Author: Bill McMillan- Owner of IndyWx.com
Date: Saturday, October 21st, 2017
2017-2018 IndyWx.com Winter Outlook
As we put the finishing touches on our annual winter outlook, central Indiana is enjoying “bonus” summertime. However, longtime Hoosiers know that these unseasonably warm, pleasant days are on borrowed time come mid-October. With that in mind, it’s time for us to reveal our annual winter outlook!
Before we dig in to the ingredients behind this year’s winter forecast, the past couple of winters have been unseasonably mild- not only here, but across a large portion of the country. Snow and ice clients have had things relatively easy over the past couple of winters.
As we look forward to the winter of 2017-2018, it’s important, as always, to start with the “basis” of our forecast. That’s with an analysis of ENSO, or El Nino/ Southern Oscillation. A look at current sea surface temperature anomalies shows the band of cooler anomalies in the equatorial PAC, suggestive that what’s currently officially classified as “neutral,” shifts towards a La Nina as winter nears. Also of note is the cooler than normal SSTs to the northeast of the Bahamas. While this won’t have much, if any, impact on our winter pattern, this is a byproduct of the busy hurricane season.
As we look ahead, data suggests a “weak” to borderline “moderate” La Nina awaits this winter.
In building long range, seasonal forecasts we feel it’s important to look back in the past at similar weather patterns and the corresponding “sensible” weather that followed. While no weather pattern is identical to another, this research can provide insight with what we can expect moving forward. With that said, we pulled all of the years, since 1950, that featured a weak La Nina during meteorological winter (December, January, February) and came up with this temperature profile:
Factor out the “blow torch” winter of ’11-’12 and that leaves us with this look:
What we’ve found is that the coldest temperatures, relative to normal, align themselves across the north-central, with unseasonably mild weather across the southern tier and eastern seaboard.
The tight thermal gradient that lies between the eastern warmth and central cold often features an active storm track, associated with a hyperactive northern jet stream. This often leads to “busy” times around our part of the county with numerous storm systems to deal with. Sure enough, a slew of model data paints a pattern that will deliver above normal precipitation across our region this winter.
While we’re as confident as we can be on heavier than normal precipitation this winter, the degree of cold, relative to average, is a bit tricky. The warm SSTs off the eastern seaboard (noted below) suggest a later starting winter along the East Coast and can also help center, or focus, the colder anomalies across the “belly” of the country, including the Mid West- especially early in the season.
Furthermore, the QBO, or Quasi-Biennial Oscillation, is currently in a state favorable for more high latitude blocking than in year’s past. The caveat is that this doesn’t necessarily mean it favors our part of the globe. This is something that will require our attention closely moving through the next couple of months. Unlike last year, this could provide more of a “blocky” look to the pattern, jamming things up and leading to more long-lasting cold, especially across the central portion of the country. By the way, you can read more about the QBO here.
Perhaps the IRI (International Research Institute) is seeing this blocky look, resulting in a cold winter across our region. It should also be noted this model has held it’s own against other long range data over the past couple of winters from this distance. This is easily the coldest look this particular model has painted in our time monitoring this data (since 2010).
Additional wild cards can also factor into the winter pattern. These include the Pacific (PAC) jet and NAO, or North Atlantic Oscillation, just to name a couple.
Despite nearly unanimous agreement with data last winter, the PAC jet wrecked havoc on the majority of winter forecasts (ours included), as it ultimately flooded the country with mild, Pacific air for the balance of the winter. This, coupled with a lack of blocking, resulted in cold air lacking any significant staying power. Unfortunately, it’s really not until we get deeper into November that we can say with any certainty what the ‘mean’ impact of the Pacific jet will be. The NAO is also one of those wild cards that’s a headache to try and forecast with any certainty from this distance for the winter season. That said, the QBO state does argue for more of a likelihood that a negative NAO is ahead this winter. This is suggestive of a cold signal.
If you’re still awake :-), we’ll close with saying we believe a slightly warmer than normal winter awaits, but one that’s also snowier than average. We are concerned the potential is present for blocking to become more of a factor, leading to a colder winter than currently forecast, but confidence at the issuance of this outlook isn’t high enough to transition our forecast colder. As mentioned above, we’re very confident on above average precipitation this winter, including the potential of a couple “big hitter” winter storms. Heavy, wet snows and ice are notorious during Nina winters. As is always the case, stay tuned to IndyWx.com for daily forecasts, discussions, and video updates!
IndyWx.com 2017-2018 Winter Outlook
- Snowfall: 30″ at IND (first flake to last flake)
- Temperatures: + 0.5° (meteorological winter, or December through February)