Cooler Temps & More Gray Ahead

September 18, 2012

I just now noticed our Fox12 7 Day forecast is significantly cooler than other forecasts for Friday and beyond.  So what’s going on?

Nature’s air conditioner is beginning to kick in.   The endless days of sunshine (that I’ve really enjoyed) are about to come to an end.

First, this evening we’ve seen quite a push of cool ocean air move inland.  It’s already cloudy at Longview/Kelso and it’s down into the 50s at Eugene and Corvallis.  You can see the low clouds and fog on NOAA’s 9pm fog image:

This is a good indication that the marine air is a bit deeper than 24 hours ago.   It’s at least 2000′ deep over and west of the Coast Range.  Rye Mountain at 2,000′ west of McMinnville is 49.  Last night it was 67 at the same time!  Tidewater RAWS at 2,000′ southeast of Astoria is 50 compared to 72 last night!  These are impressive temperature drops.  Combine that with the early cloud arrival at Longview this evening and I’m worried many of us westside may wake up to at least some low cloud cover.  The extremely dry soil might help a little; at least we shouldn’t get surface-based fog.

Beyond tomorrow, the marine layer continues to deepen through Friday as an upper-level low offshore gradually moves closer.  Mesoscale models (both the WRF-GFS and our RPM) show a major push Thursday night and Friday morning.  Here is the Friday morning WRF-GFS depiction of low cloud cover:

Here’s the lower resolution (12km) RPM for Friday morning…same thing:

Looks pretty clear-cut to me.  Low clouds packed at least up to 3,000′ west of the Cascades in late September?  I don’t think they are going anywhere very quick with the weak “Equinox Sun”.  So that’s why I lowered the high temp forecast close to 70 degrees.  Heck, the average high falls from 76 today to 73 next Monday; we are entering the period in Fall where average high temperatures drop quickly.  That’s partly due to scenarios like this.  Also of course due to more rainy weather systems that (normally) show up.

So we are just about done with the unusually warm weather, we’ve got more typical late September weather on the way.  That’s minus the rain though.  Unless we get some sort of low cloud drizzle or sprinkles this weekend, the next chance for measurable rain still appears to be at least 8-10 days away.

Speaking of long-term, there have been hints the past few days of wetter westerly Pacific flow breaking through right at the end of the month, maybe somewhere between the 28th and 30th.  The 12z GFS said the upper-level ridging was still going to be the main story into early October.  00z and other runs/models show off/on westerly flow for more typical weather.  We’ll see. 

Chief Meteorologist Mark Nelsen

Air Quality Update

September 18, 2012

Not TOO bad today for Air Quality here in the metro area, but plenty mucky and hazy out there:

It could be a lot worse!  Take a look at Sisters today:

We should see some improvement the next few days as cleaner (and cooler) Pacific air moves inland.