Summer Analogs for 2015

Here is our annual look as to how hot, hot, hot the summer will

be based on past performances.  (Download PDF version here)

A full-fledged el nino is underway in the tropical pacific. All

dynamical and statistical models keep it going, the differences

that exist are to its strength through this upcoming summer. The

dynamical and statistical models are averaging a moderate el nino

for the combined summer months. Some models, including the cfs2

and ecmwf are predicting a strong el nino. In the CPC monitoring

el nino era starting since 1950, the highest (warmest) summer

anomaly recorded was +1.5C (near or at the threshold for strong el

ninos) during the summer of 1997.

This upcoming week will really seal the deal that this May will

be unseasonably warm in Philadelphia. It "may" even be a top three

warmest. This follows on the heels of an unseasonably warm April.

Since 1872, the combination of both warm (top third of all years)

Aprils and Mays has only occurred twenty-three times. But it has

occurred eleven times since 1990 and six of the last seven

springs.

So we scoured the climate records to find budding or in progress

el ninos that coincided with both warm Aprils and Mays locally in

the CPC monitoring era. We found three past summers that met the

criteria. The one sign is that all three analog summers were

wetter than normal, hopefully keeping drought conditions from

intensifying further.

The North American Multi Model Ensemble predictions for this

upcoming summer has warmer and drier than normal weather expected

in our area. The International Multi Model Ensemble forecasts are

slightly more optimistic predicting near normal temperatures and

precipitation.

The analogs for Philadelphia are:

Year    June avg   July avg   August avg   summer avg   summer pcpn

1969      73.4        75.1      75.2         74.6        18.30

1977      68.6        77.8      76.2         74.2        15.50

1991      75.7        79.0      79.0         77.9        12.01

Avg       72.6        77.3      76.8         75.6        15.27

1981-

2010      73.3        78.1      76.6         76.0        11.28

Normal

The official CPC outlook for our forecast area is for equal

chances of above and below normal temperatures as well as equal

chances of above and below normal precipitation.