How to query weather forecasts from the past – Historical Forecasts

Analyzing historical weather forecast data is the an important facet for many weather data users beyond standard forecasts and historical observations. Historical forecasts are often more important for business analysis than traditional historical observation data because customers in many cases base their decisions on future forecast and not the actual weather on a given day. Consider an amusement park. In many cases people start planning their weekend activities earlier in the week instead of waking up on Saturday morning and deciding what to do. They do this by using forecasts. If the weekend forecast delivered on Tuesday shows a good chance of rain for the weekend, people will avoid outdoor activities. Even if the forecast changes later in the week and the actual weekend weather is sunny, those indoor activities are often committed and people are unlikely to change their plans.

This “forecast effect” influences all types of obvious activities in both the B2C and B2B space. In the consumer space, any type of travel or preplanned events can be affected. In the business space, costly decisions in construction, building trades, and agriculture must be scheduled in advance based on a forecast. In cases when the actual weather on a given day differs significantly from earlier forecasts, analyzing business results based on weather observations alone can lead to faulty conclusions.

In the past, historical forecasts were difficult to obtain. In many cases they were not available or often prohibitively expensive. Visual Crossing Weather is now able to bring you historical forecasts at a price point that makes them accessible for all types of analysis.

What is an historical forecast?

Just as the name implies, historical forecasts are weather forecasts that were given in the past as a prediction for weather on another date that is also now in the past. For example, on July 1, 2021, there was a forecast given for July 4, 2021. For a person viewing data on August 1, 2021, that forecast given on July 1 for July 4, is a historical forecast. Since that forecast given on July 1 was used by a large number of people planning their 4th of July plans, it is a very valuable data point for businesses who want to analyze their actual July 4th results. While the actual July 4th historical weather observations can be useful also to see how people reacted to the weather on that specific day, the historical forecast given a few days before shows the information which people used to make their plans.

What types of historical forecast queries are available?

There are two types of historical forecast queries. The first type gives you a single forecast record for a specific day and location. This is useful when you know the day an activity occurred and how far ahead it was planned. For example, if you know that your customer booked their Saturday tickets on the Tuesday before, you can make a historical forecast query with Tuesday as the “basis date”, Saturday as the “target date”, and your activity location. This query will return a record that shows the exact Saturday forecast that the customer was viewing on the Tuesday before they booked their tickets. Even if the actual weather on Saturday ended up being very different than the forecast, the historical forecast data will be able to show the exact information that the customer used to make their purchase decision, not what happened later.

The second type of query is one in which you need the entire 15-day forecast for a specific location as given on a specific date. This is most useful when you know how far in advance the activity is being planned, but the activity itself is done over time. Consider a vacation or a construction project. For example, in the construction business you may allocate certain equipment every Wednesday for the following week. When you want to historically analyze the allocation of equipment to a job site you want to make a query that shows the forecast for that specific job site location as it appeared on a given Wednesday. In this case, you would set the basis date to be Wednesday and omit the target date. This would provide the 15-day forecast as the equipment planner saw it on Wednesday when he or she was making the allocation.

How can I get historical forecast data?

Visual Crossing offers historical forecast data in two different ways depending upon your needs.

Historical forecast subscription

You can get a historical forecast subscription as part of any Corporate level weather data plan. With the Corporate plan you can query millions or rows of historical data as well as live 15-day forecasts and long-range climate summaries. If you are analyzing business data and need large quantities of high-quality historical weather data for comparison, the Corporate plan is the most cost-effective option available.

As an addition to a new or existing Corporate plan, you can also get historical forecast data via our Timeline Weather API. Using the API, you can specify the basis date on which the forecast was generated and the target date along with the location, and our weather engine will find the matching historical forecast for you. As in the example above, you can query the forecast for July 4, 2021 that was initially given on July 1, 2021 for any location worldwide. Alternately, you can query the entire 15-day forecast as it was given for any location on any specific day.

The cost for this is only $100 per month upgrade in addition to the Corporate license. To learn more and sign up today, please click the button below.

One-time historical forecast data

Since not everyone needs ongoing access to historical forecasts, we also offer one-time use access to this data. To make this option simple, we offer a $25 per request solution that allows up to 3 location, up to 3 basis dates, and optionally up to 3 target dates. You can then mix and match your request with any combination of those values.

That means that you can start by selecting up to 3 different locations. For an example, we’ll pick New York, NY; Washington DC; and San Francisco, CA. Now we select up to 3 basis dates. Remember that a basis date is the date on which the forecast was generated. An example would be June 28, 29, 30, 2021. These are the Monday, Tuesday, and Wednesday on which people were making their plans for July 4th (Sunday) activities. In your query, these days don’t have to be sequential as in this example, however. They can be any dates for which historical forecasts are available. Finally, you can pick up to 3 target dates also. These target dates must be in the scope of the 15-day forecast window based on your basis dates. For this example, we’ll pick a single date of July 4, 2021.

The result of our example query will be 9 hourly forecasts (24 hours each) for the day July 4, 2021. The first 3 forecasts will be for New York as they were generated on the dates June 28, 29, and 30. The next 3 forecasts will be for Washington DC as generated on the same 3 dates. And the final 3 forecasts will be for San Francisco for those dates. All forecasts will be for the single target date of July 4th as requested.

Note that you can omit the target date entirely from your request. In this case, your query result will be the full 15-day forecast as it was seen on each basis date for each location. In our example, omitting the target date would result in 9 separate 15-day forecasts. The first 3 would be for New York and would be the full 15-day forecasts as generated on June 28, 29, and 30. The second 6 would be for Washington DC and San Francisco as generated on those same 3 dates.

You can add additional combinations of locations and dates for the $25 package price mentioned above. If you have a large volume of requests, let us know, and we’ll be happy to provide a bulk discount. Simply click the button below to submit the details of your request, and we’ll send you and invoice. Once paid, your data will typically be available for download in 2-3 business days.

Summary

Historical forecast data is a powerful data source for advanced weather analysis. By using historical forecast data, you can compare business data to the forecasts that were being used by your customers or resources planners at the time they were planning their activities. In certain businesses this can be more powerful than actual weather observations, which may not accurately describe the information available earlier in the planning process. So, if your business involves activities that must be planned based on forecasts, than historical forecasts represent the best way for you to intelligently analyze your business results.

Questions or need help?

If you have a question or need help, please post on our actively monitored forum for the fastest replies. You can also contact us via our support site or drop us an email at support@visualcrossing.com.