Forecast for Fall-Winter 2004-2005

Steve Pierce
Weather Specialist - Vancouver, WA.
  

Winter 2004-2005 Synopsis:
 
Looking at several key variables in Pacific Northwest Winter weather (current equatorial sea surface temperatures, past "similar" years & the current Atlantic hurricane season) we have derived the following Pacific Northwest forecast for Winter 2004-2005:
 
After experiencing the 5th wettest August in Portland recorded history, the weather pattern in the Pacific Ocean is taking on an "October" look, much earlier than normal. This is unlike the warm fall of 2003. With an active Atlantic hurricane season already underway (eight storms to date as of August 30th, two have reached category four status) and sea surface temperatures near the pacific equator running slightly above normal (but no where near a major El Nino event) this winter will likely hold many variables. We feel this winter will be active, with many shifts in the jet stream throughout the entire winter season. The most compelling information we've noted is, in years where we have experienced an historically wet August (as we have this year), it was followed (90% of the time, or 18 out of 20 historically wet Augusts) by above normal precipitation for the remainder of the winter. In a few cases, we have seen extremely high rainfall amounts for the remainder of the winter. These years are also more likely than not to see at least one major snow event, possibly more. Some locations in Alaska have seen records warmth early this summer. If that pattern remains prevalent through the winter months, there is a greater than normal probability of abnormally cold air draining down from the arctic north.
 
We have also noted that in years where there is no major El Nino or La Nina to contend with, the Pacific Northwest can experience large swings in the overall winter pattern, from warm and wet, to a cold blast from the north. Overall, we predict two snow events (one in December and the other in January) and at least two arctic outbreaks (coinciding with the snow events). Precipitation will be at or above normal every month this winter. With the increase in Pacific Ocean jet stream activity comes the greater probability of several intense storms / mid-latitude cyclones producing damaging coastal winds, and at least one "blow" to western valley locations. This would likely occur in the November or December timeframe due to the abnormally active Pacific jet already noted in late August. Historical data also suggests that severe events follow each other. This is part of the reason why we feel we have a greater than normal probability that the Pacific Northwest will experience a lowland snowfall event, followed quickly by a rain event, likely causing flooding in many areas."
 
Note: At the time of this forecast, (late August) the current sea surface temperatures near the equator were showing signs of warming towards a minor El Nino event by years end. If this progression intensifies and speeds up, this forecast may need to be reviewed again in the fall months.
 
October 2004
Near normal temperatures
Above normal precipitation
 
November 2004
Slightly below normal temperatures
Above normal precipitation
 
December 2004
Below normal temperatures
Above normal precipitation

January 2005
Below normal temperatures
Near normal precipitation
 
February 2005
Slightly below normal temperatures
Above normal precipitation
 
March 2005
Near normal temperatures
Near normal precipitation