Wetand News

 It is looking increasingly probable that a significant freezing rain event will occur during the next day. Freezing rain can make driving dangerous and result in extensive power outages. As described in my previous blog, freezing rain occurs when temperatures warm above freezing aloft but sub-freezing air remains near the surface.   Raindrops fall into the sub-freezing air and can supercool to below-freezing, yet remain liquid.  Such droplets can freeze on contact on a cold surface. The Current Situation Temperatures are well below freezing throughout the region, as shown by the map below of 2 PM temperatures. A warm front is approaching the coast, accompanied by precipitation, as picked up by the Langley Hill Radar near the coast (see radar image).  Clouds from the approaching system have already started to spread over the western side of the region and precipitation has now reached the WA southwest coast. Precipitation will start as snow, then sleet, then freezing rain, and finally

Sometimes in the weather business, everything happens in a short period. This is such a period.  We will experience: 1.  The coldest temperatures in several years on both sides of the Cascades 2.  A freezing-rain storm particularly in the Gorge, the northern Willamette Valley, and south of downtown Seattle. 3.  Powerful easterly winds reaching hurricane strength in the Columbia Gorge and the passes. 4.  A rapid warm-up this weekend, with the return of typical rain and mild conditions. Stage 1.  Arctic Air Eastern Washington is already very cold, with some temperatures getting below zero last night.  Western Washington temps are well below normal.    To illustrate, here are the low temperatures this morning.  In western Washington, primo cold air is pushing southwestward through the  Fraser River Valley of NW Washington. Tonight even colder air will move in, coupled with good radiational cooling to space because the clouds are thinning out aloft.  Temperatures will drop as low as the te

 The most powerful technology for prediction is high-resolution ensembles of many forecasts. The UW modeling effort has one of the most advanced and largest (most forecasts--about 25) around, far superior to the National Weather Service system.  Such ensemble systems are very useful for presenting the uncertainty of the forecasts. Let me show you what it is predicting for a few locations regarding snow.  Cumulative snowfall is on the Y-axis and time is on the x-axis (in GMT/UTC, 18 is 10 AM, 06 is 10 PM PST).  Snow depth will be less than snowfall. Each line is a separate forecast and the black line is the average of them all (often a good forecast). At Seattle-Tacoma Airport, there are around 3.5 inches of total snowfall, but the uncertainty is large, ranging from .5 inches to 8 inches.  The uncertainty is closely coupled with the marginal temperatures for this event.  The snow starts this evening. At Bellingham, there is much more snow and more agreement among the predictions.  Why m

Enough of the 1/2-inch snowfalls, more serious snow will hit the lowlands (and the rest of the state) on Tuesday. Yesterday, some light snow showers reached the lowlands as cold air surged southward over the region. Amounts ranged from nothing to about an inch at lower elevations, while more bountiful snow in the mountains brought a requirement for chains at Snoqualmie. Light snow over Northeast Seattle. Eastern Washington is now in the deep freezer, with temperatures in the single digits and even below zero, while seriously below-freezing temperatures are widespread over the west (see low temps this morning, below). Be careful driving:   lots of slippery roads out there. Today will be relatively benign and dry.  But tomorrow is something else. With cold air in place over the region, a Pacific weather system will approach.  You can see the associated clouds on the latest infrared satellite image (see below). Tomorrow morning, a low-pressure center will approach, while air cold enough t

 Why travel to the northern climes when Arctic air is coming to you?    High pressure and very cold air are now moving into British Columbia.   It would like to reach us, but the mountains--the Rockies and Cascades--are initially blocking it. But like like a marginal football team, there are gaps in our defense.   Literally gaps in our terrain. And the cold offense is about to make a successful end run to score a frosty goal. Let me show you.... The situation this morning shows cold temperatures (purple and brown colors) in the Canadian Arctic.  An intense pressure change is at the interface between warm air to the southwst and cold air in the interior. Zooming in temperatures and winds in Washington State, at 10 AM today the state was divided by Cascades (just like our politics!).   Cold in the east (purple colors) and warmer in the west (green colors). By tonight at 10 PM, much colder air moves into southern BC (while shades), and cooler air pushes through the Fraser River valley nor

 The operative word for the next few days will be cold, particularly east of the Cascade crest. But there are two side effects of cold:  very high surface/sea level pressure and the potential for lowland snow. In the second segment of the podcast, I note the extreme high pressure moving down the eastern side of the Rockies, eastern WA we will get a "piece" of the high-pressure action (see the sea level pressure forecast for next Thursday shown below).  1054 hPa! But as noted in the podcast, the impressive high pressure does not beat the U.S. record (1064 hPa in 1983). My podcast starts with the forecast.  The big action this weekend will be late Saturday and Sunday as a cold front moves southward through Washington State.  There is be both rain and snow showers, with the former dominating near sea level.   The 24-h snowfall total ending 4 PM Sunday is shown below. The most lowland snow will be over Northwest WA, where cool air jetting out of the Fraser River Valley is signifi

 The last month has been considerably colder than normal over the region, with eastern Washington being particularly frigid.    The coldest air this season will arrive on Sunday. To put you in the proper mood,  take a look at a plot of the difference in our daily temperatures from normal over the past month (see below).   Eastern Washington has been frigid, with temperatures 6-12 F below normal, while western Washington has been 2-6F below normal. This contrast will get even more dramatic during the coming days.   It is interesting to note that electric energy demand increases with the cold temperatures and that hydro is providing most of the energy (see recent Bonneville statistics below).   Renewables (solar, wind) provide very, very little.   It is important that when we need the most energy (when it is very hot and very cold) wind energy is generally minimal in our region..   One reason I strongly support nuclear energy development. Our region will stay moderately cold and decidedl