dc-weather-prediction

Using deep learning to predict the temperature of the next 24 hours at the Ronald Reagan National Airport

Abstract

Weather forecasts are an integral part of our day-to-day lives. They help us plan ahead and be prepared for the upcoming hours, days and even weeks. We use the weather apps on our phones to check tomorrow’s temperature or the chances of rain in order to dress appropriately or to make sure we take our umbrellas with us. These are all weather forecasts that we use regularly without giving a second thought.
As it is such an important part of our lives, the accuracy of these forecasts are very important. Not all weather forecasts are made equal as meteorologists use a variety of approaches and a wide range of data to make predictions.
One emerging approach in the field of weather forecasting is the use of machine learning to make predictions. The abundance of data being collected these days and the increasing advancements in machine learning algorithms make this a task that machine learning is really suited for.
This project is an attempt in using machine learning (deep learning in particular) to make hourly weather forecasts for each day at Washington D.C.

Problem Definition and Algorithm

Task Definition:

Using historical hourly weather data of the previous 7 days, predict the temperature for the next 24 hours (12am to next day’s 12am).

Source of Data

URL: Wunderground
Under the hood, Wunderground sends an HTTP request to https://api.weather.com which returns historical hourly data for a particular date and location.
The format of the data is as follows:

Choice of algorithm

Since this is a time-series forecasting problem, the Long Short Term Memory (LSTM) neural network was used to build the model. For the look-back period, a period of 7 days(168 hours) were chosen. And since prediction needs to be made for the next 24 hours a multi-step (24 steps) model was trained.
A vanilla Recursive Neural Network (RNN) only has a short term memory because it suffers from the vanishing gradients problem. This occurs because during backpropagation in a vanilla RNN, only the recent hidden states are remembered as the gradients for earlier layers get exponentially smaller and don’t do much learning at all. An LSTM is much more robust to vanishing gradients and can remember information from earlier inputs much better than a vanilla RNN.
My assumption for the prediction problem is that temperature for a particular day not only depends on the day before, but on the weather conditions for a longer timespan (the entire past week). For this reason, LSTM was chosen as it remembers hidden states from the earlier timesteps better.

Fig: A simplistic LSTM representation of the modeling task

Exploratory Data Analysis

22 years worth of historical hourly weather data from 2000-01-01 to 2000-12-06 for the Ronald Reagan National Airport was used for training the model. This amounted to a total of 247349 rows of weather data records.
The first step was to figure out which columns were actually usable in my dataset. For that, I first loaded the data into a pandas DataFrame and checked the NaN counts for each column. I found that almost half of columns were NaN.

Using this information, I decided to keep only the following columns (ones that are almost always recorded during observations):

• temp

• valid_time_gmt

• pressure

• wspd

• heat_index

• dewPt

• rh

• vis

• wc

• clds

• wdir_cardinal

The next step was to check the columns and see how they were correlated. Just by the column definitions, I knew that heat_index and wc would be highly correlated to the temperature, but had no idea about how the other columns were related. Using seaborn to plot the correlations, I got the following graph:

Fig: Correlation among the columns

Some findings that I took away were that dewPt is highly correlated to the temperature, relative humidity (rh) is highly correlated to the the visibility (vis), and there is also a slight correlation between the pressure and the temperature.

Data Preprocessing

Since I want to convert the data into fixed width hourly records, the first step was to convert the UNIX timestamp to a human readable date. This was easily done with the python datetime library.

After converting the unix timestamps into datetime objects, I found that the time the observations are made are not made uniformly. As can be seen from the following screenshot, the observations are not all taken at the same hour.

Fig: Graph showing number of observations made at specific minutes of an hour

On further analysis, it became clear that while the observations in first few years of our timespan (2000 2010), the observations were not made at regular intervals, the more recent years had regular intervals. Especially, as evident in the graph above, almost all hourly records had data for the 52^nd minute. Thus, I decided to use all the 52^nd minute observations as data for our modeling.

Despite there being a lot of 52^nd minute data in the dataset, I had many missing observations (missing a few hours in some days). Since my LSTM model uses each of the previous 168 hours data as input to make predictions, missing data would cause inaccuracies in my model. To fix this, I used the following interpolations and backfill/forwardfill to fill in the missing rows and created a uniformly spaced timeseries dataframe for training:

Fig: An example of interpolation performed to fill missing 52^nd minute temperature values

One big part of predicting weather is to note that weather conditions are cyclical in nature. i.e. weather conditions in January of one year are similar to weather conditions of January of the next year, weather conditions at 1 am today is close distance-wise to weather conditions at 1 am in other days. Directly incorporating the timestamp as a feature would lose this cyclical information. So, I transformed the timestamps (hour of day, day of year) into sin and cosine waves to preserve the cyclical information.

Fig: Hour of day encoded as sine/cosine wave

Fig: Day of year encoded as sine/cosine wave

With this, the dataset was ready and I moved on to the training portion of the project.

Training

The dataset was split into 70:20:10 train, validation and test sets. A StandardScaler was fit into the train dataset and all the train, validation and test sets were standardized with this scaler.

The most crucial step for my model was to generate the sequence of inputs to feed into my LSTM layer. Since my approach was to use the last 168 hours of weather data as the lookback for the model, generating the sequence of inputs was a little confusing at first. But thanks to this excellent tensorflow tutorial, I was able to set it up just right.
After generating the sequences, my training data looked like the following:

Fig: Training Data after sequencing

From the above figure, we can see that for each sample in our training data, the past 168 hours of data have been correctly set up as input features and the next 24 hours have been set aside as labels for training.

I experimented with stacked LSTM, adding more dense layers, varying LSTM unit counts, and so on. But considering the training time constraints and performance, I found the following model to give the best results for me:

Framework: Tensorflow, Keras
Choice of optimizer: Adam with learning rate of 1e-3, default decay
Choice of loss function: Mean Absolute Error
I chose MAE as my loss because it was easier to comprehend and the model converged considerably well for my project.

Max Epochs: 100 ( I used Early Stopping with a patience of 5 such that if the validation loss didn’t go down for 5 straight epochs, the model would stop training further )

The model was configured to save every epoch if the validation loss improved from the previous best.

The best model had a validation loss of 3.5005.
Although the Mean Absolute Error gave an idea of how accurate my model was, I found it useful to compare it to a baseline model. Thus, for evaluation of my model, I created the following baseline models and trained them on the same dataset:

Fig: Baseline model that predicts a constant temperature no matter what the input.

Fig: Baseline model that just repeats the previous day’s temperatures as predictions

Looking at the following graph of the LSTM’s performance on test data, it seems that the LSTM model is indeed making more accurate predictions.

Fig: Samples of LSTM model’s performance on test dataset

Comparing the average Mean Absolute Error for all three models, the following results were seen:

Fig: Comparison of the LSTM model’s performance vs the two baseline models

Making Predictions / User Interface

After building my model, I built a website that uses this model and allows a user to check the model’s forecasts for tomorrow’s temperature for Washington D.C. The website also shows its past predictions and compares them with the actual temperatures for that day to give a sense of how accurate the model actually is.//

The website is available at http//3.235.0.237/#/dashboard.

Technology Stack

Architecture

Fig: Request/Response life cycle

User Interface

The user interface consists of a horizontal scrollable date picker that allows the user to select a date (from the current date to 30 days before the current date) to look at predictions for. The rightmost date is the current date. For the current date, since we don’t know the full day actual data yet, the predictions from the model are shown along with the actual temperatures until the time the site is accessed at. The actual temperature for future times will be shown once observation data is available from the weather API.
Selecting a date plots the predicted temperature vs the actual temperature for that date in a line graph. The red dotted line indicates the predicted temperature, blue solid one shows the actual temperature for that day. The shaded gray area indicates the absolute error in the prediction. Apart from the graph, the page also contains a tabular view of the same data at the lower half of the page.

Fig: Graph View

Fig: Table View

Conclusion

The final model had a Mean Absolute Error score of about 3.5. i.e. our model’s predicted temperatures are about (\pm3.5) from the actual temperature. Although the accuracy is not as high as I would have liked, looking at the predicted vs the actual temperatures, it seems that the model is capturing the trend (increasing or decreasing) relatively accurately.
To improve the model further, I would like to add more important features (perhaps from a completely new dataset) and see how it performs. Although I experimented with the architecture of the neural network, due to time constraints, I wasn’t able to experiment as much as I would have liked. So, I definitely want to try different LSTM architectures in the near future and see how they compare to my current model.

References

• Educational Resources

  • Time series forecasting - Tensorflow

  • Timeseries forecasting for weather prediction Prabhanshu Attri, Yashika Sharma, Kristi Takach, Falak Shah

  • Single and MultiStep Temperature Time Series Forecasting for Vilnius Using LSTM Deep Learning Model, Eligijus Bujokas

• Dataset

  • API: Weather Underground

  • Dataset descriptions

• Project Artifacts

  • Website URL

  • Colab used for training

  • Source code