Browse Tag

DJF

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.

Winter 2011-2012 forecast verification

This was an ugly forecast… pretty much the exact opposite of what actually happened. There was virtually no blocking this year (I was relying on blocking for the cold pattern), and a fairly persistent and strong trough over Alaska prevented any sort of real, long-lasting cold from entering the U.S.

DJF temperature forecast: F

December 2011: F

January 2012: F

February 2012: D-

DJF precipitation forecast: D

Winter 2011-2012 (DJF) forecast – Update

Here’s the updated forecast for this winter. I used the same six analog years, with different weights (more below).

IMPORTANT: The updated outlooks use the NEW 30-year normals (1981-2010), whereas the original forecast used the OLD normals (1971-2000). Overall, there were no drastic changes to the forecast.

Winter 2011-2012:

The monthly breakdown:

ANALOGS:
in [year (weight)] format

2010-11 (more)
1995-96 (more)
2008-09 (normal)
2000-01 (normal)
1970-71 (less)
1962-63 (less)

So what changed? Overall there was slight warming in northern California, cooler Gulf Coast and a warmer northern New England. Most, if not all, of the changes can be attributed to subtle strengthening in the blocking pattern (more negative AO/NAO) that will allow the cold to work further into the south-central and southeastern U.S. At the same time, this blocking pattern will pull slightly warmer air in off of the Atlantic into northern New England. The ridging in the western U.S. has shifted slightly further west, which is why northern California turned warmer. It is also the other contributing factor that caused Texas to turn cooler. Warm risks are in place in Texas and the Southeast as ridging could be more prevalent in these areas.

Precip/snowfall forecasts that I made previously are fairly similar to the update, so there isn’t any need to go into detail about these. There is a wet risk in the Northeast, which I decided to leave as near normal while the region is borderline normal to above normal (especially in southern New England).

From the analogs, 2010-11 was given more weight (equal to the weight of 1995), while 2008-09 and 1970-71 were given slightly less weight. I was going back and forth on whether or not to add 1955-56, but I decided that the La Niña in 1955-56 was too strong from the start of the summer through most of the winter compared to what is forecast (which will likely be a borderline weak/moderate La Niña).

I may issue an update once we’re into the season for the end of winter, but we’ll see if it’s needed.

Winter 2011-2012 (DJF) precipitation forecast

The Mid-Atlantic will struggle to get to near normal, but most should be able to edge into that category as the southeastern Mid-Atlantic goes drier than normal again.

As for snowfall, I expect the Mid-Atlantic to be near normal to slightly above normal (90-125%) throughout the region. I think the storm tracks will be similar to last winter, but the winter storms that hit the Southeast and brought anomalously-large snowfall totals to that region will be further north this year due to a weaker trough (and weaker -NAO). That would put the tracks through, or just south of, the Mid-Atlantic. These storms that we didn’t get last year will help boost the region’s snowfall totals, though each individual event may only drop 1-3 inches in most non-mountainous areas.

—–

This was last year’s DJF forecast and verification:

Winter 2011-2012 (DJF) temperature forecast – First look

Winter 2011-2012:

The monthly breakdown:

METHODOLOGY:

Used rough ENSO analogs (neutral ENSO to weak Nina summer going into weak/moderate Nina), coupled with NAO analogs based on low sun activity leading to -NAO in the winter. I also included -PDO to an extent, put all the factors together and weighted accordingly. Not all analogs fit the NAO/PDO correlations, but still fit most of the requirements.

ANALOGS:
in [year (weight)] format

1995 (more)
2008 (more)
1970 (normal)
2000 (normal)
1962 (less)
2010 (less)

NOTE: Anomalies are against 1971-2000 normals.