1. The Propagation Of Mesoscale Convective Complexes
The Corfidi Vector Method
Mike Peluso
Howard Manges
20 April 2006

2. Corfi.. What?
Corfidi Vectors are a tool that operational meteorologists can use that MAY help more accurately predict:
the motion of MCS’s
More specifically the meso beta convective elements (MBE)
heavy rain
flash flooding
damaging winds
What do these vectors
represent?

3. The “Original” Corfidi Method
Sum of two vectors:
Advective – The mean flow of the mb cloud-layer wind Newton and Katz(1958) and Chappell (1986)
Propagation – Represents new cell formation opposite in direction to the low-level jet but equal in magnitude Merritt and Fritsch, Corfidi et.al (1996)

4. Advective Component
Simplified example of vertical wind profile through mean cloud layer.
Mean flow vector would be
270°/30kts
Mathematically: (Vcl)
(V850+V700+V500+V300 )/4
300-hPa
500-hPa
700-hPa
850-hPa

5. Propagation Component
Represents new cell formation opposite in direction to the low-level jet but equal in magnitude
850-hPa wind barb
LLJ 240°/30kts
Therefore the vector representative of propagation will be from 60°/30kts

6. Addendum to Corfidi Vector Method
A major shortcoming was found in this method.
MCS propagation is not as straight forward as 2 vectors being added or subtracted.
Case studies indicate that the cold pool spatial relationship to the low level inflow (LLJ) has an additional effect on propagation patterns. Thus….

7. Cold Pool Component
Assuming that new cell development (propagation) is ALWAYS opposite the LLJ is incorrect.
The effect of this spatial relationship of the meso-high to the inflow (LLJ) plays a major role in new cell development
Cumulogenesis occurs along the leading edge of the cold pool and hence the region of greatest LLC Corfidi, WAF (2003)

8. Cold Pool Component
Corfidi et.al (2003)

9. Modes of MCS Propagation
Two Types
Quasi-stationary
a.k.a back-building or upwind propagating
Significant flood threat
Progressive
a.k.a. forward or downwind propagating
Reduced threat of flooding
Schematically……

10. Movement of MCS-Backbuilding
300-hPa
Mean flow vector (Vadv)
Region of Greatest LLC
500-hPa
Favored MCS motion
700-hPa
LLJ (Vprop.)
850-hPa
Region of greatest LLC dictates MCS motion.
Assuming sufficient instability and favorable thermodynamic environment Corfidi (2003)

11. Movement of MCS-Backbuilding
Called “training” storms
Provide significant risk for flash flooding.
Occurs when propagation exceeds advection
The result of mean cloud layer winds being nearly parallel to outflow boundary.
Strong normal component of the LLJ
Mean flow vector (Vadv)
Region of Greatest LLC
Favored MCS motion
LLJ (Vprop.)
Corfidi Wea. Forecasting 12/03

12. Movement of MCS- Progressive
Mean flow vector (Vadv)
300-hPa
LLC Region
500-hPa
LLJ (Vprop)
700-hPa
Favored MCS
motion
850-hPa

13. Movement of MCS-Progressive
Storm motion is opposite the LLJ along the downwind side of cold pool.
Vector length is directly related to rate of cumulogenesis along gust front.
Not usually associated with heavy rainfall or flooding.
Mean flow vector (Vadv)
LLJ (Vprop)
LLC Region
MCS
motion

14. Forecast Magnitude of MBE motion
A straight forward calculation can be utilized to determine the magnitude of motion for the MBE (Mesoscale Beta Element).
|VMBE| = { |Vcl|2 + |-VLLJ|2 -2( |Vcl| . |-VLLJ| ) cos Φ}1/2
Φ = angle between mean cloud layer flow and LLJ

15. MBE Forecast Direction
φ = sin-1
φ = angle between mean cloud layer flow and MBE motion
{(|-VLLJ| . sinΦ) / |VMBE|}
Mean flow vector (VCL)
(-VLLJ ) =(VPROP)
MCC φ
MBE Motion
mb thickness contours

16. The Role of Dry Air Dry air allows for:
increased evaporative cooling
Sublimation and melting
These create density differences and stronger DD’s
Strong cold pools demonstrate the potential for favoring progressive MCS movement
Weak cold pools favor Quasi-stationary or Backbuilding MCS’s that occur in moist or nearly saturated low-level environments.

17. Summary 3 factors influencing motion: 2 propagation modes: 1 grade
Advective component
Propagation component
Cold pool (outflow boundary).
The spatial relationship between them influences MCS motion
2 propagation modes:
Upwind or Backbuilding
Downwind or Progressive
Distinguished by orientation of the gust front to the mean wind and the LLJ.
1 grade A+

18. References
Corfidi, Stephen F., 2003: Cold Pools and MCS Propagation: Forecasting the Motion of Downwind-Developing MCS’s. Wea. Forecasting., 18,
Merritt, J.H. and Fritsch, J.M., 1994: Predicting the Movement of Mesoscale Convective Complexes. Wea. Forecasting., 11,
Corfidi, Stephen F., 1998: Forecasting MCS Mode and Motion. Prepared for the 19th Conference Severe Local Storms, Minneapolis, MN 1998.