Tuesday, May 12, 2015

Summer Outlook 2015



Lots of factors go into seasonal outlooks: Ocean temperature trends, location of warm and cool pools, analysis of pressure patterns over the higher latitudes and Pacific Ocean, persistence. Contrary to popular belief, outlooks are formulated differently than day-to-day forecasts. The cold winter has told us that persistence forecasting can trump other variables because it makes the most sense. The atmosphere is often times slow to respond to changes so why mess with the prevailing pattern if it's strong.  This spring has shown us that although the winter variables remain, as a collective, the result can be quite different with a lot of variation.


May has been well above normal--warmest first 11 days since 1965 in northern Ohio.


Before we talk about Summer 2015, let's head back to last summer (2014). Ocean temperatures were still dominantly warm in the north and east Pacific nearing the west coast. Tons of talk about a Super El Nino faded as the equatorial Pacific temperatures dropped into neutral territory or slightly weak/central. Below are the ocean temperature anomalies for the overlapping months starting in April and ending in September.

SEA SURFACE TEMPERATURE ANOMALIES - APRIL THROUGH SEPTEMBER 2014
The ridge in the west driven by the warm coastal water continued to dominate into the summer.

The Bermuda High made a late season resurgence in the southeast which boosted temperatures by Labor Day. Cleveland's last 90 occurred on September 5th which was also the last 80 degree day until early may of this year.

Overall, the lack of any Bermuda High signature kept temperatures across the Ohio Valley and midwest below average for much of the summer


Notice how the Pacific water temperatures were somewhat reversed during the hot summers of 2010 and 2012.
SEA SURFACE TEMP ANOMALIES - OVERLAPPING MONTHS - APRIL THRU SEPTEMBER
 The resulting temperatures were above normal coast to coast in 2010 and 2012.


The conditions in the Pacific are much different since those hot summers of 2010 and 2012.  You can see the smaller Pacific changes since last summer...

LAST SUMMER -  2014
... The warm pool along the west coast is getting warmer and more concentrated. The cool pool northwest of Hawaii is building. Equatorial ocean temperatures in the ENSO 3.4 region have risen along with some larger basin increases more than at this time in 2014.

APRIL AND EARLY MAY 2015

According to the TAO PROJECT SITE, average ocean temps increased 0.4 degrees since January in equatorial Pacific down to 300 meters.  After sifting through the data, a quick volume calculation shows the increase in the volume of warmer water in the equatorial eastern Pacific since January is equivalent to the volume of Lake Erie 29 times over! That's a ton of water but it's still 5 TIMES LESS than what was present in early 1997 before the Super El Nino formed.

Big question: Will this evolve into a more significant El Nino than this past winter? CPC forecasts are calling for it.  The IRI forecast as well so I don't think there is any reason to stray from those blends. But I am skeptical of this turning into a major El Nino event. Too much warm water off the coast of Australia which keeps pressures low. Cooler water would keep high pressure west which would promote more westerly wind bursts keeping the El Nino machine churning and building.  Check out a great El Nino/La Nino video which covers the importance of the WESTERN COOL POOL from Australia's Bureau of Meteorology.



During the Super El Nino early stages in 1982 and 1997, the eastern Australian cool water was a dominant feature. The other strong El Ninos which started in 1972, 1965 and 1957 all had cool western Pacific water.



Until some western Pacific cool water develops along with continued moderate eastern/central warming this summer resulting in an MEI response, I'm staying bearish.

El Ninos circled

In my initial analog, I used last year along with several years with similar MEI and ONI indices coinciding with a building El Nino which weakens late this year in time for the following winter. 2005, 1993, 1980, 1977 and 1953 for starters.  The late 1950s are a very good match along with the late 1960s. 

April sea surface temperature blend looks like this:
The resulting summer sea surface blend looks like this.





Without taking into account the weak El Nino, the summer blend calls for below temperatures across the Ohio Valley this summer with slightly above normal precipitation.

Summer Blend WITHOUT EL NINO
Incorporating the El Nino yields a slightly different result for JUNE through AUGUST:

TEMPERATURES NEAR OR SLIGHTLY ABOVE NORMAL



PRECIPITATION ABOVE NORMAL


Our official SUMMER OUTLOOK IS AS FOLLOWS:




2 comments:

Lyle Blosser said...

Super clear analysis and presentation - thank you!

Lynn said...

Yes!