northgawx

October has nearly arrived, and with it the return of winter forecasting. Several meteorologists have put out their winter forecasts in the past few weeks, and the CPC has updated their seasonal outlooks for the El Nino/La Nina (ENSO). Personally I don’t go for long-range forecasts, especially for winter in the SE since so many things have to come together in the short term in order to get snow/cold. However, despite these issues we can still have a pretty decent idea of whether our chances of seeing snow are above or below average based on the overall current pattern and expected pattern evolvement heading into the first of winter. I’ll keep this pretty short, no reason to go too in depth given the uncertainties, but discuss several things to keep an eye on through the winter.

PDO

First up, the PDO. This has been a pretty big story in the long-range weather forecasting community all summer, with a possible change in overall phase of the PDO (Pacific Decadal Oscillation). For the past 10 years or so we have been in a negative, or cool, phase of the PDO. Generally, cool phases lead to warmer than average temperatures across the eastern US due to a favored west coast trough, placing the east coast under a ridge. However, there have been signs of a shift in phase over the past several months (the value skyrocketed to 1.04 in May, but has since declined). Current sea-surface temperature anomalies show continuing positive anomalies off the Pacific West coast (and across much of the northern pacific for that matter),  which is in stark contrast to earlier this year. Below is a comparison of SST anomalies this past January to now.

The two things of note are the change in the “horseshoe” running along the coast towards Russia, as well as the negative anomalies beginning to show up in the warm “core” across the central North Pacific. The area of that warm core has seen significant cooling during the past 30 days as well, leading me to strongly believe a PDO phase shift is possibly underway, and will continue through the winter.
What does this mean for us? High pressure tends to dominate the west coast during +PDO phases (as it has done all summer), placing us in a trough (as it has all summer) leading to increased rainfall for the deep south and below-average temperatures for most of the eastern US.

ENSO/SOI

Next up: El Nino. This has been the other top story of the season so far in the long-range communities, with an El Nino slowly developing across the Pacific. Again, a comparison of last January vs current SST anomalies reveals the development of a weak Nino/neutral conditions across the east Pacific.

This, coupled with the current modeling for ENSO region 3.4 (below) give me high confidence in the emergence of a weak to moderate El Nino during the winter of 2014-2015.

The best analog years for a moderate/strong La Nina, followed by 1+ year of neutral heading into a weak/moderate Nino  from mid-year through the winter are ’91/’92, followed by ’76/’77, ’86/’87, ’02/’03, and ’09/’10, all moving from moderate->neutral->weak nino for the winter months.

Generally, El Nino’s tend to favor west coast ridging/east coast troughing, with increased precipitation for the SE United States.

OVERALL PACIFIC SST COMMENTS

Overall, the biggest things of note are the warming of the extreme North Pacific and US west coast, as well as the cooling in the past 30 days of the “traditional” PDO areas off the coast. Also, the emergence of an El Nino for the winter months is likely. These combined give me fairly high confidence in an above-average chance of sustained west coast ridging.

NAO/PNA

Given the expectations for the high pressure to dominate over the west coast for much of the winter, the PNA (Pacific-North American pattern) will have an above-average chance of extended periods of positive (see map below for explanation).

The NAO, however, is extremely hard to predict more than a couple weeks out. An explanation of positive/negative phases (courtesy of NOAA) is below.

It has tended towards neutral for the majority of the summer, after having spent a big portion of last winter on the positive side. Currently the Atlantic SST anomalies don’t point towards a predominant state for the NAO so I won’t venture to mention much past the fact it is rather unpredictable to begin with and is probably the #1 most important feature to keep an eye on as we head into the cold season.

MY FORECAST

So… what does all this lead me to, and what does it mean for you guys? Well, based on everything I’ve been watching over the past several weeks, and what I’m expecting for the future, my winter forecast is summed up below.

Precipitation: Slightly above average. The El Nino regime will help to increase precipitation for the winter, with more or less a continuation of the overall current pattern through at least Jan/Feb.

Temperature: Below average. I expect east coast troughing to be predominant, resulting in below-average temps for the region (just like this summer).

Snow? Ice?: I have to go with above average snowfall for the region this winter, with 2-3 warning criteria snow events. IF the wedge pattern we have been in continues through the winter, 1-2 ice events will be possible as well.

 

**The disclaimer to all this is that we still can’t forecast particularly well in the long range. If you search the internet you’ll find some very well done forecasts much more in depth than this one, so feel free to Google and explore what other meteorologists and weather geeks (the educated kind) are expecting and talking about for this winter.

If you are looking for a site to follow short/mid-range weather on this winter, check out http://www.talkweather.com, where I post on a regular basis. If you got here from somewhere besides my FB page, check out http://www.facebook.com/northeastgawx for the latest in Northeast Georgia specific weather.

Everyone have an excellent day. ~TW