Winter storm Orion is affecting Washington, Oregon, and California. With unusually cold temperatures in much of the northwest, the precipitation will fall as snow in areas that don’t often see the white stuff. More important: Several inches of rain could fall on northern California, which is in the midst of a historic drought.
The Polar Vortex is Still Impacting Weather in the United States
The displacement of the polar vortex south of its normal position has been relentless this winter. The cold air has generally spilled down into the plains, midwest, and east coast, as the vortex was oriented north-south through those regions. But now the vortex has extended its reach westward and the Pacific northwest is feeling its wrath. Portland, Oregon, normally below the elevation of the snow line, which averages about 2,000 feet, will see snow right down to I-84 along the Columbia River.
The Post-Omega Block Weather Pattern
For much of the winter, an omega block in the jet stream over the eastern Pacific Ocean directed low pressure systems far to the north, where they either dissipated or re-emerged on the east side of the omega block as Alberta Clippers, which then impacted the Great Plains and midwest. The new weather pattern features a more normal west to east progression of storms. These systems are moisture-laden (the Pacific Ocean won’t run out of water any time soon) and normally bring winter rains to California.
When the flow dips far enough south to originate near Hawaii, meteorologists call it the Pineapple Express.
Will The Storms Bring Enough Rain to California to Alleviate the Drought?
It remains to be seen whether the new pattern will hold. The atmosphere has a habit of returning to old ways. Sea surface temperatures are higher than normal in the western Pacific and this condition tends to support a ridge (high pressure) in the atmosphere. An enhanced ridge can become an omega block.
Northern California should receive at least eight inches of rain in the next week or so, but after that the pattern could change again. With half the winter gone, it is unlikely that precipitation will catch up to normal before the dry summer season begins.
Where Will Orion Hunt Next?
After Orion is finished bringing rain to California, abnormal snow to Portland, and heavy snowfall in the mountains, he will set his sights on the rest of the country.
As of now, it looks like his impact will be muted by a gap in the jet stream. The trough (dip) that is associated with Orion will probably split into northern and southern branches. Unless the energy from the two paths merges again, neither is likely to produce more than nuisance rain or snow. However, some forecast models suggest a serious icing event around the middle of next week.
Whether the Weather Channel calls this system a continuation of Orion or gives it the name Pax, it may not be peaceful. Early indications are that the upcoming storm is most likely to impact the swath from Texas to Virginia. Residents along this path, and in other locations in the eastern United States where the surface temperature is at or just below freezing, should carefully monitor forecasts for the next several days.
A Look at the Weather Ahead
The relentless cold air mass continues to plague the central U.S., with extensions east and west at various times. Now that the omega block has broken down, there is at least the possibility that the jet stream pattern will change and give the midwest a break. But it won’t be this week.
Coburn, Lisa. The Pineapple Express: Forecasting Precipitation for the Central/Southern Coast of California. Accessed on February 07, 2014© Copyright 2014 Jon Plotkin, All rights Reserved. Written For: Decoded Science