P.N.A.

DESCRIPTION

• PNA +
  
• PNA -
  
  
• INDEX
  
  
• PREDICTION OF PNA

The positive phase of the PNA is characterized by pattern of higher-than-average atmospheric pressure in the vicinity of Hawaii and over the mountainous region of western North America, and lower-than-average pressure in south of Alaska and over the southeastern United States. This phase is associated with a higher upper-level of meridional flow.

The PNA index appears more often positive in years with El Nino.

The positive phase of the PNA is associated with higher than the average temperatures on the West Coast of the United States and western Canada, but at temperatures lower than the average across the South-Central and Southeastern States States.

The precipitation anomalies are higher than the average in the West coast of Alaska and of United States (California ...), the Gulf States, Florida. Drier conditions persist on the United States Midwest and the Canadian Prairies as well as in the Pacific Northwest.

The positive phase is associated with a jet stream from the East Asia which is reinforced, going tonorth in the eastern Pacific and then down to the South East over North Dakota. Then the cold fronts coming from the Hudson Bay bring over an interval of about ten days of unusual snowfall in the Mississippi Valley on the east coast of the United States and sometimes as far away as Florida

It is characterized by pattern of higher-than-average atmospheric pressure off the coast of the Aleutian Islands and the southeast of the United States and lower-than-average pressure over the Rocky Mountains to the West of the United States as well as at the bottom of the Hudson Bay and in the vicinity of Hawaii. This phase is associated with a higher upper-level of zonal flow.

The PNA index appears more often positive in years with La Nina but this is not always the case given the other factors that come into play.

During the negative phase, the West of United States can have relatively cold temperatures, while the East of United States has rather temperatures higher than normal.

The PNA- often causes severe droughts in Mt Shasta on the West Coast of the United States, while the East and the Canadian Prairies are associated with wet conditions. The negative phase gives more snow and colder temperatures in the High Plains and the Midwest of the United States.