Over the past couple weeks I have been posting all the stuff that goes into a winter forecast and all the variables – Lake Michigan, Atmospheric Circulation, the possible La Nina late this fall/early winter, Arctic Oscillation and North Atlantic Oscillation (coming in a future post). Today I will be talking about the Pacific Decadal Oscillation.
The Pacific Decadal Oscillation (PDO) is a pattern of Pacific climate variability similar to ENSO (El Nino Southern Oscillation) in character, but which varies over a much longer time scale. The PDO can remain in the same phase for 20 to 30 years, while ENSO cycles typically only last 6 to 18 months.
Warm PDO
The broad area of above average water temperatures off the coast of North America from Alaska to the equator is a classic feature of the warm phase of the Pacific Decadal Oscillation (PDO). The warm waters wrap in a horseshoe shape around a core of cooler-than-average water. Impacts from the PDO depend in part on how it is aligned with the ENSO cycle; if the cycles are in opposite phases, then effects will be weakened. However, when both the PDO and ENSO are in the warm phase, meaning ENSO would be in the El Niño phase, expected impacts on the southeast include:
- Below average winter temperatures
- Above average winter precipitation
Cold PDO
Opposite of the warm PDO, the expansive area of below average water temperatures off the coast of North America from Alaska to the equator signals the cold phase of the PDO. The area of warmer-than-average sea surface temperatures in the central Pacific are surrounded by below average temperatures near the North American continent. Expected impacts from a cold PDO and ENSO (La Nina) phase on the southeast include:
- Above average winter temperatures
- Below average winter precipitation
I will start posting the graphics on all the current variables on its own page with on-going updates on the winter forecast. If I were to use current conditions I would say we would have a warm Christmas with highs in the mid 70’s, but as with all things I don’t believe that will hold true with the La Nina forecasted for late November/December. It is well known how Michigan weather can turn on a dime.
@Mookie Last year the Grand Rapids had a unofficial growing season of 213 days. That is the longest streak of days between the last 32° date in the spring and the first one in the fall. This year the last 32° day at Grand Rapids happened on May 9th so for this year to be longer than last year we would have to not have a 32° low until December 9th stay tuned
Slim
GR is now an incredible +8.4 degrees above average for October. The CPC is showing no end in sight to these warm temps – at least until November. With an early start and a blow torch last few weeks, this has to be one of the “longest summers” we’ve ever had.
The start of October 2017 has been very warm for most of Michigan. With 8 days now in the record books most locations are running at record warmth for the month (the departures should go down over time) anyway here are some of the departures from average at the major reporting stations around Michigan after 8 days. Grand Rapids +8.3° Lansing +9.0° Muskegon +7.8° Detroit +9.0° Flint +8.0° Tri Cities (Bay City, Midland, Saginaw) +10.0° Alpena +9.2° The Sault +10.1° Marquette +8.4°
If the CVSv2 long range guess plays out we could be looking at a record warm October
http://www.cpc.ncep.noaa.gov/products/people/mchen/CFSv2FCST/weekly/images/wk1.wk2_latest.NAsfcT.gif
http://www.cpc.ncep.noaa.gov/products/people/mchen/CFSv2FCST/weekly/images/wk3.wk4_latest.NAsfcT.gif
we shall see,
Slim
Warm christmass with temps in the mid 70’s? Yes please!! Our family’s best memories are the years when christmas time was in the 60’s and we all went golfing.