One of the things I did not factor in too greatly into my forecasts this winter was the impact the La Nina was having on our weather here in the United States. This was not a strong La Nina but it was strong enough to keep the weather pattern in a progressive west-east pattern. This has played a role in the development of storms and the staying power of the northern and southern jet streams.
As you see a La Nina is a general cooling of the equatorial Pacific waters. This causes the ridge in the Pacific to almost act as a block keeping the colder air in the north and not allowing huge temperature variations of hot or cold across the country. It also causes the Polar jet or northern jet to be very fast, but weak. It also doesn’t allow any phasing of the two jet streams. Unless there is fair blocking to our north it also keeps weather systems progressive. Thus, storms don’t “stick” around for any length of time. Neither does the cold air. We’ve been below normal temperatures for most of the Winter; however, because the northern jet is weak and progressive the storms have gone further north, or not been carrying too much moisture unless enhanced by an offshore system.
New data suggests that La Nina will continue to have an impact into the Spring. This should actually be good news for planters :} Lots of moisture from the south. Water is good!