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Boston Weather: 37.0°F | A Few Clouds

Weather: Coping with Inadequacy

By Greg Lawson

How well can we predict the weather? That is not such an easy question to answer. Personally, I am not that great at it, but the answer to the question does not really address individuals; rather it asks how well do the numerical models we run predict the weather. In practice humans provide mere second-order corrections to a first-order forecast from a computer.

So how well do computers forecast the weather? Again, it is difficult to say as it depends on how we choose to verify the forecasts. While there are published studies that indicate forecasts are mostly correct on average, it is also clear that forecast success on a day-by-day basis is highly variable. This is mainly due to the nonlinear evolution of our atmosphere and the inadequacies we have in describing that evolution.

A relatively recent technique for addressing these inadequacies is ensemble forecasting through which several forecasts are made for the same time period, each differing by some perturbation thought to be representative of the inadequacies. The hope is that the mean of this ensemble will be close to the truth and that the spread among the ensemble will give information as to which features of the forecast we are most certain of.

It just so happens that the ensemble forecasts for the upcoming week are in wide disagreement about this coming Wednesday night/Thursday morning. It is possible that we will have a large storm with moderate precipitation, possibly even snow; however, it is almost as likely that it will pass to our south and we will receive only cold temperatures and high winds. This is an example of probabilistic forecasting, and unfortunately, as of now, all I can offer is advice to be prepared.

Today: Partly cloudy and pleasant. Westerly breeze. High of 51°F (11° C).

Tonight: Scattered clouds and cool. Low of 36° F (2° C).

Wednesday: Mostly clear day with a high of 48° F (9° C). However, clouds roll-in in the evening and temperatures drop. Winds pick-up. 50 percent chance of precipitation, possibly snow. Low of 32° F (0° C).

Thursday: Overcast and cold. Precipitation could continue into afternoon. Windy with highs in the upper 30s (2-4° C). Low around 30° F (-2 - 0° C)

Friday and beyond: Clearing-up and chilly.