Since there's no Summer 2012 thread
I'll post this here. It's from Meteo Steve D so i hope you appreciate it. It's a long discussion which I havent even read fully yet.
Non-Member :: NY NJ PA Weather Forecasts
FORECAST DISCUSSION FOR 04/30/12
So I got a few emails about whether I will put out a summer forecast.
Apparently the usual suspects put out a cute map and forecast for the summer. Of course, I’ve been talking about the summer in these discussions for weeks now, but today I’ll summarize my thoughts on this summer.
The summer pattern is going to be influenced by three factors, the stratospheric conditions, the MJO, and the evolution of El Nino. These three factors will enhance the upper level ridge over the Plains and Southeast, lock in a trough over Southeastern Canada, and eventually kill off the hurricane season in August and September.
The stratosphere as you know is VERY cold. Historically cold in fact over the mid latitudes or the United States.
This cold stratospheric conditions enhances 500 MB heights and allows for hot air masses to become significantly enhanced. However, as we look at the stratosphere at the high latitudes, the stratosphere has warmed to near normal levels. At this time of year, the near normal temperatures is similar in influence to above normal temperatures, which when compared to the freezing cold anomalies over the United States, acts like a strong stratospheric warming event over the higher latitudes due to the thermal gradient. As a result, you end up with a negative NAO pattern that is naturally shifted further north.
The next aspect is the MJO which is slowly losing influence on the 500 MB pattern as El Nino slowly starts to take hold of the 500 MB pattern. The MJO is expected to spend a great deal of time in a neutral state this summer, but when the MJO goes into phases 7,8, and 1; that’s when the negative NAO pattern shifts further south and the potential for heavy rainfall over the East increases.
As for El Nino this summer. The development of this feature is going to be tricky. There is some major question on orientation of El Nino for later this summer. I simply don’t have enough data on defining the orientation of El Nino right now. However, I can say that I expect El Nino to be weak. In fact, given the lack of sea surface thermal gradient and sub surface thermal gradient, this El Nino will likely be one of the weakest we’ve seen in some time with anomalies barely qualifying.
The weak El Nino pattern will eventually help to enhance the Sub Tropical jet stream, which in turn will limit the potential for hurricanes this season, especially by August.
So to put this all together, I am expecting a ridge to be a dominant feature centered over the Mississippi Valley and at times shifting to the Southeast coast. A trough will be a persistent feature over Southeastern Canada, especially around the Canadian Maritimes with a ridge over northern Greenland. Remember, this whole pattern is shifted north due to the time of year. This will put the northern Mid Atlantic on the northern edge of the heart of the hottest air masses but will also limit the potential for severe weather and lead to long strengths of dry conditions as disturbances collapse while diving from the Great Lakes into the coastal waters of the northern Mid Atlantic.
Basically we are going to lock into the pattern we are going to see this week with a constant battle between the modified Polar air masses over central Canada and the very hot air masses over the Mississippi and Ohio River Valleys. When the MJO goes neutral, watch out for heat waves as the ridge is able to expand to the northeast and the negative NAO starts to give way. When the MJO goes into 7, 8, and 1; that’s when disturbances are able to dive and intensify off the East coast and a rain storm is possible. I don’t think this pattern configuration is conducive for severe weather outbreaks for the northern Mid Atlantic at all. However, a Mesoscale Convective Complex is possible from time to time.
Later in the summer, the influences of El Nino will start to be felt, but I don’t think we’ll see the true pattern influences until September. Still, we’ll note the first key influences with strong shear associated with the Sub Tropical Jet Stream over the Tropics. Frankly, I think the hurricane season will be rather quiet over the Atlantic with the exception of areas in the Gulf of Mexico and western Caribbean Sea. As for the northern Mid Atlantic, the evolution of El Nino will eventually allow for deeper troughs to build into the Eastern United States, however the intensify of that trough will be dependent on the state of the stratosphere by August which at this time is still debatable. I expect temperatures to average 1 to 3 degrees above normal with precipitation below normal.