WVPAW Winter 2017 & 2018 Outlook Part One
It's that time of year again where meteorologists everywhere take an attempt to peer into the crystal ball and try to predict this impending winter. The only difference between fortune tellers and us, is we have a lot of nifty tools at our disposal! Now, I mentioned in a post last week that we were holding back our Winter Outlook until the first day of "Winter Awareness Week" which started Sunday. For good reason. Most of those "preliminary" winter predictions will need changed, its par for the course if you don't wait for all of the datasets and observations for the month of October (I'll get into this more as we move on). This Outlook is part one of our total winter forecasts. Part one will be focused on the winter season as a whole rather than the monthly break down which will be authored by Eric mid month.
So, how will this winter be in comparison to yesteryears? Will it be warm? Will it be cold? Snowy? Rainy? Dry? A lot of questions that can only be answered with data. Lets dig in.
ENSO/El Nino Southern Oscillation
Above: The CFSv2 forecast for Jan/Feb/Mar 2018
Since early this year, the record strong El Nino which was responsible for our well above normal winter in 2015/16 and the massive droughts on the west coast has shift to its cooler phase, La Nina. It would appear that this winter we will see moderate La Nina hang on in the equatorial Pacific. It is my opinion that ENSO is the strongest variable when it comes to weather forecasting. The driver of the planetary climate is driven at the equator outwards, therefore I always like to talk about it first.
Above: NOAA CPC/NWS La Nina Affects
Typically, La Nina's influence of whats shown above. High pressure blocking in the North Pacific where the Pacific jet stream brings ashore moisture under the high and the Polar jet is the "highway" in which these storm systems ride along. Due to this setup, the Pacific Northwest, Mid-West, and Northeast are along the path where multiple systems bring precipitation to those regions while leaving the Southeast and Southwest typically dry. This pattern also tends to be an above normal temperature pattern as well.
However, there are variables La Nina and El Nino for that matter that are hardly acknowledged let alone used in forecasts. Sometimes I scratch my head and wonder why because this is a pretty significant variable overall and it comes down to where ENSO is based, meaning East or West. From what I am seeing is an East based La Nina this winter. Its extremely important to understand because what it does is shifts the North Pacific High eastward. This will alter the Polar jets trajectory, creating a deeper trough through North America and upwards into the Northeast.
Above: CFS Arctic Oscillation up to February 3rd.
The second variable in winter forecasting we will talk about is the Arctic Oscillation, or going forward, AO. The AO is an atmospheric oscillation is a pressure anomaly that occurs in the Arctic and to the degree in which cold Arctic air is allowed to slip south into the United States, including us in the Northeast.
Above: Arctic Oscillation phases
The AO has two phases a positive and a negative. The positive phase which we write at +AO is when the Arctic region has low pressure in control. This affects the Polar jet's trajectory in an uneventful West to East pattern. A negative phase is the opposite. High pressure controls the Arctic, this allows for strong ridging in the west while deepening the trough in the east. The effects are two fold, storms coming on shore are able to traverse the jet stream into the south while lifting north and allowing cold Arctic air to seep into the trough.
Looking above to the AO forecast/Outlook our bets are on a Negative Phase for most of winter. Whats this mean? It means we should expect the Polar jet to create a deep trough which will bring us cold snaps and snow.
NAO/North Atlantic Oscillation
The third variable we look to is the North Atlantic Oscillation or going forward, NAO. As with the AO the NAO is another atmospheric oscillation in which high and low pressure zones effect trajectory the jet stream over the North Atlantic as well as high latitude blocking.
Above: NAO Phases
As noted, the NAO has phases just like the AO. A negative and positive phase, which we use +/-NAO to denote the phase. In a positive phase, the Greenland low is strong and the Azore's high is strong. The alteration on the jet stream is it keeps it from sinking into the United States as well as limiting the blocking. This means storms swiftly push through lessing the impact. In a negative phase, the pressures are weak and the jet is forced south allowing Arctic air to sink as well as slowing the jet down and aiding in blocking.
Looking at the forecasted NAO, we look to have a neutral NAO which won't have much affect on the overall idea of winter. Furthermore, with a stronger -AO expected the idea of being cooler prevails. However, we should see the NAO take a negative dip probably mid winter which will be pretty telling and exciting for snow lovers.
Above: Quasi Biennial Oscillation
Finally, we we talk about the Quasi Biennial Oscillation or QBO. This is almost a forgotten variable and many of you have probably never even heard it before, the datasets is confusing and I would rather explain what the QBO is instead of show a bunch of numbers. The QBO index the measure of is equatorial zonal winds between the easterlies and westerlies in the stratosphere.
Eastward phases of the QBO often coincide with more sudden stratospheric warmings, a weaker Atlantic jet stream and cold winters in Northern Europe and eastern US whereas westward phases of the QBO often coincide with mild winters in eastern US and a strong Atlantic jet stream with mild, wet stormy winters in northern Europe.
We have been falling into an East phase of the QBO which coincides with the weaker Atlantic jet stream hinting at cold winter hear in the Eastern USA. In perspective, last winter if you remember, we began with a mild uneventful pattern while Central Europe was blasted with near record cold. This year appears to be the opposite.
With all that said, an Eastern based La Nina, a negative AO, a neutral to negative NAO and an Eastern QBO we can start to paint a picture on what our winter looks like. We believe winter will be below normal temperatures and above normal precipitation. You will begin to notice as we chug along in November what I am saying. The possibility of having a cold thanksgiving, snow on the ground for the first day of rifle deer season? How about a white Christmas? Absolutely looks that way based upon the datasets I am seeing currently. A far different look than winters past, it should be exciting! As mentioned, Eric will have the monthly outlook for winter out mid month.