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Showers remain from the coastal storm
on Tuesday, but abrupt changes coming
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Summer of 2016 Seasonal Outlook

After a relatively cool Spring as a whole, we now look forward to the summer months and what it could potentially bring to the region. A big part of our forecast has been following analogs, which are past years that resemble the output of the current year thus far. The use of analogs has served us well in the past, but no two years are exactly alike… so we are looking for general similarities with climate, teleconnections, and a slew of other factors. We will examine the summer months of June, July and August in detail throughout this outlook, and outline the factors that brought us to this seasonal forecast.

Note: Any image in this outlook is clickable for better viewing

ENSO: The state of the climate

elnino

Recent evolution of El Niño has shown a steady decline to near ENSO-neutral levels, and they are expected to continue that decline. For the first time in over a year, ENSO raw observations were all in a neutral state as of the morning of May 22nd. This simply means that the water (sea surface) temperatures in primarily eastern the equatorial Pacific are nearing what is considered to be “near normal” compared to climatological averages. Each region varies, as shown above, but this is expected to transition to a La Niña (cooler than normal sea surface temperatures in the equatorial Pacific) over the summer. A cool graphical representation of the sea surface temperatures in this region is illustrated below:

elnino2

Climate models all show this transition from the near-neutral state of ENSO we are in now to a La Niña over the course of the summer. This will have climate impacts of the overall pattern for summer, as well as down the road with Fall and Winter.

sst2
sst

Other climate factors: teleconnections

For an extended time now, the Pacific Decadal Oscillation (PDO) has been primarily positive. The PDO, which is a measure of sea surface temperatures (SST) in a different location, the northern Pacific, also has a hand in driving our weather patterns across North America. During a warm, or “positive”, phase, the west Pacific north of 20° latitude becomes cooler and part of the eastern ocean warms; during a “cool” or “negative” phase, the opposite pattern occurs. This is illustrated below, showing a typical positive PDO. Blues indicate cooler waters, whereas the orange/reds indicate warmer waters:

PDO_Pattern

Currently we can see a near-textbook +PDO across the northern Pacific above 20°N latitude. It has been argued that the persistent +PDO, when combined with a predominantly -EPO (Eastern Pacific Oscillation) pattern would produce at times cooler than average temperatures. We have seen that a lot in late April through the first 3 weeks of May.

PDO

The correlation between the +PDO and -EPO is well documented, and supports the cooler regime. But climate models for the summer show that the +PDO will weaken, and the EPO will turn predominantly positive. If it does that, it supports the pumping up of the southeast ridge in the U.S., and a Bermuda High is established. A Bermuda High means the dreaded three H’s for this area:  Hazy, Hot, Humid. Although I see there being stretches of these heat waves, I don’t see it in an overwhelming capacity. These stretches of heat waves will most likely center around July and August, namely the period between July 15th and August 15th, which just so happens to be [climatologically] our warmest period.

Although the climate models predict a transition to La Niña this summer, the transition has been delayed to just get back to a ENSO neutral state, and previously the model guidance suggested this transition would occur sooner. That delay combined with a usual lag time to feel the effects of a La Niña state of 4 weeks or sometimes longer, we probably can’t assume typical La Niña climate impacts for much of the summer months. It is one of the main reasons why we are not going to go as aggressive with temperatures overall as many major outlets/competitors, but still warmer relative to average overall. In retrospect, the argument some have made for a cooler and wetter summer I just don’t see enough support for at this time. Our weekly/public long range products will update this seasonal outlook in more detail on a week by week basis each month throughout the summer, and can be found at http://epawaweather.com/long-range-outlook/

The 1983 Analog Year

Our two main analog years heading into the Spring were 1973 and 1983, and those two years when matching up the current year to years’ past were the two that stood out. Given the progression of Spring from a climate standpoint, we can see in hindsight that the Spring of 1983 was as close to a match to this year as one can come using past analogs. Using ENSO/ONI index below, we can see climate has progressed almost spot on to 1983 with regard to starting in a strong El Niño, and headed toward neutral where we are embarking on now, to a weak La Niña by Summer’s end.

Why continue to use the 1983 analog? No other analog is as close to matching this year as 1983 was, and it continues to be the frontrunner by a considerable margin. The analog was nearly spot-on in Spring, so it doesn’t make much sense to abandon it now without cause.

oni
pdo-graph-110614
jun83

June of 1983 had near to slightly above temperatures across the region. Long range guidance (climo models) also show this continuing this year. No real extremes on either side.

june83precip

June of 1983 was the only month of the three summer months that ended up near/slightly above normal precip.

jul83

July of 1983 was noticeably warmer, with more heat waves, but also some near normal periods. Although above normal here, focus of greatest warmth is in the Northern Plains.

july83precip

July of 1983 saw long hot and dry periods, resulting in below normal precipitation for the month as a whole.

aug83

August of 1983 continued above normal with heat waves mixed in with the near average temps. Above normal temps here, greatest warmth remained in the Northern Plains.

aug83precip

August of 1983 showed a continuation of the dry conditions, combined with a strong Bermuda high and SE ridge.

The 2016 EPAWA Summer Outlook

Overall, we expect the three month period between June 1st and August 31st to be mostly above normal and relatively dry. There will be stretches of 90°F+ warmth that will result in several heat waves, more so than last year is a good bet, and higher than normal. The breakdown for the EPAWA coverage area on a month by month basis is below, with both temperatures and precipitation. We purposely stopped at August 31st, as most in the meteorological community consider June 1st-August 31st “meteorological summer” despite the official calendar end to summer coming and Autumnal Equinox occurring on Thursday, September 22nd.

The Autumn Outlook will follow for the three month period of Sept 1st through November 30th during the last week of August. Note: Any image in this outlook is clickable for better viewing

JUN16

June 2016 is expected overall to average near to slightly above normal across the region, with the highest chances to see slightly above across the northern tier.

Precipitation:  Near to slightly above average

JUL16

July 2016 is expected overall to average above normal across the entire region, with the highest departures above normal favoring the northern 2/3rds of the region.

Precipitation:  Below average

AUG16

August 2016 is expected overall to be the hottest for much of the central interior locations, “cooler” as you head north/northeast into New England and SE toward the coast.

Precipitation:  Below average

Forecaster:  Martrich 24 May 2016, 2:30pm

My Pocket Meteorologist

Stay ahead of all storms heading your way while outdoors this summer and never get caught off guard!  One of our meteorologists will send you an alert when storms with lightning, or severe winds/hail are approaching so that you are safe and prepared in REALTIME. To take advantage of this great program throughout the summer months and year-round, click on the image below and select “Weather Alert Service”. Daily text forecasts and premium forum options are also available.

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