Wetand News

 Update at 3PM Thursday ________________________________________ My podcast on this snow event is now available: Click the play button to listen or use your favorite streaming service  I do a weather podcast every Friday morning, including the weekend weather forecast and a discussion of some meteorological topic _________________________________ It highly probable that our region is going to have a major snow event--from the western lowlands, to the mountains, and even eastern Washington. But it will be snowstorm in several distinct acts, with the middle act being the most significant. Now, there is always uncertainty in weather prediction---but it is not as great as some folks are suggesting for this event: A major complication has been the substantial differences between the various models, particularly the European Center and American GFS prediction systems. Act 1.  Thursday afternoon to Friday morning. We have cold air over us now, cold enough for snow.   We just need moisture.   

  There is an excellent chance that western Washington is going to be hit by a major lowland snow event.    And yes, the mountains will be buried as well. It is possible that some lowland areas will experience more than a foot of snow and February snow records will be broken at some locations.  Can I absolutely guarantee this?  No.  Is a major event highly probable?  Yes. Convergence A big issue yesterday was the substantial difference in the snow forecasts of the American and European Center models, with the European model--generally the more accurate one-- going for much more snow over western Washington. Overnight the American model has moved towards the European solution. Let me show you the accumulated snowfall over time from the European model.  And let me stress, snow depth will be LESS than total snowfall (what falls out of the sky), due to melting, settling and compaction, and other reasons. The snow will begin on Thursday.  The snowfall total through 10 PM Thursday shows sign

Will update with latest model forecast by 2 PM Tuesday _________________________________________  Very cold air will be coming to the western lowlands, probably the coldest air we have experienced in years.   The cold is pretty much guaranteed. But snow is something else and the major models are not all on the same page, ranging from a dusting to a major snow event. Let me give you the latest information. As predicted, last night brought light snow above roughly 500 ft during a Puget Sound convergence zone event.   Up in the hills of Bellevue, the scene was quite snowy this morning (see below) and some snow got mixed in even near sea level (but no accumulations there). Image courtesy of Dr. Peter Benda So what is going to happen now?    The air above us right now is relatively cold (allowing snow even at sea level if there was moisture), but the air will get much colder over the next few days. The lates NOAA/NWS ensemble forecast for temperature at Seattle based on running the GFS mod

A major lowland snow event is increasingly possible starting on Thursday and Friday, but uncertainly is still substantial.  But before I get into that, let us start with the potential for light snow tonight, particularly for higher elevations north of Seattle. The latest visible satellite image (below) show cool unstable air entering our region.  The air is being forced to rise as it hits the Cascades producing substantial snow on the upper slopes and passes.  A particularly heavy snow area is indicated by the blue arrow. Snoqualmie Pass, located in that areas, has had heavy snow and chains are required in both directions. A weak Puget Sound convergence zone is in place and this is going to rev up this evening (see below).  A convergence zone is when northwesterly flow off the Pacific  moves around the Olympics and converges over Puget Sound, producing clouds and precipitation. The air above us has been cooling over time and the snow level is about 1500 ft and will drop further. This c

My new podcast is online.    In it, Ialk about the weekend forecast and the arrival of cold, Arctic air over the region.  And yes, evaluate whether snow is in the cards.  I also answer a frequently asked question:  is there a weather data void over the Pacific and does it degrade Northwest weather forecasts?   The answer may surprise. The latest NOAA/National Weather Service GEFS ensemble forecast (running the model many times to get at uncertainty) suggests a profound future cool-down  for Seattle (see below).  You can see the individual forecasts (gray lines) and the average of all them (black line).   Highs only in the 30s!  You will also note that uncertainty increases with time, with the forecasts starting to diverge by mid-week. So be prepared for MUCH cooler temperatures. Snow?   Some, but not all, of the model forecasts are bringing snow to Seattle, starting on Monday.  Lots of uncertainty.  I will update on Sunday. I wanted to mention that I will be having a special online ses

The moisture imagery from the NOAA/National Weather Service geostationary satellite, GOES-W, is absolutely stunning this evening (see below)....and even more so with a bit of explanation. The image shows moisture in the upper troposphere (roughly 20,000 to 35,000 ft above sea level) and the swirl of moisture is painting out the atmospheric flow at these levels.   There is, in fact, a HUGE ridge of high pressure over the eastern Pacific, with a deep low center embedded in it. Let me show you, with an annotated version indicating the wind fields. Some moisture is streaming northward over the western portion of the domain and the turning abruptly towards WA state.  Other moisture, at a bit lower level. is heading westward from California and then swirling into a low offshore. This pattern is called a Rex Block and you can view an upper-level map ((500 hPa pressure, about 18,000 ft) at 4 PM that shows the key features:   a big area of high pressure (a ridge) with a low tucked in to its sou

The complaints are starting to come in.    Where is the lowland snow that was "promised?" This is a La Nina Year?  Right?  La Nina years tend to have above-normal snow at lower elevations west of the Cascade crest?   Right? And the desperation is getting palpable.   We are running out of time. The probably of major snow events starts decreasing rapidly after the the third week of February. After, the first week of March, we simply don't get major lowland snow events. The Facts It is true we are in a La Nina year.  The latest sea surface temperatures for the central  tropical Pacific show it (see below).   Nino3.4 is an area in the tropical Pacific that we use as an index.  Blue colors indicate cooler than normal, which indicates La Nina. It is also true that that typically we get more lowland snow during La Nina years, something described in several NOAA and research reports (including some I have worked on).  Here is a sample, showing more snow than normal (blue color