By Joe D'Aleo
Monday, February 23, 2009
The winter still is going through its last grand finale and it’s a beaut. We are however starting to look ahead to the summer.
Mt. Redoubt may play a role should it blow soon, as that tends to produce a cooler summer. But for now let’s assume it doesn’t and see what ENSO and other teleconnections tell us.
The La Nina’s summer temperature depends on the year of the event, the warmest being the onset year, especially if it follows El Nino. Follow-up La Nina summers tend to be less hot and dry in the north.
Right now the models suggest La Nina weakens to La Nada.
The IRI global blend shows this weakened biased cool state.
First year La Nina Composite of years following El Nino shyows widespread warmth especially North central.
2007 summer was a La Nina onset after El Nino, although it was slow to spread west to the central pacific NINO regions 34 and 4. and the heat was muted and late.
This may be that during the intervening La Nina winters, heavy snows fall across the north and leave the soil moisture conditions at the start of the summer in much better shape. Moist soil retards heat and enhances summer precipitation. Last summer was as good example.
Cooling degree days were in agreement.
Third year La Ninas are fewer and seem to revert to more heat although it is south central areas.
If we look at other factors in addition and match it to the conditions this summer, we get a similar view.