In the past week we’ve seen warmer than normal temperatures persist west of the Cascades, although no real hot days in the metro area. Lots of 80s, before & after the marine push last Wednesday/Thursday. Yet just one day at 90 degrees.
Meanwhile Salem has seen 8 days at/above 90 so far this month. Why? We are in a classic “northwesterly flow” regime. The setup has been very stable for over a week. Wind is coming in off the Pacific each afternoon/evening to replace hot air rising over the interior of the Pacific Northwest. The Columbia River gap allows lots of that cooler marine air to come up through Longview, Kalama, Clark County, and into the Portland metro area. This morning’s satellite image (8am) shows enough cool air and moisture for low clouds in a good chunk of this area. Clouds tend to form central & eastern metro first because the marine air is bottled up against the the western Gorge. This is why west metro tends to be sunnier more often summer mornings than the east side.
Farther south, in the Willamette Valley, no morning clouds = warmer. The layer of cool air is thinner there. Look at the effect on high temperatures today. 77 at Longview to 90 at Salem.
Strong westerly wind through the Gorge keeps Hood River comfortable, but by the time you get to The Dalles the airmass has warmed. Way out in Hermiston, today is the 25th day at/above 90 degrees. They haven’t seen a cooler than average day since June 16th!
There are 4-5 significant fires burning across Oregon this evening. This is an amazing visible satellite image considering it’s only July 12th. You can see a new fire south of Detroit Lake (Bruler), Grandview fire NE of Sisters, Jack fire NW of Diamond Lake, and the massive Bootleg fire north of Bly
That Bootleg fire exploded in size Saturday, becoming a “mega-fire”. That’s a fire over 100,000 acres in size. It didn’t change much through this morning, then you can see it has exploded again this evening. I estimate a 25-30 mile long “fire-front” based on GOES-17 fire detection
Oregon has seen 22 megafires since 1980, most of them in the eastern half of the state. Of course 5 of those just occurred over/on the slopes of the Cascades last September. You can find a recap of that event here: https://fox12weather.wordpress.com/historic-september-2020-fires-labor-day-windstorm/
- Dry weather continues across the region through at least the next 10-15 days.
- A cooldown arrives Wednesday and spreads east of the Cascades Thursday-Saturday
- Then we warm up again early next week
- There’s no sign of a heat wave west of the Cascades through at least the 20th
Check out the 500mb anomaly map (from the GEM model) for right now. In general we’ve got higher than normal (warm colors) heights overhead
By Friday, a cool trough is sitting just offshore. But notice heights have only come down to around normal for this time of year. The hot ridge has weakened and moved back to the “Four Corners” region. This pattern gives us widespread morning clouds west of the Cascades. High temperatures drop back into the 70s…a refreshing mid-summer weather pattern.
But by Monday the hot ridge is back, just to our east.
It’s still there NEXT Thursday, the 22nd, 10 days from now. This says above normal temps, but not extreme. Especially west of the Cascades.
You can probably guess there’s very little chance for rain in this pattern. No organized weather systems come close to us. Look at a bone-dry ECMWF model forecast the next two weeks: Just a spot of drizzle out of low clouds. Not a single one of 51 ensemble members produces even a tenth of an inch through the 27th!
Let’s hope for very little lightning and no human-caused fires. 3/4 of last year’s fires in the Pacific Northwest were started by people.
Enjoy the rest of the week! Chief Meteorologist Mark Nelsen