Learning how to read weather maps
Meteorologists put symbols on weather maps to show what is happening at different locations. They use a set of symbols. Numbers indicate temperature, dew point and air pressure. The numbers are located around the symbol for clouds and wind. The symbol for cloud cover is a circle. A filled in circle is a clear sky. A circle that is blank inside is a sky totally covered by clouds or overcast. The wind symbol is a line coming out of the cloud circle. It points in the direction that the wind is coming from. The line has little lines coming off of it are called barbs. Their size indicates the speed of the wind.  Look at the diagram with the Weather Map Symbols and each diagram that looks at one symbol or number.

Temperature
The value located in the upper left corner (in the diagram above) is the temperature in degrees Fahrenheit. In this example, the reported temperature is 64 degrees.

Observed Weather
The symbol indicates the type of weather occurring at the time the observation is taken. In this case, fog was reported. If there were thunderstorms occurring when the observation was taken, then the symbol for thunderstorms would have appeared instead.
  
Dew point
The value highlighted in yellow located in the lower left corner (in the diagram above) is the dew point temperature in degrees Fahrenheit. In this example, the reported dew point temperature is 58 degrees.

Dew points indicate the amount moisture in the air. The higher the dew points, the higher the moisture content of the air at a given temperature. Dew point temperature is defined as the temperature to which the air would have to cool (at constant pressure and constant water vapor content) in order to reach saturation. A state of saturation exists when the air is holding the maximum amount of water vapor possible at the existing temperature and pressure.

When the dew point temperature and air temperature are equal, the air is said to be saturated. Dew point temperature is NEVER GREATER than the air temperature. Therefore, if the air cools, moisture must be removed from the air and this is accomplished through condensation. This process results in the formation of tiny water droplets that can lead to the development of fog, frost, clouds, or even precipitation.

Relative Humidity can be inferred from dew point values. When air temperature and dew point temperatures are very close, the air has a high relative humidity. The opposite is true when there is a large difference between air and dew point temperatures, which indicates air with lower relative humidity. Locations with high relative humidity indicate that the air is nearly saturated with moisture; clouds and precipitation are therefore quite possible. Weather conditions at locations with high dew point temperatures (65 or greater) are likely to be uncomfortably humid.

Cloud Cover
The symbol indicates the amount of cloud cover observed at the time the observation is taken. In this example, broken clouds were reported.
Use the diagram to learn the symbols for other cloud cover.

Sea Level Air Pressure
The value highlighted in yellow located in the upper right corner (in the diagram above) represents the last three digits of the observed pressure reading in millibars (mb).

Interpreting the pressure number.  
If the reported value is greater than five hundred then the first number nine is missing. Add a nine on the left, then divide that number by ten. For example, eight hundred and twenty seven becomes nine hundred and eighty two point seven millibars. 

If the reported value is less than five hundred then the first number ten is missing. Add a ten to the left, then divide that new number by ten. For example if the example says air pressure is zero twenty seven, it becomes one thousand and two point seven millibars. 

Wind
The symbol highlighted in yellow (in the diagram above) is known as a "Wind Barb". The wind barb indicates the wind direction and wind speed.

Wind barbs point in the direction "from" which the wind is blowing. In the case of the example, the orientation of the wind barb indicates winds from the Southeast.

Wind speed is given here in the units of "knots.Ó A knot is a nautical mile per hour. One knot equals one point one five miles per hour. Each short barb represents five knots and each long barb ten knots. A long barb and a short barb together is fifteen knots, simply by adding the value of each barb together (ten knots plus five knots = fifteen knots). If only a station circle is plotted and no line, the winds are calm. Pennants are fifty knots. 

Practice Reading Weather Maps
Use the diagram and explain what the weather is at the different cities in the diagram. 


Precipitation Along a Cold Front
As the front advances, the colder air lifts the warmer air ahead of it. The air cools as it rises and the moisture condenses to produce clouds and precipitation ahead of and along the cold front. In contrast to lifting along a warm front, upward motions along a cold front are typically more vigorous, producing deeper clouds and more intense bands of showers and thunderstorms. However, these bands are typically quite narrow and move rapidly just ahead of the cold front. So you donŐt have the rainy weather for too long. 

Write a paragraph describing how precipitation develops along a cold front. Be sure to keep in mind the following points: 
the shape of the cold front (vertical structure) 
strength of the air moving up 
location and intensity of precipitation 
types of precipitation that commonly develop along cold fronts 


Precipitation Along a Warm Front
A warm front is defined as the transition zone where a warm air mass is replacing a cold air mass. Warm fronts generally move from southwest to northeast and the air behind a warm front is warmer and more moist than the air ahead of it. When a warm front passes through, the air becomes noticeably warmer and more humid than it was before. The frontal zone slopes up and over the colder air mass ahead of it. Warm air rides along the front (up and over the cold air mass), cooling as it rises, producing clouds and precipitation in advance of the surface warm front. Because the lifting is very gradual and steady, generally wide spread and light intensity precipitation develops ahead of a warm front. This rainy weather can last several days. 
 
Write a paragraph describing how precipitation develops along a warm front. Be sure to keep in mind the following points: 
the shape of the warm front (vertical structure) 
strength of the air moving up 
location and intensity of precipitation 
types of precipitation that commonly develop along warm fronts 

Storm Tracking: 
A cyclone is an area of low pressure around which the winds flow counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. A developing cyclone is typically accompanied by a warm front pushing northward and a cold front pulling southward, marking the leading edges of air masses being wrapped around a center of low pressure, or the center of the cyclone.

The counterclockwise winds associated with northern hemisphere midlatitude cyclones play a significant role in the movement air masses, transporting warm moist air northward ahead of a low while dragging colder, drier air southward behind it.

Rising air in the vicinity of a low pressure center favors the development of clouds and precipitation, which is why cloudy weather (and likely precipitation) are commonly associated with an area of low pressure. Cyclones are easily identifiable on certain types of weather maps by remembering some key signatures. For example, a cyclone can be found on a map of surface observations by recognizing a counterclockwise rotation of the wind barbs for a group of stations

Storm Tracking Diagram
1) For each of the following three surface maps, (Map #1, Map #2, and Map #3), use the wind barbs to determine the location of the cyclone center. 
2) What was the cyclone's general direction of movement? 

Characteristics of Air Masses: 
Continental Polar Air Masses
Those who live in northern portions of the United States expect cold weather during the winter months. These conditions usually result from the invasion of cold arctic air masses that originate from the snow covered regions of northern Canada. Because of the long winter nights and strong radiational cooling found in these regions, the overlying air becomes very cold and very stable. The longer this process continues, the colder the developing air mass becomes, until changing weather patterns transport the arctic air mass southward.
Arctic air masses move about as a shallow area of high pressure, commonly known as an "Arctic High". Northerly winds associated with a cyclone and trailing anticyclone, (the center of the arctic air mass), transport the colder air southward. Since the terrain is generally flat and free of any significant topographical features, arctic air masses entering the United States and can easily slide all the way to Texas and Florida.

Maritime Tropical Air Masses
Maritime tropical air masses originate over the warm waters of the tropics and Gulf of Mexico, where heat and moisture are transferred to the overlying air from the waters below. The northward movement of tropical air masses transports warm moist air into the United States, increasing the potential for precipitation.
Tropical air masses are generally restricted to the southern states during much of the winter. However, southerly winds ahead of migrating cyclones occasionally transport a tropical air mass northward during the winter season.

Forecasting Tips
Today equals tomorrow. There are several different methods that can be used to create a forecast. The method a forecaster chooses depends upon the experience of the forecaster, the amount of information available to the forecaster, the level of difficulty that the forecast situation presents, and the degree of accuracy or confidence needed in the forecast.

The first of these methods is the Persistence Method; the simplest way of producing a forecast. The persistence method assumes that the conditions at the time of the forecast will not change. For example, if it is sunny and eighty seven degrees today, the persistence method predicts that it will be sunny and eighty seven degrees tomorrow. If two inches of rain fell today, the persistence method would predict two inches of rain for tomorrow.

The persistence method works well when weather patterns change very little and features on the weather maps move very slowly. It also works well in places like southern California, where summertime weather conditions vary little from day to day. However, if weather conditions change significantly from day to day, the persistence method usually breaks down and is not the best forecasting method to use.

It may also appear that the persistence method would work only for shorter-term forecasts (e.g. a forecast for a day or two), but actually one of the most useful roles of the persistence forecast is predicting long range weather conditions or making climate forecasts. For example, it is often the case that one hot and dry month will be followed by another hot and dry month. So, making persistence forecasts for monthly and seasonal weather conditions can have some skill. Some of the other forecasting methods, such as numerical weather prediction, lose all their skill for forecasts longer than ten days. This makes persistence a "hard to beat" method for forecasting longer time periods.

The trends method involves determining the speed and direction of movement for fronts, high and low pressure centers, and areas of clouds and precipitation. Using this information, the forecaster can predict where he or she expects those features to be at some future time. For example, if a storm system is one thousand miles west of your location and moving to the east at two hundred and fifty miles per day, using the trends method you would predict it to arrive in your area in four days. You would divide one thousand miles by two hundred and fifty miles per day, which equals four days. Using the trends method to forecast only a few hours into the future is known as "Nowcasting" and this method is frequently used to forecast precipitation. For example, if a line of thunderstorms is located sixty miles to your northwest and moving southeast at thirty miles per hour, you would predict the storms to arrive in your area in two hours. 

Effects of cloud cover on forecasted temperature
During the day, the earth is heated by the sun. If skies are clear, more heat reaches the earth's surface (as in the diagram below). This leads to warmer temperatures. However, if skies are cloudy, some of the sun's rays are reflected off the cloud droplets back into space. Therefore, less of the sun's energy is able to reach the earth's surface, which causes the earth to heat up more slowly. This leads to cooler temperatures.
 
Forecast Tip: ?When forecasting daytime temperatures, if cloudy skies are expected, forecast lower temperatures than you would predict if clear skies were expected.

At night cloud cover has the opposite effect. If skies are clear, heat emitted from the earth's surface freely escapes into space, resulting in colder temperatures. However, if clouds are present, some of the heat emitted from the earth's surface is trapped by the clouds and reemitted back towards the earth. As a result, temperatures decrease more slowly than if the skies were clear.

Forecast Tip: ?When forecasting nighttime temperatures, if cloudy skies are expected, forecast warmer temperatures than you would predict if clear skies were expected.

High and low pressure centers effect on forecasted temperatures
The positions of high and low pressure centers can greatly influence a forecast. Fair weather generally accompanies a high pressure center and winds flow clockwise around a high. This means that winds on the back (western) side of the high are generally from a southerly direction and typically mean warmer temperatures. On the front (eastern) side of a high, winds are generally from the north and this typically results in colder temperatures.

Forecast Tip: ?If a city is expected to be located west of a high pressure center then warmer temperatures are likely. However, if the city is expected to be in the northerly winds of a high pressure center, then forecast colder temperatures. Cities under the influence of high pressure centers can expect generally fair weather with little or no precipitation.

In contrast, clouds and precipitation generally accompany a low pressure center and winds flow counterclockwise around lows. This means that winds on the back (western) side of the low are generally from a northerly direction and typically mean colder temperatures. On the front (eastern) side of a low, winds are generally from the south and this typically results in warmer temperatures.

Forecast Tip: ?If a city is expected to be located west of a low pressure center then colder temperatures are likely. However, if the city is expected to be in the southerly winds of a high pressure center, then forecast warmer temperatures. Cities under the influence of low pressure centers can expect generally cloudy conditions with precipitation.

Effects of temperature advection on forecasted temperatures
Temperature advection refers to change in temperature caused by movement of air by the wind. Forecasting temperatures using advection involves looking at the wind direction at your forecasting site and the temperatures upstream (in the direction from which the wind is blowing). If the temperature is 70 degrees west of you and the air is blowing west, you can expect 70 degree temperatures in the near future. Advection means changes in temperature because air is moving bringing a different temperature to your area. 

Forecast Tip: ?When forecasting temperatures, look at the temperatures upstream from the station for which you making a forecast. If they are warmer, that means warmer air is being transported towards your station and the temperature should rise. Put in another way, if there is warm advection occurring at a given station, expect the temperatures to increase. In contrast, if cold advection is occurring at a given station, expect the temperatures to drop.

Effects of snow cover on forecasted temperatures
As the sun's rays hit the surface of the earth, much of it is absorbed by the surface (as in the diagram below). This in turn warms the air near the earth's surface, causing the temperature to rise. If there is snow on the ground, some of the sun's energy will be reflected away by the snow, and some of it will be used to melt the snow. This means that there is less energy available to heat the earth's surface and consequently, the temperatures rise more slowly than would occur with no snow on the ground. 

Forecast Tip: ?When snow cover is present, forecast lower daytime temperatures than you would normally predict if there was no snow cover. At night, snow on the ground readily gives off heat. This causes rapid cooling. Forecast the overnight temperature to be lower than you would predict if there was no snow cover.

Effects of wind on forecasted temperatures
At night, the earth's surface cools by radiating heat off to space. The strongest cooling takes place right near the surface while temperatures at roughly three thousand feet are actually warmer than those at the surface. On a windy night, some of the warmer air aloft is mixed down towards the surface. This occurs because the winds are faster aloft than at the surface.

To visualize this, place one hand over the other about six inches apart. The bottom hand represents the air near the surface and the top hand represents the warmer wind higher up. Move the bottom hand slowly and the upper hand faster (to indicate the faster winds aloft). The faster air above and slower air below causes the air to overturn or spin. This overturning motion is how warmer air from above is transported downward on windy nights.

Forecast Tip: ?On a calm night, the maximum surface cooling can take place. But on a windy night, some warmer air is mixed downward to the surface, which prevents the temperatures from dropping as quickly as they would on a clear night. Therefore, forecast slightly warmer temperatures for a windy night than for a calm night.

Effects of frontal lifting on forecasted precipitation
Clouds and precipitation are formed by the upward motion of air. Therefore, there must be a mechanism present to lift the air. Fronts often serve as such a mechanism. Air on one side of the front typically blows in a different direction from the wind on the other side, causing the air to converge, or pile up right along the frontal surface. Since this air has to go somewhere, it rises. As air rises, the moisture in the rising air cools, condenses and forms clouds and precipitation. For example, a cold front lifts warm moist air ahead of it as it advances. The rising air cools and the water vapor condenses out to form clouds, most commonly ahead of and along the cold front. As the cloud droplets grow in size, they begin to fall back to the earth as precipitation. Vigorous upward motions often occur ahead of and along a cold front, resulting in more vertically developed clouds like cumulonimbus clouds, which themselves can produce heavy rains and powerful thunderstorms.

Forecast Tip: ?If there is sufficient moisture in the air and a forcing mechanism like a cold front (for example) is approaching the area, then there is an increased probability that precipitation will occur.

Forecast Tip: ?If there is sufficient moisture in the air and a forcing mechanism like a cold front (for example) is approaching the area, then there is an increased probability that precipitation will occur.

Rain or snow? It is dependent on the temperature
Most precipitation that reaches the ground actually begins as snow high in the atmosphere. These snow flakes develop somewhere above the freezing level where the air temperature is less than thiry-two F, and begin to fall toward the earth as snow. If ground temperature is above thirty-two F, the freezing level must be located somewhere above the ground. The falling snow passes through the freezing level into the warmer air, where it melts and changes to rain before reaching the ground. When the air temperature at the ground is less than thirty-two F, the precipitation begins falling as snow from the clouds. Since it is falling into cold air, the snow does not melt on the way down and reaches the ground as snow. This is why cold air is important for there to be snow. 

Once in a while, a very thin layer of warm air is found near the surface and temperatures may be several degrees above freezing. However, since the layer of warm air is so shallow, the snow reaches the ground in tact before it has a chance to melt and become rain. This is how snow falls when the surface temperatures are above freezing.

Forecast Tip: ?When forecasting precipitation type, if temperatures are expected to be above freezing, then rain is most likely. If temperatures are expected to be below freezing, then forecast for snow.

Forecasting Scenarios Questions 
For each of the following weather scenarios, indicate what impact each component (cloud cover; winds; advection; snow cover) will have on forecasted temperatures. Indicate whether each weather condition will lead to lower (L) or higher (H) temperatures or indicate "None" if it is not a factor. 

Example:  Nighttime forecast; cloud cover; no winds; no snow cover
Cloud cover: L
Winds: None
Temperature Advection: None
Snow Cover: should keep temps warm

Day time forecast; snow cover; clear skies; no wind
Night time forecast; snow cover; clear skies; no wind
Night time forecast; cloudy skies; no snow cover; windy and warm advection
Day time forecast; cloudy skies; windy; cold advection; no snow cover

For the following weather scenarios, indicate if precipitation is "likely" or "unlikely" to occur given the conditions described in each scenario. Explain why. 

Example: Boulder, CO, a city on the east side of the Rocky Mountains. Downslope winds are expected. 
Unlikely.  Downslope winds (or winds blowing down the mountain) tend to be very dry, warming as it descends, creating an unfavorable environment for the development of precipitation (since rising air in the presence of downslope winds is unlikely.

Scenario one
A cold front is approaching from the west, but the air both ahead of and behind the front is very dry.

Scenario two
A warm front is approaching and the air behind and ahead of the front is very moist.

Scenario three
Upslope winds are expected in boulder, CO and the air has been very moist for the past couple of days.

Scenario four
The trend for the latest batch of precipitation is a steady eastward movement of thirty miles per hour. The latest position is roughly seven hundred west of here. Will precipitation arrive within twenty four hours?

Standard Time:
When converting from Coordinated Universal Time (UTC) or what is also called Zulu time (Z), follow the steps below. 
Step 1.  First use the conversions below. 
From UTC to Local Standard Time: 
To get to Eastern Standard Time (EST) you subtract five hours from the UTC time.
To get to Central Standard Time (CST) you subtract six hours from the UTC time.
To get to Mountain Standard Time (MST) you subtract seven hours from the UTC time.
To get to Pacific Standard Time (PST) you subtract eight hours from the UTC time.

Step 2. Next, the local time is converted from a 24 Hour Clock to an AM/PM time. 

Step 3.  If the local time on the twenty-four clock is less than zero hundred zero minutes (0000), then you have crossed over to the previous day. So for example, minus four hundred (-0400) becomes twenty hundred the day before. 

Some examples converting time
Example one; Convert May second fourteen fifty-nine UTC to eastern standard time. Subtract five hours from fourteen fifty-nine, which is nine fifty-nine. This is the same as nine fifty-nine a m. It would still be May second.

Example two; Convert May second twenty-three hundred UTC to eastern standard time. Subtract five hours from twenty-three hundred, which is eighteen hundred. This is the same as six p m. It would still be May second.

Example three; Convert May third zero hundred zero minutes (0000) to central standard time. Subtract six hours from zero hundred to get eighteen hundred central standard time. Zero hundred is the same as twenty-four hundred. Convert eighteen hundred from the twenty-four hour clock to get local time which is six p m. The date is different. It is the day before, May second. 

If you are converting to Daylight Savings Time which runs from March to November, you have to subtract one less hour from the UTC time.

From UTC to local daylight time
To get to Eastern Daylight time (EDT) you subtract four hours from the UTC time.
To get to Central Daylight time (CDT) you subtract Five hours from the UTC time.
To get to Mountain Daylight time (MDT) you subtract six hours from the UTC time.
To get to Pacific Daylight time (PDT) you subtract seven hours from the UTC time.

Some examples converting time
Convert May second fourteen fifty-nine UTC to eastern daylight time. Subtract four hours from fourteen fifty-nine, which is ten fifty-nine. This is the same as ten fifty-nine a m. It would still be May second.

Practice Converting From UTC to Local Date and Time: 

1) Convert from 2000Z 28 October 1996 UTC to Central Standard Time (CST) for Chicago, Illinois. 
2) Convert from 2000Z 28 October 1996 UTC to Eastern Standard Time (EST) for New York City, New York. 
3) Convert from 2000Z 28 October 1996 UTC to Pacific Standard Time (PST) for San Francisco, California. 
4) Convert from 2000Z 28 October 1996 UTC to Mountain Standard Time (MST) for Denver, Colorado. 
5) Convert from 0500Z 29 October 1996 UTC to Central Daylights Savings Time (CDT) for Chicago, Illinois. 
6) Convert from 0500Z 29 October 1996 UTC to Eastern Daylight Savings Time (EDT) for Nashville, Tennessee. 
7) Convert from 0500Z 29 October 1996 UTC to Pacific Daylight Savings Time (PDT) for Boise, Idaho. 
8) Convert from 0500Z 29 October 1996 UTC to Eastern Standard Time (EST) for Miami, Florida.