Big Snow Event Possible, But Only If One Particular Model Verifies
Updated: Saturday Night 10:00pm
Exciting times are coming, if you like active weather! First off, let me make a quick note that if the snow is flying on Monday, the Columbian Newspaper and I will be hosting a live web chat most of the day. All are welcome to join in. These “live chats” are a blast and we can move weather related information around quickly, no matter where you are located. The web address for the live chat is: http://www.columbian.com/chat/weather. If you click on it now, you will see the comments from our last chat a few months ago. Keep that link handy and I will let you all know if we move forward with the chat on Monday, or perhaps Tuesday as well, depending on the weather. Now let’s get on to the good stuff! A region-wide 1-2-3 snow “punch” is possible from Salem to Bellingham BUT ONLY if one particular weather model verifies! The 0z NAM this evening is a weather geeks dream, isn’t it? If the 0z NAM verifies, the next few days would go down a little something like this…
PUNCH 1 — Saturday’s front is sliding southeast through Oregon as of late Saturday evening. Snow showers will follow this front overnight. On the 1000-500mb NAM link below you can clearly see another surface low developing tomorrow morning and moving SE through Washington. This will increase the shower activity from Salem north to Olympia from about 4am to 12 noon Sunday. There is not a ton of QPF (precip) with this feature, but enough to put a light amount of snow over the valley, albeit showery in nature. Clearing overnight Sunday night will allow for a cold night. Overnight low temperatures at or below freezing will be widespread at most valley locations.
PUNCH 2 — The 0z NAM continues to drive a modified arctic front all the way to the Oregon / Washington border by Monday night and early Tuesday morning, similar to January 1980. The 1000-500mb map shows thicknesses near 512dm over Portland and about 508-510dm near Seattle by Monday. That’s modified arctic air. I also noticed that the 850mb temps drop to a whopping -15c over Seattle and -12c over Portland. When you click on the NAM loop (below) you can clearly see a batch of precip forming, along with a new surface low (that’s the arctic front) that moves right down over Seattle and Portland early Tuesday morning. It passes by Portland and stops about Salem before the next system comes in from the west / southwest off the Pacific.
PUNCH 3 — You can see at the very end of the loop (hour 84) the next juicy system takes aim at the Pac NW for Tuesday night and Wednesday morning. Overrunning precip looks to begin at some point Tuesday afternoon. The progression of the 0z NAM, if it were to go past 84 hours, would likely send the center of the low just south of Portland. Two things would happen in that case. One, surface winds would be out of the east (offshore) in Portland. That would keep anywhere from Portland north cold enough for additional snow. Two, it would pile up the snow in Portland to the tune of 6-10″ Tuesday night into Wednesday. Sure looks pretty on that run! But, this is ONLY if this particular model (the NAM) were to verify! The 0z GFS/WRF does not show this feature nearly as nice as the 0z NAM does. Here is the 0z NAM model loop I referenced above. Step frame by frame and you can see it all unfold — http://tinyurl.com/7ks4l6e
So, which model will win out? History would support the warmer GFS/WRF that kills the snow chances by Tuesday evening and leaves us with nothing but cold rain on Wednesday. But then again, it also gets the overrunning precip in here earlier on Tuesday and is heavier with the precip amounts, vs. the NAM. Either way it looks like Monday and early Tuesday will be snow for the lowland / valley areas to one degree or another. The big question remains what will transpire Tuesday afternoon and evening as the heaviest precip moves in. Will it transition to rain (GFS model) or pile up the snow Tuesday night before finally changing to rain mid-day Wednesday (NAM model). There is about a 12 hour difference between these two models for when snow will transition to rain. A lot of snow can pile up in 12 hours in a situation like this (ie; January 11th 1998 and February 19th 1993) in Portland. There is still time for the models to come into further agreement. A good friend / meteorologist Pete Parsons once told me that models are famous for making forecast “corrections” about 120 hours out and one last time at about 72 hours out. If that theory holds water, we should see one last adjustment in the models very soon, as they settle in on a final consensus. The big question is, what will that final adjustment be? Will it be a big valley snowstorm or a big warm up with the center of the Tuesday night low heading north of Seattle and Portland? Areas just north and east of Seattle have already seen as much as 2-3″ of snow this evening and that is all sliding south tonight as more showers move inland off the coast. I will plan another update tomorrow or Monday as the models settle in on a final solution.
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