Thursday, August 16, 2012

The Winter Forecast Parade Begins

It is arguably way, way, way, way too early for these but Accuweather wants to get their thoughts on the upcoming winter out there early.

I've come to expect one of two things from Accuweather's winter forecasts with regards to I-95:  Stormy winter or above average snow.

This winter, they're choosing the latter.

Accuweather winter forecast

Accuweather is predicting above average snowfall for the I-95 corridor from Boston to the Piedmont of Georgia for the coming winter...following the "trend" of what convention wisdom on El Nino winters suggests.  El Nino patterns typically provide above average moisture across the South...and sometimes the East Coast, with milder temperatures and limited snow across the Rockies and Northern Plains.

The key, however, is that not every El Nino winter, produces big snowfall.  For every 2009-2010 winter that brings Philadelphia 78.7" of snow, you have 1972-1973 (trace) and 1994-1995 (less than 10")...neither Nino was in the "super Nino" category...just like this one likely won't be either.   The goal to get snow in an El Nino winter is to have a negative NAO pattern setting up...if the pattern is favorable, produces proper cold, odds increase for above average snowfall.  In a winter like 2009-10, the NAO was textbook to produce huge amounts of snow when the jet stream was active and the result was record snows in Philadelphia and Baltimore.

Determining whether those blocking patterns will be in place this winter based on conditions in August is a stretch at best and not of the greatest accuracy.  There are many other indicators that fuel a winter forecast besides El Nino -- the state of the North Pacific (warm or cold compared to average), snow cover in the Arctic in the Fall can have an impact (especially if it is above average), and there are other considerations as well.  Putting all of this together several months out is very low confidence.

Accuweather will likely update their winter forecast in October (they did last year)...and we'll also provide an attempt at projecting this winter towards the end of October as well.