UPDATE – LOW ELEVATION SNOW THIS WEEKEND?

FRIDAY 2:05PM UPDATE —

Just a quick Friday afternoon update to pass along. This morning’s models all came in a bit colder and a bit wetter than yesterday’s did. So, what does this mean for the rest of us??? Looks like there could be snow flakes in the air down to just about ANY elevation from late Saturday night through Monday. One thing I have noticed on the new model runs is a small disturbance that slides down over the area Sunday and enhances the precipitation. If models are correct (and there is no reason at this point to believe they won’t be) there will be snow mixing in with the rain on Sunday no matter where you are in elevation, west of the Cascades. Temperatures will be above freezing during the daytime, so anyone looking for sticking snow better head for the hills, overnight. The other thing that sticks out in the models are the low temperatures on Sunday night and again Monday night. Temperatures will be below freezing at many valley locations. That would be the first such occurrence since January, for many of us. It could be a slick morning commute on Monday as any water on the ground from the Sunday showers will likely freeze. There is another system slated for Tuesday night that could be problematic if there is enough cold air still in place at that time. But I will stop here for now. More on the Tuesday system later in the weekend. For now, enjoy the nice weather today as the rain should begin by sunset tonight. Then colder air arrives Saturday night. I will update again here if anything else takes shape that was not forecasted ahead of time. Finally, here are the record low temps at PDX for the coming few nights: Saturday morning 23 degrees set in 1969, Sunday morning 18 degrees set in 2011, Monday morning 19 degrees set in 1960 and Tuesday morning 24 degrees set in 1960. Looks like these are all out of reach for now. Stay tuned!

Wednesday 2/22/12 2:54pm—

There has been a lot of talk recently about the chances for low elevation snow from Seattle south to Eugene beginning this coming weekend. Models have been all over the place for the past week, swinging widely from a full on arctic blast to nothing more than showers on the valley floor. Maybe it is just me, but it sure seems like this winter has been one of the hardest when it comes to models picking up on pattern changes at long lead times. Models have had a horrible time figuring out the overall pattern as we have moved through winter. Many times this winter I have had to rely on the old GOLU (Go Outside, Look Up) weather model. That model never lets me down. Pun intended. Ok, I have been hesitant to jump feet first into the snow bandwagon for this coming weekend, for several reasons. It is now time to make a forecast call. As of this morning (Wednesday) models appear to finally be coming into “solid” agreement on the outlook for this coming weekend. First, what I DO NOT see is a region-wide lowland / valley floor snow event. What I DO see is a prolonged period of below normal temperatures and a ton of snow for the Cascades! Just like last February and March, the mountains appear ripe for some great late winter skiing. The snow level will be well below pass level starting Friday night and lasting nearly all of next week. This is the kind of weather where the Cascade ski resorts will see tons of fresh powder. If you are traveling over the Cascades this weekend and next week, be prepared for snow.

So, what exactly happened in the models with regards to the snow idea for this weekend? Here is what the European (Euro) model looked like just a day or two ago. If this were to have verified, this would have been very cold weekend in the Pacific Northwest with snow likely down to sea level. Some forecasters were jumping on this right away while others were playing it safe. I did a little bit of both. I “teased” the idea of lowland snow, but with a clear caveat about future model runs yet to come that could look a lot different and to “stay tuned.” As I have mentioned many times, models are famous for a final shift in the 72-120 hour timeframe. Anyway, here is what the Euro was looking like a few days ago:

Now here is what the European (Euro) model looks like this morning and for that matter most of yesterday as well:

Big difference, right? In the first frame you see a nice cold shot that envelopes the entire Pacific Northwest all the way into California. In the second frame you see a warmer solution with the coldest air staying much further north. If I were to loop this image with all of other images in this “run” (before and after this image), you would see that the cold upper level trough races through the Pacific Northwest and into Idaho much quicker. The overall pattern is more progressive rather than amplified. End result = warmer for this weekend. There are plenty of other factors to look at before making a forecast. The two I have shared above are upper air maps (500mb) which is a representation of what is going on above the surface, at about 18,000ft. Surface and near surface temperature forecasts are also modeled to be warmer as well. But, let’s not get ahead of ourselves just yet. There is still a cold trough coming for the weekend and several more next week. But snow is going to stay confined to areas above 1,500ft this weekend and into early next week. There are additional systems slated for next week that look pretty cold as well, but they could also trend warmer as we get closer. Hence, “stay tuned!”

Do You Like Mountain Snow? You Will Love Next Week!

Ok, now that we have established the snow threat for this coming weekend, let’s look ahead to what the models ARE clearly showing. The following images are compliments of NCEP and Jim Little. First, here is a graphical representation of the 12z GFS Ensemble and Operational models. Simply put, both the GFS (Global Forecasting System) ensembles (think of them as 20 little GFS models all putting out their own forecast) and the Operational GFS model are in nearly complete agreement that a colder pattern will overtake most of the Pacific Northwest beginning this weekend and last through all of next week. What this graph shows is the forecast temperatures at 850mb (about 5,000ft) above Portland, in degrees Celsius. For reference, this is about the same level as the average mountain pass over the Cascades. So, anything below the 0 degree line will likely be frozen precipitation across the mountain passes, assuming no other air masses are at play here. Based on this output, it looks like a very chilly week anywhere above about 3,000ft in the mountains next week. Upper air temperatures are forecast to “tank” after the passing of Friday’s system. The blue and red lines represent the average of both the 20 member GFS Ensemble as well as the Operational GFS model. As you can see, there is a high degree of agreement in both. Hence, more confidence in the overall forecast through the weekend and likely the first part of next week as well. See below:

Follow that up with the freshly minted NCEP/NOAA long range outlook and it looks like the Pacific Northwest is going to end winter on a cool and wet note. The 8-14 day temperature forecast is calling for below normal. The 8-14 day precip forecast is also calling for above average.

To sum it all up —- snowfall this weekend on the valley floor is a not likely! If you are above 1,000-1,500ft you will likely see some flakes, but nothing serious sticking. Precipitation will be scatterd anyway. Nothing solid coming inland at this point in time on Saturday and/or Sunday. Area’s above 1,500-2,000ft are going to pick up overnight snow this weekend. Areas above 3,000ft including ski resorts in the Cascades will pick up quite a bit of snow this weekend and through much of next week. Several systems will slide down from the northwest next week and that is perfect for building some mid-late season snow powder. If you like to ski, you will love next week! For the rest of us it is the usual, “cold rain!” Finally, don’t forget about the great weather meeting we have planned next Tuesday in Portland. The topic is “Summertime Lightning Forecasting” and is hosted by KPTV and the Oregon Chapter of the American Meteorological Society (AMS). Our guest speaker will be Meteorologist John Saltenberger. This is going to be a really informational meeting. You can see all of the details at: http://www.ametsoc.org/chapters/oregon. Hope to see some of you there!

Stay Tuned!
Steve Pierce

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