Correction of model output to forecast – 95.5 WSB

Let me share a couple of quick examples of things a meteorologist does to improve the model output when forecasting the weather.

A meteorologist is trained to know how the atmosphere works in the real world, so when the computer models show things that don’t make sense in terms of atmospheric physics (which they often do), then the forecaster knows to adjust and correct the model and ignore things it shows that are probably wrong.

In the ECMWF model, the forecast below the green circled area on the 500 mb jet stream plot is favorable for upper-level shortwave disturbances triggering thunderstorm clusters, sometimes squall lines, complex convective mesoscale or even a Law. However, being imperfect, the model’s rainfall forecast (right panels) is for drier than normal weather. So a meteorologist crosses that off (X) and makes a normal to above normal rain forecast, ignoring the dry forecast from the models.

But automated weather websites and phone apps would only show you the wrong model forecast, so you would be misled. The same is true for model forecasts of temperatures and snow/ice, etc. A trained meteorologist doesn’t just say that what the model shows must be the forecast. People look at an APP and mistakenly think… that must be what every meteorologist forecasts. No no and no.

You can see from the actual rain check below that the model went out to lunch, it wasn’t dry in area X:

So when the website or app you use is constantly changing or giving you a false forecast, don’t blame the meteorologists unless you check with one, we have nothing to do with WEB or APP forecasts.

The same goes if you get a broken forecast from a meteorologist, that DOES NOT MEAN that all the meteorologists had the exact same forecast. Before I retired, my forecast was routinely some or a lot different from other tipsters. There were even people who criticized me for a bad prognosis when they had not heard or seen MY prognosis, simply fictional mine was like the one you saw. The public may have no idea how this works lol smh.

ANOTHER EXAMPLE:

In the model output below, there is a HUGE difference in rainfall forecast between the two main global model equations.

Where the two models locate the most humid climate and the driest climate is very different in much of the country:

Wet or dry?

A good meteorologist does not blindly accept the model output as a forecast.

How do you know which one is correct? Or if both are wrong?

Instead, I would use research, my background in meteorological physics, synoptic weather pattern recognition, known model biases and shortcomings, and years of experience to fix and adjust the models to make my own forecast.

Your website or weather app does not and CANNOT do that!

And do you know what model your website or app uses? Do you know when to trust them and when not to?

In easy patterns apps will be fine, and many use radar and just move rain or snow forward for a number of hours and that can work, but only AFTER precipitation has already formed and is moving through of the area. But that is an extrapolation and not a true forecast of the future when the radar is still clear.

So now you know a lot more than most of your friends and family about weather forecasts.

For more information, follow me on Twitter @MellishMeterWSB.

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