Sunday, December 1, 2013

Winter Forecast 2013-2014

The follow winter forecast is based on current observations and historical data and will only forecast temperatures departures for normal, snowfall percent of average, precipitation percent of average and some added forecast comments.

A. Big Picture (driving mechanisms)
     1. Arctic Sea Ice
     2. ENSO phase
     3. NAO & AO
     4. PDO & AMO
     5. QBO
B. The Checklist
C. Final Forecast
     1. Temperature anaomalies
     2. Snowfall compared to average
     3. Precipitation percent of average
A.  The Big Picture

1. What's better to start of with than the current sea ice extent in the arctic? This can directly linked to northern hemisphere winters by aiding in the creation of arctic air masses with more ice and more of the suns energy reflected back out into space instead of being absorbed by darker bodies (land/ocean).

The October ice extent was very impressive compared to last year and was even close to the 30 year average, a rare occurance these days. This tells us that cold air is being generated much quicker and arctic air masses will be in high supply and occur early in the season, but this alone doesn't tell us everything. We need to look at much more.

2. El Nino Southern Oscillation

Below is the sea surface anomalies for the equatorical pacific. Right now we are in a neutral (slightly positive) phase of the of the ENSO, meaning there is no El Nino nor La Nina. The neutral phase is expected to continue through the spring of 2014. A vital player in precipitation and weather patterns over North America.

3. North Atlantic Oscillation & Arctic Oscillation

Even if the arctic has a large supply of arctic air it needs to be able to reach lower latitude and it does so during certain type of "weather patterns". The NAO and AO are blocking patterns and when both phases are negative we can expect cold airmasses and storms systems to ride up the eastern seaboard. These indicies cannot be predicted more than a few days out and vary in cycles of days, weeks, months, years, and multi-decadal! Either way when these indices go negative this season (not predictable when) expect colder arctic outbreaks than in previous years. While it's not predictable when they go negative,
"? more than a few days out the NAO and AO have their strongest influence on us during the mid to late winter when wave lengths in the jet are at their peak. We look for these troughs, retrograding, and cut offs which make for some interesting weather. 

These oscillation are forecasted off the daily model output and you can find the updated charts on my model site or the climate prediction center

4. Pacific Decadal Oscillation & Atlantic Multidecadal Oscillation

The oceans make up 70% of this planet and to ignore them in forecasts would be like forgetting to set the locking arm on an extension ladder. It's just plain risky. Unlike the NAO/AO these are regular cycles of about 30 years and play a role in storm formation and temperatures. 

PDO went negative back in 2007 and has stayed there ever since. This means cooler waters off the coast of Alaska and increased snowfall over the Pac Northwest. The implications for the northeast is still somewhat unknown but cooler and dryer winters seem to be the likely trends. 

The AMO entered its warm phase in 1995 and it still stongly postive with a change not expected for another 10 years or so. This not only plays a role in our weather, but the whole northern hemisphere aiding in increasing air temperatures and melting away sea ice (the most likely cause for arctic sea ice loss in the past 20 years). For this reason I don't expect record breaking cold across the northern hemisphere, something to just keep in mind for the next decade. 

5. The Quasi-Biennial Oscillation (QBO)

Every two to three years the winds over the equatorial stratosphere shift directions from easterlies to westerlies. This is called the QBO to keep it simple. The QBO shifted positive or "westerlies" in March of 2013 which means stratospheric warming over the arctic will be at a MINIMUM. This means blocking patterns such as NAO and AO may be primarily postive this winter. Not good for snow lovers. The QBO is still in a fairly weak westerly phase so maybe we will still some chance, but each month the westerlies grow stronger. 


B. The Checklist (red=bad for snow lovers / blue=bad for snow haters / black= equal chances)

-QBO (westerly-postive)
-NAO (postive influence by QBO)
-AO (postive influence by QBO)
-AMO (warm phase)
-PDO (cold phase)
-Solar cycle (very weak) 
-Neutral ENSO
-Arctic Sea Ice extent

C. The Forecast

1. Temperature Anaomalies

With the evidence at hand I put the coldest temperature (with respect to average) over the central US where some very cold arctic outbreaks will occur but modify as they come east. The SW and SE will end up a little warmer than average but that doesn't mean winter will be a bust in these locations. Temperatures don't represent season snowfalls and snowy winters can occur during warming winter and the opposite with cold winters.

2. Snowfall Compared To Average

The map isn't very detailed and shows average snowfall for the northeast but increased snowfall over the NW and over the lakes do to the arctic outbreaks which will cause a good deal of lake effect snow this season. Now just one storm and make or break this map in the northeast and it's a safe bet to say average snowfall with a lessened chance of blocking patterns setting up but with plenty of cold for some systems to tap into just west.

3. Liquid Precipitation Percent of Average

Now looking at my own forecast as a snowboarder I realize it's not the best outlook. This winter will have plenty of cold air in stock and the majority of our snow will come with frontal systems, clippers, or warm air advection systems. With blocking at a minimum this year Nor' Easters will have issues laying down the white along the I-95 corridor but during times where blocking is in place these storms could work their magic. Overall by the time April rolls around, we will be able to look back at winter and realize it gave us our fair share of pro and cons. In my eyes it's pretty much an average looking winter in store and I'm ready. Are you?

1 comment:

JackZ said...

Great analysis. Thanks for posting.