Why is it so warm here? (And not elsewhere)

So my mother asked me the question the other day: why is it that the rest of the US (or at least, the lower 48 states) has been so cold lately, but here in Florida, it’s been so hot? Well, my first thought was to ask what ENSO was currently doing to see if that would offer a clue: no dice, ENSO is doing nothing right about now. So I told her “I don’t know mom, weather is just weird sometimes” and let the matter rest there. But the question “Why?” kept eating at me. Finally I decide to do a bit of a “forensic” analysis. First, I decided to ask the question: when, in the past, has the US as a whole, seen Decembers colder than average, while at the same time Florida, as a whole, has seen Decembers warmer than average? It turns out that since 1895 (relative to the 1895-2012 mean), the answer is in the years 1897, 1902, 1911, 1916, 1919, 1924, 1926, 1932, 1948, 1951, 1961, 1964, 1967, 1972, 1978, 1990, 1992, 2008, and 2009. Now, looking at the years since 1948, I can create composites for those from ESRL’s composite page. The result looks like this:

DecembersColdUSWarmFlorida48on

A couple of things stood out to me: that these years tend to feature a warm Antarctic and a cold Arctic, at least in the Reanalysis. But on the other hand, the reanalysis is least reliable in those areas due to sparse data. Moreover, this December has, so far, been warmer than average in Alaska, where the above map shows it cold. One interesting place where the maps *do* match, however, is the North Pacific, where much of it is above average in temperature in both. This got me to thinking, “what about the PDO? ENSO is neutral, but the PDO is probably negative right now.” And sure enough, yup, it is! Which got me wondering, again, how the PDO correlates with December Weather in the US. This is the plot:

DecemberPDOCorrelation

Indeed, Florida is in the Negatively correlated region, so a negative PDO would tend to be associated with a warm December in Florida-but oddly enough, also much of the rest of the US. However, negative PDO values are also often associated with La Nina conditions, which presently are not prevailing. This lessens the impact of the PDO in being associated with a cold US *generally*. So the explanation for our warm weather and the rest of the US’s cold weather? I think, but need to investigate further, that we can attribute it to the conditions in the Pacific: the presence of warm water in the middle of the North Pacific, in the absence of cold water in the Equatorial Pacific:  Cold PDO-No La Nina pattern.

Advertisements

3 Responses to “Why is it so warm here? (And not elsewhere)”

  1. None Says:

    Interesting post. However, additional heat does not just appear from nowhere. There was be some reason, for example reduced cloud coverage due to higher air pressure (if that is a rational combination i have no idea), that causes the extra heating. Of course, the higher air pressure must also be caused by something etc etc. There has to be a chain of causes from some conditions in the pacific (which of course must have their own cause).

  2. timetochooseagain Says:

    The physics is an interesting question. For now I am focused on operational seasonal weather forecasting.

  3. Warm weather part deux | Hypothesis Testing Says:

    […] Previously, I began an investigation into why we have recently had warm weather in December here in Florida, when most of the rest of the country has not. I identified the likely culprit as being a teleconnection between US weather and warm anomalies in the middle of the Northern Pacific. To investigate this further, I decided to use HADSST3 to examine the anomalies (relative to the mean value for all Decembers available) in the region in question, which I estimate to be about 30-50N and 180-208E. Downloading the data from KNMI, I then looked at the years I had identified as probably matching our recent pattern historically (below average US, above average Florida). As it turns out, the average anomaly relative to the long term mean for those Decembers was about .4 K above average, which confirms my suspicion, I think, that our recent pattern has a bit to do with warm water in that region: there is at least some association between warm anomalies there and a pattern of below average temperatures for the US as a whole and above average temperatures for Florida, in the month of December. Of course, this is probably not the only phenomenon that can be associated with a warm Florida and a cold US: at least some of the years I selected had below average temperatures for that region (those that didn’t, had an average anomaly of ~.87K). At any rate, I figure it was worth looking into a couple of additional details. First, the PDO: For the official PDO data, the average December value in the years (excluding 1897, not available) I selected as analogs, was in fact about -0.68 below the long term mean (1900-2012) and the value for the years where there was, in fact, a warm anomaly in the region I selected, was about -1.2 below the long term mean, which confirms that the analog Decembers were generally during negative PDO conditions. In fact, in the subsample of years with actual positive temperature anomalies relative to the long term mean in the selected region, only 1992 had a PDO value for that December above the long term mean; it seems probable that the actual reason for the cold weather in the US that year was the eruption of Pinatubo in 1991, which probably also disrupted the PDO pattern’s connection to weather phenomena somewhat. I think this more or less confirms my diagnosis: a negative PDO (warm central North Pacific Ocean) is teleconnected to warm December weather in the South East US, a link especially strong during La Nina years, but present to a lesser extent, and in  a reduced area, in years without a La Nina. Similarly, a negative PDO is associated with cold weather in December in much of the US, and this is even more true absent a La Nina. […]

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s


%d bloggers like this: