1. Defining a Threat Area and Miller Techniques
PASPC
Start asking what are some of the key things to look for when defining a threat area….lead in to the Mantra

2. Seeing Through the “MIST”
Four Requirements for Sustained Deep Convection
Moisture: latent energy fuels thunderstorms (depth of BL moisture important)
Instability: to realize latent energy (via CAPE, instability parameters)
Wind Shear: cold pool interactions, deep shear tilts updraft, generates rotation
Trigger: mechanism producing vertical motion to release the latent energy (i.e., lift parcel to LFC, e.g., PVA, front, dryline, SFC trof…)
Quick overview of Neil Taylor’s Mantra, often helps to think in these 4 terms

3. Miller Techniques Method to help diagnose areas of:
Moisture
Instability
Shear
Trigger (vertical motion or lift)
Construct a threat area where the ingredients come together.
3D look through the atmosphere.
Similar techniques for non convective assessment.
A structured method to create convective zones

4. 250 mb J 120 250 mb jet Enhance vertical motion Straight Jet
RE/LE = LIFT
Cyclonically curved
LE = LIFT
Anti-cyclonically curved
RE = LIFT
Difluent areas favoured
Patterns….Splitting Jets J
120

5. 500 mb J 50 500 mb jet (30 kt or more) Cold Trough Thermal Ridge axis
Areas of difluence
500mb height fall centres
PVA
May consider 500 mb lift J 50

6. 700 mb 700 mb Thermal ridge and thermal trough 700mb temp 10-12 C
700 mb moisture (T-Td <6 C (75% RH))
Dry Prod (T-Td >>6C)
Lift
Lapse Rates (T700 – T500)
Optimal 700mb RH zone is between 70% and 45%...often back edge of a cloud deck

7. 850 mb
850 low level jet (LLJ) - Often responsible for moisture advection into the region.
850 Thermal Ridge -the boundary between WAA and CAA; can be associated with the strongest capping lid and CAA may erode the “nose”.
850 Convergence zone -Area of lift
850 Moist Axis -superimposed over SFC moist axis to indicate depth of moisture. X X

8. Surface Frontal structure and trofs/ zones of convergence
Streamlines can be useful
Surface Moist tongue outlines where Td <12 C
Td analysis every 2 C.
Dry lines
Issallobars
What you chose to illustrate on Miller workup can vary with the situation
Zones of convergence can also occur in areas of elevated terrain and speed convergence

9. Personal Favorites 250 Jet Buoyant Energy & CIN SWEAT Lapse Rates
Low Level Jet
Dewpoint axis (with contours)
Surface fronts/trofs (low level conv)
thermal ridge
700 mb moisture (cloud areas)
Profile Plots
Short Waves or PVA
500 mb Z change
Areas of strong descent
SRH (when applicable)
This is of course combined with Tefi analysis

10. DeLimiters Where will convection NOT occur
Subsidence greater than 4 ubs-1
Downwind of mid level thermal axis
Areas sfc divergence or sfc ridges
T700 >10-12 C
Anticyclonic side of low level jet
Significant building 500mb heights
CIN >50-100
CAPE<300
Sometimes useful to think in terms of where convection will not occur

11. Threat Areas Now that we have Miller in our back pockets, what now?
Areas where Moisture, Instability and Trigger intersect creates zones of garden variety convection….use sounding lifts for details such as CB tops, hail size, gust potential
Pattern Recognition extremely helpful
Apply general rules of delimiters
Shear is generally the parameter which determines storm severity.

12. A Convective Forecast Decision TreeNO
storms unlikely
A Convective Forecast Decision Tree
moisture
YES NO
storms unlikely
instability
YES NO
storms unlikely
trigger
YES
storms likely but what type?
SFC-500mb shear
SFC-700mb shear
short-lived
cells check
700mb shear
30-50kt
>20kt
>50kt
>30kt
<30kt
supercells
likely
new cell
development
down shear
long-lived
multicells
long-lived cells possible supercell

13. Shear 0-6km Shear Bulk Richardson Number: 10-45 (supcell)
Vector Difference >30-40 knots
Shear Magnitude >40-50 knots
Bulk Richardson Number: (supcell)
SRH > 150 m2s2
EHI > 1
Mean Shear (Shear magnitude/depth)
Multicell 5 x 10-3 s-1
Supercell 7 x 10-3 s-1
HodoGraph is key tool
The hodograph is the shear vector
Shear Magnitude better accounts for curvature in a hodo

14. E N D

15. INSTABILITY Parameter Strong Moderate Neutral Weak Adequate Marginal
Negative
Lifted Index
< -6
-4 to -6
0 to -3
>0
CAPE
>2500
>0 to 1000
Vertical Motion
> +4
+2 to +3
-1 to +1
< -1

16. SHEAR Parameter Strong Moderate Neutral Weak Adequate Marginal
Negative
850 LLJ (kt)
>35
25-35
20-25
<20
500 mb Jet
>50
35-50
30-35
<30
shear
Speed (kt)
Dir (deg)
>60
30-60
15-25
20-30
<15

17. Limiting Factors Subtropical jet axis Upward Motion
(limit on south side) Wind Shear
850 mb LLJ Upward Motion
(limit to right of axis) Wind Shear
700 mb T > C Capping Inversion
500 mb T -6 C (warm side)
0 to 1 km SRI kts (limit on low side)
0 to 2 km Helicity of 150 for super cells (low side)
0 to 6 km shear of 40 kts for super cells (low side)
500 to 600 mb SRF 15 to 20 kts (low side)

18. Limiting Factors LI zero line (stable side) Instability
45% 700 mb mean RH line (dry) Instability
75% 700 mb mean RH line (wet) Instability
Potnl Neg Buoyancy
552 or 558 dm (cold side) Instability
dm (warm side) Capping Inversion
Surface Boundaries Upward Motion
Instability
Wind Shear

19. LIFT Parameter Strong Moderate Neutral Weak Adequate Marginal Negative
850 temp advection
warm
neutral
cold
Low Level Flow
convergent
divergent
850 mb Therm/Moist axis
Thermal upstream
coincident
Thermal down
stream

20. MOISTURE Parameter Strong Moderate Neutral Weak Mean RH Adequate
Marginal
Weak
Negative
Mean RH
50-70%
70-80% OR
40-50%
>80%
<40%

21. Limiting Factors
Directional difference between 500 and 850 mb is less than 90 deg
850 mb wind 20 kt (low side)
500 mb wind 30 kt (low side)
Directional difference between 500 and 850 mb is 90 deg or more
850 mb wind 15 kt (low side)
500 mb wind 20 kt (low side)