Northwest Outlook
January 2017
December 2016 Weather Recap
Strong onshore flow in the jet stream dominated precipitation and temperature patterns along the
coast. In the interior, cross-polar flow from the Arctic introduced bitterly cold air in multiple waves.
Below are the highlights:
 The entire Pacific Northwest experienced below-average temperatures for the month.
 Livestock in Montana and the Columbia Basin dealt with temperatures that averaged 8
degrees below normal. This was not record setting, but as is typical with winter, calories are
used for warmth rather than meat or milk.
 Nearly all of the Pacific Northwest is drought free.
 Mountain snowpack is above average for many of the reporting stations across the west.
Figure 1.a. 30-day temperature anomalies for December 2016. Image credit: NOAA.
Figure 1.b. Total accumulated precipitation for December 2016. Image credit: Eric Snodgrass; data from
NOAA.
Big Snow Coming for California
The Pacific branch of the jet stream has resisted long-term, large-scale blocking, which has
allowed the flow to be strong and onshore. Over the first two weeks of January, this flow pattern
will run all the way across the Pacific Ocean and pick up moisture near Hawaii before entering the
lower-48 in California and Oregon. This moisture transport process is called the “Pineapple
Express” and is known for producing a lot of precipitation in the western U.S. Impacts:
 3-4 feet of snow are forecast to fall in the Sierra Nevada Mountains.
 Drought relief is forecast for Southern California, which is recovering from 5 years of
exceptional drought. Drought relief for the 2017 growing season in California will increase
the production of fruits and vegetables in this state that compete with Pacific Northwest
crops.
 Expect snowpack to continue to build this winter, which will increase water availability for
spring and summer irrigation.
Northwest Outlook, January 2017
Page 2
Figure 2.a. Total snowfall forecast by the GFS model from January 4 to 13 (in inches). Image credit:
http://www.tropicaltidbits.com.
Northwest Outlook, January 2017
Page 3
Figure 2.b. Basin average snow water content (percent of average) as of January 3, 2017. Image credit:
http://www.wrcc.dri.edu/snotelanom/snotswen.gif.
Outlook for January 2017
The first half of January will have a weather pattern that will be dominated by a negative Pacific
North American pattern (PNA). This pattern is characterized by ridging in the jet stream over
Alaska, a broad trough forming over the Pacific Northwest, and a ridge in the eastern U.S. Impacts
of this weather pattern:
 High probability of colder-than-average temperatures for the month.
 High probability of continued wetter-than-average conditions, especially along the coastal
mountain ranges.
Northwest Outlook, January 2017
Page 4