WX-SIM Professional Price: $249.00 Availability: Electronic delivery

WX-SIM Standard Price: $129.00 Availability: Electronic delivery

Say goodbye to cheap programs that use your barometer to forecast the weather. It's not the 1950s anymore!

Nowadays your personal computer has the power to use your observed weather together with atmospheric equations to predict weather at your exact location. We are delighted to present WXSIM, the Weather Simulator. WXSIM is the cream of the crop for single-station forecasting and is a vital tool for all forecasters -- hobbyists and professionals alike.

WXSIM is the creation of Tom Ehrensperger. Living in Atlanta, Georgia, Tom, who has an M.S. degree in physics, first developed WXSIM in 1983, drawing upon his physics and math knowledge to create a sophisticated forecasting program. Tom has gradually tweaked it over the years, adding extensive physical parameterizations of the atmosphere. There's all sorts of uses for WXSIM, from playing "god" with your local atmosphere to finding out whether your tomatoes are really in any sort of danger from an overnight freeze.

Tom Ehrensperger creates WXSIM copies individually for each customer, consulting his climatology references to tweak the program to accurately represent your station's climatology, vegetation, and terrain. This way the program can best parameterize the atmosphere for your particular microclimate. You have some control over this via a slider bar.

When Tom set up my review copy, he researched his references and even asked for additional info: "I'll need to know about any characteristic differences you may have noticed from Oklahoma City, especially in overall temperature and in diurnal range, mainly in clear weather with light winds. For example, I'm only about 3-4 miles from Atlanta, but on a calm clear night am generally 2-4 degrees cooler, and about the same as Atlanta in the afternoon, except in summer, when I'm a couple of degrees cooler - these being differences due to vegetation vs. pavement (and jets!) and local topography (I'm about 50 feet lower and deeper in the inversion at night)."

Within a couple of days Tom E-mailed me a customized version of the program, all ready to go. Here's what it looked like!

	Data entry When I first loaded up the program, I saw panels for time, temperature, pressure, wind, clouds, and local effects. With it being a scorching hot August morning in Oklahoma, I looked at my Davis weather station (Monitor II with all sensors shielded and properly sited) and adjusted everything I could find. I set the temperature to 90, the dewpoint to 62, the pressure to 30.04 inches, and the wind speed to southwest at 6 mph. The sky was clear, and I set the haze to "autohaze" (which estimated a visibility of 13 miles). I also set "recent precipitation" to zero for the entire week so that WXSIM could accurately figure the soil moisture and adjust temperatures accordingly. I then chose Start > Test For Midpoints. The program checked all my entries. Then I chose Start > Calibration Run. NOTE -- You can click any of the sample images at left to get a larger, clearer version.
	Upper Level Data Verification A menu popped up titled "Upper Level Data Verification", prompting me to enter anything that I knew about the upper level winds. I played dumb and assumed I knew nothing, but it already seemed to have a very good idea of the upper level conditions based on current weather, typical lapse rates, and principles of hydrostatic balance. The upper air panel lets you easily and quickly adjust the atmospheric profile to reflect current conditions from radiosonde observations. The window starts out with a basic guess derived from climatological and observed values, including given cloud cover and more. Changing the temperatures within any of 5 layers or the dewpoints in the lowest 2 layers is as easy as moving a slider bar. Satisfied with a basic first-guess, I clicked OK without changing anything.
	Advection Data Entry Next came a window titled "Advection Data Entry". I was asked anything I knew about weather at surrounding stations. This way, WXSIM could account for changes upwind that might affect the weather here. The interface has the ability to import METAR data from any surrounding sites. Once again I played dumb and clicked OK without changing anything.
	Interrupt Planner Next came the Interrupt Planner window. This interface allows you to insert any meteorological expertise you may have, and "force" the occurrence of rain, a wind shift, thickness (such as from the ETA or NGM runs), and make any other changes. Then again, if you have absolutely no forecasts to go on, it's expected that you'll leave this window blank. The interrupt window uses a time series graph -- you simply click the mouse on the time graph to introduce a parameter or change its trend. Introducing rain is as easy as clicking on "precipitation", then painting out its approximate intensity as a time series. Additional parameters can be changed on-the-fly during the forecast run. Yet again, eager to see the basic accuracy of the program, I played dumb and clicked OK.
	Stunning forecast accuracy Finally comes the eagerly anticipated Output Window. WXSIM spent a few seconds plotting an incredible graph and a lengthy text summary of the future weather. How did it do? Check out this graph. The accuracy floored me. It predicted a high of 103.8 (actual was 103.6), and its hour-by-hour temperature forecast error during the day was usually not more than 1 degree. It also accurately forecast the onset of cumulus clouds at 2:30 pm (actual was 2:00 pm). The accuracy remained around 1 degree or less until dusk, when a weak cold front passed through. It would have been quite interesting to see how the advection parameterizations handled the cold front. Needless to say, even on a benign weather day during a heat wave, WXSIM showed its remarkable ability to accurately predict conditions using minimal amounts of data. Forecasters will like using the program to refine their spot temperature forecasts, and pilots will love how it provides an accurate estimate of density altitude later in the day. Although WXSIM can't tell when rain will start or when a cold front will arrive, its proven capability as an reliable physical model is certain to help forecasters fine-tune nearly any forecast. Some detailed studies done by the author during a 3-month period in early 1999 showed that WXSIM had an accuracy out to 48 hours on par with NGM and AVN output as well as NWS zone forecasts (of course this is when making full use of WXSIM with its advection and upper air parameters). Its best accuracy was, not surprisingly, in the short term time frame (less than 12 hour) where it beat the NCEP models and NWS forecasts. Naturally WXSIM is not a large-scale model since it cannot assimilate and forecast data over multiple regions, however it can "see" nearby weather systems through its use of the advection window. Since it is a short-term model, this type of simple input goes quite far in delivering the accuracy that WXSIM offers.
	Data Review WXSIM also allows you to review the predicted data in time graph format. Click on any forecast time point to see a detailed graph of atmospheric conditions.
	EXAMPLE: Freak snowstorm It's a forecaster's worst nightmare: rich mid-level moisture, dry boundary-layer air, and near-freezing temperatures. This combination has blown hundreds of forecasts throughout the years. Abilene in January 1995 and Oklahoma City in January 2000 come to mind. WXSIM's accurate thermodynamic modelling gives you a good idea of how much cooling will occur and how the precipitation will develop. All you need is a reasonable estimate of radar-indicated precipitation rates. In the example at left we used a slightly unstable lower troposphere, solid altostratus cover, an afternoon temperature/dewpoint of 40/22, and a rainfall rate of 0.50" per hour starting at 6 pm. The illustration shows how much a cloudy 40-degree day can change, without any thermal advection!
	EXAMPLE: The Dark Day of 2000! It was an incredible day in history: on Wednesday August 16, the sun simply failed to appear in the sky! Experts are baffled! How cold did it get? Did any weather occur? WXSIM's powerful capabilities helped us recreate the chilling events of that mysterious day. (This is a fictional scenario that illustrates WXSIM's capabilities) Click here for the details