The snow event yesterday had major impacts (generally negative) for transportation, but major benefits for water resources and late-season skiing.
It provides a highly educational lesson about snow and freezing levels.
As I write this Saturday morning, both Snoqualmie and Stevens Passes have reopened after being closed much of yesterday. There have been major snow dumps in the mountains, with Snoqualmie getting 42.5 inches and Stevens receiving 34.5 inches on Thursday and Friday.
A big problem for the ski areas has been the major power outages, which are now resolved at Snoqualmie.
To get an idea of how the regional snow water situation has changed, here is the percentage of normal (1991-2020) of snow water equivalent of the regional snowpack. A month ago, there were significant areas of red (less than 50% of normal) over the northern portion of the state.
Now the red is gone. Western Washington has gone from 54% of normal to 66%, and the Yakima Basin from 41% to 63%. There has been a large and significant improvement in the amount of water stored in our regional snowpack.
This snowpack improvement, coupled with our above-normal reservoir levels, bodes well for water supplied this summer. For example, the Yakima Basin storage is hugely ahead of schedule and will easily fill (see levels below, blue is the current year, red is normal).
Yesterday's lowland snow over western Washington was fascinating. Before I discuss it, I want to remind you of some snow science 101: the difference between freezing level and snow level (see below)
Nearly all of our precipitation starts as snow aloft. It falls until it hits the freezing (or melting) level at which the temperature is 32F. It takes about 1000 ft for all the snow to melt below the freezing level. The elevation of total melting is called the snow level, below which the precipitation is all rain.
Between the freezing level and snow level, there is a mixture of melting snow and rain. On Friday, much of western Washington was in this layer, with a lot of wet snow falling.
Snow that melted rapidly on the relatively warm roadways.
During Friday (and this morning), the freezing level has ranged from 1200 ft to 300 ft, which resulted in a lot of mixed precipitation reaching the surface. If you were lucky enough to live above 1000 ft in the hills above Bellevue, you enjoyed a foot of snow (see below).
Picture courtesy of Peter Bender
The rapid melting of snow between roughly 500 and sea level was evident if you looked at some of our hills: very white on the top, with little snow at the bottom (see some images below).
Just for fun, I drove from near sea level to around 350 feet in north Seattle on Friday afternoon.
Near sea level, there was no snow on the grass and a few flakes mixed in with some rain.
A different story at 350 ft. Grass and roofs were covered with snow, but most of the snow melted on the warm pavement.
Elevation was not only a key element. Where the precipitation was heavier, the greater amount of snow falling from aloft caused more cooling (it takes energy to melt snow), which drove the snow level lower, resulting in more snow at the surface.
There was a band of heavier precipitation over the South Sound that produced a band of heavier snow (see below, showing snow depth measurements on Friday). As much as 4 inches in Federal Way! Not very impressive by mountain standards.😉
In the east hill of West Seattle known as Pigeon Point, snow began around 3AM and continued throughout the day without any interruptions until 7 PM. The complete absence of wind was a real curiosity, as watching snow fall without swirling or anything different than sheer verticality was mesmerizing and fascinating. I measured over four inches, but the compaction from melting made that difficult, and the snowfall would have probably amounted to 6 inches if below freezing temperatures were present. A beautiful day to watch from my patio door
ReplyDeleteCliff: the Yakima basin will still likely see its 4th year of water rationing. If we have adequate water resources, why is water being restricted? It would be great if you could cover this topic in more depth.
ReplyDeletehttps://www.applevalleynewsnow.com/news/yakima-basin-faces-potential-fourth-straight-year-of-drought-as-water-supply-forecast-shows-reduced/article_116a4e00-1a97-48a9-8df3-e316caa3c7f6.html
Are you not used to media sources feeding you lies on the daily? You just saw the real time data here, and they are telling you a wildly different story. I wonder how many other "issues" this type of discrepancy occurs.
DeleteI do think it depends on where the measurement was taken as in, if in the grass areas, like around Central Tacoma mid afternoon, might have seen up to 2 inches in spots, otherwise, a dusting to a trace, at best with some slush on the roadways on lesser traveled roads, like where I live, which is in a higher elevation in town, but likely as you descend down hilltop to Pacific Avenue, likely little to no snow there, but up where I live, a light dusting to 2 inches, at best.
ReplyDeleteNow, it's sunny and mid 40's with snow melting all around me and it's mid to late afternoon (3:45PM).
We had 4" on Lea Hill, in Auburn at 440 ft elevation. The station temperature never varied beyond 31F-33F the entire 24 hours day.
ReplyDeleteI measured 4.5” on my back deck only a half mile from the water near Point Defiance in Tacoma. Just two miles up the street at HWY 16, it was only about 2”. As another commented, it didn’t stop from dawn until about 7:00 PM. If it had been even 1 degree colder I’m certain we’d have gotten well over 6”, but it was melting even as it was building up.
ReplyDeleteI think we'll need to see what next week's weather does to the snowpack before getting too excited. It looks like a lot of rain and high temperatures in the mountains incoming.
ReplyDeleteLooks like i90 at Snoqualmie pass is in the 50s early this coming g week with rain. Not good for the skiing.
ReplyDeleteWe had 4+ inches in Boston Harbor (7 miles North of Olympia) elevation of 22 feet, two blocks from Puget sound. Snowed all day Friday.
ReplyDeleteCliff, Yakima basin has a man made problem; 70% of water goes to "senior rights holders" and they will be fine, but then 30% runs through water districts like Roza. If past predicts future, that district always has a restriction when Snowpack on April 1 is below 80% of normal, regardless of how full the reservoirs are. I can share my work, but its just from taking Reservoirs, SWE and Roza shortfalls since 1970. Again, its a bit of a man made thing; historic water rights govern who suffers and who doesn't.
ReplyDeletewill the predicted Pineapple Express arriving mid-week melt a lot of the snowpack?
ReplyDeleteIt looks like the GFS won out over the Euro models. I had about 5" on the ground in Maple Valley. It snowed continuously for more than 24 hours. It was slightly above freezing the whole time- if it had been 5 degrees colder I'm guessing we would have had a foot of accumulation.
ReplyDeleteWhat should we make of Harrison Rademacher's statements to the Seattle Times? Should we stop listening to NWS?
ReplyDeleteBut meteorologists with the National Weather Service's (NWS) Seattle office said the storm likely isn't enough to help the region's dwindling snowpack this winter.
"The Cascades and the Olympics are still abnormally dry for this time of year," said Harrison Rademacher, an NWS meteorologist.
For the Central and South Cascades, snowpack is around 60% of the median, Rademacher said. Snowpack at the Olympics is closer to 50%.
At minimum, the Times should have asked Professor Mass for his take. Our region's snowpack may still be below normal, but to say that the storm likely didn't help seems very disingenuous. Every area saw substantial inprovement.
DeleteI live in Covington, elevation is around 460 feet. We received snow all day, mainly heavy, clumped snow. We probably got around 6 inches, which didn’t fully melt until yesterday. My kids made giant snowballs which are still hanging out in the yard. I wish we’d set up a proper measuring system so we could have seen the rate at which it was falling. It was really amazing to see.
ReplyDeleteThank you for the snow science lesson. It really helps explain why some locations recieved a lot of snow while others saw none.
ReplyDelete