Wetand News

In this blog I talk a lot about the Puget Sound convergence zone, in which air moves around the Olympic Mountains and converges over Puget Sound, producing a band of clouds and precipitation somewhere between Everett and Seattle (see figure from my NW weather book) But sometimes, when the wind approaches the coast from a more southwesterly direction, the convergence line can shift northward, producing a line of precipitation from roughly Port Townsend to Bellingham.  This is exactly the situation that occurred this morning. The radar image at 6:46 AM this morning shows the story, with moderate (green) to heavy (yellow) rain in a band stretching to the northeast.  Was really raining hard in parts of Bellingham and in the hills to the northeast of town! The visible satellite imagery about an hour later is pretty dramatic--you can see the cloud band stretching from the Olympics northeastward and profound rainshadowing north and south, with essentially clear skies in the lee of

Things are not going well these days regarding predicting the future of coronavirus in the U.S., with the epidemiological community, including critical government agencies, not succeeding in these important areas: They do not know the percentage of the U.S. population with active or past COVID-19 infections. They do not have the ability to quality control and combine virus testing information into a coherent picture of the current situation.  This is a big-data problem. The epidemiological simulation models used by U.S government agencies or American universities have a poor track record in their predictions, with their quantification of uncertainty unreliable. >media , social media ,  and several new research papers .  The UW IHME model, often quoted by local and national political leaders, has been particularly problematic ( this paper describes some of the issues), including the fact that its probability forecasts are highly uncalibrated.  The UK Imperial Model in mid-M

I have had a number of people ask me:  with CO2 emissions collapsing from the economic downturn, are CO2 levels no longer going up or declining?   In fact, a brief search on the web reveals some headlines that seem to be suggesting this: The bottom line of this blog is this :  CO2 levels are  not falling, and it is difficult to see much impact on the rate of rise.  And it will be a good opportunity to talk about some aspects of the variation of CO2 in the atmosphere. Let's start by looking at the concentrations of CO2 in the atmosphere as measured by NOAA at its Mauna Loa observatory on the Big Island (below).  This is an excellent place to measure CO2--away from any localized sources.  CO2 is relatively well mixed in the lower atmosphere (both spatially and in the vertical) so the measurements at this observatory are highly reflective of global variations over time. You will note that CO2 has risen from around 317 parts per million (ppm) in 1960 to around 413 ppm today

For those those worried about dry conditions, additional relief is on the way. Two strong fronts are approaching for this weekend. The first arrives Saturday morning and it is interesting to watch it get modulated and weakened by our mountains..  Let me show the the 3-h precipitation predicted by the UW model. For the period ending 8 AM Saturday, you can see the front making landfall, with the precipitation just reaching Puget Sound. Three hours later is has reached the Cascades, with the mountains locally enhancing rainfall.  But then dramatic change in the frontal rain is evident (2 PM shown): as the front descends the eastern side of the Cascades, the downslope flow greatly weakens the front and its associated rainfall. And by 5 PM the frontal rain has reached the Rockies, where it is enhanced .  Note the residual showers on the western slopes of the Olympics and Cascades well behind the front.  Quite typical.  The total precipitation for the entire frontal pa

April showers have been celebrated in music and verse, and after a lapse in the April-shower department, it is evident that they have returned for at least the next fortnight. When April showers may come your way They bring the flowers that bloom in May The forecast of the European Center model is enough to get a May-flower enthusiast excited, with 1-2 inches in the lowland and perhaps twice that in the mountains.   Southern California, sodden from unending precipitation during the past month, will dry out completely. As indicated by the "plume diagram" showing precipitation at Seattle for the remainder of the month (this is from the National Weather eEnsemble system of 21 forecasts, the black line is the average of all of the predictions), there will be several light precipitation events.  Enough to keep things moist.  Flowers like that. Our April shower regime is the result of the shrinkage and southward shift of the ridge of high pressure, which was pr

Some lucky folks in our region viewed an impressive aurora last night and perhaps a hint of it might be visible tomorrow morning. Here is a picture provided  by Greg Johnson of Skunk Bay Weather of the aurora at 3:39 AM, looking northward from Kitsap towards Whidbey Island: Greg also provided a magnificent video of Monday mornings event: This aurora was associated with a coronal mass ejection (CME) event several days ago, which resulted in a relatively high planetary K index (about five) last night (see plot below). The simulated distribution of the aurora provided by the NOAA Space Weather Prediction Center , shows the core of the event over southern/central Canada. What about tonight? It will certainly be clear enough, but as shown in the figure above, the K-index has dropped considerably.  The latest Space Center forecast is for a decline  of Kp to 3 tonight...which might not lead to a decent aurora show.  Might check their webpage tonight for an update

During the past month, the fear of coronavirus had spurred political leaders to close parks and nature areas throughout the country. In Washington State, all state parks and state lands managed by the Department of Natural Resources are closed through at least May 4.  Here in Seattle, all major city parks were closed last weekend and parking lots for city parks are still shuttered.  Picnicking, barbecuing, and any sports are illegal in Seattle parks.  In California, hundreds of state parks, including many major beach areas, have been closed, and parking has been blocked off for all state recreation facilities. Lidia Morawska , professor and director of the International Laboratory for Air Quality and Health at Queensland University of Technology in Brisbane, Australia.”: Outdoors is safe, and there is certainly no cloud of virus-laden droplets hanging around... Firstly, any infectious droplets exhaled outside would be quickly diluted in outdoor air, so their concentrations would q

April in our region has not only included "dry storms" of desiccated air and lots of sun.  Not surprisingly this month has been extraordinarily dry in terms of precipitation, with Seattle only receiving .01 inch this month. Some folks are already asking me about drought ---but as we will see below, such worries are premature.  Let's start with the percentage of normal precipitation for the past two weeks, which is a study in contrasts.  Portions of the Northwest have received less than 25% of normal, while southern California have been crazy wet, with a large area being hit by 800% of normal.  You read that right. Los Angeles and San Diego have been like Seattle in January.  Obvious this is good for delaying the wildfire season in a large portion of the Golden State. Although April has been dry in the Northwest (because the weather systems have been going into California), our long-term precipitation is generally fine.  For example, below is plot of the accumula

During the past few days have you noticed the dryness of the air?  See a spark when you touched a doorknob or that your skin seemed unusually dry?   Or a dry throat and the urge to drink more water?  Garden soils seem desiccated? You are not alone.  Many on the western side of Washington State noted the phenomenon, which I will term a Dry Storm.   And it is about to get revved up again! To get some perspective, here is a plot of the relative humidity at Seattle Tacoma Airport over the past six months.  Two days ago, the relative humidity dropped under 15%, the lowest since October 29th.  At Olympia, Monday brought the lowest relative humidity for the entire six months. As many of you know, relative humidity describes the degree to which the air is saturated :  the amount of water vapor in the air divided by the maximum amount of water vapor air can hold at the current air temperature.   Since warm air can "hold" more water vapor than cold air, there are two