The met office just issued a severe weather warning.
It says: Strong thunderstorms with gusty winds,
heavy rain, and frequent lightning are likely.
What does that mean?
Will there be damage to my house from wind or rain?
How certain are they that anything will even happen.
The impacts-based approach for weather warnings
is designed to enable effective communication of potential impacts
so that timely actions can be taken
to reduce disruptions to society and prevent harm to the public.
It combines the impact of a weather phenomenon
with the likelihood of that phenomenon taking place.
With impacts-based forecasting, the Barbados Meteorological Service (BMS)
will produce a matrix for each phenomenon that can lead to hazards to society:
rain, wind, severe convection, storm surge, and others.
Each matrix shows the potential impact, from minimal to severe,
and the likelihood of its occurrence, from very low to high.
The progression in color from green to yellow to orange to red
alerts emergency management and other users
about increasing levels of preparation and necessary actions.
It is important for forecast users to know how to interpret impacts-based matrices.
The information that they provide
supports preparations and actions for emergency management
and other critical users as well as the general public.
The position in the matrix is just as important as the color.
A yellow warning in this cell shows that the forecaster is highly confident
and expects only minor impacts.
However, a yellow warning in this cell shows greater uncertainty,
perhaps because the storm is still a few days away,
but the potential exists for severe impacts.
The color and position in the matrix and how that evolves as the storm approaches
are important for the decision making process.
Let's look at an example.
A large Crop Over festival celebration is scheduled in Bridgetown for Saturday evening.
A forecast matrix is issued showing very low likelihood for severe impacts from heavy rainfall
three days from now on Saturday afternoon and evening.
There is still great uncertainty about the path and strength of a tropical wave
moving toward Barbados.
Although the yellow color might not seem to convey much urgency,
the position catches the attention of local officials
at the Department of Emergency Management or DEM.
No major actions are taken, but preliminary plans are discussed at the DEM
regarding the small chance of severe flooding
and the possibility of postponing the celebration.
Two days before the storm is due,
the matrix changes and the color shifts to orange.
There is still low likelihood for severe impacts from this heavy rainfall
Saturday afternoon and evening.
Local DEM officials meet to discuss necessary actions.
If the BMS is more confident regarding severe impacts as the storm draws closer
they will have to notify the Crop Over festival organizers
regarding the possible postponement of events on Saturday.
In addition, severe rainfall impacts will trigger certain actions around Barbados,
not just in sensitive areas like Bridgetown, including closure of major roads, evacuations
and the opening of emergency shelters.
One day before the storm hits it has re-developed into a tropical storm.
The path of the storm becomes much more clear
and forecasters revise the impacts matrix and contact the DEM.
The level is still orange but the position has changed.
The effects from the storm are expected to be significant,
but it now is forecast to move more quickly,
striking on Saturday afternoon but ending by evening.
At this point the matrix shows the forecasters have high confidence in significant,
rather than severe, impacts.
The DEM contacts the Crop Over event organizers
and recommends that afternoon preparations be postponed.
Evening events will likely be able to proceed, perhaps with a small delay.
It may take a while for revelers to arrive
due to some street flooding along flood-sensitive travel routes,
like the Baxter's Road.
The DEM prepares to close some roads in the flood prone areas.
Officials have detours ready for implementation
and people stationed to assist vulnerable populations, if necessary.
Some of the more costly and difficult actions that were being planned,
such as evacuations and opening emergency shelters,
are no longer necessary due to the changed expectations
surrounding the impacts of the rain.
In this example, we can see how using the matrix to communicate both the confidence level,
in terms of expressing likelihood,
and the severity of the impact
helped local officials make decisions
about an impending rain storm.
Actions by officials kept societal functions running as safely and smoothly as possible
by postponing public events,
and closing off those areas that expected flooding during significant rainfall.
The office of the Barbados Meteorological Services, the BMS,
is responsible for issuing forecasts and warnings regarding weather events
that have the potential for significant impacts on Barbados.
The BMS works closely with the Caribbean Institute of Meteorology and Hydrology
and the Barbados Department of Emergency Management
to provide timely warnings and to help ensure appropriate actions and preparations.
The guidance and warnings provide emergency management,
businesses, the media, and the public in general
with useful information for important decision making
regarding the impacts from weather hazards on commerce and recreation.
For more information on the impacts-based forecast matrix, please contact.......