With Memorial Day almost upon us, we are approaching the start of summer. The summer weather affects air conditioning/cooling load. So, what sort of summer can we expect? What do summer forecasts look like? And what are the key drivers behind these forecasts?
A second consecutive warm winter, the second warmest since 1950, has left North America with warmer than normal water conditions. These water conditions are affecting both the east and west coast. This has created the potential for a warmer than normal summer. Some current forecasts are even calling for a summer that could be a top five hottest summer, on a population weighted cooling degree day (CDD) basis, since 1950.
A consequence of the warm 2016-17 winter has been that water temperatures on coasts are warmer than normal. Another important trend influencing summer forecasts is changes to the eastern equatorial Pacific region water temperatures. There have been movements from La Nina (colder than normal) conditions in the equatorial Pacific to weak El Nino (warmer than normal) conditions.
The map below illustrates these key weather factors. Note the developing weak El Nino and Atlantic Decadal Oscillation (AMO). These represent warmer risk trends. Historically they have been associated with above normal temperatures across most of the southern U.S. The current NOAA forecast is working off of the assumption that the weak El Nino pattern will remain steady over the course of the summer.
NOAA Summer 2017 Outlook (June-August)
The above summer forecast from NOAA (issued April 20th) reflects a weak El Nino driven pattern. This is warmer than normal for much of the U.S. However, there are two long term ocean patterns that could pose bearish risks to the forecast. This potential risk would introduce below normal temperatures to parts of the Lower 48.
In the Pacific, the Pacific Decadal Oscillation (PDO) can either have a below normal or above normal water temperature pattern that can as long as 15 years. The PDO is centered in the northern Pacific Ocean from the Sea of Japan to the Gulf of Alaska. When the PDO is in a positive phase, the cooler waters of the Pacific Ocean and impact of the jet stream bring cooler than normal temperatures to the West and Northeast.
Summer Correlation (Positive PDO)
In the Atlantic, water temperatures off of Nova Scotia remain below normal. An above normal snow pack in eastern Canada that built up in March could pose a risk to the U.S. Northeast. This would allow colder Canadian air to back into the region, especially during the first half of the summer. The risks mentioned above are hard to forecast more than 14 days out. We will likely need to see how June patterns develop with the progression of El Nino. This example will help us to know more and see what influence the +PDO may have, if any.
Currently, it is likely that the summer of 2017 could average near the middle of the pack based on the past 10 years. We have had several warm summers with 2016 being the warmest on record. While we may not break any records, gas fired generation demand could still be strong overall.
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