Snow Update – 8:45AM Wednesday

8:45am Update —

Good morning everyone! Well, are you all digging out from “Megastorm 2010?” 🙂 Ok, not exactly a home run, but most forecasts were pretty darn close across the board. Would I have liked to see more snow, sure! Speaking of snow, I am getting e-mail reports of snow falling across Vancouver as of 8am as a heavier shower rolls through. I also have one e-mail of a few inches near Larch Mountain. But that is to be expected. Any precipitation we get today will fall as snow all the way to sea-level. Technically it would be a snow/rain mix since we are not at or below freezing. By the way, if you have snow reports, please post them here. Include location and depth (if any). Here are a few WSDOT cam pics snapped about 8am around Vancouver. (WSDOT pic 1) (WSDOT pic 2) (WSDOT pic 3) Also, get ready for some chilly temps over the next few days. Highs will climb no higher than 40 and lows will be below freezing. If there is any moisture left around it will be in the form of snow showers and roads may get icy tonight if we get any clearing. More later…

10:45pm Update —

Getting reports via e-mail of snow in the West Hills of Portland between 750-1000ft as of 10:45pm, as well as a rain/snow mix in Ridgefield. From the posts below, it also looks like snow in Vernonia at 700ft of elev. Looking at the latest sat pic loop and radar, looks like the back edge of the main precip will be through the metro area about 12 midnight or so. Snow will continue to mix in at lower elevations. After midnight we should see the main precip band pass by and the snow level will fall to the valley floor. The main precip will have moved east by then, but anything that falls overnight and tomorrow morning will be all snow down to the lowest elevations. Best chance for sticking / accumulating snow will be above 500ft. If any of you in the outlying areas see any accumulating snow overnight, please post your location, temperature and snow amount here.

7:30pm Update —

Just got a look at brand new 0z NAM (model) update. GFS is not quite done yet. Looks like we will see a decent temperature drop in the next few hours and snow should start to show up at the higher elevations first, before lowering down after 10pm to near the valley floor. But I also see that we only have about 6 more hours of steady precip before it starts to lighten up and turn showery. Here is the latest water vapor sat pic. I have added the approximate location of the center of the low as of 7pm and its forecast track. The area with the black circle is the general area that will be under the gun for snow tonight when the main precip is over us. Then check out the 0z NAM (North American Model) forecast temps for Friday here. They are much colder than past runs. This would be good for lows easily into the mid-20’s in the metro area. It has also trended colder for daytime highs on both Thursday and Friday, likely staying in the upper 30’s both days. Have not had a chance to look at precip beyond tonight as I have a meeting I am supposed to be at in 20 min. I will look at more of that later tonight. So, bottom line is, snow will be lowering over the coming few hours with a sharp drop in temps between now and 11pm. Lets see if the models are correct. Feel free to post your location and temps here. More later!

11:30am Update —

Will it snow tonight in NW Oregon and SW Washington? I have been “teasing” folks with the idea since last weekend. Things are beginning to come together late this morning. A complex system is getting its act together this morning off of the southern Oregon coast. An area of low pressure will move across the central Willamette Valley this afternoon and evening. The storm is forecast to take a path from the southern Oregon coast, to Bend, and finally to Pendleton before heading into Idaho tomorrow. This kind of a set up looks somewhat similar to January 1st 2004 and February 7th 2002. Both of those events brought some snow to the Portland / Vancouver area. Areas north of the February 7th 2002 system saw snow and areas south of the low saw strong south winds and plenty of rain. On January 1st 2004 the Portland / Vancouver area was coated in white as a similar system pulled cold air from the gorge as it passed by just to the south of the metro area. It is important to note that both set ups featured colder air over the area initially, so that helped in those situations. I do not see another January 1st 2004 repeat at this point as the air over us right now will have to cool quite a bit more than it did in back then. Areas from Woodland south to Salem saw as much as 5-8″ with the 2004 system. So, what’s a prognosticator to do in a situation like this? Snow? No Snow?

Bottom Line — The forecast is going to be very tricky. Some forecast models show valley locations below 500ft seeing only a rain/snow mix. However, there are others that have recently come on board with snow all the way down to sea level in the areas from Salem north to Kelso. The approach I take is a blended view. There also appears to be a centralized area of concentrated precipitation east of I-5 and towards to Cascade foothills between 7pm and 11pm. This will be the best shot for snow! There is no doubt that it will be a close call tonight at the lowest elevations. If the precipitation is heavier than forecasted or sticks around longer, I think there is a greater than normal chance of sticking snow even at the lowest elevations. It will be close for sure! Those of you located at or above 750ft will likely see accumulating snow. Areas near the cascade foothills and the coast range will see mostly snow this evening. Expect slick roads in those areas later this evening.

Here are my more specific forecast thoughts as of 11:40AM for valley areas from Salem north through Kelso —

Remainder of today – Rain, highs in the mid 40’s

This evening – Rain changing to a rain/snow mix after 7pm at the highest elevations first, then lowering to near sea level.

Late tonight / early Wednesday – Snow above 500ft, with Rain and snow mixed below, changing to mostly snow after midnight. Light accumulations possible below 500ft with 1-2″ expected above 750ft.

Wednesday – Snow showers ending. Cooler, with highs in the upper 30’s to near 40.

What about the extended? After Wednesday, colder air will be well in place for the rest of the week. This is NOT arctic air, but rather colder continental air that slides down east of the cascades tomorrow. East winds will increase through the gorge. The most interesting part of this weeks weather may be the chances for pure snow down to the valley floor again on Thursday and again on Friday evening, just in time for New Years Eve celebrations. Both of those possibilities are far enough out to where things could change. As I said last weekend, whatever falls after Wednesday will likely be snow down to sea level. Those thoughts remain unchanged today. The amount of available precipitation will be the key. At this point anything we see on Thursday and Friday looks to be light.

I plan to update this post again later today as things begin to take shape. Please check back! Finally, who wants to be the first EVER to post a comment? Any thoughts on my diagnosis? I encourage all posts, both professional and beginner.

Stay tuned!

Steve