Presentation on theme: "Wet and Dry Microbursts"— Presentation transcript:
1 Wet and Dry Microbursts Daniel R. Adriaansen&Baylee A. BalschmiterSUNY BrockportDepartment of the Earth SciencesESC 452 Mesoscale Meteorology20 April 2006
2 What is a microburst?Downburst: Strong downdraft which induces an outburst of damaging winds on or near the ground. (Fujita 1985)- 2 types:Macroburst: A large downburst with its outburst winds extending in excess of 4km (2.5 mi) in the horizontal with maximum wind speeds of 60 m/s (134 mph). (Fujita 1985)Microburst: A small downburst with its outburst, damaging winds extending only 4 km (2.5 miles) or less with maximum wind speeds of up to 75 m/s (168 mph). (Fujita 1985)
3 Conceptual Model - Vortex ring model - Meso Low on either side of meso High
4 Two (three) varieties (Intermediate?) (Intermediate?)
5 Dry MicroburstA microburst that is accompanied by little or no rain between the onset and the end of the high winds. (Wakimoto 1985)
6 Dry Microbursts - JAWS (Joint Airport Weather Studies, 1982) - Further defined microburst characteristics, particularly involving dry microbursts.- Denver, CO
7 Physical Characteristics - Time scale 2-5 minutes- Peak wind speeds exceeding 30 m/s (67 mph)- Reflectivities of ≤ 30 dBz- Precipitation ≤ 0.25 mm (0.01 inches)- Lightning often limited- Limited synoptic forcing/influence- Sometimes associated with fair weather
8 Thermodynamic environment - Morning Inversion- Inverted V signature- Nearly dry-adiabatic ABL- Large Dew-point depressions in ABL- Moist layer located ~ 500mb (DPD 0)- Light ABL winds
11 Visual Identification - Virga is defined as wisps or streaks of water or ice particles falling out of a cloud but evaporating before reaching the earth's surface as precipitation. (NOAA 2001)- Blowing dust/dust rings at surface- Very good indicators of dry microburst potential
18 Wet microburstA microburst accompanied by heavy precipitation at the surface. A rain foot may be a visible sign of a wet microburst.
19 Wet Microburst Formation There is a layer of nearly saturated air that is close to ΓmAbove this layer is an elevated dry layerWhen Tw is brought to saturation and mixed with warm air, it creates a negatively buoyant atmosphere that leads to a severe downdraft
21 Characteristics Little or no capping inversion. A moist mid-tropospheric layer between 5000 ft and 15,000 ft.An elevated dry layer above 15,000 ft.When combined there is a high potential for a wet microburst
24 References1. Caracena, F., Holle, R. L., & Doswell III, C. A. (2001, June). Microbursts: A Handbook for Visual Identification. Retreived April 10th, 2006, from2. Fujita, T. (1985). The Downburst: Microburst and Macroburst. Chicago: The University of Chicago.3. NOAA. (2001). Question of the Month. Retreived April10th, 2006, from4. Wakimoto, R. M. (1985). Forecasting Dry Microburst Activity over the High Plains. Monthly Weather Review, 113, ( ).