Let me start by stating this is not a winter forecast,
but a review of what La Nina winters in the past have looked like when composited together for a mean outcome. La Nina says its gonna be a shorts wearing winter, Almanacs and persimmon seeds say its gonna be de ja vu last winter.
I say both those camps are too extreme. Yes La Nina usually means a warm winter, but there are other things like the North Pacific, the sun spot cycle and Atlantic Ocean hurricane season that argue the other way. So don't write off winter this year yet. I'll have my forecast out Dec 1st at the latest.
No two El Nino or La Nina seasons are ever exactly the same, first the El Nino and La Nina itself is never the same, and the other factors that impact seasonal weather in addition to the EL/LA signal are never the same. The long name for the ocean-atmosphere system is El Nino Southern Oscillation or ENSO.
Just because it looks like we will have La Nina (cooler than normal Pacific Ocean temperatures) this winter, does not guarantee that we will have the usual La Nina winter weather. To drive home that point, last winter we had the opposite of what we expect this winter--El Nino (warmer than normal Pacific Ocean temperatures). Normally this argues for a lot of warm air flooding the United States for a mild winter in much of the country. But instead it was quite cold for much of the nation, especially in the East and South. This is because other factors in the oceans and atmosphere/stratosphere overcame the El Nino factor, or more precisely combined with it, to create a more unique winter pattern.
So what we are looking at in this report is background information on the La Nina norm or average, simply laying the foundation for the future winter forecast which will be issued later, it will build on the La Nina base set forth here. The slide show maps and charts depict the La Nina temperature patterns from past La Nina's.
Map one shows the results from all past La Nina. Map two shows only La Nina winters that followed an El Nino, which is the case this year. Notice there are some differences, such as less warmth in the South. The third map shows the actual mean temperature for all La Nina winters: daytime highs and night lows averaged together.
Other maps and charts are labeled and are statistical analysis based. You may need to use zoom features on your computer to enlarge them for a better view, or save them and enlarge them for greater detail. We next look at the precipitation basic La Nina results from history. Note the tendency for some dryness along the Southern and Eastern fringes of the United States. See the maps for details. Note the snowfall signal is quite different in Georgia compared to what the El Nino signal was going into last winter. The snow outlook does not tell us anything about freezing rain or sleet for which national data is not readily available.
The two Farmers Almanacs are calling for a snowier and colder winter in much of the nation than would be indicated by a standard La Nina. But as I pointed out, there really is no standard La Nina or El Nino. Mother nature is a chaotic system with infinite outcomes for all seasons that we can only hope, at best, to estimate in advance. La Nina research charts and maps click here.