1. Uncertain Forecast
Peter Gibbs
Broadcast meteorologist, BBC and Met Office
© Crown copyright Met Office

2. Obstacles and Assumptions
Why are we not communicating it already?
• …the public don’t understand probabilities…
• …uncertainty is too difficult to communicate…
• …the Press don’t get it…
• …the Met Office (or BBC) is just covering
itself…
• …you can’t say 50% chance - that is admitting
defeat…
• …just tell me what will happen…I just need to
make a decision…
• or is that “just make my decision for me” ?

3. Storm of 16th Dec 2011
© Crown copyright Met Office

4. 5-day forecast
Both EPSs flag small risk exceptional low over UK
EC 944
© Crown copyright Met Office Ensemble Training 2012 MOGREPS 938

5. Forecasters communicate low
risk of very high impact
• BBC shows two
alternative tracks:
• Track 1 is low probability
but highest impact
(severe gales and heavy
snow).
• Track 2 has a higher
probability but lower
impact (some snow, but
lighter winds).
© Crown copyright Met Office Ensemble Training 2012

6. Max Temp uncertainty 1-5
Feb 2012
• Cold block over Europe
• Frontal system approaching
from Atlantic
• Uncertainty about
progression
BBC
Graphic
presentation
© Crown copyright Met Office Montreal Workshop, March 2012

7. Decision-making with
Uncertainty
• There is always uncertainty in forecasts
• Recent study in US showed that where
uncertainty is not shown, people make own
assumptions (Joslyn et al, 2011)
• Often over-estimate uncertainty
• By explicitly providing uncertainty, people make
better decisions
•…
© Crown copyright Met Office

8. • Do ensemble forecasts
Randomised design
cause confusion?
Collected basic
• Can playersdata
demographic make
better decisions using
Addressing assumptions:
Outcomes generated on-
ensemble forecasts?
“the public don’t understand uncertainty”
the-fly (based on
• How does this vary with
probabilities)
“uncertainty is too difficult to communicate”
presentation type?
Ability to separate 1st time
• Demographic
players
influences
© Crown copyright Met Office

9. Playing the game
How confident are
you about each
shift – tests ability Choose location or shift – tests
to assess ability to understand relative
probability from probability from presentation
presentation
© Crown copyright Met Office

10. Scoring
• Each shift is
allocated an
outcome
randomly
selected from
the forecast
distribution
• Element of
luck!
• Amount of ice
cream bought
and sold
depends on
advice and
outcome
• Total score at
end of game:
© Crown copyright Met Office

11. Weather Game – “Engaging online users to
gather feedback on the best way to represent
forecast uncertainty”
-11,000 responses – Largest
meteorological survey of its kind
-Collaboration with UK
Universities – Bristol &
Cambridge
-Showed that people make better
decisions when presented with
uncertainty
- Consistent across all age
groups and educational levels
- People made best decisions
with the most complex
presentations
Courtesy of Liz Stephens
© Crown copyright Met Office