La Nina and Winter 2010-2011 Outlook

Winter is upon us. Last winter was one of the coldest winters on record for Southeast Texas and throughout the nation. This was due to El Nino we had. Right now, it is the opposite, La Nina. La Nina is when the equatorial Pacific cools down, unlike El Nino, when it warms up. La Nina and El Nino are part of the El Nino Southern Oscillation (ENSO) cycle.

What does La Nina winter mean for us and the nation? Typically, La Nina gives us a warmer and drier winter. The last time we had a La Nina winter was in 2008-2009. That winter was warm and dry. There were no big freeze that time in Southeast Texas. One difference with the current La Nina from 2008-2009 La Nina is that the current one is a strong La Nina.

Here is a scatter plot that shows a correlation of La Nina and El Nino winters in Upper Texas Coast in terms if temperature and rainfall. December to February is defined as winter season by the NOAA.

ENSO and Upper Texas Coast Precipitation

The scatter plot shows that the strong or warmer ENSO is, the more wetter the winter will be. La Nina for the Upper Texas Coast means a drier winter. However, sometimes there are heavy rain events in a La Nina winter. The winter of 1949-1950 had a strong La Nina and yet the Upper Texas Coast rainfall total from December 1949 to February 1950 was 14.89 inches. So, it could be possible to see heavy rain during a La Nina, but that is an outlier. In general, La Nina winters are going to be dry for the Upper Texas Coast. I expect this winter will be dry.

ENSO and Upper Texas Coast Temperature

The cooler the La Nina, the warmer the winter it is for Upper Texas Coast. Does this mean we are not going to have freeze and have no storms? No, in fact some of the biggest freeze have occurred in La Nina. The winter of 1988-1989 was a La Nina winter and there was this huge freeze that came in early February of 1989. It was below freezing for five days straight. I remember it because it was cold and there was frozen rain which iced up roads. There was even a few snow flurries during the freeze. Another La Nina winter was 1950-51 and there was a huge freeze that occurred from late January to February of 1951 and the duration remains the longest even to this very day for Southeast Texas.

How does La Nina affect the nation? I think the best analog for the 2010-2011 La Nina are:

Why did I choose those years? The current La Nina is a strong one and those winters had moderate/strong La Ninas.

Here are divisional maps I generated from US Climate Division Dataset Mapping Page.

Let’s start with precipitation.

La Ninas analog to the current one show that a large area of America is drier than average, especially in Texas, Gulf Coast, Florida, and Southwest. What does this winter bode for us? It is likely going to be drier than normal. There is a real possibility that we could see a serious drought situation by the time spring is around.

If you want to find a wetter than average area, you would have to go north. La Nina causes the jet stream to be further north than usual. The jet stream carries low pressure systems and cold fronts that give rain and cold weather. During a La Nina, the low pressure systems and cold fronts are further north, which makes most of the nation drier and warmer in the winter.

Let’s look with temperature.

La Ninas analog to the current one for America are warmer than average. In fact, most of the nation is warmer than average. We are less likely to freeze ourselves out in the middle of winter. That means less heating bills to be paid. If you want to find cooler than average in a La Nina winter, head out West. It is cooler than normal. Now, just because we are in a La Nina does not mean we are going to be free of Arctic blasts. As I have mentioned, Arctic blasts can occur in a La Nina winter. Next time I will look at other atmospheric and oceanic patterns besides El Nino and its impact on winter. They are North Atlantic Oscillation (NAO), Arctic Oscillation (AO), and Pacific-North American (PNA).


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