Reading Weather Observations

By the time you see a weather map it probably looks very simple, but in reality there’s a lot going on before a meteorologist simplifies the graphic.

As already mentioned in the previous blog posting there may be high, lows, and fronts drawn on a map, but what about the science behind all of that?

Down on Earth’s surface there are weather observations taken from thousands of different weather stations, but how does all of that information get used? And trust me it does. Meteorologists and scientists are very grateful for the amount of information we get from the public because it does help a weather forecast.

If a weather station reports information, not just for personal use, it’ll probably be graphed into something that looks just like the graphic above. A bunch of weird symbols and numbers that probably doesn’t make much sense now, but will by the time you’re finished reading this it will.

Every single group of information is a different weather observation and within that group tells you the temperature, dew point, wind speed and direction, and the type of weather that’s going on.

Surface Observations. Courtesy: NOAA

The above photo is a single data point and as you can see it tells a lot to the weather story.

Starting at the top left: That is the current temperature that the thermometer is reading. The bottom left is the dew point. These are both read in degrees Fahrenheit at the surface. (If it were in the upper atmosphere, when a weather balloon reports data, it will be observed in degrees Celsius).

The symbol between the temperature and dew point is the observed weather. This is based on what’s happening at the time of observation… usually at the top of the hour or a few minutes beforehand.

Weather symbol observations. Courtesy: NOAA

There are a lot more symbols than just this, but you can get the general idea.

Heading over to the right side of the weather observation graphic you can see that this deals with pressure. This is plotted in millibars, not inches of mercury, and a few numbers are dropped in order to simplify the graphic. On this graphic the pressure is reading as 107. This really translates to 1010.7 mb. The first 3 digits shown are the first 3 in the number. It is either a 10 or 9 added to the front of the number when deciphering the pressure.

If the number is generally shown with a 9 or 8 first the likely addition to the pressure will be you adding a 9 to the beginning. The opposite occurs when its a lower number. For example. Say the pressure read 309. Unless there’s a really strong storm you probably won’t add a 9 making it 930.9 mb. You’ll probably add a 10, making it 1030.9 mb. This would lead an area of high pressure.

The observation below the current pressure is the change in pressure over the past 3 hours. Indicated by rising or falling pressure levels. This shows a change in the weather may be coming soon. The symbol also changes based on how the trend in the pressure has been changing.

Change in pressure symbols. Courtesy: NOAA

There’s two rhymes and reasons to this. Notice there’s a kink in each one? It’s showing what has happened to the pressure so far over the past 3 hours.

The last bit of information in a weather observation is the center… the winds and sky cover.

See the clear circle in the center? That’s showing a clear sky at the time of the observation. If it were full or colored then it’s a cloudy sky. Show it half and half then partly cloudy. A quarter? Then some clouds there and there. Then 3/4 full. Mostly cloudy.

The wind barb is next. This is the line that sticks out and has little lines attached. The direction of the wind barb shows what direction the wind is coming from. In this case, it’s point from the northwest direction. Meaning a northwest wind. The strength of the wind is also 15 knots.

There is a long stick and a short stick. Each long stick represents 10 knots and a short stick indicates 5 knots. Add each one together and you have the total wind speed. If it’s a full triangle, then 50 knots is being observed. Just a circle then calm winds.

Wind observations. Courtesy: NOAA

The above graphic shows just how it could exactly look like when on an observation plot.

From all of this information you can then decipher what type of weather you are observing at your location, what type of weather may be coming, and if you are in a high and low pressure system. Of course, some of this may take more time to figure out with further analysis.

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