Satellite View Of
Cloud Tops Might Warn Of Storms Brewing
(7 July 2008) For three years a new
way to use data collected by NOAA weather satellites has been giving North
Alabama short-term warnings of "pop-up" thunderstorms.
Developed
by scientists at The University of Alabama in Huntsville, this new computer
program is now spreading to other parts of the U.S. and the world: Later this
summer a version of the UAHuntsville weather program will begin forecasting
storms throughout Central America, Southern Mexico and the Dominican
Republic.
The UAHuntsville Satellite Convection AnalySis & Tracking
System (SATCASTS) monitors cumulus clouds as they develop, move and grow
through time, according to the person who brainstormed the idea behind the
program, Dr. John Mecikalski, an assistant professor of atmospheric science at
UAHuntsville.
The program uses data from NOAA's GOES weather satellites
to provide 15-minute to one hour warnings of local thunderstorms. This is the
first time forecasters anywhere have had a tool to forecast storms that develop
locally. This differs from Doppler radar, which only tracks rain after it
starts to fall.
"The radar tells you what's happening, but not what's
going to happen," said Wayne MacKenzie, a research associate in UAHuntsville's
Earth System Science Center and a member of the SATCASTS development
team.
Operated by UAHuntsville scientists for the National Weather
Service forecast office in Huntsville for about three years, SATCASTS has been
accurate in its storm forecasts between 65 and 75 percent of the time. It has
successfully identified hazards generated by thunderstorms, including
lightning, hail, high wind, flash floods and turbulence.
Mecikalski got
the idea for SATCASTS in 2001, when he was affiliated with NOAA's Co-operative
Institute for Meteorological Studies. He was looking for a way to determine
which of the thousands of cumulus clouds present on any given summer afternoon
will become thunderstorms. (One percent or less of clouds develop into rain
clouds.) He has continued his research since joining the faculty at
UAHuntsville in January 2004.
Using data from the GOES visible and
infrared sensors, SATCASTS tracks changes in both cloud temperature (height)
and water vapour. This data is updated every 15 minutes.
The
UAHuntsville team has determined that one of the most important factors in
predicting thunderstorms is temperature change. If the top of a cloud cools by
4 C (about 7.2 degrees Fahrenheit) or more in 15 minutes, that means the cloud
is growing quickly and there is a growing probability of rain beginning within
30 minutes to an hour. A 4 C drop in temperature typically means a cloud top
has climbed between 1/4 to 1/3 of a kilometre.
Based on its success in
the Huntsville forecast office, scientists at UAHuntsville are working with the
National Weather Service to transition SATCASTS into the storm prediction
systems in forecast offices in Birmingham, AL, and Nashville, TN, as well as
both Melbourne and Miami, FL.
The UAHuntsville team is also working with
NASA and the Federal Aviation Administration (FAA) to test SATCASTS' possible
utility in aviation and air traffic control. The system is being tested at the
FAA's New York City air traffic control centre. If successful, SATCASTS might
be used world-wide to warn pilots of storms, turbulence and other weather
threats before they occur.
Other organisations evaluating the
operational implementation of the SATCASTS algorithm include the European
Meteorological Satellite agency and the South African Weather Service.
Discussions are also underway to bring SATCASTS capabilities to East
Africa.
While SATCASTS joins a sophisticated and extensive network of
weather monitoring systems in the U.S., it is expected to have special value in
regions where storm forecasting and monitoring have been limited or
non-existent. The system is relatively inexpensive to install and operate,
since it uses freely distributed weather data from existing satellite
sensors.
NOAA-funded research at UAHuntsville will focus on expanding
SATCASTS' capabilities. In areas where Doppler radar networks do not exist,
SATCASTS might be used in the future to track frontal storm systems and provide
severe weather warnings that are not presently available, Mecikalski
said.
"This makes SATCASTS and satellite-based rainfall predictions very
relevant in many developing countries, when ground-based radar is absent but
high quality satellite data are in place."
The UAHuntsville SATCASTS
team includes Mecikalski, two other scientists and three graduate students. The
project has been supported by more than US$ 1 million in funding from NOAA,
NASA and the FAA.
Research on improving SATCASTS is ongoing and is
expected to continue for at least five years. New areas of research include
30-to-90-minute lightning and flash flood forecasts.
The UAHuntsville
team is also working on a next generation SATCASTS, which will take advantage
of the improved sensing systems that will be available when NOAA launches it
GOES-R series of satellites beginning in 2016. Sensors on those satellites will
collect data in more channels, more often and at higher
resolution.
(source: University of Alabama in Huntsville)
