How to Read a Weather Surface Chart - Part 1
Do Weather Surface Charts just look like so much Chinese food to you? With weather in Baja often very regional, it is helpful to be able to interpret a surface chart to determine the weather in your locale.
What is a Surface Chart? ( Click here to see the current Eastern Pacific Surface Chart) It is a map of weather conditions and forecasts for the next period. According to Answers.com a Surface Chart is as follows:
"An analyzed synoptic chart of surface weather observations; essentially, a surface chart shows the distribution of sea-level pressure (therefore, the positions of highs, lows, ridges, and troughs) and the location and nature of fronts and air masses, plus the symbols of occurring weather phenomena, analysis of pressure tendency (isobars), and indications of the movement of pressure systems and fronts. Also known as sea-level chart; sea-level-pressure chart; surface map. "
The most noticeable features on a Surface Chart are the High and Low pressure systems. Indicated by large letters, and when in color Highs are blue and Lows are red. In the northern hemisphere High pressure systems orbit clockwise, Low pressure systems orbit counter-clockwise. Movement of a Low pressure system is indicated by an arrow indicating direction of movement and a 
, located at the forecast position of the system at the end of the forecast period. Movement of a High is also indicated with an arrow of direction of movement and a 
. The direction of movement arrow is sometimes omitted if space doesn't allow. If the system is not moving "STATIONARY" is usually printed next to the system. The current barometric pressure reading for the system is indicated in millibars located usually above the symbol and underlined, (i.e. 1006). The future barometric pressure can be indicated by an underlined two digit number, near the future location of the system (i.e. 04 ) If the system is new, rapidly strengthening or this can be indicated with the written words such as "DISSIPATING, NEW or RAPIDLY STRENGTHENING" Hurricane strength conditions are indicated with "XX".
The reason our Eastern Pacific Hurricane usually move off into the Pacific is this counter-clockwise rotation of 
these extreme Low pressures. Like a rolling tire, the rotating action drives them to the southwest. Other environmental factors push them more to the north, and as the northern hemisphere cools the jet stream pushes them back toward the northeast and sometimes into Baja after late July.
Isobars are the long lines forming unusual shapes on a surface chart. and are directly associated with Highs and Lows and relative barometric pressures. indicated in solid or dotted lines, brown on color charts, these are rough demarcations of barometric pressure, taken from reporting stations. The closer together the lines, the greaterthe wind in that area. Wind does not blow parallel to these lines, because of the earth's rotation, but slightly off a
xis to a point of lower pressure. In the case of intense winds "DEVELOPING GALE" or "GALE" will be written on the chart.
Fronts are a very visible and important feature too, although not usually for hurricane weather. (although Tropical Waves are a form of a front) In a color chart cold fronts are indicated in blue, Warm fronts in red, stationary fronts in red and blue and occluded fronts in purple. Fronts are a line, indicating position of the front. Warm Fronts have semi-circles, Cold Fronts triangles and stationary fronts have both. The side of the line on which the added symbols exist indicate the direction of flow from the front. Stationary fronts have both semi-circles and triangle on opposing sides of the line, indicating that the front isn't moving. Occluded front is where cold air has overtaken a warm front, using both triangles and semi-circles in purple, indicating the movement of the front.
Station reporting symbols are perhaps the most complicated and information packed little items on a surface chart. If you know the 'code' you can tell wind direction, wind speed, temp, dew point, sky and precipitation condition of each provided plot. In our next Hurricane Watch Report we will take a look at that tiny little type and symbols within a symbol and other surface chart features.
Today's surface charts are available from the US National Weather Service. A world wide detail chart is located here and a Eastern Pacific Basin Surface Chart is located here.
The first surface charts were created in the middle 18th century from information from reporting stations. Through much of weather forecasting history most of the tools used to predict the weather come from each of these stations. It is only in recent years that satellite imagery, radar and other high-tech tools have supplanted the station report as the most valuable tool in forecasting. Today, through the internet, the National Weather Service also takes in data from thousands of civilian weather stations, connected to home computers around the globe. There are more than 
650 civilian reporting stations in Los Angeles alone. This large number of data points are obviously not plotted on the weather charts we see here, but add to the amount of data and understanding of weather anomalies and future forecasting techniques.
Therefore, it is arguably said, that the station model is the most important weather feature on a surface chart, as almost all other features are drawn from its data. The station model is in fact, jam packed with lots of information in a tiny little space. Unfortunately, to conserve space on the map one needs to write in code. Station models are coded to express almost all weather phenomenon. From the station model ascertain weather closer to you and if you are a sailor, predict the best course to plot for the wind and seas.
Station models are also probably the most prolific of all features on the surface chart as well. Looking like so many tiny golf course flags scattered haphazardly across the map, most are airports and military installations with calibrated instrumentation. Some reporting stations are ships as the example above shows. This is most likely the US Coast Guard Cutter running interdiction off the coast of Baja. There is also a seemingly endless number of symbols applied to Station Models and we will cover the most significant. There are so many different symbols that in my research I did not find one site that defined all of them. (here are some of the best examples found... Station Model Symbols01 Surface Model Symbols02 and Station Model Symbols03)
The graphic left shows a majority of the information provided in a standard Station Model. Click in the descriptive titles to learn more about each of the weather characteristics encoded in a Station Report.
There is additional data that can be included in the Station Model, but these are the most common and most useful to those using surface charts to predict the weather in their area.
The first frame shows a semi-complete Station Report. By clicking on Layers 1 and two you can view the definitions of each of the code locations.
If you want to test your understanding of Station Reports and Surface Charts click here to see the World Detail Surface Chart for today (3mb PDF)