Reading Surface Maps

If you’re watching the local news you’ve probably noticed a few red L’s and blue H’s, red and blue lines, and random white lines on the tv screen. But what do they mean?

A surface map is no longer in the upper atmosphere, but well, at the surface of the earth (or at least close to it).

Over the past few blog posts we have worked our way down the atmosphere and now we are at the final stage! The Surface.

This is where meteorologists see air masses change at the surface, the rain will fall, and winds impacting daily life.

Surface analysis. Courtesy: NOAA

In the map above you’ll notice that there is a lot going on. There’s the red and blue lines, highs and lows, and random numbers all over the place. Each of these features is actually really important.

We’re only going to scratch the surface on what these mean as we will discuss in later blogs, but for now…

Looking at the blue lines. These are cold front. These indicate that cold air is moving in. This separates warm air from cold air. Notice the arrows on the blue line? These lines are drawn in the direction the cold front is moving. Meaning, if your ahead of the front, you’re probably expecting to cooler air to move in soon.

When I say colder air that doesn’t necessarily mean a big difference in temperatures, it can only mean a few degree difference at times. It depends on the strength of the front.

The red lines are just the opposite. These are warm fronts. These indicate that warm air will likely be moving in. This also separates warm air from cold air. Instead of arrows, warm fronts are drawn with half circles and also drawn in the direction that the air mass is moving towards.

Warm air masses move much slower than cooler air. So you can probably expect that the warm and cold fronts can occasionally collide and this will create an occluded front. This will be drawn in purple and shown with both features from a warm and cold front.

If you’re in the area between the warm and cold front that is called the warm sector.

Now to the H’s and L’s. These are simply high and low pressures on the map. We have discussed these at the higher levels in the atmosphere and are associated troughs and ridges.

Now at the surface… a highs pressure is the center of a high pressure circulation. A low pressure is the exact opposite. A good rule of thumb is to associate a highs pressure with nice weather and lows with cloudy skies and often times rain.

A high pressure flows in a clockwise circulations and will often times flow to areas of low pressure. Air from above will move in or sink and from there the circulation will spread the air outwards since it has nowhere else to go.

A low pressure flows in a counter-clockwise motion and feeds air up to the atmosphere since it circulates air inward at the surface or an upward motion.

Motion of high and low pressures. Courtesy: wisc.edu

In the picture above, you can see such features as to why the air sinks in a high pressure at the surface and why a low rises with it’s air circulation.

If you’re looking at a surface analysis there are also other fronts that develop and may get more complicated at times. There are fronts know as drylines, stationary fronts, and double barrel lows. It can get very complicated and we will continue to discuss these features in following blog posts.