A Warm Week, Then Wet & Cool 1st Weekend of June

June 1, 2020

10pm Monday…

The warm weather showed up as expected last week, and we saw our first 90 degree day of the season on Thursday. As expected, a fast-moving upper-level low moved north along the West Coast, setting off a round of thunderstorms. Saturday morning was crazy in east metro with hundreds of lightning strikes. That was the 1st/2nd most intense thunderstorm I’ve seen at my home. I’ve lived there 16 years!

Then the main event; the Storm Prediction Center had north-central Oregon in the “enhanced risk” zone for Saturday afternoon evening. Lots of lifting and some super-cell thunderstorms were expected. The weather pattern delivered! Lots of videos of heavy rain, damaging wind, hail, and beautiful thunderstorm cloud structures. From central Oregon over into NE Oregon and then into eastern Washington. Check out the storm reports for Saturday:

One particularly intense super-cell storm passed over Jefferson county. Parts of Crooked River Range to Culver and Metolius were hit the hardest. It appears extremely strong “straight-line” wind brought 70-100 mph gusts to this area. Pendleton NWS folks drove down to see if it could have been a tornado. They could not find enough evidence to support calling it a tornado:

There were two reports of huge hail as well. 2.00″ hail was seen in Tumalo, near Bend. Also near Helix, north of Pendleton. That’s the size of a pool cue ball! Or an average size chicken egg. West of the Cascades anything golf ball size or larger is almost unheard of, but a bit more common east of the mountains. There was one bizarre 2″ hail event in Seaside one January morning in 2018, otherwise you have to go back many years to find anything close to golfballs west of the Cascades. I remember that massive storm in July 1995 that moved from central Oregon northeast to Hermiston. Grapefruit size hail…amazing.

What’s Ahead?

June is here and this is the beginning of summer in the Northern Hemisphere; just four weeks from now days start getting shorter and the sun angle begins to lower.

We have some very nice early June weather through Friday. It’s weak westerly flow in the upper-atmosphere, which in summer doesn’t tend to produce rain. This is the 500mb chart for Wednesday evening. That’s around 18,000′ overhead.

Expect Just enough onshore flow the next few days to keep temperatures below 80 degrees, but plenty of sunshine.

By Friday things are changing; a cool upper-level trough is approaching

That unusually cold trough (for early June) should be overhead Saturday through Monday.

This is the classic “Rose Festival Low”; clouds, showers, and chilly temps. In fact snow levels will go below Timberline Lodge, possibly a mix at Government Camp…here’s our 7 day forecast. Thinking of some early season camping up at Trillium, Timothy, Olallie, or Lost lake? Don’t, unless you have a cozy RV. Temps only in the 40s during the daytime and mixed snow/rain showers at those lakes.

How much rain? I figure we should get at least .50″ from Friday evening to next Monday/Tuesday. The WRF-GFS gives even the driest parts of the valley a decent soaking

So how long will the cool/wet weather stick around? The ECMWF ensembles think it’s just for a few days. This morning’s run ensemble members show the big surge of wet weather this weekend through early next week, then much drier. Or at least more reasonable for early-mid June.

Last night’s monthly run of the ECMWF implied we’ll be near normal next week and then much warmer beyond about 15 days (summer temps) with upper-level ridging over the West Coast. We’ll see, accuracy goes way down after two weeks.

Chief Meteorologist Mark Nelsen