Wetand News

An unusual weather system is approaching Washington and the models are suggesting a significant snow event tonight, with the potential for more snow than Sunday around Seattle.  But uncertainty is substantial. The feature of interest is a trough offshore (area of low pressure, indicated by the white oval) in a forecast of sea level pressure (black lines) for 4 PM today.  The colors are low-level temperatures, with blue and purple showing air cold enough to snow. The latest infrared satellite image shows the feature.  Not very impressive-- would not call my mother about it. But the models are putting down substantial snow with it:  2-5 inches in places. For example, the latest NOAA/NWS high-resolution rapid refresh modeling system (HRRR), brings the leading edge of the snow into the Olympic Peninsula by 7 PM.  With a strong snow band over central Puget Sound by 10 PM tonight. The latest UW model forecast for snow accumulation through 7 AM Wednesday is a bit differe

There are a number of moving pieces that have been occurring during the past six hours, but the most significant was the convergence zone that set up between Lynnwood and Everett, resulting in 2-4 inches of wet snow. And then there is the cold air (the Arctic front) that is now pushing southward, with strong flow coming out of the Fraser River Valley.  As shown by this radar image a few hours ago, there has been a band of often heavy convergence zone precipitation over the North Sound, which was stronger than the models predicted. The convergence was produced by the  confluence of air moving eastward in the Strait of Juan de Fuca and air from the southwest coming around the Olympics. The air aloft had started cooling after around 1 PM as the low center aloft moved through, and by later in the afternoon the combination of this cooling air aloft and the cooling effects of heavy precipitation (melting and evaporation) were enough to bring wet snow down to the surface in the converg

I am going to go against one of the rules of the click-baiting online world.  I am not going to even hint there is going to be a big snowstorm over Puget Sound land.  Yes, most of you will see some flakes, but for most the ground will be barely whitened. As we shall see, a highly transient Arctic Front/convergence zone will bring a few hours of snow showers, with totals ranging from a few tenths of an inch near the Sound to perhaps 1-2 inches in the far eastern suburbs. I am going to show you some forecast snow totals....but keep in mind there is lot of uncertainty regarding the exact distribution of snowfall. The latest super-high resolution (1.3 km grid spacing) UW WRF forecast (below) for 24-h snowfall (through 4 AM Monday), shows light snow ( 1 inch( over NW Washington, with 2-4 inches over the northeast Olympic Peninsula. Most of Seattle is around 1 inch, with some heavier snow east of the city.  LOTS of snow in the Cascades. But you should NEVER depend on one forecast

We are now close enough in time that we can apply some of our most powerful prediction tools to the snow forecast problem for Sunday/Monday.  Plus, we are close enough so that uncertainties have lessened. Before I talk about that, let me note that as expected the Cascades are being hit very hard with a large snowfall, with Snoqualmie Pass receiving about 2 feet of snowfall during the past day.  Snoqualmie was closed for a while, and both Snoqualmie and Stevens require chains at this time. But let's talk about the situation in the lowlands.   It is clear that the Arctic Front will push southward across western Washington Sunday afternoon and Monday morning, with snow associated with its leading edge and when cold air is forced up terrain.  The snow action should be over by 4 AM Monday morning. Below is the latest super high resolution forecast of total snowfall for the 48-h period ending 4 AM Monday.   There is, of course, a huge amount of snow in the mountains, particularl

Sunday Snow Update at noon Saturday ____________________________ This is a lot of discussion about snow, but there is something we should keep firmly in mind:  the arctic air that is going to reach western Washington will be the coldest in years.  Backed by strong winds in some areas, this cold will not only test our housing infrastructure (freezing pipes), but will be life threatening to those living outside or for the unprepared in higher terrain. Take a look at the latest National Weather Service ensemble temperature forecast for Seattle-Tacoma Airport.  The solid line is the average of all the many forecasts (the gray lines) and the blue is the single high-resolution forecast.  Wow .  The highs on Tuesday (14th), will only get in the mid-20s, with lows that morning in the teens. The excellent weather.com (IBM) forecasts suggest a high of 29F that day (see below). And the European Center forecast is going for highs of mid-20sF for both Tuesday and Wednesday (w

Some flakes are falling over the western Washington lowlands right now--but this is not a serious issue.  Roads are still quite warm and there is some minor accumulations on grass for some higher elevation locations (see the picture below at the intersection of I-90 and SR 18 east of Issaquah. The freezing level (and thus the snow level) has dropped considerably over the past day, with the freezing level (the temperature aloft where the atmosphere cools to 32F) now around 800 ft (see image from Seattle SnowWatch below).  A few melting flakes have reached sea level as a weak weather system moves through this morning. But if you live at a higher elevation, the scene was more winterlike (take a look at the picture at 1170 ft in Bellevue at the home of Dr. Peter Benda). A stronger weather system is approaching the Northwest and will reach us tonight...and we will have some cooler air in place.   This is not an ideal situation for lowland snow (temperatures are marginal), but

I would not run to the food store yet.    But there is a significant chance for some light lowland snow over portions of western Washington during the week. Uncertainty is still high, but sufficiently cold air will be in place to allow snow to reach sea level for substantial portions of time.  The issue is getting precipitation during those cold periods. The large-scale flow pattern that will dominate during the next week is a classic for cold and snow in the Northwest (see upper level map below for 1 PM on Saturday---500 hPa level, about 18,000 ft). A big ridge/high pressure area will be positioned over the central Pacific, with northwest flow over the West Coast--which brings in colder air from the north. Snowstorms are generally associated with a trough moving southward on the eastern side of the ridge/high.   Such a trough causes upward motion, resulting in clouds and precipitation, and helps produce a low pressure area near the SW WA coast, a feature associated with many Pug