Download Cold Front or Warm Front?

7 KEY FORECAST VARIABLES
1. Wind Direction
«^ Remember that wind is always reported as where it is coming from,
a. A north wind means from the north and therefore most likely cooler temps.
b. A south wind means from the soutii and therefore most likely warmer temps.
2.
Cloud Cover
a. Clouds prevent incoming sunlight while preventing outgoing radiation overnight
b. When all other factors are considered:
i. Clouds during the day cause cooler afternoon temps.
ii. Clouds overnight cause warmer morning temps
3. Wind Speed
a. Wind has a moderating effect on temps.
b. Assuming no major air mass changes (nofronts)and when considering all other factors:
i. Windy nights are warmer and windy days are cooler.
ii. Calm nights are cooler and calm days are warmer.
4.
Thickness
a. Thickness values relate to air density which is primarily due to the average air temperature in the
lower troposphere.
b. Higher thickness indicate a warmer lower atmosphere.
c. Lower thickness indicate a cooler lower atmosphere.
5. 850 mb Temperature
a. Temperature of the air near 5,000 ft. above sea level.
b. Rapidly changing values indicate an air mass change, and most likely afrontalpassage.
6. DevsT)oint Temperature
a. Air temperature cannot drop below the dewpoint value.
b. Therefore, dewpoints help to forecast the lowest possible temperature overnight.
c. Dewpoint temperatures do not influence daily high temperatures.
7. Air Pressure
a. Air pressure changes can signify the passage of weather systems, including weather fronts.
b. Typically, pressure falls fairly rapidly before the arrival of a cold or warm front.
c. After a cold frontal passage, pressure normally rises rapidly due to an increase in air density.
d. After a warm frontal passage, air pressure may remain constant or fall even lower due to a lower air
density.
Cold Front or Warm Front?
WEATHER VARIABLE
Wind Direction
Thickness
850 mb Temp
Dewpoint (TD)
Pressure Tendency
Precipitation
COLDFRONT
Warm direction before, Cool
direction after (ex. SW to NW)
Decreasing trend
Decreasing trend
Decreasing trend
Falls before. Rises after
Usually nearfi*onton either side
WARM FRONT
Cool direction before. Warm
direction after (ex. E to S)
Increasing trend
Increasing trend
Increasing trend
Falls before
Usually ahead of fi^ont