Ready Data - What is it and how does it help?

Hi All

I’m a bit of a novice at all this and I was just wondering what the ‘ready’ data is and how does it help WXSIM to make accurate forecasts. From what I can gather, it appears to tell WXSIM what the cloud cover will be like at a certain time and when and how much rain is expected. Does this mean that WXSIM does not calculate this itself? Does it use it as a guide? It’s almost as if it uses a forecast to calculate another forecast… I’m confused.

I have been really impressed with WXSIM’s forecast over the last few days, it’s been spot on. This is just making me wonder, that if the ready data tells it that rain is likely on say Thursday, then what does it need to forecast if it is told this already by the ready data?

Thanks in advance.


Addition… I’ve also noticed that if I don’t use the ready data and just use my local station data and advection, that the cloud cover predicted is the same for the whole forecast. So if I start off with partly cloudy, it will remain partly cloudy for the next 4 days. This is with the auto clouds feature turned on too. Is it possible for the program to calculate cloud cover and precipitation without the ready data and if so what I’m I missing?


READY data helps WxSim to estimate conditions, but the data (which comes from the US GFS model) covers a fairly large area. A GFS forecast region covers (roughly) 3535 miles (5555kms). WxSim is working much closer to home…probably a 10 mile radius around you.

There’s a lot more on this in the manual (especially the first part which recounts the history of how I developed WXSIM), but it’s a good question so I’ll attempt at least a brief answer here.

First, technically, most users (at least if they are using WXSIMATE) are not actually using READY data these days, but instead the convenient equivalent (or better) GFS model data culled from huge GRIB files. U.S. users can also use FOUS data from the NGM and/or NAM models to supplement this. Model data like this is vital for WXSIM to forecast cloud cover, rainfall, upper level temperatures, and wind direction. Without it, you’re right - these things pretty much just stay the same.

WXSIM started as a single site near-surface temperature model. It really calculates sun angle and all kinds of thermal processes on its own. A major enhancement of this is its advection routine (especially if you’re using regional data). This is still all WXSIM’s territory. Other things that WXSIM does very much on its own are forecasts of dew, fog, frost, diurnal variations in wind speed (though this can be overwhelmed by imported data), and precipitation type (though whether or not precipitation occurs is determined almost entirely by imported model data).

Actually forecasting large scale weather changes (passage of fronts, rain, cloud changes, etc.) is utterly beyond the ability of any single station model. Various governments and some universities run supercomputer models that take in huge data streams in order to come up with what have become pretty good forecasts. The U.S. government (and no others that I know of) has made its model data publicly, freely available, for the entire world. WXSIM quite “willingly” imports this data.

You have probably seen algorithms for forecasting weather based on conditions and trends from a single station. In fact some weather stations sport such forecasts. You must understand that these are only a little better than a guess. I’ve thought about trying to use such rules in WXSIM, but performance would be poor and it makes a lot more sense to use the excellent, freely available stuff. I recall back in the early-mid 90’s as I was starting to make WXSIM public (after over 10 years of developing it on my own and just showing friends, family, and students), there were a couple of “competitors” out there. These were forecasting programs that took things like barometric pressure and tendency, and wind direction, and tried to make a forecast. They didn’t use any physical calculations that I know of - just sort of an if-then decision tree. They basically did the same thing a little forecast icon on a weather station console, or a one-page list in a book, would do - again not very much and greatly lacking in specificity of timing and other details.

In cases (such as in the U.S.) where multiple models are available, WXSIM can import up to three at a time for a sort of average or consensus. Also, WXSIM has adjustments that can be made to this data to correct for biases in the models. These should be used with care, as I find the models are pretty good in the first place.

One way to look at this is that WXSIM is handling very local things, mainly temperature and humidity, on its own and borrowing from the big models what it needs and couldn’t do itself. The result is a sort of “symbiosis” with hopefully the best of both worlds (the local world of WXSIM and the global view of the models).

Bottom line: yes, WXSIM does heavily rely on outside model data for many important parts of its forecast, but it also does a great deal on its own (mainly regarding temperature and humidity), and tailors this specifically for the customized site.

One more thing: I didn’t intend WXSIM solely as a forecasting tool. It’s a modeling tool in which you can experiment with its virtual world of weather. This is why it retains (perhaps seldom used) tools for putting your own weather into it manually. YOU can make it rain, make the wind direction change, etc. and see how these affect things like temperature. It has tremendous educational potential and is completely unique, as far as I can tell, in this regard. Playing with it in this hypothetical mode can give you years (perhaps a lifetime) of experience in weather forecasting (again, mainly temperature) in a few weeks.

Hope that helps! :slight_smile:


Tom - I am very impressed with your time taken to explain some of the tools you use behind Wxsim and why it does what it says so accurately - and also what makes it different from the rest… :wink:

I am a newbie to this weather station thing but have been interested in the weather as a part of my life for a long time - being an arable farmer’s son - with sheep to shear, barley & peas and maize to sow and harvest and hay too and also livestock to shift and protect, the list goes on. I am now an engineer at a pulpmill where the weather plays a much smaller part - but - I ride a racing bike the 6 miles to work every day (well most) :wink:

Do you have data to assist with local NZ weather forecasts or do you need a family of stations with data or a close one with history (- yes there is), or is there national info available?

Having a reply as detailed and supportive as you wrote speaks volumes for your support of the software…



Thanks so much for your response. You have answered my questions and following a more in-depth read of the manual, I believe I have a better understanding of how the program works. I have been very impressed with its performance and local temperatures and wind speed etc are spot on.

I also like the idea that you can input your own weather conditions and then sit back to see how the that affects the development of the weather over the next few days.

Once again, thanks so much for taking the time to explain this. It’s very much appreciated.

Kindest regards


Mark, you’re welcome - I’m glad the answer made sense! I kind of like talking about my program. :slight_smile:

TokKiwi, I have done a few customizations in New Zealand now - all on the North Island. There is sufficient data to run the program well, and I can characterize the climate of a spot even without a long station history (though if its a fairly new station, a few days worth of data can help pin down certain characteristics of the temperature curve, especially by comparing to nearby official sites). NZ is a bit short on internationally reported METAR data, as only about five stations seem to send out to that data stream. There’s more data (synoptic) available from the NZ MetService, which can be used in WXSIM (though you have to grab that particular item manually if you want to use it).

Hope that helps!


Thanks Tom - for the quick response - and for the support :wink: I didn’t expect there was anything developed for NZ sites but I guess Brian and others have been interested for a while. I am very close (10 miles away) to the Rotorua Geyserland Observatory station - 3 years of data on WU. So it all sounds feasible and interesting!

Now to just sort out the future finances, a bit tight with 4 teenagers as home still and only one income.

yes, Ricky, in Auckland, has wxsim working:

Thanks Windy! :wink: