Bill Jennings: Shift in omega block weather pattern presents hope for area ski conditions
Scarce powder days have left me with recreational space to fill. Unseasonable cycling opportunities have made riding a special treat. Yet I can’t help thinking as we mountain bikers enjoy firm, tacky terrain in February, will we be eating July-flavored dust in April? Things could be about to change.
Recently a friend of mine turned me on to the Cliff Mass Weather Blog (cliffmass.blogspot.com). Mass, a University of Washington atmospheric scientist, provides a running commentary on climate, with clear explanations about why we’ve experienced spring in the middle of winter.
I gave him a call earlier this week to talk about our situation. He said, “The pattern has been extraordinarily consistent, that’s the story.”
A strong high pressure ridge parked over the Pacific Northwest has caused the jet stream to undulate in such a way that winter has gone out of its way to avoid us on its way to the east. Meteorologists call a ridge like this one an “omega block.” On weather maps the pressure gradients form lines that are shaped like the Greek letter Omega – imagine a horseshoe with the ends pointing down.
Airflow from west to east has to go around the bow of the horseshoe. The region within the omega block experiences dry weather and light wind for an extended period of time. Because of how heat is transferred in the atmosphere, the west side of the omega block will have a southwesterly flow with warmer temperatures and heavy precipitation, while the east side will have northwesterly flow and colder temperatures.
There have been brief periods this winter when the ridge shifts a few hundred miles to the east. On these occasions, the barricade would be removed just in time for the atmospheric river of the Pineapple Express to pass over us and devastate mountain snow conditions. Omega’s bubble then returns, trapping us once more.
According to Mass, the ridge is weakening and moving west. You may have noticed that temperatures have dropped to about average recently. As the ridge moves toward the coast, so does the northwesterly flow. Our neighborhood is in its flight path for the time being, on the cold side of the jet stream.
“The temperature alone will be helpful,” Mass said. “Cold is good. That’s pretty much in the bag. But now you need moisture. The way you get moisture is with upper level disturbances that go up over the ridge and come down the other side. These disturbances will have some snow with them, but not huge amounts.”
Modest amounts of snow are predicted by Friday. It could either be enough to allow Mount Spokane and 49 Degrees North to resume operations, or another ugly inch. Mass said it’s not unusual for snow in March during these bad years. There’s a chance ski conditions will improve. But it’s unlikely the snowpack will return to normal.
“Around here, once you get past the third week of February, the game’s over,” he said. “We’re going into meteorological spring. We can still get snow in the mountains, but sun is going to win out. Sun is getting stronger very quickly now and it’s getting late.”
I still believe in calendar spring. The season will be as good as the latest snowfall. Better late than never.