Colder Weather On Tap This Week!

Update: Sunday 5:45pm

Well folks, it looks like winter is not done with us just yet. This afternoon’s NAM continues to indicate modified arctic air is going to pay a visit to all of SW Washington and NW Oregon beginning as soon as overnight tonight into Monday. As of 5pm Sunday, dew points are steadily dropping over Washington and surface winds are from the north. Based on surface observations, I would put the modified arctic boundary in a line from Walla Walla to Yakima and across the Cascades from Centralia to Hoquiam on the coast with slow but steady progress southward. Looks like the more trusty WRF model is going to get beat by the NAM model this time around. This has happened before in cold solutions just like this.

So, what is the bottom line? Get ready for colder weather this week, especially at night! Colder air will begin to filter into the metro area overnight tonight and into Monday. After seeing temperatures in the lower 50’s today, expect much colder conditions over the next few days. Cold east winds are going to get cranking through the gorge by Monday and last most of the week. I do not see any snow coming with this system. It will be mostly dry. Overnight lows are going to be quite cold, with lows well below freezing on Tuesday and Wednesday morning. I would not be surprised to see low temperatures as cold as 20-25 degrees in some outlying locations across the metro area this week, if we see clearing and calm conditions at night. After seeing temperatures ranging from 50-60 last week, high temperatures this week are going to be as much as 15-20 degrees colder in some locations. Longer range models are also introducing the idea of an even colder push of air into the area around February 10th. More on that as we get closer. I plan to post another update tonight in the 7-9pm timeframe as new data becomes available.

Saturday 9pm

Happy weekend everyone!

Hope you are enjoying the warm weather (by January standards) that we have been seeing over the past week. By now, most of the hard core weather guys (and gals) out there have had a good look at the latest model data showing the potential for a big arctic blast in the second week of February (about the 9th or 10th). But, that is a long way out there. There is likely to be plenty of flip flopping between now and then. The odds really start to stack against us seeing really cold air after February 15th. So if it is going to happen, it has to get its act together pretty soon. As I look back at the record books, there are only a few truly “arctic” outbreaks that have occurred after February 15th. I consider an arctic outbreak in the Portland metro area to be anything where we see high temperatures at or below 32 degrees for a few days. We can still see good sized snow events in February, but they are rarely associated with big arctic blasts. The last one that comes to mind was Feb 19th 1993. That was a rare event that left the area under 6-12″ snow and temperatures topped out right about 32 degrees that day. But we warmed up quickly after the snow ended. Either way, that 1993 event still holds the record in Portland (airport 1940-2010) for the most February snowfall in a single day at 6.1″ on February 19th. I also recall Feb 12th 1995, but that was a little less in the way of snow. Either way, it has been about 15 yrs since a good February snowfall and or arctic blast. Other honorable mentions for cold outbreaks earlier in the month of February (pre-15th of the month) include 1996, 1990, 1989, 1979, 1956 and 1950.

Ok, so lets get back to the here and now. While everyone is looking at something that could be potentially cold 10+ days down the road, I am keeping my eyes on the next 72 hours. For the past few models runs, the NAM (North American Model) has been showing a very strong 1050mb (31.01″ WOW) arctic high pressure ridge sliding into Eastern Washington by 10am Tuesday morning with a fairly strong easterly gradient squeezing very cold air through the gorge into the Portland metro area. In fact, if taken at face value, the NAM surface maps have the metro area seeing high temperatures on Tuesday struggling to get to 30 degrees, with a low temperature of 20-25 Tuesday and about 15 degrees Wednesday morning. Now that would almost surely be quite a weather “shock” to those who have been enjoying temperatures near 60 in some spots this past week.

Now for the flip side of that coin — the more trusted GFS model shows the cold air making a glancing blow to eastern Oregon and Washington, then slipping south and east into Utah and Wyoming, leaving us with more dry weather. In fact, the GFS shows overnight lows not dipping lower than 30 or so over the next 5 days. So, which model will win out? I have seen models be at odds like this in the past, but this normally occurs at lead times of greater than 72 hours. I am quite surprised to see this much model disagreement when we are within 72 hours of the projected weather “event.” At this point I am going to stick with the more trusted GFS model as the NAM has pulled tricks like this in the past. The 0z NAM run tonight showed a little pull back from its super cold output from earlier today. So, we may be seeing the NAM backing down from the really cold air and moving to a solution that is more less like the GFS. Basically, one model shows sub-freezing high temperatures for daytime highs in a little more than 48 hours and the other shows lows of barely 32 and highs reaching into the 40’s. Now that is quite a spread.

I will keep my eye on everything. If there are any updates to pass along they will be posted here, so check back for updates.

Stay tuned!
Steve