The dew point temperature map shows not only surface

dew point temperature but also wind direction and speed.

A contoured surface dew point temperature map

Surface Dew Point Temperature: Dew point can be defined as the temperature to which air would have to be cooled for saturation to occur at constant pressure and constant water vapor content. It is a good indication of the air's actual water vapor content. When the dew point is equal to the air temperature, saturation is said to occur, however; dew points can never be greater than the air temperature. Different dew point temperatures (in degrees fahrenheit) are shown by the different colors on this map. The closer the colors are to red, the higher the dew point will be and thus the more moist the area is. The different countours are determined by dew point temperature ranges of 5 degrees fahrenheit. During the severe weather season (May, June, July), we look for sharp changes in dew points called a dryline. Drylines usually have around a 25 degree change in dew point in an area of about 75 miles. They are often seen around the New Mexico/Texas border during the spring and summer. Severe weather often tends to focus on the east side of a dryline.

Wind Direction/Speed: The solid black stick like lines on the map represent the wind speed/direction at that location. The direction is determined by where the shorter black line extending from the stick is located.

Direction

Stick points to bottom of map = wind from the south

Stick points to left of map = wind from the west

Stick points to top of map = wind from the north

Stick points to right of map = wind from the east

Speed

Wind speed is determined by the number and length of lines

coming out of the end of the stick.

Short line = 5 mph (miles per hour)

Long line = 10 mph

Triangle = 50 mph

Helpful Questions and Answers:

• What is a good dew point level for severe weather?
• For severe weather, dew points of 60s and 70s are generally good values to look for in the Summer. During the Spring, dew point values can be in the 50s and 60s.
• What does it mean when there is a sharp change in dew point values? For example, dew point levels are 65 degrees in central Texas, but only 45 in west Texas and New Mexico.
• When there is a sharp change in dew point levels close to each other, it means there is either a cold front or a dryline causing the gradient. This is a good thing to look for when predicting severe weather, as storms tend to form along fronts and drylines. A dryline is just a boundary separating dry air from moist air.
• What does it mean when the winds are from the south on the dew point map?
• When winds are pointing from the south, it means moisture is advecting up from the Gulf of Mexico and dew points should begin to rise.
• What does it mean when the winds are from the north on the dew point map?
• When winds are pointing from the north, it means dry air is moving into the region and dew points may decrease.