|WHAT IS A "NEGATIVELY TILTED TROUGH"?
METEOROLOGIST JEFF HABY
In forecast discussions you will come across the terms positive, neutrally and negatively tilted trough.
When a trough is positive or neutrally tilted it is usually not referenced at such. However, when it becomes
negatively tilted it will be referenced as such. The tilt of a trough is the angle the trough axis makes with
lines of longitude. A negatively tilted trough tilts horizontally (parallel to surface) from the northwest to
the southeast. What is the big deal about having a negative tilt?
(1) indicates a low pressure has reached maturity,
(2) indicates strong
differential advection (middle and upper level cool air advecting over low level
warm air advection). This increases
(3) Indicates good vertical wind shear.
A deep low pressure, a negatively
tilted trough, and a warm and moist warm sector combination east of the Rockies often produces a
What causes the negative tilt?
(1) Strong middle and upper level winds wrapping around the base
of the trough,
(2) A strong jet streak near the base of a trough
(3) A ridge to the east of the trough (like a sideways inverted trough)
(4) Occlusion of low pressure.
Below are a positive and negative tilted trough.