WINTER FORECAST 2018-2019
The past four winters have all been warmer than average in the Carolinas with below average snowfall. This year the signals for the upcoming winter are mixed, to say the least. Which makes this year forecast much less uncertain. Even as far as seasonal forecasts go, but there are few things that are more certain, so let’s start with those.
INDICATOR #1: El Nino/La Nina phase: 2018-2019 Winter Weak El Nino.
IMPACT #1 : WET winter and active storm track.
This year a weak El Nino is forecast to be in place for the bulk of the upcoming winter season. An El Nino pattern on average brings wetter and cooler than average conditions to the southeast during the winter months. With the weaker signals, the cooler part is a bit more uncertain, but the wet part looks like more of a sure bet. The fact that we have seen this wet pattern already set this Autumn is a pretty good sign that the winter pattern will remain wet. This is highlighted by an active southern Jetstream and storm track. The cooler part is usually due to more clouds and precipitation more so than cool air outbreaks.
INDICATOR #2: October snowfall in Siberia and Asia: Slightly below average October snowfall this October.
IMPACT #3: Near average temperatures to slightly below
One of the strongest correlations to a colder winter for the eastern part of the U.S. Is above average or plentiful EURASIA snowfall in October. This is the area mainly in northern Russia/Siberia. When the autumn has lots of snow in this region it causes the polar vortex to be weaker which then allows more arctic outbreaks into the eastern U.S. This year the snow cover there is running below to slightly near average, but it has surged as of late. This is a mixed signal but likely means mild to near average temperatures.
INDICATOR #3: Arctic Sea ice:
IMPACT #3: Mild temperatures but an erratic polar Jetstream
Arctic sea ice continues to be at record lows. The lack of Arctic sea ice can actually make for cold outbreaks for parts of the U.S. Depending on where the sea ice remains low the polar vortex will weaken and often get displaced further south. This can cause rapid arctic air outbreaks, but they are erratic and come after rapid warmups. Recent research shows that the lack of arctic sea ice also makes for a very amplified Jetstream, basically meaning you get a lot of wild extremes during the winter. We have seen this pattern in the past few winters. Last year, for instance, we had a very mild to warm start to winter, but it actually got coldest in late February and most of March. I would expect a similar wild ride this winter.
INDICATOR #4: Climate Change and recent trends
IMPACTS #4: Mild Temperatures and less snowfall.
It’s hard to ignore the long-term trend of less snowfall in the Carolinas, especially in the mountains. We still seem to always get some snow, but the overall trend is for less snow. The long-term regression line shows that slow downward trend. Even though the long-term trend is down another impact of a warming climate is more extremes in the winter. Which means we get lots of warm spells but also more storms with more moisture. Combine that with a weak El Nino, and it might mean we actually have a few big storms with lots of warm weather in-between.
OVERALL FORECAST:
A wet winter with near average to slightly below average temperatures.
PRECIPITATION: WET
This year has a lot of mix signals on what to expect. The one signal that is strongest and the one I have the most confidence in is a wet winter. The active storm track should bring frequent storms and lots of precipitation. The question is will they all be cold rains or more of the wintery set-up?
TEMPERATURES: NEAR AVERAGE TO SLIGHTLY COOLER
I struggled with the temperatures forecast. While we are heading into an El Nino even in a weaken staged should mean cooler temperatures. On the other hand, many other factors point to mild but not super warm. Especially when considering the long-term trend only 5 of the past 15 winters have been cooler than average and only two considerable colder. Even with these conflicting signal, the fact that we will have frequent storms with precipitation and cloud cover makes me lean towards near average if not slightly below. My confidence in this part of the forecast is low.
SNOWFALL: SLIGHTLY ABOVE AVERAGE
In many ways, the chances of a snowy winter hinge more on the storm track and frequency of storms more so than cold temperatures. We still need cold air, but often our coldest winters are cold and dry because of the arctic highs that bring consistent cold air which can suppress the storm track too far south. So if you want snow, you actually want a wet winter over just a cold winter. It’s easier to sync up some cold air with an active storm track than it is to try and move storms into the colder air. For that reason and the active storm track and wet winter, I expect we could have several opportunities for a few bigger storms versus a whole bunch of small storms. It may very well be that we get lots of rain events and just a few big storms this winter. Especially late winter which is by far our snowiest time of the year February into March. Keep an eye on late winter there other, other indicators I didn’t talk about that point to more cold be around late winter. Which if we were to combine that with this active storm track watch out for a few big storms. Also of note, we are way overdue to for a significant ice storm. The Carolinas have been knowing as the ice storm capital of America due to Cold air damming. We just haven’t seen that in many years, so be ready.
