1. The Dryline The dryline can be defined as the near surface convergence zone between moist air flowing off the Gulf of Mexico and dry air flowing off of semi-arid high plateau regions of Mexico and the southwestern United States: Temperatures in degrees Celsius

2. Dry Line A surface boundary between warm, moist air and hot, dry air. Found in the western Great Plains in the United States Also found in China, India, and over Central West Africa

3. Dry Line Surface boundary between warm, moist air and hot, dry air. New Mexico / Tx Panhandle Abilene, TX Houston, TX Warm, Moist Air Hot, Dry Air

4. Dry Line After sunrise, the sun will warm the surface which will warm the air near the ground. This air will mix with the air above the ground. Since the air above the moist layer is dry (and is much larger than the moist layer), the mixed air will dry out. The dry line boundary will progress toward the deeper moisture. The dryline tends to “jump” in discrete steps

5. Dry Line Warm, Moist Air Hot, Dry Air Top of moist layer before mixing Boundary after mixing Initial Position of the Dry Line Position of the Dry Line after mixing New Mexico / Tx Panhandle Abilene, TX Houston, TX

6. Dryline Evolution and Movement Here is the situation in the morning hours before surface heating creates thermals in the boundary layer: New Mexico / Tx Panhandle Abilene, TX Houston, TX

7. Dryline Evolution and Movement With time:

8. Dryline Evolution and Movement With time, the dryline moves east as thermal turbulence mixes out the western part of the shallow moist layer.

9. Dry Line After sunset, a nocturnal inversion forms and the winds in the moist air respond to surface pressure features. The dry line may progress back toward the west – in sharp contrast to fronts (i.e. the dryline advances eastward in the day and retreats back toward the west at night) Dry line can act as a focal point for surface convergence and severe weather formation. When radar cells exist within 200 miles either side of the dryline, the first echoes usually develop within 10 miles of it

10. Southern Plains Dry Line Temperatures in degrees Celsius ©1993 Oxford University Press -- From: Bluestein, Synoptic- Dynamic Meteorology in Midlatitudes, Volume II Dry Line

11. Dry Line -- Southern Plains USA Behind the Dry Line Westerly winds (often strong) Clear Skies Warm Temperatures Low Moisture In Front of the Dry Line S or SE winds Hazy or Cloudy Skies Warm Temperatures High Moisture

12. Dryline Example DFW ABQ

13. Sounding West of the Dryline NCAR

14. Sounding East of the Dryline

16. The Dryline The dryline is observed generally from April through June about 40% of the time It’s observed from the southern Great Plains up into the Dakotas – from the Rockies eastward to about 96 degrees W longitude. It is easiest to identify with a moisture variable such as mixing ratio: From Shaefer (86)

17. Storm Initiation Along the Dryline

18. Dryline Bulges Somewhat common 80-100 km in scale Preferred locations for convective initiation Shaefer (86)