Miller Diagrams

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Miller Diagrams

• A Brief Introduction

2
Outline

• Origins
• Overview
• Fields to Analyze
• Pattern Types
• Final Points

3
Origins

• Developed in 1948 by Robert Miller and Ernest
  Fawbush.
• A tornado struck Tinker AFB on 20 March, and
  Fawbush and Miller were directed to investigate
  the forecastability of tornado-producing
  thunderstorms.
• So, they pored over all the available data (for
  the Tinker tornado as well as several other
  previous tornado outbreaks).

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Origins

• Fawbush and Miller noticed similarities in the
  synoptic patterns associated with the tornado
  outbreaks.
• On the morning of 25 March, they noticed that the
  synoptic pattern was similar to what was observed
  on 20 March.
• When a squall line was detected on radar at 2pm,
  they decided (very nervously) to issue a tornado
  forecast.

5
Origins

• Fawbush and Miller waited expectantly over the
  next three hours to see if the squall line would
  generate severe weather, let alone a tornado.
• At 5pm, Will Rogers airport (7 miles southwest of
  Tinker) reported only a light thunderstorm, wind
  gusts to 26 mph and pea-sized hail.
• The forecast was apparently a bust, and Miller
  left the base and drove home, certain he and
  Fawbush would be harshly reprimanded the next day.

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Origins

• But, lo and behold, the system intensified and
  believe it or not Tinker AFB was hit by another
  tornado, only 5 days after the first!
• Fawbush and Miller became legends, and Miller
  Diagrams became a standard prognostic tool of
  weather forecasters in the plains (and elsewhere).

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Miller Diagram Overview

• Provides an efficient means of analyzing the
  relevant synoptic features important in severe
  weather outbreaks
• Cartoon-style analysis is performed for the
  surface, 850mb, 700mb and 500mb (occasionally 250
  or 300mb) and the results are plotted on a single
  chart.

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Surface Fields

• Fronts
• Dryline(s)
• Surface low center

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850mb Fields

• Dryline(s)
• General Flow
• Low-Level Jet(s)
• Thermal Ridge
• Moisture Tongues, Moisture Axes
• Confluent Zones

10
700mb Fields

• Dry Tongue(s)
• General Flow
• Wind Max Axis/Axes
• Moisture
• Confluent Zones
• Diffluent Zones

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500mb Fields

• Isotherms
• Thermal Trough
• Jet Flow
• Diffluent Zone(s)
• Horizontal Speed Shear Zones

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Jet-Level Fields

• Jet Flow
• Jet Max
• Speed Shear Zones
• Diffluent Zones

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Synoptic Type A Pattern

• Well-defined southwesterly jet (500mb)
• Well-defined dry tongue at 700mb, moving from SW
  to NE
• Influx of low-level moisture from the south
• Streamline convergence at 850 to 700mb, at the
  boundary between the moist and dry air

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Synoptic Type A Pattern

• Usually occurs around 3-4 pm to 10pm
• Max in late afternoon/early evening
• Thunderstorms form in clusters, not squall line

15
Synoptic Type B Pattern

• Similar to Type A, but with a major upper trough
  (500mb) and eastward-moving surface cold front to
  the west of the threat area
• Initial development occurs along the front (often
  as a squall line) and then becomes severe /
  tornadic as the storms move farther east into
  more unstable area
• F2-F5 tornadoes possible
• Very diurnally persistent

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Synoptic Type C Pattern

• Well-defined westerly jet (500mb)
• Quasistationary surface frontal boundary
• Dry air most pronounced at 700mb, moving from SW
  to NE
• Initial development occurs in the vicinity of the
  surface front, south of the jet, and rapidly
  becomes severe when the dry air at mid levels
  arrives from the SW

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Synoptic Type C Pattern

• Not much diurnal variation (max 6 hours after
  surface heating)
• Smaller scale than other types
• Produces singular tornadoes
• If surface air behind front is below 50 degrees,
  chances for severe weather go down

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Synoptic Type D Pattern

• A southerly jet and closed low at 500mb
• Deepening surface low
• Destabilization occurs when warm, moist air at
  surface undercuts cold air aloft
• Moist flow from SE, dry air at mid levels from SW
• Typically not as favorable for tornadoes as
  patterns A,B or C
• More favorable for hail

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Synoptic Type E Pattern

• Westerly Jet at 500mb
• Similar to pattern C, but with major cyclogenesis
  at surface
• Squall line formation likely
• Diurnally persistent (max at 3-6 hours after max
  surface heating)

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Final Points to Consider

• Sometimes, patterns may be difficult to classify
  (hybrids) or transition from one type to another.
  
• Typically, the transitions follow
• Pattern A becomes Pattern B (as a cold front
  sweeps through)
• Pattern C becomes Pattern E (as cyclogenesis
  occurs along surface front)

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One Last Point

• No matter what the pattern, the area of violent
  weather is located by the position of the
  convergence zone in low / mid levels, the
  position of the jet, and the leading edge of the
  dry air advancing from the SW.