Miller Diagrams A Brief Introduction

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

Origins Developed in 1948 by Robert Miller and Ernest Fawbush. 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. 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). So, they pored over all the available data (for the Tinker tornado as well as several other previous tornado outbreaks).

Origins Fawbush and Miller noticed similarities in the synoptic patterns associated with the tornado outbreaks. 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. 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. When a squall line was detected on radar at 2pm, they decided (very nervously) to issue a tornado forecast.

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. 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. 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. 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 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! 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). Fawbush and Miller became legends, and Miller Diagrams became a standard prognostic tool of weather forecasters in the plains (and elsewhere).

Miller Diagram Overview Provides an efficient means of analyzing the relevant synoptic features important in severe weather outbreaks 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. 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 Fronts Fronts Dryline(s) Dryline(s) Surface low center Surface low center

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

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

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

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

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

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

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 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 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 F2-F5 tornadoes possible Very diurnally persistent Very diurnally persistent

Synoptic Type C Pattern Well-defined westerly jet (500mb) Well-defined westerly jet (500mb) Quasistationary surface frontal boundary Quasistationary surface frontal boundary Dry air most pronounced at 700mb, moving from SW to NE 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 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 Not much diurnal variation (max 6 hours after surface heating) Not much diurnal variation (max 6 hours after surface heating) Smaller scale than other types Smaller scale than other types Produces singular tornadoes Produces singular tornadoes If surface air behind front is below 50 degrees, chances for severe weather go down If surface air behind front is below 50 degrees, chances for severe weather go down

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

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

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

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. 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.