Transcript UndergradtalkNN.ppt

The Technology and Future of Weather
Forecasting
Cliff Mass
University of Washington
2012: Hurricane Sandy
125 dead, 60+ billion dollars damage in an area
with a population of tens of millions.
Well predicted, more than a week
ahead
ECMWF 6-day Forecast of Sea Level Pressure
1938 Hurricane: Similar in
Strength to Sandy
Nearly a thousand died
Not forecast the day before
1962 Columbus Day Storm
Not forecast the day before either
Seattle Times
Jan 1993: Inauguration Day
Storm: Near Perfect Forecast
Something Has Changed
Before 1990 the National Weather Service got
virtually every major storm wrong, even the
day before.
After 1990, they gave good warnings for
nearly all.
P
Forecast Skill Improvement
NCEP operational S1 scores at 36 and 72 hr
over North America (500 hPa)
75
e
r
o
c
s
National Weather Service
65
"useless forecast"
55
36 hr forecast
1
S
72 hr forecast
45
Forecast
Error35
10-20 years
Better
"perfect forecast"
25
15
1950
1960
1970
1980
Year
Year
1990
2000
Skill Improvements (ECMWF)
Major improvements, mainly due to satellite data and
improved models
Weatherman Jokes Are No
Longer Appropriate
The Key Technology of Modern
Weather Forecasting is
Numerical Weather Prediction
The First Numerical Weather
Prediction
• The first successful numerical prediction of
weather was made in April 1950, using the
ENIAC computer at Maryland's Aberdeen
Proving Ground
Numerical Weather Prediction
• The basic idea is that if you can determine
the current state of the atmosphere (known
as the initialization) , you can predict the
future using the equations that describe the
physics of the atmosphere.
• These equations can be solved on a threedimensional grid.
Observation Collection Needed to
Create the Initialization
Numerical Weather Prediction
One of the equations used to predict the weather
is Newton’s Second Law:
F = ma
Force = mass x acceleration
Mass is the amount of matter
Acceleration is how velocity changes with time
Force is a push or pull on some object (e.g.,
gravitational force, pressure forces, friction)
This equation is a time machine!
F = ma
•The initialization gives the distribution of
mass (how much air there is and where) and
allows us to calculate the various forces.
•Then… we can solve for the acceleration
using F=ma
•With the acceleration we can calculate the
velocities in the future.
•Similar idea with temperature and humidity
but with different equations.
The
“Primitive”
Equations
Numerical Weather Prediction
• Numerical weather prediction is limited by the
available computer resources.
• As computer speed increases, the number of
grid points can be increased.
• More (and thus) closer grid points means we
can simulate (forecast) smaller scale features.
National Weather
Service Weather
Prediction Computer
NGM,
80 km,
1995
1995
2007-2008
4-km UW
MM5
System
1.33 km resolution available on
the UW web site
But just as important as the
computer revolution has been the
weather data revolution, with
satellites giving us three
dimension data over the entire
planet
Example: The Pacific Data Void
No Longer Exists
Cloud Track Winds
Better than Star
Trek!
NOAA Polar
Orbiter Weather
Satellite
Satellite Sensors Provide Thousands of High
Quality Vertical Soundings Daily over the Pacific
Cosmic GPS Satellites Provide
More Soundings!
Impacts
• The addition of massive amounts of
new observations is causing a steady
improvement in weather prediction
• We are now starting to see frequent
examples of forecast skill past one
week:
• Hurricane Sandy is only one example
Observed
180 hr (7.5 days)
Forecast Skill Will Continue to
Extend Further in Time…with
limits (about 2 weeks)
• More satellite assets will provide a far better
description of the atmosphere.
• Better models and higher resolution
• Better data assimilation: how we use the
observations to produce an initialization for
our models.
Increasing Resolution and Better
Models Will Not Be Enough
The Next Major Revolution in
Numerical Weather Prediction
Will Come Elsewhere
The Transition from
Deterministic to Probabilistic
Prediction
A Fundamental Problem
• The way we have been forecasting
has been essentially flawed.
• The atmosphere is a chaotic
system, in which small differences
in the initialization…well within
observational error… can have
large impacts on the forecasts,
particularly for longer forecasts.
• Not unlike a pinball game….
A Fundamental Problem
• Similarly, uncertainty in processes, like the
development of clouds and precipitation, also
produces uncertainty in forecasts.
• Thus, all forecasts have some uncertainty.
• The uncertainty generally increases in time.
This is Ridiculous!
Forecast Probabilistically
• We should be using probabilities for all
our forecasts or at least providing the
range of possibilities.
• There is an approach to handling this
issue that is being explored by the
forecasting community…ensemble
forecasts
Ensemble Prediction
• Instead of making one forecast…make
many…each with a slightly different
initialization or different model
physics.
• Possible to do this now with the vastly
greater computation resources that are
available.
Ensemble Prediction
•Can use ensembles to give the
probabilities that some weather
feature will occur.
• Ensemble mean is more accurate
than any individual member.
•Can also predict forecast skill!
•When forecasts are similar, forecast
skill is generally higher.
•When forecasts differ greatly,
forecast skill is less.
Prediction!
• The meteorological profession is rapidly
gaining the ability to produce highresolution probabilistic weather forecasts
AND analyses.
• Probabilistic forecasts and analyses will be
available for a wide range of weather
parameters.
The Nowcasting Revolution
AMS Nowcasting Definition
A description of current weather and a
short-term forecast varying from minutes
to a few hours; typically shorter than most
operational short-range forecasts.
American Meteorological Society’s
Glossary of Weather and Climate
During the past decade or so the
geographical and temporal specificity of
the information that the weather
profession can provide has greatly
increased.
Pacific
Northwest
Surface
Observations
3000-4000
observations per
hour over WA and
OR
Traditional Approaches of Weather
Information Dissemination Are Incapable
of Delivering the Specificity and Detail
Meteorologists Can Now Provide
Typical TV weathercasters have only 2.5 minutes!
An Irony
There has never been such a large
difference between what meteorologists
know about current weather and what
we are communicating to the public.
A Worry
The Solution? Smartphones are
Ideal for Weather Data Delivery.
• Lots of bandwidth
• They know where they are, so forecast
information can be tailored to the user
• Substantial computational capacity.
Smartphones Offer a Powerful,
Portable Platform for Viewing Weather
Information, Forecasts, and Warnings
There are now thousands of
weather apps for
smartphones…and the best are yet
to come!
WeatherProtector
WEATHER
PROTECTOR
Tells you whether
heavy precipitation,
winds, or other
weather issue are
approaching your
position.
BikeWeatherGuard
Bike
Weather
Guard
•Using a map interface,
describe your planned
route and when you
want to travel.
•Tells you whether you
should delay your trip,
or perhaps leave a few
minutes early, to stay
dry.
The Weather Adaptive Society
• Advances in computation, control, and
communication allows society to react
quickly and effectively to weather
information.
• At the same time, weather forecasts will
rapidly improve.
• Together they allow effective real-time
weather adaptation.
Traffic Can Be Slowed During
Dangerous Weather
Can use flow control to limit the
number of cars entering the
roadways near heavy rain.
Power Generation
• Coordination of power generation by
weather-sensitive renewables and reserve
power sources (e.g., hydro, gas turbines).
Weather Forecasting is Only One
Part of Atmospheric Sciences
• Climate research and prediction
• Severe weather research and prediction
(hurricanes, tornadoes, severe
thunderstorms, windstorms, snowstorms)
• Atmospheric pollution and chemistry
• Mountain meteorology
• And many more…
The End