BLOG: 1st Half of July Recap, Hot Weekend Forecast, El Nino and Our Winter

This blog post will cover a lot of things, including what the winter may bring. Buckle up! (Click on images to enlarge)

July is half over and of course most know that it has been cool and damp so far. Here’s how temperatures and precipitation look in calendar form:

julytempscal julyprecipcal

Look at all those below average days; only 4 days out of 15 have been at or above average. The wet pattern that started at the end of May has continued. This map shows precipitation anomalies (difference from average) over the last 60 days: precipanom

Some parts of the region have had over DOUBLE their average precipitation since the middle of May.

How has the 1st half of July shaped up versus previous years? 2015 is the last dot on the right hand side. Temperatures: july1sthalf

After several warm openings to July in a row, the last 2 have been cooler.

Precipitation:

july1sthalfprecip

So what about the rest of the month? Well after a beautiful day Thursday, we have the hottest weather of the summer coming Friday-Monday. The jet stream right now features a familiar pattern, with a trough, or dip, in the Northeast. That’s why it is cool.

JETTODAY

But over the weekend, the ridge in the middle of the country will flex it’s muscles and the heat will finally get the green light  to come east. Notice how different things look by Sunday:

JETSUNDAY

So the heat is coming and it will be accompanied by tropical dewpoints. Heat Index values will be, well, no fun Saturday and Sunday. Find a pool.

hisat hisunday

Overall, the second half of July is not likely to be too remarkable. The CFS (Climate Forecast System) model shows temperatures perhaps being a bit below average overall:

cfstemps

Precipitation, if the model has the right idea, may be near or a bit above average: cfsprecip

You probably have heard about El Nino coming on strong this year. A reminder: El Nino does not “come” or “go” places…you see a lot of silly headlines about “El Nino Coming to California!” in the national press. (Side note: the national press is, in general, AWFUL at covering weather and science. But I digress.)

El Nino is a warming of the water in the equatorial Pacific Ocean, near South America.  The one that is evolving may end up being a record strong event. While the effects of El Nino (or the opposite, La Nina) on our weather are typically not as pronounced in the Summer, it can have a big impact on our Winter.

We are a LONGGGG way from Winter but just for fun let’s look at a couple of things.

First of all, in addition to a strong El Nino we have to pay attention to all the warmer than average water off the west coast of North America.

sst

This is the positive phase of something called the Pacific Decadal Oscillation and it has had a big influence on our weather over the last 2 winters. All that warm water tends to promote ridging near the West Coast of the US and Canada and when there is a ridge out there often there is a trough over parts of the East. It is a big reason why the last 2 winters have been so cold.

To get a hint at what this coming winter might bring, I looked back at moderate to strong El Ninos that occurred in concert with a positive PDO. When you throw all those winters in the hopper and average them, here’s what the map looks like in terms of temperatures:

analogs

Cool in the South and warm (compared to average) in the North. A bit warmer than average here.

Precipitation:

precipanalogs

Wet along the West Coast and in the Southeast. Dry around the Ohio Valley.

These are just a couple of the factors that go into a winter forecast. We will be looking at many more variables as we prepare our official forecast in October. I will say at this early juncture that this winter is not likely to be the 3rd harsh one in a row. Will it be as warm as some El Nino winters are? I am not sure about that; the positive PDO could still play a big role. What about SNOW?? That’s a much tougher call and always is. It can still be a snowy winter even if it is not that cold.

A look at the years that most closely match our El Nino and PDO conditions shows a variability in snowfall, but a few do come out below average (about 60″).

: SNOW

Much more on the winter in a few months!

Thanks for reading.

Eric

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