A review of the El Nino-La Nina forecast model ensembles suggests a rebound from a moderate/strong La Nina to neutral (the "El Nono") or even a weak El Nino is already well underway, with the La Nina forecast to disappear by July. Trends in sea surface temperature data over the last several weeks suggest the tranformation will be faster than the models suggest. However, late spring-summer effects on temperature for both cycles are rather muted, compared to winter. In any event, a forecast of neutral conditions suggests the best forecast for this summer's temperatures is climatology. Climatology doesn't preclude short duration heatwaves or cold snaps...it just evens them out.
PNA -Pacific North America pattern- (http://www.cpc.ncep.noaa.gov/data/teledoc/pna.shtml) forecasts support a warmer spring in the west and a cooler east but, as summer approaches, the linkage between the PNA and temperature anomalies weakens. PNA has a significant autocorrelation with ENSO.
In the short term (now to 2 weeks out) dynamical forecast ensembles and the NAO (yes, another cycle - see cpc.ncep for details) suggest much warmer than average conditions will develop the week after next especially over the southern Rocky Mountain states and lower Mississippi valley.
This week will see a large disturbance traverse the US from west to east; California today and tomorrow, exiting New England next weekend, with significant precipitation througout the Mississippi valley developing Wednesday, spreading to the entire east coast by Friday.
Cooler than normal temperatures will contine near the Great Lakes, New England and northern CA/Oregon, with near normal conditions elsewhere.