Miller Diagrams
A Brief Introduction
Outline
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Origins
Overview
Fields to Analyze
Pattern Types
Final Points
Origins
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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).
Origins
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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.
Origins
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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.
Origins
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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).
Miller Diagram Overview
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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.
Surface Fields
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Fronts
Dryline(s)
Surface low center
850mb Fields
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Dryline(s)
General Flow
Low-Level Jet(s)
Thermal Ridge
Moisture Tongues, Moisture Axes
Confluent Zones
700mb Fields
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Dry Tongue(s)
General Flow
Wind Max Axis/Axes
Moisture
Confluent Zones
Diffluent Zones
500mb Fields
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Isotherms
Thermal Trough
Jet Flow
Diffluent Zone(s)
Horizontal Speed Shear Zones
Jet-Level Fields
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Jet Flow
Jet Max
Speed Shear Zones
Diffluent Zones
Synoptic Type A Pattern
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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
Synoptic Type A Pattern
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Usually occurs around 3-4 pm to 10pm
Max in late afternoon/early evening
Thunderstorms form in clusters, not squall line
Synoptic Type B Pattern
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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
Synoptic Type C Pattern
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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
Synoptic Type C Pattern
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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
Synoptic Type D Pattern
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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
Synoptic Type E Pattern
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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)
Final Points to Consider
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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
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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.