Now that the worst of summer is behind us and temperatures will soon begin to cool down, it's time to think about what's in store for the upcoming winter here in the ArkLaTex. Since most of the globe is covered by oceans, it's no surprise that variations in sea surface temperatures play a big role in the climate around the world. Thus, it seems logical that one can look at the state of the oceans now and find years in the past where ocean conditions were similar and use the weather from years gone by to make a very general forecast for the future.
If you study sea surface temperatures, you will find that there are many patterns during which SSTs rise and fall over a certain period of time. The three biggest of these oscillations are the AMO (Atlantic Multi-decadal Oscillation), the PDO (Pacific Decadal Oscillation) and of course the ONI (Oceanic NINO Index). The AMO is in the last half of the warm part of the cycle. Typically when the AMO is positive or above normal, then winter temperatures are warmer than normal. Remember the cold that we experienced back in the 1970s and early 80s? You guessed it. The AMO was negative. We are in the beginning of the part of the PDO cycle where it tends to be negative. A negative PDO can enhance the effects of La Nina. You might remember that the extreme drought that we experienced in 2010-11 came during a double dip La Nina. So just looking at where we are in the AMO and PDO cycles can lead one to believe that we will experience a slightly warmer and near or slightly drier than normal winter season (December-February). During my first edition of the winter outlook it looked like the wild card for determining the winter forecast would be the ONI index. I has reversed its trend and now looks to stay neutral for the winter.
Looking to the past to predict the future UPDATED 10/30/2013
I mentioned above that it doesn't take much to see that our winter will likely be warmer and near or a little drier than normal. That is the official forecast from the Climate Prediction Center as of this writing. My goal with this outlook is to give a little more detail on how much and where. I figure that the answer could lie in the intensity of the AMO, PDO and ONI cycles. The latest AMO reading came in at 0.290 with an upward trend. The PDO reading is -0.48 with a downward trend. If you have read this article in the past then you know that the PDO has increased rather dramatically in the last few months. This has changed my winter outlook somewhat. More on that later. The ONI is neutral at -0.2. Since we have data on the AMO, PDO and ONI that go back several decades, I tried to find years where the January AMO was 'strong positive' (above 0.15), the PDO was 'weakly negative' (between 0 and -1) and the ONI was neutral. (-0.5 to 0.5). It turns out that there is only one winter since 1950 where the AMO, PDO, and ONI are classified as they are now. That was the winter of 1962-63 and it proved to be much different than what I posted here previously and what the Climate Prediction Center is forecasting.
The map on the left shows the average temperatures around the country during the winter months (Dec-Feb). It shows a very cold winter for the Great Lakes and rather cold temps for the ArkLaTex. If this repeats this winter then we should expect temperatures that will average out to be 3 to 4.5 degrees below normal. That may not sound like much but, January of 1963 now stands as the 9th coldest January on record. Overnight temperatures that month dropped as low as 6 degrees above zero. The map on the left indicates that we should expect the rather soggy conditions that we experienced during the past few months to change. Back in the winter of 1962-63 we experienced rainfall totals for the December through February period that were 7 to 10" below normal. In Shreveport that winter now stands as the 7th DRIEST winter on record with only 6.23" of rain for the entire 3 month period. That's less than half of our normal rainfall.
Will it Snow? (Updated)
Probably the most popular question about winter that we meteorologists get here in the south is, "Will it snow this winter?" My answer for this winter is that the chance is better than normal. This has not changed from what I posted here earlier, however, the amount of snow that we experience could. Earlier it looked like we could expect to see a decent snow event, however now it looks like our snowfalls should be rather light. During the winter of 1962-63 Shreveport received on 2" snowfall during the month of February and Texarkana had two dustings of snow. One in January and another in February.Why this outlook is not set in stone
I often like to say that any forecast longer than 10 days is not really worth the paper it's printed on. Admitedly, you should take this outlook with a grain of salt. There are many....many....many more factors that influence the weather patterns around the globe than I have the time and/or space to write about here. There is also the possibility that the assumptions on the values of the oceanic oscillations that were used to create this outlook could change. It they do, of course I'll update the outlook. This has already happened once and could happen again. Another concern is the fact that there is only ONE winter similar to our current oceanic indices. Statistically, I would feel much more confident if I could take the average of many more. If you read this article before the October edit, you may remember that I was able to take the average of 5 winters to create that outlook.
The latest 90 day outlook from the Climate Prediction Center indicates that we will likely experience above normal temperatures and near normal precipitation. Because oceanic conditions in the Pacific have changed over the past few months, my outlook for the upcoming winter has dramatically changed and is very different from the CPC outlook. It now appears that we will experience below normal temperatures with cold that we have not experienced here in several years. It also looks like our wet autumn conditions will give way to a rather dry winter. Rainfall amounts could be anywhere from 7 to 10" below normal which is less than half of our normal precipitation. It also appears that we will have an above average chance for some light snow. Of course, this outlook is not set in stone. A good way of interpreting what you just read is "Odds are that the ArklaTex will experience below normal temperatures, below normal rainfall and a better than normal shot at some light snow". New ocean data will come out next month. I'll post an update to the winter outlook if needed.