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seasonal forecast

Winter 2014-2015 (DJF) Forecast

I like to keep my seasonal forecasting short and sweet, so here it is:

Reasoning:
– Latest model guidance and ENSO trends suggest DJF will likely be a weak El Nino.
– +PDO to support ridging in the western U.S. and troughing over the Midwest/eastern U.S.
– +AMO could help keep the Southeast milder (read: less cold).
– -QBO will allow for a greater chance for blocking in the Atlantic (-AO/-NAO) as well as stratospheric warming events. This would promote colder temperatures in the eastern half of the country.
– Drought conditions in the West will promote warmer and drier conditions there.

Risks:
– The western U.S. could go warmer given favorable +PDO and long term drought.
– If -NAO/-AO becomes the main forcing mechanism for the U.S. weather pattern, it could bring colder air into the Midwest, Mid-Atlantic and Southeast while providing warm and wet risks in New England.
– If a moderate Nino develops, a stronger subtropical jet associated with it could allow for wetter conditions across the southern U.S. and Mid-Atlantic.

A note on my track record… I have been about 50/50 with long-range forecast skill since I started in 2010. There are many others out there with more long-range knowledge, reasoning and a better understanding of how the atmosphere works on a longer timescale. That said, nearly every forecast I have seen so far favors a warmer West and cooler East, so I’m not exactly breaking the mold with this forecast. It looks like we’re all in the same boat with this one. The only thing left to see is if we can sail to victory or go down with the ship in defeat.

As always, the forecast anomalies are based off the latest 30-year normals (1981-2010).

Winter 2012-2013 (DJF) Forecast – Update

My original forecast from August had to basically be thrown out due to a few key factors.

1. ENSO faltering. While the positive trends have recovered, there was a major misstep in the trend as the values for most of the ENSO regions started to fall. The latest data indicates that the positive trend has resumed, which led me to go with an ENSO value bordering on positive neutral and weak Nino for DJF. A new ENSO prediction means new analogs, which can be found at the end of the post.

2. Siberian snow cover. As you can see from the graphic below, significant gains have been made in Siberia compared to the start of the month. Studies show a correlation between positive snow cover trends over Siberia and cooler temperatures across eastern North America.

3. The North Atlantic Oscillation (NAO). The NAO has generally been negative since May, and it shows no signs of going positive any time soon. A -NAO helps pull cold air into the eastern U.S. during the winter months.

Along with this new data, I also used the PDO and AMO signals to help weight my analog years.

The monthly breakdown:

Winter 2012-2013:

ANALOGS:
in [year (weight)] format

1976-77 (more)
1958-59 (more)
1952-53 (more)
2003-04 (less)
1990-91 (less)
1979-80 (less)
1960-61 (less)

NOTE: Anomalies are against 1981-2010 normals.

Winter 2012-2013 (DJF) Forecast – First Look

The monthly breakdown:

Winter 2012-2013:

METHODOLOGY:

Looked at the possible/likely ENSO forecast (around +0.9 for DJF holding steady or fading slightly) and matched years within +/- 0.3 of this. Analogs that had negative ENSO anomalies the previous winter and near neutral ENSO during the summer were favored. I then took the previous summers’ temperature anomalies into consideration when weighing the analogs.

ANALOGS:
in [year (weight)] format

2006 (more)
2002 (normal)
1994 (normal)
1986 (normal)
1953 (less)

NOTE: Anomalies are against 1981-2010 normals.

RISKS:

– A persistent -PDO could keep the West Coast cooler.
– The +AMO could allow for warmer temperatures in the Southeast and southern Plains.
– The -QBO might trigger blocking earlier than expected and allow cooler temperatures to work into the north-central U.S.
– Drought conditions over the central U.S. might keep drier and warmer weather over the central Plains and southwestern Midwest.