Dry Line Initiation Video URL: .

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

Inversion or cap

Well-mixed warm air

Typical Dryline

Temperatures indegrees Celsius

©1993 Oxford University Press -- From: Bluestein, Synoptic-Dynamic

Meteorology in Midlatitudes, Volume II

Southern Plains Dry

Line

Temperatures indegrees Celsius

©1993 Oxford University

Press -- From: Bluestein, Synoptic-Dynamic

Meteorology in Midlatitudes,

Volume II

Dry Line

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.

L

DRY LINE

Warm, Moist

L

NODRY LINE—Get ColdFront

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

Warm, Moist Air

Hot, Dry Air—Usually Well MixedTop of moist layer

before mixing

Boundary after mixing

Initial Positionof the Dry Line

Position of theDry 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 surface dry line

Sounding West of the

Dryline

NCAR

Very Dry

West Winds

Albuquerque, NM12Z -- 26 June 1998

Sounding East of the

Dryline

NCAR

Moist

South Winds

Oklahoma City, OK12Z -- 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 risingmotion