Wetand News

It was 40 years ago, at 8:32 AM on May 18, 1980 that Mount St. Helens exploded, producing an ash plume that rapidly expanded westward.   Within a few hours, much of eastern Washington was in mid-day darkness and by that evening the volcanic plume had reached Idaho. What were the weather effects of this extraordinary eruption?   This is something I am in a position to talk about, after examining the issue in detail and co-authoring two articles with a colleague, Professor Alan Robock Alan and I visited the eruption zone the following summer and it looked more like Mars than Earth (see below, I am the one on the left!) The relatively primitive weather satellites at the time illustrated the growth of the dust plume, from near the initial eruption time (8:45 AM): To its expansion across eastern Washington by 1:45 PM Lights turned on in eastern Washington as day turned into night (take a look at the mid-day picture at Yakima).  Now that is impressive. The th

During the spring it is not unusual to have sunny skies over Puget Sound, with a clear zone extending northward up the Strait of Georgia.  In contrast, away from the water, clouds reign. The visible satellite image at 1:20 PM yesterday (Friday, May 15th) shows the story.  The lowest elevations are essentially clear.  Generally more cloudy even in eastern Washington...but look closely...there are some narrow clear zones there too. So what is going on?  Why are the clouds avoiding Puget Sound?   And why are there no clouds immediately offshore? Interestingly, whatever is going on was captured by our high-resolution weather forecast models.  The UW WRF model run at very high resolution (1.3 km spacing between the grid points) had a 21h cloud forecast that showed the effect. Yesterday was a great day to see this effect:  We are now in a period with a very strong sun and the large scale winds were light. The strong, mid-May sun heated the ground, causing the difference  in

A number of people have asked about the water situation this summer, both in terms of water resources for agriculture and drinking, as well as the potential for wildfires. At this point, the situation seems nominal:  relatively close to normal . First, consider snowpack.  On April 1st, the snowpack water content over the region was very close to normal over the mountains of the Pacific Northwest.  What about the long-term trend?    To answer that question, here is a plot of the NW snowpack on April 1st from 1984 to today prepared by UW atmospheric research scientist, Mark Albright.  The yearly values are shown by the blue line, a five-year running average by pink, and the overall trend is shown by the orange line.   Last few years have been near normal and there is only the slightest downward trend (which is not statistically significant). After a dry period in April and very warm temperatures last week, there was considerable melt of the snowpack.   Snowpack amounts measure

If you want to drive to a major Seattle park, you will not be able to park there. And if you are looking forward to a walk on a Washington State ocean beach, forget it.  The beaches are off limits. And at many parks you will be hectored and bullied in way that is contradictory to the values of a free society. > blog  post and there has been more recent research during the past few months. For example, recent lab studies carried out by the U.S. Army’s high-level biosecurity laboratory at Fort Detrick, Md. (see below) found that the virus survived for only 2 minutes on a surface and as an aerosol droplet for only 90 seconds during the summer.  And noted in my earlier blog, there is no documented example of COVID transmission in the outside air and there are many reasons for this, including the effects of solar ultraviolet radiation, the higher relative humidity, and the huge potential for dispersion (and thus low concentrations) in the vast quantity of outside air, enhanced b

For many locations in western Washington, temperature stayed quite high overnight.  Normally, when there are clear or nearly clear skies aloft, temperatures cool rapidly in the evening as the earth radiates heat to space. But much less so last night.   Consider the temperatures at Sea Tac Airport over the last week (below).  Red lines are the observed temperatures and the purple/cyan lines are the average highs and lows, respectively.  The highs on the last two days were way above normal, but look at the lows!  The low temperatures were roughly the same as the typical high temperatures. But there is more interesting aspects of the low temperatures.  Below are the minimum temperatures last night (click on image to expand).  In places like Cle Elum temperatures dropped into the 30s, and in much of eastern Washington 40s were prevalent.    But western Washington was way warmer, ranging from the LOW SEVENTIES to the mid-50s.   It was particularly along the Cascade foothills in pla

The next four days will be stunning:  sunny, warm, with many locations enjoying temperatures in the 80s.  But there will be interesting subtleties that the meteorologically informed will enjoy. Picture courtesy of Ferd Frederick Let me describe the steps to weather heaven. The First Step The surface weather map for Thursday at 5 PM shows step 1 (solid lines are sea level pressure, barbs are surface winds, shading is low-level temperatures).  Higher pressure builds inland over southeastern BC, Idaho, western Montana, and Wyoming.  The resulting offshore pressure difference (pressure higher inland than along the coast) forced easterly (from the east) flow, which warmed as it descended the western slopes of the Cascades, Rockies and northern Sierra Nevada. The warming caused pressure to fall along the Oregon coast, producing a thermal trough  that pushed northward out of the Central Valley of California.   With the core of the trough south of us, a large north-south pres

Yesterday evening, western Washington had the visual treat of a magnificent lightning display along the western foothills of the Cascades.   A stunning picture by Sigma Sreedharan, illustrated the active thunderstorms that hit the region after roughly 5 PM And the lightning strike map over the 24-h ending 1 AM today (Wednesday) shows the hundreds of lightning strikes west of the Cascade crest.  Theses thunderstorms were associated with huge towering cumulonimbus clouds as illustrated by this wonderful cloud shot by Dr. Peter Benda, looking east from Bellevue.  Virtually mountains in the sky. The huge cumulonimbus clouds were associated with the approach of an upper-level trough (low pressure), which caused upward motion (which helps initiate thunderstorms) and cooler air aloft (which helps to promote a large decline in temperature aloft, which in turn produces instability). Low level westerly winds pushed the unstable air up the western side of the Cascades, releasing