El Nino Update: Rain in the South, but What about the North?

The winter of 2015-16 is still on track to have one of the strongest El Niños on record, and the question is no longer whether there will be a strong El Nino, but what effects will it bring to the United States. Forecasters for NOAA’s Climate Prediction Center (CPC) just issued their Winter Outlook (for the months of December, January and February), and they are looking for a good chance of above average rainfall for about the southern third of the conterminous states. This makes the prospects good for at least partial relief for the drought in California, but strong El Ninos bring the risk of dangerous and destructive flooding to the region.

The situation is a bit murkier for the Pacific Northwest, also in the midst of a drought and plagued by numerous large fires this year. The CPC outlook is diffident on the subject, predicting equal chances of being wetter or drier than normal for part of the area, trending toward more likely drier than normal in Idaho and Montana.


One clue might come from the NOAA’s Climate Forecast System version 2, or CFSv2. Looking at the current winter forecast from the CFSv2 we see that the coastal Pacific Northwest is forecast to also have above average precipitation during the winter.


Unfortunately, there is one very serious caveat to this forecast: the CFSv2 has very little skill forecasting precipitation in that region during winter; on the other hand the CFSv2 does have good skill forecasting for California. Of course, that could be at least one reason that the CPC forecast is a toss-up, while they’re confident in above average rainfall for Southern California.

Forecast for the East Coast: Rain, Rain, and More rain

The eastern seaboard of the U.S., already waterlogged from several days of heavy rain, can expect even more over the next week. A combination of an upper level low pressure area over the deep south and Hurricane Joaquin (now pummeling the Bahamas) are combining to send a non-stop stream of moisture laden air up the east coast.

As of late Thursday evening the forecast path of Category 4 Hurricane Joaquin was still up in the air, although most models are now keeping the storm offshore from the U.S. east coast as it heads north. If this turns out to be the case, the east coast will be spared the very strong winds and large storm surge that would accompany the storm, but flooding rains are still expected.


This plot, taken from the U.S. global numerical weather prediction model, the GFS, shows rainfall expected over the next 6 days for North America. Some of the forecast amounts are quite astonishing, the entire state of South Carolina is forecast to have over 5 inches of rain, with most of the state expected to see between 10 and 15 inches, with some of the higher elevations getting up to 20 inches! Pretty much the entire east coast should be wet, but the heaviest stuff is concentrated from northern Georgia to Virginia.
Of course, this will be dependent on the exact track of Hurricane Joaquin. If the storm tracks closer to land, the high precipitation areas will extend farther north, perhaps into Long Island and New England.