Saturday Snow & Cold – Round 2
4:40pm Saturday Update —
The picture above was sent in from my brother who is in Sunriver, Oregon this weekend. Looks a little chilly, eh? How about those record cold overnight low temperatures this morning? Buurrrrrr!!!! Portland recorded a record low of 18F, besting the old record of 20F set in 1962. Vancouver dropped to 17F this morning. But the big winners (depending on how you look at it, I guess) is eastern Oregon where temps dipped to -25F at Meacham and -27F at Seneca. Now that is cold!
So, what about the “S” word? It has been flying around once again. After a good look at all the latest data this afternoon it certainly looks like some light snow will fly across the area this evening. One of the big reasons why this is likely to be the case is because daytime heating was capped by all of the clouds that rolled in this morning. Thus, temperatures have not climbed much higher than 33 degrees. Once darkness falls and the precipitation moves in, we will see additional cooling. Dew points are between 10-15 degrees across the metro area this afternoon. That is really cold and dry air. Once you precipitate into that air mass, two things will occur. First, it will tend to eat up the moisture at first. But once the air mass becomes saturated enough, the temperature will have fallen. I have ran some rough numbers in my head and if the precip remains light, temps wont fall much tonight. But if we can get enough moisture in here, evaporative cooling will drop temperatures into the upper 20’s. We shall see. Either way, that is cold enough to see snow no matter where you are in the metro area tonight. On the other hand, models don’t show a ton of moisture at this point, so anything that falls will be light. Later tonight, we will see more moisture across the area and that will be our best shot at accumulating snow at the lowest elevations. The NWS has a Winter Weather Advisory up for the local area and I think that is a good call.
The big question remains — when will it all change over to rain at the lowest elevations? It has been well documented that models are normally to quick to erode the cold air and it ends up holding on longer. This time I am up in the air. One model shows a fairly quick eroding of the cold layer and the other shows a much slower transition from snow to rain. If I were to take half of one and half of the other (a split) I would say the chances are good that we will see light snow most of the night and then a change to rain on Sunday. But the fly in the ointment is the one model that I trust the most (the WRF) is already 7-8 degrees to warm for the highs today. It was forecasting 40 and it made it to 33 so far. It also shows about 4-5 degrees of cooling tonight with the onset of the snow. So, in reality that could end up being 27-28 degrees tonight instead of the 34-35 which obviously is not going to happen.
So, here is my 4:40pm Saturday call —- snow and sleet (now called ice pellets) will increase tonight and last through the night. It will be light. Snow or ice pellets will change to rain tomorrow, but the timing for that change-over is up for debate. I want to get a look at the 0z models tonight after 7pm. I bet they will adjust (colder) to reflect more of what is really going on outside right now. If that is the case, it could prolong the snow on Sunday before southerly winds finally erode the cold layer away and we see a mix of rain and snow and then just rain. I wont even address the 12z NAM model which keeps us as pure snow through Tuesday as I don’t see that being the case either. There is no doubt, it will be an interesting 24 hours. Since it is my birthday today, I may not have time to post again tonight. So, enjoy whatever snow falls and maybe (for the first time in my 38 years of life) it will snow before 12 midnight and then I will be able to say it has snowed on my birthday! 🙂