Earlier this year, we shared that work was underway on a new Local Forecast for Ferny Grove Weather, combining forecasts from multiple weather models with what could be learned from their performance at Ferny Grove. After a long period of further development, testing and refinement, we are pleased to announce that the Local Forecast is now available.
The Local Forecast has been developed specifically for Ferny Grove using observations recorded here on the website. Rather than simply displaying an existing forecast, it brings together guidance from a range of major international weather models and combines and improves upon it with what has been learned from their performance at Ferny Grove.
The aim is to produce a forecast that is specifically tuned to this location.
The Local Forecast currently focuses on temperature, producing a single best estimate forecast of how the temperature is expected to develop at Ferny Grove over the coming days. This is the first operational forecast element produced by this system, with additional weather variables intended to be added as the system continues to develop.
As outlined when we first announced this project, the Local Forecast is not intended to replace official forecasts, warnings or advice. Official forecasts from the Bureau of Meteorology serve a different and essential role. The Local Forecast provides an additional, highly localised perspective for Ferny Grove and is best considered alongside official forecast information.
Where to find the Local Forecast
The Local Forecast can now be viewed from the Ferny Grove Weather home page, with the complete forecast available from under the forecast section of the website as Local Forecast.
The forecast provides both an overview of the days ahead and more detailed information about how the temperature is expected to change through the forecast period.
For each day, the forecast includes the expected minimum and maximum temperature, together with the estimated time of each. You can also examine how the temperature is expected to change throughout the day.
The forecast is generated and published automatically four times each day as new weather model guidance becomes available.
The forecast can also update between these main runs. The system continues to monitor observations from Ferny Grove after a forecast has been produced. If the temperature begins developing sufficiently differently from the forecast, this can adjust the short-range forecast to take account of what is actually happening.
Where does the forecast come from?
Behind the Local Forecast is a forecasting system we developed specifically for this purpose called LACO — Local Atmospheric Corrected Output.
LACO uses guidance from weather models produced by major forecasting centres around the world. These models have different strengths, limitations and biases, so they can produce different forecasts for the same place. No individual model is consistently the best in every situation.
LACO brings these sources together using approaches that are well established in operational forecasting. It compares earlier model forecasts with temperatures later observed at Ferny Grove, allowing it to learn how the models have been performing locally. LACO can also learn about systematic differences between model forecasts and local observations and make corrections for them.
This can also give different models a different influence when producing the next forecast. Models that have been performing particularly well can receive greater influence, while poorer recent performance can reduce a model’s influence.
The resulting forecasts are combined to produce the consensus that becomes the Local Forecast.
Using observations as the weather develops
Past observations help LACO learn how to produce the next forecast, but current observations have another role.
Weather models only provide new guidance at particular times. Meanwhile, the Ferny Grove weather station continues recording what is actually happening.
If the observed temperature begins to depart meaningfully and persistently from the forecast, LACO can make a controlled adjustment to the short range forecast rather than simply waiting for the next complete model update. This process is known as nowcasting.
It doesn’t mean that every small difference between an observation and the forecast causes the forecast to change. Adjustments are made only when the system determines that the departure is sufficiently meaningful, and those adjustments are controlled in both size and duration.
Daily minimum and maximum temperatures
The produced forecast contains temperatures at hourly intervals, but the temperature changes continuously between those times. The warmest or coolest point of a day also doesn’t necessarily occur exactly on the hour.
LACO can therefore constructs a smooth temperature curve between the hourly forecast values.
That allows the Local Forecast to estimate both the value and time of the daily minimum and maximum more precisely. A forecast maximum might, for example, occur at 2:42 pm rather than simply being assigned to either 2 pm or 3 pm.
How accurate is it?
No forecasting system can eliminate uncertainty, and the Local Forecast will not always match what is eventually observed.
An individual weather model will sometimes outperform the combined forecast. Unexpected developments will occur, and some weather situations are inherently much harder to predict than others.
An important part of LACO is therefore verification. Forecasts are retained and can subsequently be compared with what was actually observed at Ferny Grove. This allows the performance of both LACO and the underlying weather models to be measured rather than simply assumed. You can also explore this performance on the Forecast Verification page rather than having to take the forecast’s performance on trust.
As more operational forecasts are produced, that will also build a growing record of how the Local Forecast performs.
As with any weather forecast, the forecast outcome will not always match exactly what is subsequently observed. Forecasting describes the most likely evolution of the weather from the information available at the time, rather than a statement of exactly what will happen. Performance is therefore better assessed across many forecasts and different weather situations than from any single forecast result.
A forecast made for Ferny Grove
The intention is to take the best forecasting information available and turn it into a useful forecast specifically for Ferny Grove.
After considerable development and testing, we are very pleased to finally make the Local Forecast available on Ferny Grove Weather.
The Local Forecast is the result of a much larger project than would be apparent from looking at the forecast page.
Behind it is an automated system for processing forecasts, learning from previous performance, correcting and combining model guidance, responding to observations, calculating forecast extremes, verifying results, monitoring system health and publishing the resulting forecast.
For those who would like to understand the methods in more detail, the About the Local Forecast page explains the forecast guidance, local learning and corrections, model weighting, near-term updates, 15-minute processing, verification and limitations.
We will also explore the details behind the system in a second blog post tomorrow: Behind the Local Forecast: How LACO Works.
As always, please reply below or contact us if you have encounter any issues or have any thoughts.