Sunnier, But Cool This Weekend

September 22, 2012

A nice surprise on visible satellite imagery this morning.  Even though we still have a very thick marine layer, the upper level low passing overhead must have “stirred things up” a bit; you can see plenty of clearing west of the Cascades.    This is a sign of a much brighter day ahead.  And it will still be a cool day so everyone should be happy.

Astronomical Fall started this morning (about an hour or so ago).  Meteorologically we consider Fall to be September-November.  That’s because across most of the northern hemisphere the warmest three months are June-August and the coldest are December-February.  That leaves the 6 months in the middle as Fall and Spring.  It’s all very arbitrary and there are only 3 weeks difference between the two so it sure isn’t worth an argument.  But here’s a curious fact that adds to the debate:  West of the Cascades in Oregon and Washington (and parts of California too), September is slightly warmer than June.  A quick check across the rest of the USA (including eastern Oregon and Washington) shows that we are alone along the west coast with this phenomenon.  June, July, and August are the warmest just about anywhere else.  This likely contributes to the general feeling that summer is “delayed” here.  The past two years sure have helped that along too!  Part of the reason is the slow to warm and slow to cool Pacific Ocean, and the general weather pattern often features more upper-level (cool) disturbances passing overhead. 

But think about the main difference between the two months (June and September).  We get far more cool onshore flow in June.  In a normal September we get more offshore (easterly) flow events in September than June.  That would mean that if all else is equal temperature-wise in the atmosphere between the two months, then September should average warmer west of the mountains.  We’ve seen what a difference the wind direction can make this week.  The 5,000′ temperature was about the same Monday-Thursday, yet we had a high of 90 one day and 63 another just due to a low-level wind switch.  Occasional episodes like this are enough to make September slightly warmer.  And why do we get more offshore flow in September?  Because the continent starts to cool with the longer nights.  That equals more episodes of higher pressure to our east.  So I suppose one could argue that because the interior USA is cooler in September, we end up slightly warmer (on average).

Chief Meteorologist Mark Nelsen

Fall in The Lowlands; Summer in the Mountains

September 20, 2012

Expect another day of mostly gray skies and highs only around 70.  It’s Fall in the lowlands but still Summer in the mountains!  Look at the visible satellite image this morning:

It shows low clouds & fog have totally filled in west of the Cascades below about 2-3,000′.  That’s due to the cool and moist Pacific air; the moisture condenses during the long night into cloud cover and fog.  This guarantees another cool day.  As mentioned in the previous post, the sun angle now is as weak as it is in mid-late March.  So the cool air that settles into the valleys at night is very slow to mix with much warmer air above.  Look at the ODOT cam from Government Camp…it’s around 70 up there this morning and sunny:

In fact the morning balloon sounding at Salem showed a +22 degree celsius temperature!  The  atmosphere above is warm enough to get us to 90 or higher, but only if the warm air were to mix down;  it definitely won’t.   So if you want summer today (albeit a bit smoky) head to the mountains.  It’ll be the same tomorrow.

Models had shown the increase in marine air in general, but they were 2 days too slow.  That sad part, if you’re looking for some sun, is that they show the marine layer deepening as we head into the weekend.  We may only see highs in the 60s Friday-Sunday if the WRF-GFS is correct.    This is the 4km cross-section, time goes from RIGHT TO LEFT.  That’s yesterday at 5pm through Sunday 5am.  You can see the marine layer this morning, a little less this afternoon, then much deeper Friday and Saturday.  The green colors are relative humidity.

A thick marine layer to 5,000′ through Monday or Tuesday…yuck.  There will be plenty of gray in October and November so I was hoping to hold off on that a bit longer.  Apparently the gloom is back west of the Cascades.  Too bad we couldn’t get a 2″ soaking of rain to go with it.

I’m off yesterday through Sunday due to a planned family medical issue but have PLENTY of time to blog while hanging out with doctors and nurses; everything is doing okay though so that’s good news.

Chief Meteorologist Mark Nelsen

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.

Another 90 Degree Day

September 17, 2012

A real scorcher (for mid-late September) out there.  We officially hit 90 degrees here in Portland.  I think it’s unlikely we’ll see that again in the next week.  Expect 80s the next few days and then MAYBE just 70s over the weekend and beyond.


Back to Smoky Skies Monday

September 16, 2012

The visible satellite image this evening (it’s almost dark) clearly shows thick smoke from the Cascade Creek fire near Mt. Adams and central Washington fires headed right for us.  Windflow is switching around to the northeast and that means a mucky day tomorrow, especially in the morning.

Here’s the link…it’ll show something until about 8pm, then go all dark:

And the last (barely) lit image showing the clusters of smoke to our northeast:

Chief Meteorologist Mark Nelsen

7:15pm: A “Rogue” Thunderstorm Near Amboy

September 14, 2012

Looks like that line of sprinkles/light showers has produced a few lightning strikes just north of Amboy as it heads farther north into the National Forest.

Otherwise we are in the clear for the rest of the evening (and weekend) here in the metro area.

Chief Meteorologist Mark Nelsen