It Must Come Down, Right?

We get a lot of requests in the weather department.  Today I am going to grant one.  No, I can’t do much to relieve the drought.  And no, I can’t do much to help your A/C bill, at least not for a few days.  There’s not much I can do with requests regarding the actual weather.  But, I am happy to answer requests as far as this weather blog is concerned.  Earlier this week I was asked via twitter to write a blog explaining why we are under a “La Nina Watch” and what the heck is this “La Nina” thing anyway.  Ask and you shall receive…

La Nina is the opposite of El Nino.  That was easy.  Any other questions?  OK.  Here’s more info…

Actually, this was a very timely question because we only get updates on the El Nino/La Nina situation from the Climate Prediction Center once a month and this week happened to mark the release of the July update.  The final “El Nino Advisory” was issued with the June update as the very strong El Nino we witnessed this past winter finally faded away.  Now we are under a “La Nina Watch.”  A “La Nina Watch” means conditions are favorable for the development of La Nina in the next 6 months.  So what does that mean?

Every few years, for a variety of reasons that we don’t entirely understand, the ocean water near the Equator in the eastern half of the Pacific Ocean (near South America) gets warmer than normal.  We call that “El Nino.”  Why?  Because it generally peaks around Christmas it is named for “The Child,” as in The Christ Child, and “El Nino” is Spanish for “The Child” as you probably know.  When the same area of the Pacific Ocean gets cooler than average, we call that “La Nina.”

We aren’t talking much warmer or much cooler.  Usually its only a 1/2 degree Celsius or maybe up to 2 degrees Celsius for a stronger event.  But, because we are talking A LOT of water and because water has the ability to store A LOT of heat energy (you know this if you’ve every tried to boil water), that little change in water temperature has a big impact on the atmosphere worldwide.

 

In the past 60 years, strong El Nino events have often been immediately followed by strong La Nina events.  In fact, the stats show the stronger the El Nino, the more likely you are to get a La Nina in the following year.  We just witnessed a VERY strong El Nino.  So, it makes sense that we would be expecting a La Nina to develop.  In fact, the CPC said there was a 75% chance that La Nina would develop this fall and winter in their June update.  In the July update just released a few days ago, that had decreased to a 55-60% chance.  Why are they less certain now?  Well, La Nina isn’t developing as fast as it did after the last very strong El Nino in 1998.  In other words, the temperatures aren’t falling as fast now as they did this time in 1998.  Over the last month the water temperatures have been within a fraction of a degree either side of normal.  Plus, the atmosphere isn’t behaving like it should be for a developing La Nina.

Those observations have shaken the confidence of the CPC forecasters a bit.  They believe that if a La Nina develops, it will likely be a weak one.  The average of the model predictions indicates that water temperatures may only cool around 1/2 degree Celsius.

Either way, don’t let the words “La Nina Watch” concern you.  You don’t need to check the radar, stay tuned for updates, or keep your eye to the sky.  La Nina would only impact us this winter, if at all.  The impacts of La Nina are generally felt more in the southern and western US, and not so much here in the northeast.  A weak La Nina, if it develops, may have little to no impact on the weather in New England.  However, if La Nina sticks around into next summer, it may have an impact on the hurricane season of 2017.  Generally, La Nina conditions in the Pacific lead to more hurricanes in the Atlantic.

How about those other requests?  Today will be almost as hot as yesterday, but not nearly as humid.  So, there is some slight relief from the heat in that sense.  There is a slight chance of pop-up late day showers and storms, but only in western MA.  So, there won’t be any drought relief today.

There will be more clouds around on Sunday and a better (about 40% chance) of showers and thunderstorms during the middle of the day for the entire area.  This won’t be a drought buster, but a few of us might get some measureable rain Sunday.  Plus, the clouds and spotty showers should be enough to keep us out of the 90s for one day.

The heat and humidity are back in a big way on Monday.  In fact, Monday will probably be just about as uncomfortable as it was yesterday.  A cold front arrives late on Monday and that brings us another 40% chance of showers and storms.  Behind the cold front it gets…well not cold…but cooler and much more pleasant with lower humidity for the middle of the week.

I’m happy to answer any other weather/science related questions via twitter (@CBMRob), facebook (facebook.com/RobEicher), or email (reicher@whdh.com).  If you want to keep up with the latest on El Nino/La Nina you can read the technical discussions from the CPC here and a fantastic blog for laymen from NOAA here.  Thanks goes to both of those sites for the information and graphics used here.