Typically, the boundary between two air masses is a front. In the U.S. Southern Plains, however, another phenomenon separates the dry air blowing from the Mexican Plateau from the moist air from the Gulf of Mexico. This boundary is called the "dryline". In the U.S., it exists most commonly in western and central Texas, western Oklahoma, southern Kansas, eastern New Mexico, and southeastern Colorado. The dryline rarely extends beyond this region and, when it does, it does not travel more than a few hundred kilometers beyond the region.
Focusing on the western half of Oklahoma (west of I-35), describe how the air temperatures change during the animation.
Does western Oklahoma heat uniformly, or are there areas which heat faster than others? If some areas heat faster, explain why you think this is the case.
Using the dewpoint temperature animation, can you detect a dryline? How?
In general, how is the dryline oriented (e.g., north/south, east/west)?
To which side of the dryline is the dry air located?
In which direction does the dryline move before 5:00 PM? After 9:00 PM?
Using the solar radiation animation, can you confirm where the dryline is located? How?
Using the wind animation, from what direction are the winds blowing to the east of the dryline? To the west of the dryline?
Find where your school is located on the map. If the dryline passed by your school, how did the weather change?
List any similarities and differences between the characteristics of a dryline and a cold front.
Why do you think weather forecasters are concerned with the dryline and its movement?
[Advanced] Using your knowledge of weather patterns near a dryline and the ingredients necessary for clouds to develop, explain why weather forecasters watch the dryline carefully for thunderstorm development.
Given animations of several atmospheric variables (e.g., temperature, rainfall) during a cold front passage, the student will be able to locate the dryline, determine its direction of movement, and list at least two weather conditions (e.g., cloudy behind dryline) associated with the dryline.
The student will be able to list one characteristic of a dryline that allows the student to differentiate a dryline from a front.
Pencil
(per person)
Oklahoma road map
(per group)
Computer
(per group)
The following movies are needed: TAIR06181998.mov, TDEW06181998.mov, SRAD06181998.mov, and WIND06181998.mov. They are found at the URL below. Download these at least a day before doing the activity. (All movies are used by permission from the Oklahoma Climatological Survey. Copyright© 1998-1999 Oklahoma Climatological Survey. All Rights Reserved.)
(Copyright©1999 Apple Computer, Inc. All rights reserved.)
This OCS-developed software for the Mac OS can be used as the QuickTime movie player. (Copyright© 1995-1999 Oklahoma Climatological Survey. All Rights Reserved.)
Using WxImage or another QuickTime® movie player, animate the movies depicting air temperature, dew point, solar radiation, and wind. Examine each animation for patterns and changes. Pay particular attention to the changes in the western half of Oklahoma.
If you desire to use a recent dryline case for this activity, verify that it is a dryline and not a front. A front will continue moving eastward across the U.S.; a dryline will retreat to the west during the night. Another way to be sure is to read the National Weather Service weather discussions or listen to NOAA weather radio.
The location of the dryline is determined solely from the dewpoint temperature field.
Duration: 45 to 60 minutes
VOCABULARY:
Convergence
Dew point
Dewpoint temperature
Dryline
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