As meteorological summer begins, it is worth looking at what
to expect. Of course the big name being thrown around has been El Nino, and
that could certainly have an effect on our weather patterns. Although it’s the
biggest name, the El Nino is not the only player around that will influence the
coming months. I am going to take a look at the possible influences on the
summer and break them down.
The El
Nino
SOI (?)
MJO
PDO
Let’s start with the developing El Nino. Forecasters have
been calling for a strong El Nino to form this summer, but so far that has not
been the case. Past ENSO (El Nino Southern Oscillation) values, beginning in
September 2014, maxed out at +0.7 in October and November, but has since
stagnated, if not decreased in strength since then. Values December through
March have hung around +0.5-+0.6. For a more definitive El Nino to form these
values will have to show a distinct rise, and to fulfill the possibly overblown
El Nino forecasts, it would need to reach above +1.0-+1.5. The strong El Nino
forecasts have happened before, most recently this past summer and early fall,
where forecasters called for a very strong El Nino going into winter, but that
never materialized. ENSO values are given over a month after they happen, so
the values for April and May are not out yet. If they yield a strong rise in
ENSO values, then the strong El Nino forecast may be right, but observations so
far are not supporting the idea of high ENSO values.
This is important to consider because the strength of the El
Nino will influence our summer weather, which includes; the tropics,
temperature, and precipitation. If the El Nino is as weak as is currently
believed, then other factors will have more influence on our summer weather. If
the El Nino forms we may be in for a seasonable to cooler than average summer.
Precipitation for the Northeast will not be effected significantly by the El
Nino this summer. For many the most important portion of an El Nino summer
could be a less active Hurricane Season and some drought relief for California.
If the El Nino weakens any more or does not strengthen the
effects will be more negligible, and the summer could be more variable, and
other factors, which I will introduce, will be more influential.
Recent forecasts made by WSI and The Weather Channel are
more focused on the SOI values being shown, which are measurements of pressure
differences between Tahiti and Darwin, Australia. These fluctuations are a
product of ENSO shifts, and thus a forecast referencing these values are more
or less references the state of the ENSO. I have spoken about the effects of El
Nino on the summer and most likely do not need to go into further detail. I
will however provide with the forecast from
WSI and
The Weather Channel for
reference.
Now for the MJO (Madden–Julian oscillation), this is a gauge
of activity across the tropics. As of this moment the MJO has moved into the
western hemisphere. This means that tropical energy has shifted into the tropical
Atlantic and will be an influence on weather. The MJO moves west to east, and
is important for mid to long range forecasts. It will not help us understand
what August will be like, but can get us through June and early July. While the
increased MJO is around, which it has been for almost two weeks, intense precipitation
events are more likely, as there will be more tropical moisture and energy to
tap. This has been witnessed in the south and northeast recently, where mist
air that originated from the tropics, came up and prepared the stage for hefty amounts
of rainfall. As long as the MJO is around, storms packing tropical moisture
will be quiet potent.
Finally, the Pacific Decadal Oscillation, PDO. At the moment
the PDO is at .99, and presumably dropping. A lower PDO, although not negative,
will hamper the growth of a strong El Nino event, and lead to summer heating
across the eastern two thirds of the United States. The PDO has been dropping
at an average rate of .18 per month since December, which, it being June, would
put us at roughly .81 or lower, assuming it’s a steady drop. This will set up a
pattern where the El Nino will struggle to strengthen, and the MJO + PDO will
go to work to warm up the country east of the Rockies. Warm and moist air will
dominate for a time being, with interspersed moments of cool air as usual.
In regards to Hurricane season, having the MJO around and
warm air, may give life to the tropics, contradicting current forecasts. It is
a possibility. I am not making a hurricane season forecast of my own.
Here’s the Run Down
June-
With the MJO around and a weak El
Nino, the Northeast will be warmer than average, with a
heat wave toward the
end of the month. Precipitation for the past few months has been below average,
but I believe June will erase these deficits.
July-
The early part of July should be
warmer than average, and with continued higher precipitation. From mid-July to
the end of July, temperatures should begin to average out.
August-
Average temperature, but without
the MJO, lower amounts of precipitation.
*Disclaimer: This is my first ever season forecast. Do with that information what you want*