Dry Line
Initiation Video URL: http://www.nssl.noaa.gov/users/ziegler/public_html/initiation.html
Dry Lines
or
Dry Lines
• Associated with large horizontal gradients in
moisture, but not necessarily temperature.
• Results from the interaction of cyclones and
fronts with large-scale terrain.
• Found over the U.S. Midwest, northern India,
China, central West Africa and other locations.
• Acts as a focus for convection, and particularly
severe convection.
• Most prevalent during spring/early summer in
U.S.
Dry Line
• Surface boundary between warm, moist air
and hot, dry air.
Surface dry line
Well-mixed warm air
Inversion or cap
Typical Dryline
Temperatures in
degrees Celsius
©1993 Oxford University Press -- From: Bluestein, Synoptic-
Dry Line
Southern
Plains Dry
Line
©1993 Oxford
University
Press -- From:
Bluestein,
SynopticDynamic
Meteorology in
Temperatures in
degrees Celsius
Trajectories
• Fundamentally the dry line represents a
trajectory discontinuity between moist
southerly flow and flow descending from
higher elevations.
• Can only happen relatively close to the
upstream barrier (no more than 1000 km)
since otherwise air would swing southward
behind the low system and thus would be
cool and somewhat moist.
DRY LINE
L
Warm, Moist
L
NO
DRY
LINE—
Get Cold
Front
Dry Line: Tends to Move Eastward
During the Day and Westward At
Night
• 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,
the mixed air will dry out.
• The dry line boundary will progress toward
the deeper moisture.
Dry Line
Top of moist layer
before mixing
Boundary after mixing
Hot, Dry Air—Usually Well Mixed
Warm, Moist Air
Initial Position
of the Dry Line
Position of the
Dry Line after
mixing
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 .
West
East
Note weak inversion or “cap” over low-level moist layer east of the surf
NCAR
Sounding
West of the
Dryline
West Winds
Very Dry
Albuquerque, NM
12Z -- 26 June 1998
NCAR
Sounding
East of the
Dryline
South Winds
Moist
Oklahoma City, OK
12Z -- 26 June 1998
Aircraft Study of the Dry Line
Convection Tends to Focus On
the Dryline
Storm Initiation Along a Dry Line
Simulation of a Thunderstorm Initiation
Along Dryline in TX Panhandle
Storm
Note converging winds and rising
motion