Model and forecast your local weather on your own computer!

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

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

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Ordering Information
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Updated May 11, 2014

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.


WXSIM Version 12.12.1 Released!

Including WXSIMATE 5.5 and optional new Autolearn-WX 1.4

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

Also, see the multi-site controller program WXSIMPRO.

Version 12.12.1, in combination with WXSIMATE 5.5, has significant improvements since versions 12.11, including improved use of archived data in the "learning routine". Other improvements in the last several version include a suite of agricultural data (active only in professional mode), such as soil temperature and moisture, evapotranspiration, and various heat transfer rates of interest especially to soil scientists. See New Features and Revision History to learn about these and other new features, in addition to the numerous enhancements implemented over the last few versions.

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.

Other improvements to WXSIM over the last few years include:

If you haven't tried the program since versions 10.x, you're in for a number of other pleasant surprises, including automated downloading and forecasting and the ability to directly compare forecasts with actual results from home weather stations. Also, see below concerning the new version, 5.5, of WXSIMATE. You can now order directly from this site. To learn what's new, see New Features and Revision History . To get it now, see the Downloads section. NOTE: installing this version will NOT overwrite versions prior to 10.0, so you can safely try it out in parallel with pre-10.0 versions (it goes in the same directory, but uses different file names).

Data provision

All data for ingestion into WXSIM (via the included tool WXSIMATE) is provided free of charge. 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). As of now, there are no subscription fees for any of these, nor any plans for such fees. If it ever does become necessary to cover these costs other than through new sales (which is what has been the case for many years), any subscription fees will be truly nominal (less than $20 per year), and the READY data alternativewould remain free anyway. There is an option for donations (on the Donwnloads and ordering page - appreciated but certainly not expected!) for defraying expenses such as those associated with processing this data, but the costs are small on a per-user basis.

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

Before Version 10.0, I hadn't charged an upgrade fee in at least 7 years, through over 50 steadily improving versions. Versions 10.0 and 11.0 were major upgrades, though, so if you are upgrading from a pre-10.0 version, there is a one-time fee of $49. This will get you a unique registration code which will unlock the program for use with your existing custom site; otherwise it will default to Atlanta. I am offering an optional accessory, 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). Autolearn does have a $40 registration fee, though it can be run in a sub-optimal demo mode at no charge.


Also, the WXSIMATE data collection tool, Version 5.5 available for download as an integral part of the WXSIM system.

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 (

In the past, 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 now packaged and sold with WXSIM.

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 Version 12.12.1 of WXSIM, 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. Note to current users: As always, you can easily upgrade from this site. After the $49 upgrade to 10.x or 11.x, upgrades of the main programs are free, and probably will be for years, 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.