Last week we discussed how conditions in the northern Atlantic and North America were evolving to support an active and overall cool Summer pattern for New Jersey and much of the northern Mid Atlantic. In fact, this past week we saw just that influence with disturbances dropping south around an upper level low developing just east of New England. However, there is more to this pattern than just the Atlantic influences. In fact, what is happening in the Pacific is directly influencing and supporting the changes we are seeing in the Atlantic and North America.
The Pacific Ocean is featuring well above normal Sea Surface Temperatures in the northern Pacific and along the Equator and tropical Pacific. The conditions over the northern Pacific have been in place going back to last October. When warm water pools in the northeastern Pacific, specifically in the Gulf of Alaska, this is called a positive PDO. Meanwhile, the tropical Pacific is slowly transitioning into an El Nino with warm water anomalies developing from 140 East to 100 West Longitude between 5 degrees and 15 degrees North.
The positive PDO state is the primary driver in the weather pattern here. The positive PDO supports an active weather pattern around the North Pacific and typically leads to a prolonged trough to the south of the Aleutian Islands of Alaska. This trough position in the Winter was a key driver for the very cold and active weather pattern seen in New Jersey this past winter. The same pattern is in place now, although with a slightly different wave length set up due to this being Summer. Basically you end up with a parade of storms that enter the Pacific Northwest and redevelop over eastern North America. Much like shaking a rope, the wave length started in the Pacific translates to a trough over eastern North America and specifically from the eastern Great Lakes to the northwestern Atlantic. As a result, New Jersey is and will continue to be in a northwesterly to northerly upper level wind pattern that transports air masses from central Canada, northeastern Canada, and the northwestern Atlantic. Every once in a while when the pattern relaxes, the ridge that is in place from the Ohio River Valley on south to the southern Plains builds into New Jersey to provide a brief stretch of hot and humid conditions, much like this Memorial Day Weekend!
As far as the developing El Nino, the primary adjective here is developing. The influences of this El Nino are still minor for the Garden State. Still, there are some clear influence evolving. For one, there is far more moisture to work with in this pattern due to the Sub Tropical jet stream. As a result, when low pressure systems and troughs from the Polar jet stream are able to tap this moisture from the Gulf of Mexico, impressive heavy rain events can and already have transpired.
The combination of these features in the Atlantic and Pacific sets up an interesting dynamic for the Garden State that will likely lead to many Flash Flooding events and rather raw, wet Summer weekends. The three air masses that will be in play this Summer will be the Atlantic Marine air mass (moisture loaded yet cool), the Tropical air mass (from the Gulf of Mexico, moisture loaded, and hot), and the Polar Canadian air mass (cool and dry). The interaction of these air masses can and already have lead to a variety of weather impacts from severe weather (Polar and Tropical); prolonged showers, fog, and raw weather (Tropical and Maritime); and extremely heavy rainfall events (Tropical, Maritime followed by Polar interaction). Combine these factors with tropical moisture from remnants of tropical low pressure systems or direct hits from tropical low pressure systems and you have a set up for significant urban, stream, and river flooding throughout the region.
This Summer will likely to continue to feature near to below normal temperatures overall and above normal rainfall. Unless significant changes start to unfold in the Northern Pacific, expect this volatile weather pattern to continue right into the Fall of 2014.