Mid-latitude Cyclone Climatology Read Ch. 10 Read Ch. 1

When are cyclones strongest? When are cyclones strongest?  Summer or Winter? When are cyclones farthest poleward (north for us)? When are cyclones farthest poleward (north for us)?  Summer or Winter? WHY? WHY?

More cyclones in January than July More cyclones in January than July Ratio of Cyclones to Anticyclones is 1.8:1 (both Jan. & July) Ratio of Cyclones to Anticyclones is 1.8:1 (both Jan. & July) More activity East of Rockies than West More activity East of Rockies than West Cyclones and Anticyclones are: Cyclones and Anticyclones are:  More intense  More numerous  Farther south in Jan. vs. July  Farther south in Jan. vs. July (in our hemisphere)

 Cyclones-Genesis – January – East Coast/Rockies  Cyclones-Genesis – July – East Coast/Rockies  Anticyclones-Genesis – January – NW Canada/Great Plains  Anticyclones-Genesis – July – SW Canada  Cyclone motion – East/Northeast from genesis region  Anticylone motion – East/Southeast from genesis region

Zishka, K. M., and P. J. Smith, 1980: The climatology of cyclones and anticyclones over North America and surrounding ocean environs for January and July, Mon. Wea. Rev., 108,

From Zishka and Smith (1980)

 January – East Coast Cyclones stronger than Rocky lee storms  July – East Coast Cyclones more similar to Rocky lee storms  genesis – creation  lysis – destruction

What factors affect cyclogenesis? What factors affect cyclogenesis?  East of Rockies or Appalachians  Conservation of PV P θ = -g (ζ θ + f)/ ∂ p/ ∂θ P θ = -g (ζ θ + f)/ ∂ p/ ∂θ  East Coast  Strong thermal gradients, esp. between coast & Gulf Stream