Saturday, July 25, 2015

Preliminary 2015-2016 Winter Forecast

Hello everyone, and welcome to The Weather Centre's Preliminary 2015-2016 Winter Forecast. As always, the standard caveats of very-long range forecasts apply here; in other words, do not take this at face value. Rather, this should be interpreted as an introduction to the conditions that are probable in the coming winter, which will be built on in coming months.
As a note, this outlook will be far shorter than previous seasonal outlooks. This comes from a combination of items, which have significantly restrained my time available to work on this. However, I'm committed to putting out this product, as I have been advertising.

We will begin with a look at the sea surface temperature picture across the world.

Glancing around the globe, we see a few points of interest.

1) We do have a Moderate to Strong El Nino coming on, continuing to manifest itself in well-above-normal SST anomalies off the western coast of Ecuador, well into the central Pacific. These El Nino's tend to result in warmer than normal temperatures in the North US, cooler than normal temperatures in the South US, as well as stormy conditions in the South and East US.

2) The warm pool continues to persist in the Gulf of Alaska and entire Northeast Pacific region. This is the same warm pool that brought us severe cold in the last two winters, through the abundance of ridging along the West Coast. If this warm pool is to persist into the coming fall and winter, the threat of a third consecutive cold winter skyrockets, especially given the warm pool's geographic location immediately upstream of North America, maximizing its effects.

3) There are below-normal SST anomalies around the island nation of Japan. The Typhoon Rule states that storms and high pressure systems that occur over Japan are 'replicated' in the US about 6-10 days later. The Sea of Japan experiencing below-normal SST anomalies could hint at a stormier than normal weather pattern for that area, which could spell a stormy winter if it continues into the fall and winter.

I will not be discussing the QBO or sunspot factors in this outlook. If this were a normal outlook, I certainly would, but there are things out of my control that have simply made the prospect of such an extensive outlook unattainable. I apologize for the inconvenience, and hope you can understand.
In spite of these time constraints, I have been glancing at long range models and some other seasonal factors, so I could come up with my preliminary thoughts on the coming winter.


Pacific Northwest: Very much a toss-up. Warm pool in Gulf of Alaska could spell a hot and dry summer, while the El Nino could bring about more wet conditions. I'll lean towards a warmer and slightly drier than normal Pacific Northwest this winter, with low confidence.

Southwest: Expecting a cooler than normal and slightly wetter than normal winter, as a result of the expected strong El Nino. Have to keep an eye out for interference from that warm pool in the Gulf of Alaska, which could dry things out yet again. Once again, a low confidence forecast.

North Plains and Midwest: A Strong El Nino predicts a warm winter ahead, but I'm not completely convinced so long as the body of warm water exists in the Northeast Pacific. Still, a slightly dry, slightly warm winter is my best projection for now.

South Plains and Gulf Coast: Decent probability of cooler than normal to average temperature pattern for the winter, along with some stormier than normal activity.

Southeast: Difficult forecast for this region, as the El Nino could result in a very wet and cool winter. However, there are other variables which significantly complicate this region's forecast, namely the Atlantic Multidecadal Oscillation, which I'm not prepared to discuss due to very low confidence. I'll side with a wet and cool winter for now.

Ohio Valley: Early projections do favor a slightly warm, slightly dry winter, and for now I agree. This is one of the less complicated forecasts (for now).

Northeast and Mid-Atlantic: This certainly has the potential to be a 'feast or famine' winter for the Northeast, in terms of snow. I do think we see around average temperatures for the winter, but I'll go ahead and favor a snowier than normal winter.


Saturday, July 4, 2015

Long Range Lookout: Cooler Than Normal July Ahead

This post is dedicated to the servicemen and women who are serving our country, who have served our country, and those who have made the ultimate sacrifice for our country.

It appears that a cooler than normal July is on the way for the nation.

We'll begin by looking over shorter-range indicators; in this case, the Typhoon Rule.

Tropical Tidbits
The above image shows forecasted 500 millibar anomalies over the West Pacific. Here, blues indicate negative height anomalies, symbolizing a trough or storm system in the area. Oranges and reds correlate to positive height anomalies, indicative of warmer and quieter weather.
This forecast is valid for July 14th, and we see a system just southeast of Japan, making its way north and east. This system was previously a typhoon, which looks to develop in coming days further to the south. As the typhoon approaches Japan, it will curve and head out to sea. Using the Typhoon Rule, we can expect a cooler bout of weather about 6-10 days after this happens. Recognizing that this forecast is for July 14th, we can extrapolate that to forecast a cool-down around July 20th to 24th, probably spilling over those dates a bit.

However, it's also likely that the entire month will end up cooler than normal for many in the country, due to what is happening in the Central Pacific.

A quick overview of the columns, going from left to right: The date for the data, the daily barometric pressure reading in Tahiti, the daily barometric pressure reading in Darwin, the daily value of the Southern Oscillation Index (SOI), the 30 day averaged SOI, and the 90 day averaged SOI.
In a nutshell, when the SOI is negative, El Nino conditions are favored in the United States in the following couple of weeks. We see that the SOI has been consistently negative since June 19th, and it's no coincidence that the United States has been predominantly cool since late June.
You can see how El Nino conditions, which are signaled by a negative SOI, make for a cooler than normal summer in the composite chart below:

Typical temperature anomalies during an El Nino summer
Since we remain in a negative SOI state this 4th of July, I'm expecting the rest of the month to end up cooler than normal for much of the country. Those in the Southeast and East could see slightly warmer conditions, however.

To summarize:

- A cooler than normal month of July is expected for much of the United States.