About that Sunday snow...Plus lunar eclipse tonight and a look ahead

Yesterday was a strange weather day, nestled in a chilly & wet weekend. I have been sick since late Friday, so I was actually in bed much of Sunday. Nothing serious, and I’m on the rebound so I’ll be back at work this evening. But I want to recap the surprise snow to some lower elevation spots during the daytime Sunday. To get snow to the valley floor on November 6th? Everything has to be exactly right for that to happen.

You may recall we had the atmospheric river and initial cold front pass through Friday and Friday night, models just nailed that one with about 2″ rain in the center of the metro area and 8-10″ in the wettest parts of the Coast & Cascade ranges. Then we were in the scattered showers behind the front Saturday; an uneventful weather day.

A cold front was forecast to move onshore Sunday morning and this would be the leading edge of cooler air. Snow levels would come down to around 2,000′ at times Sunday (the forecast), and 5-10″ would fall in the Cascades. That DID happen. Models were also forecasting very heavy rain to fall south of the Portland area down into SW Oregon with yesterday’s system. Note the rainfall forecast with very heavy rain south of Salem and down to about Roseburg. This is from the WRF-GFS model. That DID happen

Then notice the snowfall forecast for 4am Sunday to 4am Monday...almost all of this was expected before sunset Sunday when precipitation changed to showers.

A closer view shows that there would likely be spots with snow below 2,000′. This forecast would imply anyone could see snowflakes mixed in and it could stick down to 1,000′ in the Cascade foothills around Silverton, Mill City, & Sweet Home. That DID happen.

So there were hints that snow could fall down to at least 1,000′ as the cold front slowly moved south. But it’s very tough to get snow down to the valley floor anytime, and really tough so early in the cold season.

What Happened?

This was another case of extremely heavy precipitation dragging the snow level all the way down to sea level (or the valley floor) under calm conditions. In 3 hours, Corvallis and Eugene both picked up about 3/4″ inch of rain, and Salem saw 1.13″! Portland’s rainfall was less intense, at .55″ in 3 hours ending at 10am, although temperature did drop to 40. The heavy precipitation caused the sticking snow level to drop 1,000′+ lower than it “should have been”. This happened during the April 11th snow event, and our first snow event back on December 18th last year when 0.5″ fell in Portland on a soaking wet Saturday night. Except models caught the change to snow ahead of time during those two events. This time they did not. Sometimes it’s called an “anafront” as well, when most precipitation occurs on the back side of a cold front. Looking back at maps, I don’t even see an obvious signature this could happen. The wind WAS forecast to go mainly calm in the valley. One other complication yesterday was that the Portland radar seemed to be having some issues which made diagnosing what was going on difficult. You can see the WRF-GFS did imply wind wind go calm at Corvallis (circled area around 10am-4pm lowest part of atmosphere). Then southerlies would resume during the night and lift the snow level again. That DID happen. Most of us warmed during the night at the lowest elevations

This isn’t a perfect map, but at least those that reported snow to the COCORAHS network. You can see the snow reports in the southern valley, mainly up against Coast and Cascade range foothills

To summarize...1-5 degrees can make all the difference under heavy precipitation, calm wind, and a relatively low snow level. Magical things can happen, but most times nowadays the highest resolution weather models will catch that “magic” ahead of time. This time they didn’t.

What’s Ahead?

Much drier weather is ahead! How quickly the mood has changed; 4 months of dry weather followed by 2 weeks of wet and I’m already excited by a dry spell. At home in the western Gorge I’ve picked up over 10″ of rain since the dry spell ended. Portland has seen 6″; things are soaked nicely...

The cold upper level trough overhead...

Will slide east of us and be replaced by an upper-level ridge and a sort of “split-flow” later in the week.

This means if any systems make it through the ridge, they will be weak with respect to rain/wind/snow. This is generally a very “boring” weather pattern for meteorologists, but good for regular folks that don’t want weather to mess up their life.

A fun/neat chart below shows the dry spell the rest of this week (after this evening’s showers) and mainly dry for at least part of next week.

It’s 6 hourly precipitation for the next two weeks based on the 51-member ensemble ECMWF model. Each horizontal line is one model run (each 12 hours) and the latest is at the bottom. Taking a look at that bottom line, I’ve boxed in this work week and next (1 & 2). Little/no chance for rain the rest of this week, and just light amounts for next week. Remember these numbers are averages of many ensemble members, so if just 5 of 51 members show rain on a certain day, for example Monday of next week, it’ll just show light amounts. You can go back 3 days worth of model runs (boxed weeks up above) and see how the model has gradually dried out this week’s forecast as we get closer.

Temperatures will be a bit cooler at night as drier easterly flow develops this week. Not any sort of arctic chill, but long overdue frost for outlying areas. Mid-20s wouldn’t surprise me in the colder suburbs within the next week and finally some sub-freezing temps in the city either Wednesday or Thursday morning. East wind does not look especially strong for this week, just the usual areas near/in the western Gorge turn windy. But that’s normal...it’s November.

Total Lunar Eclipse Tonight

It’s nothing like a total SOLAR eclipse, but we get to experience another total lunar eclipse in the middle of the night. We typically get 1-2 a year. I’ll be asleep, but if you are awake, the moon will be fully eclipsed in earth’s shadow from around 2:15am to 3:45am Tuesday morning. It may be visible since clouds will be breaking up a bit during the night. Cloud cover forecast says all hope is not lost...partly cloudy across much of the region