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.

Forecast Skill Improvement

ForecastError

Year

Better

National Weather Service

NGM, 80 km,1995

NGM, 1995

2001: Eta Model, 22 km

2007-2008

12-kmUW MM5Real-time

12-km WRF-ARWand WRF-NMMare similar

December 3, 20070000 UTC Initial12-h forecast3-hr precip.

NWS WRF-NMM (12-km)

2007-2008

4-km MM5Real-time

PREDICTION

Trend to Hyper-resolution (1-2 km) during the next five years

UW’sNew 1.3 kmWRFruns

Surface Temperature-12km

Temperature-1.3 km

Increasing Resolution Will Not Be Enough

The Transition from Deterministic to Probabilistic

Prediction

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

CamanoIslandWeatherRadar

Now

But there were major gaps in coverage, particularly along the coast

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!

PREDICTIONTV Weather Broadcasts on

Nightly News Programs Will be Supplanted by Distribution via

the Internet and Portable Digital Devices

PREDICTIONHumans 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.

Forecaster at the Seattle National Weather Service Office

The National Weather Service

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)