For my 2013-2014 winter forecast please click HERE
Why do meteorologists and climatologists care so much about sea surface temperatures when forecasting the upcoming Winter conditions? Oceans cover 71% of the Earth’s surface and play a significant role in climate and weather.
Water warms and cools more slowly than the continents and directly impacts the behavior of the westerlies (jet stream). A driving factor for the back to back La Nina winters of 2010 and 2011 was the cool phase of the Pacific Decadal Oscillation (PDO).
The last time the United States was covered by such widespread drought was from 1954 to 1956. The New York Times published a fascinating ‘Drought’s Footprint‘ atlas mapping drought conditions in the United States from 1896 to 2012. Researchers have continued to study the connection between drought conditions and ocean oscillations in the Pacific (PDO) and Atlantic (AMO).
- The very latest forecast models just released predict that the current weak El Nino conditions will weaken further , possibly into ENSO neutral conditions (Neither El Nino or La Nina) as we head into the upcoming winter season. I personally believe that until the cold phase of the PDO weakens a moderate to strong El Nino is not very likely.
- The strength of El Nino is significant because most of the forecasts that were issued during the late summer were using analogs (historical weather records) during moderate and in some cases strong El Nino years. Stronger El Nino winters typically feature mild conditions across the northern tier as well as a very strong, dominant, sub-tropical jet stream. Now that the strength of the El Nino has weakened substantially you can practically throw out some of the analog years that were used in some of these premature forecasts.
The recent moderate El Nino winters of 2002 and 2009 produced several of Washington’s most memorable winters in recent history with the President’s Day Snow Storm of February 2003 and of course the December 2009 and February 2010 snow storms during the winter of 2009-10. Storms carried by the sub-tropical jet stream along with high latitude blocking and arctic air produced perfect conditions for the high snowfall totals during those moderate El Nino winters. Without the blocking and arctic air, those winters would have produced a lot of rain. The graph below paints this picture well: El Nino winters typically produce more moisture in the National Capital Region but not necessarily delivered in the form of snow.
The Arctic Oscillation and North Atlantic Oscillation can not be accurately predicted more than about 2 weeks in advance. I expect a split jet stream this winter with both an active northern and subtropical jet stream. If the current very weak El Nino can hold or strengthen, then the sub-tropical jet stream may dominate more this winter. If the sea surface temperatures weaken rapidly, then I suspect the northern branch of the jet stream will dominate more (especially during the second half of winter).
Factors I used when choosing my analogs:
- Winters characterized by a cool/cold PDO & weak/neutral El Nino conditions
- The winters in the early to mid 1950s featured previous summers with severe droughts
- The weak El Nino winters of 1976-77 & 1977-78 followed a parade of La Nina years
- I expect that the east coast will have several chances of coastal storms developing aided by the sub-tropical jet stream. If the northern branch of the jet stream phases (comes together/unites) with the sub-tropical branch, and there is an adequate amount of cold air in place, several snow storms are likely. If the jet streams remain separate (lack of cold air and phasing) we will see some lighter mixed precipitation events and possibly even cold rain.
- Based on the analogs I chose, there is an equal chance of above normal or normal precipitation in the Mid-Atlantic and New England.
- There is an equal chance of below normal or near normal temperatures this winter.
Based on the Analog Years I chose, here is what may fall at the Washington Area Airports this Winter:
Average Seasonal Snowfall in the Washington DC Region: