Miller Diagrams: Miller Diagrams A Brief Introduction


Outline: Outline Origins Overview Fields to Analyze Pattern Types Final Points


Origins: 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).


Origins: 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.


Origins: 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.


Origins: 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).


Miller Diagram Overview: 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.


Surface Fields: Surface Fields Fronts Dryline(s)


850mb Fields: 850mb Fields Dryline(s) General Flow Low-Level Jet(s) Thermal Ridge Moisture Tongues, Moisture Axes Confluent Zones


700mb Fields: 700mb Fields Dry Tongue(s) General Flow Wind Max Axis/Axes Moisture Confluent Zones Diffluent Zones


500mb Fields: 500mb Fields Isotherms Thermal Trough Jet Flow Diffluent Zone(s) Horizontal Speed Shear Zones


Jet-Level Fields: Jet-Level Fields Jet Flow Jet Max Speed Shear Zones Diffluent Zones


Synoptic Type A Pattern: 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


Synoptic Type A Pattern: 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


Synoptic Type B Pattern: 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


Synoptic Type C Pattern: 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


Synoptic Type C Pattern: 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


Synoptic Type D Pattern: 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


Synoptic Type E Pattern: 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)


Final Points to Consider: 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)


One Last Point: 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.