September 2019 Weather Discussion for the PNW

[stuffradio]

[snow_wizard]

Yeah, Snoqualmie is only 3,000’. I think 3,500’ is the lowest the snow level was supposed to go in that part of the Cascades.

 

I think Snoqualmie could have scored easily if precip of any intensity had set up there.  Ironically the north wind set in too quickly to allow a C-Zone to develop for them.

[Jesse]

Pretty impressive considering the incessant warm nights we were seeing until now.

 

If those lows end up close to my conservative estimate, PDX would end up with an average MIN of 56.8, which would tie 2013 for the warmest average September MIN on record.

 

Nowhere close to a record warm average MIN for September compared to the downtown station, though. All of theirs were 57.5-57.9. Given the increased UHI at PDX in recent decades it almost seems more fair to compare them to downtown for historical reference, at least with regard to minimum temps.

[snow_wizard]

Speaking of snow in October....1984 had a system much like this in September and we did go on to have lowland snow in October 1984.  I'll never forget that one.  It snowed about an inch on Halloween Eve and Halloween morning there were icy roads.

[Jesse]

If it clears off then most likely yes.

I was surprised how bullish the overnight NWS forecast discussion was for widespread frost down here tonight. They must be envisioning a quick cloud burn off by sunset.

[Rubus Leucodermis]

At least 3" of snow at Washington Pass. Fantastic drive along US 20. Should pick up another couple inches overnight as well.

 

SR 20. US 20 is in Oregon.

[SilverFallsAndrew]

Snow fell down to 1700' in the Hood River Valley this morning. 

[snow_wizard]

SR 20. US 20 is in Oregon.

 

Good catch.

[Jesse]

Snow fell down to 1700' in the Hood River Valley this morning.

 

What is your source.

[snow_wizard]

BTW the mechanism for gettig rid of the blob or trasforming it to a -PDO configuration is the surface pressure reversal over the NE Pacific.  Anomalous low pressure out there as we have seen in recent weeks causes warm SSTs right along the coast.  Anomalous high pressure over the NE Pacific / GOA creates a clockwise gyre which is favorable for upwelling / cooling along the West Coast.  The upwelling along the coast will push the warm water from the blob westward.

[Rubus Leucodermis]

Only made it down to 49°F at KBLI overnight, because the Fraser outflow kept things well-mixed. It was actually cooler at most central Puget Sound reporting stations!

[TT-SEA]

Some snow on the very top of Mt Si again... but no snow on the ridge behind our house which is at roughly 3,000 feet.

 

[ShawniganLake]

Fall leaf color is showing up pretty well. Could be an early leaf drop this year.

[TacomaWaWx]

Fall leaf color is showing up pretty well. Could be an early leaf drop this year.

There was some excellent leaf colors up in the cascades when I went up there yesterday. Leaves are starting to change a bit here in Tacoma but the leaves in the mountains were certainly changing faster.

[Phil]

The pattern has been ridiculously stuck again... just like February. Hope that is a sword that cuts both ways eventually.

When the NPAC ridge and Greenland/NE-Canadian ridge occur together like this, it’s often indicative of a very persistent pattern that is difficult to shake-up (same with the opposite pattern of Aleutian Low/Greenland Vortex).

 

Remember those maps I posted of this background state dominating the 1950s-70s and 2008-12? It tends to reflect weakened warm pool convective exhaust and narrowing z-cells relative to previous boundary conditions of analogous structure/budgetary requirements. In this case it’s intraseasonal, rather than a background state, but the fact it’s showing up with more ease in recent years suggests we may be moving in that direction in the coming years.

[Rubus Leucodermis]

Some snow on the very top of Mt Si again... but no snow on the ridge behind our house which is at roughly 3,000 feet.

 

 

Baker had a fresh coat of snow on it (extending fairly low down) when I last saw it yesterday evening. No snow evident on lower, closer ridges.

[ShawniganLake]

[TT-SEA]

Baker had a fresh coat of snow on it (extending fairly low down) when I last saw it yesterday evening. No snow evident on lower, closer ridges.

Just got back from SEA picking up my parents and Mt Rainier looked awesome from there.

[snow_wizard]

Holy crap!  The 12z GFS is showing a trough as cold as this one about a week out now.  It's an open trough instead of a closed low so it will unfold slightly differently.  This is proving to be an amazing pattern shift.

 

One interesting thing to note is the emergence of cut off lows in the sweet spot under the Aleutian block again.  The same thing that was the hallmark of the late winter cold snaps we saw last winter.  It would appear that the historic propensity for the late winter patterns of the previous season to reappear in the early part of the next cold season is proving itself out once again.

[ShawniganLake]

Holy cow!

 

That looks chilly! Would probably see some snow on the hills and freeze here if that verifies

[Phil]

The pattern has been ridiculously stuck again... just like February. Hope that is a sword that cuts both ways eventually.

I wouldn’t mind this pattern in Jan/Feb at all. The thermal gradient would be close enough here for some okay snowfall/cold fronts with plenty of warm/dry days mixed in, thanks to the SE ridge. Pretty much my ideal winter pattern...variety.

 

It’s just a miserable pattern here May-October. The Bermuda High is still way too close and we end up roasting like it’s a typical summer day.

[Jesse]

Will be interested to hear how low the 850s bottomed out over SLE today. Should be close to a September benchmark.

[Jesse]

I wouldn’t mind this pattern in Jan/Feb at all. The thermal gradient would be close enough here for some okay snowfall/cold fronts with plenty of warm/dry days mixed in, thanks to the SE ridge. Pretty much my ideal winter pattern...variety.

 

It’s just a miserable pattern here May-October. The Bermuda High is still way too close and we end up roasting like it’s a typical summer day.

 

You just walk right into these.

[Phil]

Holy cow!

 

Would be all snow if it weren’t for the blob.

[Jesse]

We might have our baby in the next day or 2. We can tell her stories about being born during the arctic blast of September 2019

 

Congrats.

[Phil]

You just walk right into these.

What are you talking about?

[Deweydog]

[SilverFallsAndrew]

 

What is your source.

[Jesse]

Mark Nelsen.

 

That's a legit source.

[Jesse]

East wind blowing and only 45 here still. This setup reminds me of mid-October 2009 in some ways, but a few weeks earlier.

[Phil]

I totally disagree about the blob. The 7 day change map has already shown dramatic cooling along the west coast. It will likely shift to warm well off the coast and cold along the coast which is a -PDO. Keep in mind the NE Pacific is my specialty.

Okay Jim, I’ll defer to you. What do you think the O/N/D PDO number will be?

 

The problem I see is these patterns need to persist for quite awhile (as a multi-season background state) to profoundly affect the depth/vigor of the mixing layer coupled to the eastern boundary current. Last February is a prime example of this..it was an anomalous short term excursion but there was no long term effect..the “blob” is actually stronger now than it was last year at this time.

 

I’m sure the “blob” will take a hit, and the PDO will drop, as a result of this pattern. But when the addition of AAM resumes and the structure of the NPAC circulation changes again, what will happen?

 

The place to look for *low-frequency* shifts in the NPAC wavetrain is in the tropics..specifically the Indo-Pacific region. That’s typically the domain of low pass inception.

[SilverFallsAndrew]

East wind blowing and only 45 here still. This setup reminds me of mid-October 2009 in some ways, but a few weeks earlier.

 

44 with light rain in Roseburg.

[Deweydog]

Went outside this morning and split some kindling then came inside and turned on the gas fireplace.

[Jesse]

44 with light rain in Roseburg.

Do you remember the reports of snow to the lowest elevations of the eastern Gorge on 10/13/09. I ‘member.

[Phil]

BTW the mechanism for gettig rid of the blob or trasforming it to a -PDO configuration is the surface pressure reversal over the NE Pacific. Anomalous low pressure out there as we have seen in recent weeks causes warm SSTs right along the coast. Anomalous high pressure over the NE Pacific / GOA creates a clockwise gyre which is favorable for upwelling / cooling along the West Coast. The upwelling along the coast will push the warm water from the blob westward.

But again, how do you get the “surface pressure reversal” you’re talking about to sustain for more than a 2-4 weeks a time? You’re making a multi-season prediction based off a pattern that has existed a few weeks.

 

I’m probably being a bit OCD here, but you can’t close this thermodynamic loop on such a short time resolution.

[MR.SNOWMIZER]

Was 28 at my cabin 4 inches of snow. Looks like December.

[Phil]

[MossMan]

[SilverFallsAndrew]

Do you remember the reports of snow to the lowest elevations of the eastern Gorge on 10/13/09. I ‘member.

 

I lived in Oklahoma then. It was the coldest October on record out there. 

[Jesse]

Went outside this morning and split some kindling then came inside and turned on the gas fireplace.

Little House on the Hockinson Prairie.