Update: A Bit Icy Overnight

8:45pm Tuesday Update —

I just took a long look at the latest models that just came in this evening and a few things stand out — 1. The low level easterly flow is going to stick around through about 1-3am, which is about 4-5 hours later than first forecast. Seems like that happens a lot doesn’t it? That means those of you who are seeing some icing now will likely stay that way for a few additional hours. Those of you who are just wet won’t likely freeze. Models continue to show a warm up in time for the morning commute. 2. Those of you on the east side of the metro area, including eastern Clark County will continue to see cold easterly winds and temperatures near freezing overnight. Another round of rain (or freezing rain depending on your location and temperature) will roll through the area after 10pm. Those traveling east into the gorge need to be prepared for some ugly driving conditions. There are reports of accidents east of Cascade Locks, due to the road conditions there. So, fire up a hot cup of your favorite beverage and watch a good movie tonight. Ice is never fun to drive on.

Stay Tuned!
Steve

7:30pm Tuesday Update —

Warmer air is beginning to move in above us, as previously forecasted. The first band of moisture moved through as mostly snow in the 5pm hour. Subsequent bands have now turned to rain across most of the metro area in response to the warmer air above. Some areas in Clark County are still reporting a little light snow mix along with sleet. Some areas of freezing rain are also being reported. As long as the east winds continue to blow, temperatures will remain close to freezing, or slightly above, for the next few hours. Later tonight winds will switch to southerly and temperatures will rise to levels sufficient enough to melt anything that may be frozen now. For the most part fences, car roofs and shaded areas are most prone to a little glazing. The gorge will be the last place to moderate, as expected. New modeling data is coming out now and if it varies largely from my thoughts here, I will post them.

Stay tuned!
Steve

4:00pm Tuesday Update —

Ok folks, I am getting reports of a snow & rain mix to the south near Salem as well as out in the coast range, SW of Portland. Does this mean “Snowpocalypse 2011” is back ON again? Not exactly. But what is does mean is that the layer of air just above us is thick enough to not allow the precip that is falling to melt before hitting the ground. As long as the KPTV tower temps stay below 32 at all three sensors, snow will mix in with the rain all the way to the valley floor this afternoon and early evening. See KPTV tower temps here. The transition to all rain is still expected this evening as warm air will erode the cold layer over us. Models continue to bring in plenty of warm air above us later this evening. Keep an eye on the temps at the top of the Ch 12 tower. They will likely warm up first, as the warm air comes in aloft. Will you be sledding down the hills with an extra day of vacation tomorrow? Not likely. Temperatures will slowly increase throughout the night. One thing that is almost certain — at least one TV station will be in “storm mode” all evening long, with crews all over the local area. Drama! It’s all about the drama, folks! 🙂

P.S. Special thanks to Doppler Dave, HIO Phil and Aloha Rainshadow for “fighting the good fight” when it comes to hoping for snow in the Portland area. Yes, that is an inside joke.

Stay Tuned!
Steve

11:00am Tuesday Update —

Good morning all. As of 11:00am it looks like temps are all above freezing now across the metro area. Things are playing out nearly exactly like I had mentioned in my 3pm update yesterday. Looks like precip will make it in here after dark today, but with it will come plenty of warmer air at the mid levels of the atmosphere. That equates to “all rain” in the metro area with perhaps a flake or two of snow to start and some spotty freezing rain in the outlying coldest locations. Sorry kids, there WILL be school tomorrow. Parents, you will be getting up for work as well. Doesn’t it always seem like we just miss out? It just goes to show what a giant body of water called the Pacific Ocean can do to areas west of the cascades.

Stay Tuned!
Steve

3:00pm Monday Update —

La Nina strikes again! In what I would best describe as one of the biggest computer model shifts I have seen in a number of years, the latest data out as of Monday morning has taken away nearly any chance for frozen precipitation in valley areas of western Oregon and Washington this week. For the past five days, computer models were in near total agreement with the idea of a widespread lowland snow / freezing rain event for Tuesday night and Wednesday. Those chances, in my opinion, have now dwindled to less than 20%. Precipitation is still forecast to move into western Oregon and Washington Tuesday evening, however, warmer air will rapidly erode any colder air that was first forecast to be trapped west of the cascades. In light of this “large” adjustment in the models, I fully expect that major valley locations will only see spotty areas of freezing rain Tuesday evening before transitioning to all rain overnight. In fact, it would not surprise me to see 50 degree high temperatures on Wednesday, continuing into Friday in western valley locations.” We will likely dodge the bullet on this one. Since we all live in an era of near real-time electronic communication, I believe that updating a forecast that is not likely to verify is just as important as the initial forecast.

So, why the big model shift at the last moment? Here is my theory. This year we are seeing the strongest La Nina in decades. Models have a smaller data set to pull from when it comes to “analog” or years with similar conditions. In other words, if this winter’s weather pattern was more of the normal than the outlier, models would be more apt to picking up on pattern changes at longer lead times. Models perform pretty well when we are not under the influence of La Nina or El Nino. Let’s call these “La Nada” years, for the sake of this discussion. So, my latest update is to un-batten the hatches and be thankful that “Snowpocalypse 2011” as others have suggested, will not be occurring anytime soon. However, this winter is far from over. The last strong La Nina in 1988-89 featured a fairly moderate winter before the bottom fell out in February 1989. Many areas saw their coldest arctic outbreak since January 1950 that February.

Stay Tuned!
Steve

1:00pm Sunday Update —

Happy Sunday all. I have taken a good look at all of the latest data this morning and will detail my synopsis first, followed by technical details below that.

Synopsis —

After taking a good look at the latest data out as of Sunday morning, it now appears increasingly likely that scenario #2 will be the end result this coming week. See my previous post below for scenario #2 details. Now, this does NOT mean that snow is a “no go” altogether, but what it does mean is that several things will likely come together that will limit the duration of low elevation snow this coming week. Is there still time for the model outputs to change? Sure! But usually once we are within 72 hours the models have settled in on a single overall solution. We are now within 72 hours and in my view it was easy to see the “72 hour adjustment” being made on the models last night.

The two things that are loud and clear as of Sunday afternoon are, 1. the center of the storm for Tuesday night and Wednesday is likely headed north of Portland / Vancouver, which will turn the surface winds from east to south sooner than would be the case in scenario #1 (below). 2. The easterly gradient through the gorge is forecast to be less than first modeled, thus our source for the coldest air will be less significant. Models also show the amount of cold air available east of the cascades will be less than in December of 2008.

So, what does this all mean in a few sentences? Ok, how about this — “The storm is still on track for late Tuesday afternoon and evening. The center of the storm will pass to the north, which will limit the amount of snow we see. Precipitation should begin as snow in most areas near Portland and Vancouver Tuesday after 4pm. A transition to freezing rain, sleet and then rain is likely at some point Tuesday night into Wednesday morning. Models are in general agreement that enough precipitation will fall to accumulate some snow across the metro area Tuesday night before it all changes to rain. How much snow is still up in the air and we will know more by Monday and Monday night.

What this DOES NOT look like is a BIG snowfall that remains here for days, followed by even colder weather later in the week. Some local forecasters have been calling for as much as 12″ of snow locally. For the record, I see nothing at the present time that would suggest something like that. This is now looking like a quick hit storm with not much remaining on the ground Wednesday. Is there room for final adjustments to this forecast? Yes! Will I update often over the next 48+ hours, Yes! So, stay tuned!

Technical details (for the serious “weather nerds”) —

Latest 4-5 runs of GFS, NAM and WRF meso scale models shows a clear path north of Portland with the center of Tuesday night’s low. This mornings 12z run of the 4km and 12km WRF and 12km NAM show outflow through the gorge is still on schedule to begin Sunday night into Monday morning. This will usher in cold, dry air into Portland / Vancouver area Sunday night into Monday. Dewpoints will likely fall to the upper teens to lower 20’s on Monday.

Next system approaches from the west Tuesday afternoon. Models have been consistent in bringing warm frontal moisture into NW Oregon and SW Washington quicker than previous runs, with onset sometime after 4pm Tuesday. NAM is slightly later, around 7pm or so. Will need to keep and eye on Tuesday morning’s low temperatures. If east winds ease late Monday night and stratus deck arrives just after sunrise Tuesday, daytime heating could be limited more so than currently modeled. Either way, forecast highs for Tuesday not expected to be much above 35-37 degrees in Portland / Vancouver metro area. With ample cold, dry air in place, snow is likely to begin across metro area just after dark Tuesday, as warm frontal precip arrives. Sounding and cross section data show support for some additional evaporative cooling. QPF amounts are also forecast to be enough to bring accumulating snow to areas around Portland and Vancouver after sunset Tuesday night. How much snow is still up in the air, but general model consensus has done away with the earlier “snowpocalyptic” idea and replaced with perhaps 1-3″ instead.

NAM lifts warm front north of metro area by 11pm Tuesday night, with post frontal southerly winds. 12z NAM sounding reflect this well, with a change to freezing rain and then rain by 12 midnight. That would give the metro area 3-4 hours of -SN per the NAM before a change to -RN. If QPF rates are significant enough, could be a few inches of wet snow. The 12z WRF on the other hand shows precipitation into the metro area by 4pm Tuesday and keeps the easterly low level winds blowing through 6am Wednesday morning with plenty of QPF. However, temperatures above the surface are forecast to warm enough after midnight to turn any snow at the surface to -ZR or -RN as warmer air moves in between 900 and 950mb’s. Both models show available precipitation could be moderate in intensity from 7-10pm Tuesday night.

Will need to watch this all very closely, as any change in the current solutions will potentially have an impact on final SN amounts and duration. This should be stressed. It would not take much fluctuation to add or take away from the total SN amounts. Further adjustments in model outputs are still likely as we get closer to the event, as is the case with all snow events in the metro area. The gorge is likely to see quite a bit of SN and potentially ZR into the day on Wednesday, as the cold air will be dense enough there to prolong the event. Longer range models now show a near consensus in keeping the coldest air bottled up to our north and allowing westerly jet to punch into the area. This will eliminate the idea of low elevation SN after Wednesday. 12z ECMWF shows bitterly cold arctic air just to the north in Canada next weekend, but the forecasted 500mb pattern will not allow us to tap into it, yet?

I plan to post updates as new information becomes available. Check back often for updates. Discuss amongst yourselves and I will check back in later.

Stay tuned!
Steve

Widespread Snowstorm Possible

Happy weekend everyone! I am back from a nice little vacation. I thought it would be pertinent to store up some of my “weather energy” for what could potentially be a “wild ride” over the next week or so. By the way, the picture above is one that I shot just before Christmas 2008. That’s the I-5 Bridge over the Columbia River in Vancouver. Could we see a repeat of that event? Here is the latest as of Saturday —

A complicated weather pattern is expected to take shape early next week that could lead to the most significant lowland snowfall event for parts of western Oregon and Washington since Christmas of 2008. The latest data available suggests that valley locations from Salem, Oregon north to Seattle, Washington would be prime targets.

Act 1 – A cold Pacific system passed through the Pacific Northwest Friday night, ushering in colder air this weekend. Snow levels will fall to near 500ft through Sunday, with some light accumulating snow on the higher hills. A weak secondary system is expected to pass through NW Oregon and SW Washington early Sunday morning. This system will likely bring some light snow to the hills and a mix of rain and snow down to the surface early Sunday morning. Little accumulation is expected, with high temperatures remaining above freezing at the lowest valley locations through the weekend.

Act 2 – A reinforcing shot of colder continental air will slide down from the north, as well as east of the Cascades on Sunday evening. East winds will increase and begin to funnel cold dry air through the Columbia River Gorge into parts of NW Oregon and SW Washington overnight Sunday night. Monday and Tuesday will remain mostly dry, with daytime high temperatures in the 30’s across valley locations.

Act 3 – Tuesday night and into Wednesday morning, a complex system approaching from the Pacific will spread moisture over the deep layer of cold air already in place over the region, resulting in the potential for a widespread snowfall event. At leads times such as this, adjustments to the final outcome / storm path will likely take place. As of Saturday, two scenarios are most likely;

Scenario 1 – The center of the storm passes just south of Portland on Wednesday, keeping easterly gorge winds blowing throughout the day Wednesday into Thursday. In this set up, areas north of the center of the storm could see significant snowfall accumulations for the entire day Wednesday into Thursday, before the storm passes by. Although there are some subtle differences, this scenario is somewhat similar to the white Christmas of December 2008 in Portland. In that set up, the center of the storm also stayed just south of Portland. The precipitation amounts forecast for this coming week, regardless of storm trajectory, are not currently forecast to be as significant as December 2008. In that particular storm, areas near Portland received as much as 10-20″ of snow over a 4 day period.

Scenario 2 – The center of the storm passes just to the north of Portland. In this set up, areas south of the center of the storm, from Salem north through Portland, would likely see snow for a portion of the day on Wednesday, followed by a transition to mostly rain for Wednesday night before the storm passes by.

Act 4 – Regardless of the path of Wednesday’s storm, models show additional cold air will slide back across western valley locations of Washington and Oregon again Thursday night into Friday morning. Later Friday, a second system is expected to take a similar path to the first. If this solution comes to fruition, a second snow event is possible across the same areas that were affected by the first storm. After Friday, models diverge in their output data. Some model data suggest that modified arctic air, along with sub-freezing daytime high temperatures, will overspread most the Pacific Northwest for next weekend, keeping any snow that fell in place. While other model data show a return to a warmer westerly flow and moderating temperatures. Again, at lead times such as this, accurately forecasting temperatures and potential snowfall amounts is arduous at best. A better handle on how events will unfold should be known by Monday.

Stay tuned!
Steve