I love a good snow storm, but I usually don't get too excited about a widespread valley snowfall when we're still dealing with onshore flow. That means the winds are coming in from the ocean, which has a warming influence on cold air masses from the north. That influence may only reach 500 feet or so above sea level, but almost every time, with onshore winds, it's enough to keep the valley from seeing a widespread snowfall. This time, after the initial front passed by, the air wasn't cold enough and the moisture wasn't solid enough to deliver a big snow in Portland. Sure, there were areas that received and inch or two, more above 500 ft, but these accumulations were from showers. The difference being that showers are smaller in areal coverage, and while they can produce intense precipitation: rain or snow with hail, they tend to be short-lived and don't impact the whole area.

One of the best set ups for snow in Portland is offshore flow with cold dry Arctic coming down the Gorge and spreading across the entire Willamette Valley. Then, a storm comes in from the west bringing the necessary moisture, but the center of the storm stays south of Portland so that the cold offshore wind field is maintained. We can get several inches very quickly over a broad area under that scenario. It can also degenerate into a freezing rain situation as the cold air layer at the surface is eroded from above by the warmer Pacific winds.

And speaking of freezing rain, my co-anchor Tracy Barry brought up a great point tonight when she asked about what happens when we transition out of the cold air mass that is moving in tonight. That can also be a freezing rain set up, but this time, it looks like temperatures will moderate before rain returns.

Winter 2006-2007 continues!

Thanks for watching and surfing KGW.

Matt Zaffino
KGW Chief Meteorologist

Posted by at 7:55 PM | Permalink | Comments (4)

Remember the ol' Star Trek movie Wrath of Khan. I've got my own twist on that trekkie favorite. Wednesday's snow showers are widely scattered but sticking only in outlying areas. Locations west and north of the city have seen some sticking snow. The lack of a good winter's snow storm has not made me popular with school kids in Portland. Oh the wrath I've endured from many a child hoping this would be day to play in snow and escape the classroom. Thousands of kids hoping mother nature would bring enough snow to keep school buses parked and the classrooms empty. Bottom line,
when you can't complain to mother nature, your local weatherman will do! I think a collective howl was heard across Portland, when only scattered flurries fell this morning. I know Pat Dorris's two sons are not to happy with me. But the complaints from the Dorris boys are nothing compared to the slings and arrows from my own daughter. My 14 year old said if I didn't produce snow in amounts to cancel school she feared for her life! "Dad, kids at school are counting on you to cancel school. If it doesn't snow I going to get beat up! You better bring snow, or you're in trouble." It's those three words, "You're in trouble" that are ringing in my ears right now. Just how much trouble? Will she talk to me when she gets home this afternoon or just roll those blue eyes in an icy stare that freezes me in my tracks? Stay tuned for details, I may be spending another all nighter at camp KGW sleeping in the down stairs weight room on a yoga mat. Afraid very afraid to go home and face the Wrath Of Karen

Posted by at 10:53 AM | Permalink

Snow lovers in Portland are like Charlie Brown trying to kick a field goal: Lucy keeps pulling the ball away at the last second and we end up on lying in the mud. Time and again, computer forecasts show promising signs of Arctic air invading the Northwest, with moisture coming in off the Pacific for that magical snow making combination that so often eludes us. And then, as we get closer to the advertised event, the models back off on the Arctic intrusion and become more accurate, and the cold air stays mainly to our east. We get a chilly east wind for a day or two and maybe a brief burst of valley snow. Disappointment once again, but why?

It comes down to basic climatology and geography, and Portland snow storms have to buck both to really have a chance. Weaher systems in our part of the world in general move from west to east, with a lot of north south variation, but the overall trend is to the east. The air masses that originate to our west, over the Pacific, are generally too warm to produce sea level snow. So we look north for Arctic air. As those air masses form and move south, they also tend to move east because of the basic nature of weather patterns as noted above. That's where we fight climatology. But there are also some major geographic barriers, namely the Rockies and to a lesser extent the Cascades, that literally act as a road block to the southward moving Arctic air and prevent it from expanding west to the Pacific Northwest coast. That's where we fight geography. And even when Arctic air manages to make it west of the Cascades, we still need moisture to make snow. That typically comes from the west, which also means the warmer Pacific air is returning. So everything has to fall in place just right, and against the natural tendency of our weather patterns, to produce a big Willamette Valley snow storm. It does happen, however, and it will happen again, so snow lovers don't lose hope!

Matt Zaffino
KGW Chief Meteorologist

Posted by at 12:43 PM | Permalink | Comments (1)