending on one index.
• You should look at skew-Ts and hodographs
  (observed and forecast) to better understand what
  the numbers mean.
• Increase your situation awareness by using near
  storm environment data, but do not use it solely
  to make warning decisions.

4
Objective Analysis

• Available on AWIPS using MSAS, LAPS, or RUC40
  analysis (Thompson/Edwards (2002) found RUC
  analysis is a reasonable proxy to observed
  soundings in supercell environments.)
• Or, the SPC Mesoanalysis Page
• http//www.spc.noaa.gov/exper/mesoanalysis/
• Displays three movable regions that is usually
  available by 20 minutes past each hour
• Displays a robust set of hourly objective
  analysis datasets using the latest surface
  observations and upper air analysis from the RUC.
  Depicted contours highlight important
  thresholds.
• Several new parameters available this year.

5
Ingredients for Deep, Moist Convection

• Moisture (Gulf of Mexico, evapotranspiration)
• Instability (Steep lapse rates either from the
  Elevated Mixed Layer off the Rockies, or large
  scale dry ascent ahead of a trough.)
• Forcing (Surface frontal boundary, convective
  outflow, 900-800mb moisture convergence at nose
  of nocturnal low level jet, orographic lift over
  the eastern Ozarks)

6
Moisture Return
Lanicci and Warner (1991)

• Look for rapid moisture advection from the Gulf
  of Mexico in strong pressure gradients ahead of a
  strong storm system.
• Ridging associated with surface highs in or
  near the Gulf can inhibit moisture return.

7
Assessing Instability

• Which is best?
• SBCAPE
• MLCAPE
• MUCAPE

8
From Peter Banacos, SPC (2003)
SBCAPE Surface Based. Uses the surface
temperature and dew point. Will show large
diurnal swings. Can give significant
overestimates (an order of magnitude) in cases of
shallow moisture and underestimates in cases of
elevated convection.
9
From Peter Banacos, SPC (2003)
MLCAPE Mean Layer. Uses the mean temperature
and mean mixing ratio in the lowest part of the
atmosphere (SPC uses lowest 100 mb). Less
variable in time and space, and more conservative
than MUCAPE when lower atmosphere is not well
mixed.
10
From Peter Banacos, SPC (2003)
MUCAPE Most Unstable Parcel. Uses most
unstable parcel in lower atmosphere (SPC uses
lowest 300mb). Helps with nocturnal or other
types of elevated convection.
11
CAPE vs. Parcel Selection
April 22nd, 2004
Mean Layer CAPE
Surface Based CAPE
From Jon Davies Webpage
12
Surface Based Parcels
Violent tornado outbreak over western
Missouri. May 4th, 2003
13
Elevated Based Parcels
Numerous Reports of Hailin Eastern NE/ Western
IA May 4th, 2003
14
How Tall is the CAPE?
April 22nd, 2004
From Jon Davies Webpage (http//members.cox.net/jd
avies1/)
15
How Tall is the CAPE?
April 22nd, 2004
From Jon Davies Webpage
16
How Wide Is the CAPE?
Larger differences between parcel temperature and
the environmental temperature means stronger
updrafts that are less susceptible to entrainment.
17
Lapse Rates

• Craven (2000) found in a study of 65 major
  tornado outbreaks that 6.7o C/km is a useful
  lower limit. He also found low shear
  environments that produce tornadoes have steeper
  lapse rates.
• Steep mid level lapse rates (850-500 mb) have
  more conditional instability and increased CAPE.
• Steep low level lapse rates (0-3km AGL) can give
  a better idea on how quickly convection will
  develop.

18
Mid Level Lapse Rates
19
Assess Vertical Shear

• Distribution of vertical shear will determine
  dominant thunderstorm type.
• Can be determined using either
• Traditional fixed layers (0-6km bulk shear, 0-1km
  SRH)
• Effective shear which accounts for sounding
  dependent inflow layer through CAPE and CIN
  constraints. (Large sample testing suggests that
  effective layer is best defined by gt100 J kg-1
  CAPE and lt250 J kg-1 CIN. (Thompson et al, 2004a
  b))
• Low level curvature can determine if
  right-movers, left-movers, or both kinds of
  splits are favored.

20
Storm Type Ordinary Cells

• Dominant Type in Weak Shear Environments
• Pulse Type Severe Storms.

21
Storm Type Multicells
Moderate to strong shear is confined mainly to
the lower levels (0 to 3 km AGL)
22
Organized Multicells

• gt40kt 0-6 km shear
• gt30kt 700-500mb wind
• Dry (low theta-e) midlevel air (strong cold)
• Downshear SBCAPE max
• System relative convergence acting downshear to
  enhance forward propagation

23
Storm Type Supercells

• A storm that possesses a persistent mesocyclone
  that can be sustained on the order of tens of
  minutes.
• 90 of this type associated with some kind of
  severe weather (Burgess and Lemon, 1991)

24
0-6 km Shear Magnitude

• General deep layer shear thresholds
• 40 kt suggests if storms develop -- supercells
  are likely (provided convective mode favors
  cellular activity)
• 30-40 kt supercells also possible if
  environment is very or extremely unstable as
  storm can augment local shear (gt5,000 J/kg
  (Burgess (2003))
• About 15-20 kt shear needed for organized
  convection (multicell or supercell) with mid
  level winds at least 25 kt
• While 0-6km shear is a good discriminator between
  cell types, it isnt a good tornado forecast tool
  (Thompson et al, 2002).

25
0-6 km Shear Magnitude
Supercells Non-Supercells
From Thompson et al (2002)
26
BRN Shear
(Weisman and Klemp (1982), and Thompson (2000
2002)
BRN Shear is the vector difference between the
density weighted mean winds in the lowest 6 km
and the lowest 500 m above ground level. BRN
shear can be a used as a good predictor of storm
type and severity.
Supercells Non-Supercells
40 m2/s2 35 m2/s2
From Thompson et al (2002)
27
Supercell Composite Parameter (Thompson et al,
2003)

• The Supercell Composite Parameter (SCP) is a
  multi-parameter index that includes 0-3 km SRH,
  CAPE, and BRN Shear. Each parameter is normalized
  to supercell threshold values.
• SCP (muCAPE/1000 J/kg) (0-3km SRH/100
  m2/s2) (BRNShear/40 m2/s2)
• Computed every hour on the SPC Mesoanalysis Page.

28
Supercell Composite Parameter (Thompson et al,
2003)
May 4th, 2003
29
What Causes Supercell Type
Rasmussen and Straka (1998) found in an
observational study of 43 isolated supercells
that supercell type is much more dependent
precipitation efficiency based on its ingestion
of hydrometeors.
30
Classic Supercells

• The real value of a CL supercell is that it
  appears to be the most efficient of the three
  types to produce significant tornadoes.
• Can occur nearly anywhere in U.S. when NSE
  supports them.

31
High Precipitation (HP) Supercells
32
High Precipitation (HP) Supercells

• Lower mid-level and anvil-relative flow.
• Interactions with other storms seeding, more
  storms can occur with weak caps.
• Typically associated with weaker tornadoes, but
  can produce significant tornadoes (Plainfield
  IL).
• More of a severe wind (Pakwash), hail, and flash
  flooding threat.
• Are the more-common supercell type east of the
  Mississippi owing to NSE conditions there (weaker
  caps, etc.), and may be the most common type
  everywhere in the U.S.

33
Supercell Dimensions
Burgess (2003)
34
Supercell Movement
Bunkers et al (2000)
A physically based, shear-relative, and Galilean
invariant method based on 290 supercell
hodographs.
35
Supercell Movement
Bunkers and Zeitler (2000)

• There are some caveats to this method
• Stronger deep-layer vertical wind shear (0-6 km)
  leads to a stronger mesocyclone and thus to
  greater deviation from the mean wind.
• Weaker mid-level storm-relative winds allow for a
  stronger cold pool, and thus a tendency for the
  supercell to move rapidly downshear.
• Depth of thunderstorms need to be considered.
• Supercell motion can be altered by wind shear
  from boundaries and orography.

36
Storm Coverage and Mode

• Whats the Problem?
• Evans (2003) noted Strong Forcing Derechoes and
  discrete, significant tornadic supercells (F2-F5)
  can occur in similar environments.
• Unfortunately, differences can be very subtle and
  difficult to diagnose operationally.

37
What Controls Storm Coverage?(Thompson, 2004)

• Widespread coverage expected with
• Rich moisture influx and steep lapse rates
• Combination of Q-G and mesoscale ascent
• (Differential CVA and WAA with surface
  frontogenesis)
• Little CIN (Everything goes up.)
• Isolated (or no) storms with
• Marginal moisture and lapse rates (weak CAPE)
• Neutral to subsident large-scale environment
  (Rely on small-scale/shallow processes for
  initiation)
• Large CIN (Confine storms to strongly forced or
  in areas of most persistent ascent)

38
What Causes Convective Mode?
Discrete Squall Line
stronger and/or deeper (or confined near
boundary) less greater more parallel
weaker more weaker more perpendicular
Strength and Depth of Boundary Forcing Amount of
CIN compared to Boundary Forcing Potential for
Cold Pool Shear Vector w.r.t. Boundary
Orientation
39
Initiating Boundary w.r.t. Deep Layer Flow
(Bluestein and Weisman, 2000 Dial and Racy, 2004)

• Parallel (lines dominate, with end supercells)
• 45o (discrete supercells, little storm
  interaction)
• 90o (colliding storm splits, but depends on
  storm spacing and hodograph shape)

40
Progressive Trough
May 4th 2003 Tornado Outbreak, Progressive Flow
Aloft
0-6 km shear across dryline, and storm motion
faster than boundary motion
From Rich Thompson, SPC
41
High Amplitude Trough
April 6th 2001 Great Plains High Risk Squall
Line
0-6 km shear largely parallel to dryline, and
storm motion slower than boundary motion
From Rich Thompson, SPC
42
Derechoes or Tornadoes?
Anvil SR Winds may show some discrimination
(Evans 2003).
43
Surface Pressure Changes

• 1-2 hourly pressure changes help identify
• Mesolow /mesohigh couplets and boundaries
• Concentrated fall/rise couplet enhance low- level
  convergence/shear by backing surface winds
  (enhancing tornado threat)
• Clouds associated with surface pressure falls may
  be linked to a dynamical feature
• Implications on thermal advection
• Rise/Fall couplets may indicate severe wind
  threat in marginal CAPE environments

44
Convective Severity
From DLOC Hazards Assessment
45
Tornado Parameters

• Mesocyclonic Tornadoes
• Low Level Shear Vector and Storm Relative
  Helicity
• Low Level Thermodynamic Profile
• Height of LCL
• Height of LFC
• Low Level CAPE and CIN
• Boundaries
• Non-Mesocyclonic Tornadoes

46
0-1km Shear Vector
Brooks and Craven (2002)
Supercells associated with significant
tornadoes Non-Tornadic
20 kts 15kts

• Markowski et al (2002) states this is a measure
  of the amount of horizontal vorticity available
  near the earths surface.
• The shear magnitude in the lowest 1 km
  discriminates well between tornadic and
  non-tornadic supercells, and is a good proxy for
  0-1km helicity (Thompson et al, 2002).
• Does not require knowledge of storm motion.

47
0-1km Storm Relative Helicity
Thompson et al (2002)
Supercells associated with significant
tornadoes Non-Tornadic

• SRH can vary up to two orders of magnitude within
  100km and 3 hrs.
• No good threshold, but 100 m2/s2 is considered a
  good lower number with increasing threat as the
  numbers grow. Outbreaks 200-300 m2/s2. (Rasmussen
  and Blanchard, 1998 and Thompson et al, 2002).

48
0-1km Storm Relative Helicity
May 4th, 2003
April 22nd, 2004
From Banacos (2003)
From Jon Davies Webpage
49
Height of the LCL (Mean Layer)
Markowski (2000) speculates that lower LCL
heights mean high boundary layer RH and increased
buoyancy in the RFD.
50
Height of the MLLCL
From Thompson et al (2002)
From Brooks and Craven (2002)
51
Lets Take a Look
Classic supercells which produced several strong
tornadoes.
52
Height of the LFC

• Why is this important?
• Lower LFCs (below 2km or 750mb) have more
  instability above the LFC and less CIN above that
  higher LFCs.
• Lower LFCs require less lift for the parcel to
  reach convective initiation
• In a study of over 300 soundings associated with
  supercells, most tornadoes are found with LFCs
  below 6,600 ft, though may occur as high as
  7900 ft with large amounts of vertical shear.
  (Davies, 2002)
• Rasmussen and Blanchard (1998) found that 75 of
  tornadic classic supercell environments had CIN
  lt25-50 J/kg) and 60 of non- tornadic supercell
  environments had values greater than this

53
Lets Take a Look
Several supercells, one producing a F3 tornado.
54
Lets Take a Look
Several classic supercells along I-44, including
a F3.
55
Lets Take a Look
Several supercells in central MO, producing F2
tornadoes.
56
What About Boundaries?

• Boundaries serve two important functions
• Local forcing mechanisms for convective
  initiation.
• As a source of vorticity augmentation in
  mesocyclones.
• Significant tornadoes usually require higher
  quantities of SRH than is normally provided.
  They often require augmentation from boundaries.
  (Markowski et al (1998a))

57
Forward Flank Downdraft

• Streamwise vorticity occurs along the boundaries
  of the FFD.
• Parcels generally only acquire 0.001 s1 shear
  because of small residence times.
• For FFD boundaries to be the primary source of
  streamwise vorticity, it is speculated that the
  environment must be highly helical (I.e. SRH gt
  500 m2 s2 or 0-10 km shear of 100 kts per
  Markowski et al (1998b).

58
Outflow From External Thunderstorms
Rasmussen (2000)
Cool side of outflow boundaries Look for
modified outflow (gt6 hrs old) where theres
sunshine and growing CAPE (a.k.a. cooked
outflow), and surface dewpoints are great than
the warm sector. .
59
Boundaries
Markowski et. al. (1998b)
Tornadic development most likely from 10 km on
warm side of boundary to 30 km on cool side of
boundary.
60
Local Example
May 6, 2003
61
Local Example
From of Fred Glass
April 21, 2002
62
Anvil Boundaries
Preferred direction for longer parcel residence
times.

• Requires limited cloud coverage around
  periphery of storm.
• May be more important than the FFD because of
  much long parcel residence times in the boundary
  depending on the inflow vector.

63
Significant Tornado Parameter (Thompson et al,
2003)

• The Significant Tornado Parameter is a
  multi-parameter index that includes 0-6-km shear
  magnitude, 0-1km storm-relative helicity, 100-mb
  mean parcel CAPE, and 100-mb mean parcel LCL
  height.
• SCP (mlCAPE/1000 J/kg) ((2000 -mlLCL)/1500 m)
  (SRH1/100 m2/s2) (SHR6/20 m/s)
• Computed every hour on the SPC Mesoanalysis Page.

64
Significant Tornado Parameter (Thompson et al,
2003)
May 4th, 2003
65
Non-Supercell Tornadoes

• Typically associated with ordinary cells
• No CIN
• Steep low level lapse rates
• Sharp boundary with low level vertical vorticity.
• Rapidly developing CBs

66
Non-Supercell Tornadoes
May 25, 1997
From Wakimoto and Wilson (1989)
67
Wind Parameters

• Microbursts
• Bow Echoes and Derechoes

68
Microbursts

• Atkins and Wakimoto (1991) found wet
  microbursts occurred on days when the delta
  theta-e between the surface and mid-levels is
  gt20K. Null days occurred when this value is
  lt13K.
• Dry microburst tend to occur with high LCLs and
  steep low level lapse rates.

69
Bow Echoes and Derechoes

• Bow echoes and derechoes are associated with
  moderate to strong shear in the low levels
  (Przybylinski, 2001)
• lt23 kts Weak Shear (Bow echoes less likely)
• 22-37 kts Moderate Shear (Bow echoes likely
  with the greatest threat of damaging winds)
• gt37 kts Strong Shear (Bow echoes likely with
  strongest winds remaining above the surface.

70
Bow EchoesTypical Morphologies
Squall Line Bow Echo (LEWP)
Bow Echo
Supercell
Cell Bow Echo
Bow Echo Complex
Bow Echo
71
Forward Propagating MCS
72
Forward Propagating MCS
Low Level Boundary
73
Back-building and Quasi-Stationary MCSs
74
Classic Bow EchoWind Shear Profiles
(Hodographs)
75
Elevated Hail Storms

• Steep mid level lapse rates (850 500 mb lapse
  rates 7 deg C/km or greater)
• MUCAPE gt 1000 J/kg
• Large CAPE in the -10 to -30oC /-20 to -40oC
  range on a sounding
• Strong deep shear (through mean cloud layer wind)
• Minimized melting effects (lower Freezing levels
  , WBZ lt 10K ft)

76
Surface Based Storms

• Mid level updraft rotation (need enough deep
  shear gt 35 kts between 0-6 km AGL)
• Need steep lapse rates , sufficient low-level
  moisture, sufficient lifting mechanism (related
  to CAPE in hail growth zone)
• Note in absence of 1., greater dependence on 2.)
  

77
Supercell Hail Forecasting

• Large CAPE in the layer from -20 to-40oC (-10 to
  -30oC) favors rapid hail growth.
• 0-6-km shear in excess of 30-40 knots supports
  supercells with persistent updrafts that
  contribute to large hail production
• Lower freezing level heights suggest a greater
  probability of hail reaching the surface prior to
  melting

78
Hail Forecasting Parameters

• Hail Parameters depicts three forecasting
  parameters used to predict hail. They are CAPE in
  the layer from -20 to -40oC, 0-6-km shear vector,
  and the freezing level height.
• The Sig. Hail Parameter (SHIP) was developed
  using a large database of surface-modified,
  observed severe hail proximity soundings to
  determine the potential of hail gt2" diameter.
• SHIP (MUCAPE j/kg) (Mixing Ratio of MU
  PARCEL g/kg) (700-500mb LAPSE RATE c/km)
  (-500mb TEMP C) (0-6km Shear m/s) /
  44,000,000
• Both are computed every hour on the SPC
  Mesoanalysis Page.

79
Summary

• Steps for severe weather forecasting
• Will I have TSRA? (Moisture, Instability, and
  Forcing)
• What will be my primary convective mode and
  coverage? (Instability, Shear, and Forcing)
• What kind of severe weather will I have?
  (Tornadoes, Hail, Winds)

80
References
Atkins, N.T. and R.M. Wakimoto, 1991 Wet
Microburst Activity over the Southeastern US
Implications for Forecasting. Wea. Forecasting,
6, 470-482. COMET Forecasters Multimedia
Library, 1996 Anticipating convective storm
structure and evolution. Bluestein, H.B. and
M.L. Weisman, 2000 The interaction of
numerically simulated supercells initiated along
lines. Mon. Wea. Rev., 128, 3128-3149. Banacos,
P.C., 2003 Severe Weather Threat Assessment.
Presentation at the, WDTB Severe Weather/Flash
Flood Workshop Course 03-4, Boulder, CO. Brooks,
H. E., and J. P. Craven, 2002 A database of
proximity soundings for significant severe
thunderstorms, 1957-1993. Preprints, 21st
Conference on Severe Local Storms, San Antonio,
Texas, American Meteorological Society, 639-642.

81
References
Burgess, D.W., 2003 Supercells. Presentation at
the COMAP Course, Boulder, CO. Burgess, D.W. and
L.R. Lemon, 1991 Characteristics of
Mesocyclones Detected During a NEXRAD Test.
Preprints, 25th Int. Conf. On Radar Meteorology,
Paris, France, AMS, 39-42. Craven, J. P., 2000
A Preliminary Look at Deep Layer Shear and Middle
Level Lapse Rates Associated with Major Tornado
Outbreaks. Preprints, 20th Conference on SLS,
Orlando, FL, AMS, 547-550. Davies, J. L., 2004
Tornadoes in a Deceptively Small CAPE Setting 
The "Surprise" 4/20/04 Outbreak in Illinois and
Indianahttp//members.cox.net/jondavies3/042004il
in/042004ilin.htm Davies, J. L., 2002 A Primer
on Low-level Buoyancy Parameters When Assessing
Supercell Tornado Environments.
http//home.kscable.com/davies1/LLbuoyprimer/LLbuo
yprimer.htm
82
References
Dial, G.L. and J.P. Racy, 2004 Forecasting Short
Term Convective Mode and Evolution For Severe
Storms Initiated Along Synoptic Boundaries.
Preprints, 22nd Conference on SLS, Hyannis, MA,
Amer. Meteor. Soc.. Evans, J. and C. Doswell,
2003 Presentation given to WFO Tulsa
Staff.http//www.spc.noaa.gov/staff/evans/talk4/t
alk4_frame.htm Edwards, R., 2000 Personal
Communication. Edwards, R. and R. L Thompson,
2000 RUC-2 Supercell Proximity Soundings, Part
II An Independent Assessment of Supercell
Forecast Parameters. Preprints, 20th Conference
on SLS, Orlando, FL, AMS, 236-239. Klimoski,
Brian A. and R. W. Przybylinski, 2003
Observations of, and Forecasting the Formation
and Early Evolution of Bow Echoes. Presentation
at the COMAP Course, Boulder, CO. Lanicci, J.
and T. Warner, 1991 A synoptic climatology of
the elevated mixed- layer inversion of the
southern plains. Part I Structure, dynamics,
and seasonal evolution. Wea. Forecasting, 6,
181-197.
83
References
Markowski, P. M., C. Hannon, J. Frame, E.
Lancaster, A. Pietrycha, R. Edwards, and R
Thompson, 2002 Characteristics of RUC Vertical
Wind Profiles Near Supercells. Preprints, 21st
Conference on SLS, San Antonio, TX, AMS,
599-602. Markowski, P. M., E. N. Rasmussen, and
J. M. Straka, 1998a The occurrence of tornadoes
in supercells interacting with boundaries during
VORTEX-95. Wea. Forecasting, 13,
852-859. Markowski, Paul M., E. N. Rasmussen, J.
M. Straka, D. C. Dowell, 1998b Observations of
Low-Level Baroclinity Generated by Anvil Shadows.
Monthly Weather Review Vol. 126, No. 11, pp.
29422958. Markowski, P. M., E. N. Rasmussen, and
J. M. Straka, 2000 Surface Thermodynamic
Characteristics of RFDs as Measured by a Mobile
Mesonet. Preprints, 20th Conference on SLS,
Orlando, FL, AMS, 251-254.
84
References
Przybylinski, R.W., 2001 Personal
Communication. Rasmussen, E. N., and D. O.
Blanchard, 1998 A Baseline Climatology of
Sounding-Derived Supercell and Tornado Forecast
Parameters. Wea. Forecasting, 13,
1148-1164. Rasmussen, E.N., S. Richardson, J.M.
Straka, P. M. Markowski, and D. O. Blanchard,
2000 The association of significant tornadoes
with a baroclinic boundary on 2 June 1995. Mon.
Wea. Rev., 128, 174-191.
85
References
Rasmussen, E.N, and J. M. Straka, 1998
Variations in supercell morphology. Part I
Observations of the role of upper-level storm
relative flow. Mon. Wea. Rev., 126,
2406-2421. Thompson, R. L., 1998 Eta model
storm-relative winds associated with tornadic and
nontornadic supercells. Wea. Forecasting, 13,
125-137. Thompson, R.L., 2000 Personal
Communication. Thompson, R.L., R. Edwards, and
J.A. Hart, 2002 An Assessment of Supercell and
Tornado Parameters with RUC-2 Model Close
Proximity Soundings. 21st Conference on SLS, San
Antonio, TX, AMS, 595-598. Thompson, R. L., 2004.
Presentation Forecasting Thunderstorm Coverage
and Configuration
86
References
Thompson, R.L., C.M. Mead, and R. Edwards, 2004
Effective Bulk Shear in Supercell Thunderstorm
Environments. Preprints, 22nd Conf. Severe Local
Storms, Hyannis MA Thompson, R.L., R. Edwards,
and C.M. Mead, 2004 Effective Storm-Relative
Helicity in Supercell Thunderstorm Environments.
Preprints, 22nd Conf. Severe Local Storms,
Hyannis Thompson, R. L., R. Edwards, J. A. Hart,
K. L. Elmore, and P. Markowski, 2003  Close
proximity soundings within supercell environments
obtained from the Rapid Update Cycle. Wea.
Forecasting, 18, 1234-1261. Wakimoto, R.M., and
J.W. Wilson, 1989 Non-Supercell Tornadoes. Mon.
Weather Rev., 117, 1113-1140. Weisman, M. L., and
J. B. Klemp, 1982 The Dependence of Numerically
Simulated Convective Storms on Vertical Wind
Shear and Buoyancy. Mon. Wea. Rev., 110,
504-520.