# What is the easiest way to forecast future weather?

Meteorologists forecast future weather using a variety of principles. One of the most important is advection. How does it work? The kinetic concepts are quite simple.

The wind blows. It might carry a cloud of dust or smoke across the sky.

Similarly it can can transport a pool of warm or humid air, or that defined by some other attribute. That's advection.

We forecast future weather over the short term by talking about advection of gradients. A gradient is an abrupt of change in temperature or other property over a short distance. These boundaries exist near the edges of the warm or humid air masses and fronts, for instance.

What happens when such a front passes over? As Bob Dylan once said…

The Times They are a-Changin'

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Get with the changing times? Here's how I did it….
I still had to work at it, but it didn't seem like work.

## When do we have advection, to forecast future weather?

It's easier to tell when we don't.

1. No wind,
3. Wind blows across rather than along the gradient,
And cannot move it. As math geeks would say, the dot product is zero. In other words, the dot product between the velocity and gradient vectors.

It then becomes easier to forecast future weather. Just predict little or no change on the immediate term, because the two sets of contours are nearly parallel.

## What contours?

Here is an example of upper winds advecting fronts.

Look at a map used to forecast weather. The pressure, the upper wind field would appear as a set of roughly concentric curves or swirls centered about some point.

At the same time the temperature field, if that is what we are examining, would be represented by a separate set of isopleths, called isotherms. They would surround a nearby spot.

Imagine the temperature gradient mentioned above as an arrow cutting straight across the isotherms and pointing downstream. Naturally, you would expect the two sets of contours to cross each other at several points in this case.

As a science project idea to help you visualize this, sketch two bulls eye patterns near each other on a piece of scrap paper. Maybe similar to this design below. Where the lines cross, they should form several small-area parallelograms, little four-sided boxes.

The smaller these so-called solenoids appear on the weather map, the stronger the advection. The faster the temperature will change in this example. The predicted weather can be spectacular when this happens. With high winds or storms in the outlook, severe weather can be expected.

Is it getting warmer or colder? Look upstream on the wind contours to and see if the incoming air is warmer or colder. Remember, wind flow goes clockwise around a high pressure center and counter-clockwise around a low. Go back from Forecast Future Weather to the Forecast Map Weather webpage.

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