1.2: Weather Maps and the Station Model

Weather Maps

While questions 1-3 have focused primarily on changes in temperature over time/place, there are numerous weather conditions that Meteorologists are concerned with. There is more to weather than just temperature! In fact, here are some of the other weather conditions commonly measured at weather stations:

• Humidity (Relative Humidity, Dew Point Temperature, etc)
• Cloud Cover
• Precipitation (Type and Amount)
• Wind (Direction/Speed)
• Barometric Pressure
• Other weather events (such as Fog, Smoke, Thunder, Tornadoes, etc).

Most weather stations measure most, if not all, of these conditions. The data is then distributed and presented in many ways to Meteorologists and to the public. One of the key ways that weather data is presented is through the use of weather maps. Meteorologists want to gain as big a picture of the weather (both locally and nationally) as possible. Thus, they need to view as much data as possible. There are many ways to do this, including having numerous weather maps, each with a single weather variable (temperature, wind direction, wind speed, etc) plotted on the map. However, that would quickly become very cumbersome. Imagine having to toggle between six or seven weather maps to get a decent picture of the overall weather for a region. Trying to view ALL weather data on a single map can also cause problems due to data cluttering. Weather maps provide a happy medium between too many maps and too much data on a single map. At first, a new reader may feel overwhelmed by the amount of information on a weather map. Meteorologists use these maps daily and have slowly gained years of experience understanding and studying the data displayed on weather maps. So make sure to take it slow, since we're just starting our journey.

Figure \(\PageIndex{1}\) is a weather map displaying data collected across the United States at 2200 UTC (3 pm Pacific Time, 6 pm Eastern Time) on June 26, 2020. Before moving on, take a moment to consider the different weather parameters from the previously mentioned list and how they can be represented on the map.

Figure \(\PageIndex{1}\): Weather Data for Continental United States at 2200 UTC on June 26, 2020. (CC BY-NC 4.0; American Meteorological Society via Unidata) Alternative description of image.

The Station Model

In Figure \(\PageIndex{1}\), you'll notice that the map is filled with many small circles, with some degree of shading, numbers on both sides of them, and barbs or flag poles sticking out of them. These symbols are called “Station Models,” and they provide a convenient way to display a large amount of weather data in a straightforward and user-friendly manner. It’s better than having to flip between numerous weather maps or list all the data from each weather station next to it in a tiny font. It may take you a few minutes to get used to the station model data, but using the guide in Figure \(\PageIndex{2}\), you’ll quickly become comfortable with decoding it.

Figure \(\PageIndex{2}\): The Station Model Guide showing air temperature (°F), dew point temperature (°F), symbols for precipitation, barometric pressure (mb), wind direction, wind speed, and cloud cover. (CC BY 4.0; Alicia Mullens) Alternative description of image.

Let’s take these one at a time: Figure \(\PageIndex{2}\) shows the different components of a station model.
The left side: Air Temperature is shown in the upper left, and Dew Point Temperature is shown in the lower left.

4. Go back to Figure \(\PageIndex{1}\). The observed air temperature at San Antonio in central Texas is:
   1. 77°F
   2. 159°F
   3. 70°F

5. The observed Dew Point temperature at San Antonio is:
   1. 77°F
   2. 159°F
   3. 70°F

Notice that between the two numbers on the left side is a series of dots representing precipitation. An excellent guide to precipitation symbols can be found in Figure \(\PageIndex{3}\) and Table \(\PageIndex{1}\).

Figure \(\PageIndex{3}\): The NOAA convention showing precipitation type and intensity on a station model. Table \(\PageIndex{1}\) presents a condensed version of the salient features from Figure \(\PageIndex{3}\) in tabular form.  (Public Domain; Station Model via NOAA/NWS)

Table \(\PageIndex{1}\): Precipitation symbols on a station model and their meaning.

Symbols	Meaning
One, two, or three solid dots in a column	Rain (light, moderate, heavy)
One, two, or three asterisks in a column	Snow (light, moderate, heavy)
A lightning bolt with a dot or asterisk	Thunderstorm (with rain, snow, or no precipitation)
An inverted triangle with a dot or asterisk	Shower (rain or snow)
Two short apostrophe-like marks	Drizzle
Curved lines resembling the number 2	Freezing rain or freezing drizzle
Triangle with a dot	Ice pellets or sleet
Two or three stacked horizontal bars	Fog (thin or thick)
Infinity symbol	Haze

6. Going back to San Antonio in Figure \(\PageIndex{1}\), the two dots along the station model indicate that ______ is occurring at this time.
   1. snow
   2. rain
   3. hail
   4. fire and frogs

The Middle: The circle in the middle of the station model represents cloud cover. The circle is shaded based on the amount of cloud cover currently present over the station. The more shaded-in the circle is, the cloudier the sky is. A guide to cloud cover shading can be found in Figure \(\PageIndex{4}\) and Table \(\PageIndex{2}\).

Figure \(\PageIndex{4}\): The NOAA convention showing cloud cover on a station model. Table \(\PageIndex{2}\) presents a condensed version of the salient features from Figure \(\PageIndex{4}\) in tabular form. (Public Domain; Station Model via NOAA/NWS)

Table \(\PageIndex{2}\): Cloud cover symbols on a station model and their meaning.

Symbol	Sky Condition Description
Open circle	Clear sky
Circle with thin vertical line	Few clouds (less than 12% cloud cover)
Circle one-quarter filled	Scattered clouds (approximately 25% cloud cover)
Circle half-filled	Partly cloudy (approximately 50% cloud cover)
Circle three-quarters filled	Mostly cloudy (approximately 75% cloud cover)
Completely filled circle	Overcast (100% cloud cover)
Circle with an "X" inside	Sky obscured (e.g., fog, smoke, or heavy precipitation blocking visibility)
Empty circle with question mark	Sky cover missing (data unavailable)

Based on this information, let's try to answer the following questions.

7. At the time of Figure \(\PageIndex{1}\), the cloud cover over Brownsville in southern Texas is approximately:
   1. clear
   2. partly cloudy
   3. mostly cloudy
   4. overcast

8. Along the Gulf Coast and southeastern United States, most stations ______ experiencing at least some varying amount of cloud cover.
   1. are
   2. are not

9. For example, Brownsville, in southern Texas, Little Rock, in Central Arkansas, and Tallahassee, on the Florida Panhandle, are all experiencing ______ skies.
   1. clear
   2. partly cloudy
   3. mostly cloudy
   4. overcast

The long pole with feathers sticking out of the center circle represents Wind Direction (the pole) and Wind Speed (the feathers at the end of the pole). The Wind Direction is defined by where the wind is coming from (WARNING: This is different than typical convention, where the direction of movement is often defined by where something is headed towards), and the long pole points to the direction of oncoming wind (similar to a needle on a compass). For example, at Bownsville, TX, the wind is blowing FROM East-Southeast since the long pole is pointing right and slightly down. Is there an equivalent in the table?

10. The wind at San Antonio, TX in Figure \(\PageIndex{1}\) is coming FROM the:
    1. north-northeast
    2. south-southeast
    3. west-northwest

The feathers at the end of the pole have nothing to do with wind direction. Instead, they indicate wind speed. One long feather represents a speed of 10 kts (knots, or nautical miles per hour… 1 kt = 1.15 mph… knots are commonly used in Aviation, Sailing, and other travel/trade related industries), while a short feather represents 5 kts. The short feather is always placed slightly away from the end of the pole to make it easier to differentiate from the long feathers. The total number of feathers represents the wind speed. For example, at the time of Figure 3, Brownsville’s station model had one long feather and one short feather, representing a speed of 15 kts. In contrast, in Amarillo, TX, the furthest north station on the Texas Panhandle, had two long feathers, representing a speed of 20 kts.

11. The wind at San Antonio in Figure \(\PageIndex{1}\) has a speed of:
    1. 5 kts
    2. 10 kts
    3. 15 kts
    4. 20 kts

Sometimes, the wind is calm (meaning there is no wind blowing), and when that occurs, you will see a circle surrounding the station’s circle. In general, the winds over the continental United States (excluding Alaska and Hawaii) can be represented using the long and short feathers mentioned previously. However, sometimes the winds may be so strong that an additional symbol, a triangular pennant (representing 50 kts), may be necessary and is placed at the end of the pole.

The Right Side: While some station model guides may include various information (such as pressure trends and accumulated precipitation), we will focus only on the three-digit number in the Upper-Right side, which represents Sea Level Air Pressure. This is the air pressure that the location would have at Sea Level, accounting for the location's altitude. Air Pressure is another common weather quantity that the weather app on your phone will tell you about. Air pressure is the force exerted by the weight of the air above a given area of the Earth's surface. Think of our atmosphere as a giant ocean. But instead of water, it is filled with air. If you've ever tried to swim along the bottom of a swimming pool, you may have felt the higher water pressure near the bottom. That's the weight of the water above pressing down on you. Similarly, as we live on the floor of the great ocean of air that is our atmosphere, the weight of the atmosphere presses down on us each day, and we call it air pressure. We'll learn more about air pressure in Investigation 6.

Similar to other weather quantities, such as temperature and relative humidity, air pressure changes depending on geographical location and time of day. Thus, to identify locations of high/low pressure and other weather systems (such as fronts), every surface map calibrates, their location to sea level (to remove elevation’s influence on air pressure). At sea level, average pressures typically range between 950 millibars (mb) and 1050 mb. However, this number can become large and cumbersome, considering how complex the map already appears. So Meteorologists often abbreviate it on a station model by removing the first digit (or two digits). To convert the three-digit number to an actual sea level pressure, a two-step procedure is needed:

• Step 1: Focus on the 3-digit number:
  • If the 3-digit number is LESS than 500, place a 10 in front of it.
  • If the 3-digit number is EQUAL to or GREATER than 500, place a 9 in front of it.

Example: The number 149 on the right side would be converted to 10149 by placing a 10 in front, and 549 would be converted to 9549 by placing a 9 in front.

• Step 2: Place a decimal (“.”) between the last two digits: Air pressure doesn’t vary much at sea level, so Meteorologists want to notice the slight differences to identify variations. As a result, they commonly round air pressure numbers to one decimal place. Example: 10149 would be converted to 1014.9 mb, and 9549 would be converted to 954.9 mb.

12. Returning to San Antonio, the sea-level pressure at San Antonio at the time of Figure \(\PageIndex{1}\) is:
    1. 159 mb
    2. 915.9 mb
    3. 1015.9 mb
    4. 115.9 mb

13. On the other hand, Grand Junction, in Western Colorado, has a “071” in the upper-right corner of its station model, indicating a pressure of (hint: don't drop any of the digits. Keep and work with all three of them, including 0. So 071 IS NOT 71).
    1. 71 mb
    2. 907.1 mb
    3. 1071 mb
    4. 1007.1 mb