The Future of Northwest
Weather Prediction
Cliff Mass
University of Washington
The best way to predict the
future is to invent it.
Alan Kay
Some Questions
• How will the technology of NW prediction
change?
• How will observing technologies change?
• How will delivery of forecasting change?
• How will the role of human forecasters
change?
Numerical Weather Prediction
• The equations describing the atmosphere can
be solved on a three-dimensional grid.
• 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.
A Steady Improvement over the
past 50 years
• Faster computers and better understanding of
the atmosphere, allowed a better representation
of important physical processes in the models
• More and more data became available for
initialization
• Increasing resolution (more grid points).
• As a result there has been a steady increase in
forecast skill from 1960 to now.
P
Forecast Skill Improvement
NCEP operational S1 scores at 36 and 72 hr
over North America (500 hPa)
National Weather Service
75
S1 score
65
"useless forecast"
55
36 hr forecast
72 hr forecast
45
Forecast
Error 35
10-20 years
Better
"perfect forecast"
25
15
1950
1960
1970
Year
1980
Year
1990
2000
NGM,
80 km,
1995
NGM, 1995
2001: Eta Model, 22 km
2007-2008
12-km
UW MM5
Real-time
12-km WRF-ARW
and WRF-NMM
are similar
December 3, 2007
0000 UTC Initial
12-h forecast
3-hr precip.
NWS WRF-NMM (12-km)
2007-2008
4-km MM5
Real-time
PREDICTION
Trend to Hyper-resolution (1-2 km)
during the next five years
UW’s
New
1.3 km
WRF
runs
Surface Temperature-12km
Temperature-1.3 km
Increasing Resolution Will Not
Be Enough
PREDICTION!
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 More Fundamental Problem
• Similarly, uncertainty in our model physics
also produces uncertainty in forecasts.
• Thus, all forecasts have some uncertainty.
• The uncertainty increases in time.
This is Ridiculous!
Or this…
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
• Possible to do 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.
•Can also predict forecast skill!
•It appears that when forecasts are
similar, forecast skill is higher.
•When forecasts differ greatly,
forecast skill is less.
Probabilistic Prediction
• So instead of saying the temperature in two
days will be 67F. We might tell you:
50% probability it will be between 64 and 69F
90% probability it will be between 62 and
72F.
Probability Density Functions
(PDF)
Ensemble-Based Probabilistic Products
PROBCAST: www.probcast.com
But How Do We Communicate
Probabilistic Information?
Will People Accept and Use It?
Prediction
• In ten years, the meteorological profession
will be able to produce high-resolution
probabilistic weather forecasts AND
analyses.
• Probabilistic forecasts and analyses will be
available for a wide range of weather
information.
PREDICTION:
Weather Satellites Will Provide
Extraordinary Amounts of
Information over the Entire Earth
• The idea of a data void over the Pacific will
seem quaint and old-fashioned
• New satellite are planned that will give huge
numbers of vertical soundings and other
information over the oceans!
Better than Star
Trek!
New Hyperspectral Satellite Systems Will
Produce Thousands of High Quality Vertical
Soundings Daily over the Pacific
The Cosmic Satellites Will
Provide More Soundings!
The NASA Global Precipitation
Measurement (GPM) Satellite
Will Put a Radar In Space
PREDICTION
Northwest Weather Radar
Coverage Will Get Much
Better
Until the Mid-90s the Northwest Had
Extraordinarily Poor Radar Coverage
• Before the early 90s, only
Portland had a dedicated
weather radar and the rest of
the area tried to get weather
information from air-traffic
control radar.
• In the early-1990s, the NWS
installed the NEXRAD
Doppler radars
Camano
Island
Weather
Radar
But there were
major gaps in
coverage,
particularly along
the coast
Now
Senator Maria Cantwell Intervenes:
A New Coastal Radar Will Be
Installed in 2011
Probable
Location:
Langley Hill
NW of
Hoquiam
But our radar future also includes
something else: dual polarization
• The new coastal radar will be installed with the
dual-polarization option and all existing NWS
radars will be upgraded.
• Dual-polarization provides radar information
using two perpendicular orientations of radar
waves.
• Allows much better estimation of precipitation
intensity and determination of precipitation type.
Even More Radars
• Hopefully, citizens of Oregon will rise up to
demand a radar for the Oregon coast-another major gap.
• And perhaps smaller gap-filler radars on the
eastern slopes of the Cascades!
The Problem of Delivery
During the past decade or so the
geographical and temporal
specificity of the information the
weather profession can provide
has greatly increased.
• High resolution forecasting, NWS forecasts
on a 2.5 km grid, radar data, satellite
imagery, huge numbers of surface stations,
and now probabilistic prediction!
Traditional Approaches of Weather
Information Dissemination Are Incapable
of Delivering the Specificity and Volume
of Data
Typical TV weathercasters have only 2.5 minutes!
Many of us worried about this
problem in the 90’s but now the
solution is literally at hand
There are now HUNDREDS of
weather apps for smartphones…and
the best are yet to come!
PREDICTION
TV Weather Broadcasts on
Nightly News Programs Will be
Supplanted by Distribution via
the Internet and Portable Digital
Devices
PREDICTION
Humans Will Increase Get Out of
Forecasting and More Into
Communication and
Interpretation
There will be changes
• Today, humans generally don’t improve
on objective forecasts based on models,
except for a small percentage of the time
• With the advent of probabilistic
prediction and better underlying
forecasting technology, human forecasters
will have an increasingly difficult time
beating objective guidance, especially for
longer forecasts.
The Role of Human Forecasters
• Once all the numerical simulations and
statistical post-processing are done, humans
will still play an important role:
– Evaluating the model output
– Making adjustments if needed
– Attempting to consider features the model can’t
handle (this will decrease in time)
– Communicating to the public and other users.
Where can humans still add
value?
• Very short-term forecasts where our ability
to analyze and understand radar and satellite
imagery give us the advantage over
objective measures.
The National Weather Service
Forecaster at the Seattle National Weather Service Office
The End
Product Generation
• Some completely objective and automated.
• Others depend on human intervention
• Example: the National Weather Service
IFPS system
Interactive Forecast Preparation System (IFPS) and
National Digital Forecast Database (NDFD)