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

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

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

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

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

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

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

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

Personal Favorites 250 Jet Buoyant Energy & CIN SWEAT Lapse Rates Low Level Jet Dewpoint axis (with contours) Surface fronts/trofs (low level conv) 850-500 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

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

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.

A Convective Forecast Decision Tree NO 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

Shear 0-6km Shear Bulk Richardson Number: 10-45 (supcell) Vector Difference >30-40 knots Shear Magnitude >40-50 knots Bulk Richardson Number: 10-45 (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

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

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 <30 850-500 shear Speed (kt) Dir (deg) >60 30-60 15-25 20-30 <15

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 > 10 - 12 C Capping Inversion 500 mb T -6 C (warm side) 0 to 1 km SRI 20-25 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)

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 579-582 dm (warm side) Capping Inversion Surface Boundaries Upward Motion Instability Wind Shear

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

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

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)