Model and forecast your local weather on your own computer!

Sunset over the marine layer, from Mt. Tamalpais, near San Francisco, CA

User Comments

Screen Shots
News Briefs
Who uses WXSIM?
New Features and Revision History
History and Technical Information

Downloads and Purchases

Ordering Information
Other Stuff

Updated June 20, 2017

Automated WXSIM forecasts for Atlanta, updated four times a day, along with current conditions, are available here. Also see a list of links to users' WXSIM forecasts on the web.


Announcing WXSIM 2017(Build 1.1) !

Including WXSIMATE 6.3 and two great tools:

Autolearn-WX 3.3 and WXSIM-Lite 2.3

Other programs by Tom Ehrensperger, including the Clima-Sim Climate Simulator

Also, see the multi-site controller program WXSIMPRO.

WXSIM was recently featured in an article in From Scratch Magazine. See page 84 here.

WXSIM 2017, Builds 1.0, had several improvements over 2016 versions, including the potential for customization of shadowing my mountains. 2016 versions introduced improved handling of learned bias correction data. 2015 intorduced several new features, the most significant being the addition of the new, optional program WXSIM-Lite. This program takes an independent approach to forecasting temeprature and dew point, by continually updating a set of station-specific bias-correction values, which are then applied to raw model data (i.e. from GFS) to generate a greatly improved forecast of temperature and dew point. This forecast (which is usually a bit more accurate than WXSIM's raw forecast) can then be ingested into WXSIM (in professional mode) so that the mixture is better than either program alone. This is likely the most significant single improvement to WXSIM's accuracy in many years, reducing mean absolute temperature forecast errors by about 15-20%.

Other improvements to WXSIM over the last several years include:

See New Features and Revision History to learn about these and other new features, in addition to the numerous enhancements implemented over the yearss.

There are two 'modes' of program operation: standard and professional. Standard mode disables many or the specialized, rarely used options and tools, thus streamlining use for novices or relatively casual users. Professional mode enables all options and tools, allowing meteorologists or other experienced users to take full advantage of WXSIM's great versatility. Standard mode retains the same price WXSIM has had for a year and a half, while there is an extra charge to enable professional mode. There are also now two levels of customization: basic and enhanced. More information about these options appears under ordering options.

To get a demo copy of the entire WXSIM family of programs, or to upgrade your existing system now, see the Downloads section.

Data provision

All data for ingestion into WXSIM (via the included tool WXSIMATE) is and will continue to be provided free of charge for the foreseeable future. (Note: I am planning to make the separate, special WXSIM-Lite data a low-priced subscription in the near future). Much of this (METAR, RAOB, SYNOP, ozone, etc.) is courtesy of various web sites, generally associated with universities or governmental agencies (mostly, but not entirely in the U.S.). Additionally, data from the GFS model (generally regarded as the second-best medium range model with global coverage, right behind the extremely expensive ECMWF model data) is downloaded and processed into custom datasets, four times a day, for each customized WXSIM site, on two servers - one in England and the other in the U.S. You can get the same types of GFS data, albeit less conveniently, from NOAA's READY site, should there ever be any interruptions in WXSIM's custom data stream (unlikely, with two independent sources).

Discussion board

See the Weather-Watch forum, operated by Chris McMahon (who also made the one of the GFS data sources mentioned above available), at This has been active for some time and there are quite a few discussions of ways to use WXSIM, as well as help with the program. Also, on WXSIM's "child" board "WXSIM Display Utilities", you can find how to post output on web pages, including translation into several foreign languages - for free! Thanks to numerous WXSIM users, including Ken True, for being so industrious as to come up with this!

Upgrade policy

Other than a one-time upgrade fee of $49 about 10 years ago, I have never charged upgrade fees for WXSIM or its (now almost essential) companion programs WXSIMATE and wret.exe. It is my full intention to continue this practice for the foreseeable future. There is a $40 registration fee for the optional tool Autolearn-WX, which runs wret.exe automatically on a schedule to simplify WXSIM's learning routine (which otherwise requires the user's attention for a few minutes to perhaps half an hour once a week or so). The new program WXSIM-Lite is provided at no charge, though, as mentioned under Data Provision above, I am likely in the near future to institute a small subscription fee (no more than $5 a month) for its data, to cover server costs and further development of this system, perhaps extending it to use other models in addition to GFS.

WXSIMATE data collection tool, Version 6.3

WXSIMATE is a very handy and time saving tool for collecting internet data as well as home weather station data, for easy import into WXSIM. It can now be scheduled to run automatically, to collect data for WXSIM even while you're asleep, and can also now gather local station data over the internet. A brand new feature is the ability to import data from Ambient's Virtual Weather Station, as well as from Davis WeatherLink, Brian Hamilton's Weather Display, and SandaySoft's Cumulus. Starting with Version 4.0, WXSIMATE allows import of ozone data from KNMI/ESA (

Many years ago, WXSIMATE could be considered an optional companion program to WXSIM. However, while it is still technically a separate program, it has become almost essential to WXSIM as it is most commonly used. For this reason, it is included with WXSIM as standard.

To see what's new in WXSIM, see New Features and Revision History. Also see News Briefs and the WXSIMATE section of this page. For a review of (an older version of) WXSIM, or if you wish to order there by credit card, take a look at Tim Vasquez's Weather Graphics page. I now accept orders through PayPal (including a credit card option), in addition to checks or money orders.

To download WXSIM 2017, for any Windows versions from the last decade, at least, either click here or go to the Downloads section of this page. This shareware program is exactly the same software as you have when registered (no time limits, and nothing disabled), but certain files must be customized with climatological and geographical data for your site to get full functionality. This customization (which takes me anywhere from 2 to 5 hours to complete) is a service that I perform upon receipt of your order, and I then forward the modified files to you. Upgrades of the main programs are free, and probably will be for the foreseeable future, though non-essential related or ancillary products may be developed from time-to-time (such as the new AutoLearn-WX tool). If you decide you want a new customization job, contact me at about reduced rates for re-customization.