Wet and Dry Microbursts
Daniel R. Adriaansen
&
Baylee A. Balschmiter
SUNY Brockport
Department of the Earth Sciences
ESC 452 Mesoscale Meteorology
20 April 2006
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)
Conceptual Model
- Vortex ring model
http://www.cimms.ou.edu/~doswell/microbursts/Figure_04.JPG
- Meso Low on either side of meso High
Two (three) varieties
http://www.cimms.ou.edu/~doswell/microbursts/Figure_08.JPG
(Intermediate?)
Dry Microburst
A microburst that is accompanied by little or no
rain between the onset and the end of the high
winds. (Wakimoto 1985)
http://www.cimms.ou.edu/~doswell/microbursts/Figure_08.JPG
Dry Microbursts
- JAWS (Joint Airport Weather Studies,
1982)
- Further defined microburst characteristics,
particularly involving dry microbursts.
- Denver, CO
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
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
http://www.cimms.ou.edu/~doswell/microbursts/Figure_09b.JPG
http://www.cimms.ou.edu/~doswell/microbursts/Figure_09a.JPG
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
http://www.cimms.ou.edu/~doswell/microbursts/Figure_17a.JPG
http://www.cimms.ou.edu/~doswell/microbursts/Figure_17b.JPG
http://www.cimms.ou.edu/~doswell/microbursts/Figure_13.JPG
http://www.cimms.ou.edu/~doswell/microbursts/Figure_14.JPG
http://www.cimms.ou.edu/~doswell/microbursts/Figure_16.JPG
Wet microburst
A microburst accompanied by heavy
precipitation at the surface. A rain foot may be a
visible sign of a wet microburst.
http://www.cimms.ou.edu/~doswell/chasesums/chase97_18.JPG
Wet Microburst Formation
There is a layer of nearly saturated air that
is close to Γm
Above this layer is an elevated dry layer
When Tw is brought to saturation and
mixed with warm air, it creates a
negatively buoyant atmosphere that leads
to a severe downdraft
http://www-frd.fsl.noaa.gov/~caracena/micro/FACEsons.gif
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
http://www.cimms.ou.edu/~doswell/microbursts/SW_Texas_rainfoot_c.JPG
http://www.nssl.noaa.gov/~doswell/microbursts/SW_Texas_virga_sm.JPG&imgrefurl
References
1. Caracena, F., Holle, R. L., & Doswell III, C. A. (2001, June).
Microbursts: A Handbook for Visual Identification. Retreived April
10th, 2006, from
http://www.cimms.ou.edu/~doswell/microbursts/Handbook.html
2. Fujita, T. (1985). The Downburst: Microburst and Macroburst.
Chicago: The University of Chicago.
3. NOAA. (2001). Question of the Month. Retreived April10th, 2006,
from http://www.noaa.gov/questions/question_081701.html
4. Wakimoto, R. M. (1985). Forecasting Dry Microburst Activity over the
High Plains. Monthly Weather Review, 113, (1131-1143).
Questions?
Comments?
Rude Gestures?