the dryline the dryline can be defined as the near surface convergence zone between moist air...
TRANSCRIPT
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 indegrees Celsius
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
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
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
Dry Line
Warm, Moist Air
Hot, Dry AirTop of moist layerbefore mixing
Boundary after mixing
Initial Positionof the Dry Line
Position of theDry Line after
mixing
New Mexico / Tx Panhandle
Abilene, TX
Houston, TX
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
Dryline Evolution and Movement
With time:
Dryline Evolution and Movement
With time, the dryline moves east as thermal turbulence mixes out the western part of the shallow moist layer.
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
Southern Plains
Dry Line
Temperatures indegrees Celsius
©1993 Oxford University Press
-- From: Bluestein, Synoptic-Dynamic
Meteorology in Midlatitudes,
Volume II
Dry Line
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
Dryline Example
DFWABQ
Sounding West of the
Dryline
NCAR
Sounding East of the
Dryline
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)
Storm Initiation Along the Dryline
Dryline Bulges
•Somewhat common
•80-100 km in scale
•Preferred locations for convective initiation
Shaefer (86)