September 2017 PNW Discussion Thread

[Jesse]

I'm envious. Pattern progression is beautiful for you guys in the long run..that Scandinavia/Eurasia pattern is removing a bunch of AAM upstream, which is going to build the NPAC High/-PNA and favor a -NAM. Meanwhile, I'm gonna roast for a third consecutive autumn.

 

We saw last winter how the Scandinavian Ridge preceded all of the western cold shots/-PNA bursts. One of the more reliable indicators I've been able to uncover (in years with similar boundary conditions).

Removing AAM. That's an interesting way of putting it. So it's essentialy slowing down the jet? Or at least helping put kinks in it in a spot that teleconnects favorably for western troughing/-PNA downstream.

[Geos]

Looks like a sunny morning around the Seattle area and at home.   Low clouds here.  

 

Yeah it is a sunny morning. I noticed the low clouds against the mountains. The colder of the mornings I've noticed fog/mist down in the Snoqualmie Valley.

[Jesse]

Looks like a sunny morning around the Seattle area and at home. Low clouds here.

I'm not sure about up in Seattle but the next three days have trended much cloudier down here.

[Phil]

Doesn't get more classic than this. Scandinavian wavebreak builds poleward -> Eurasian trough activates the east-Asian mountain torque -> AAM removal -> builds NPAC high -> trough develops in western US.

 

The process takes ~ 2 weeks, so expect western troughing to develop between October 4-8th.

 

http://i724.photobucket.com/albums/ww243/phillywillie/Mobile%20Uploads/EC9A544B-1FFB-4D14-BD21-88A4CCDD0C82_zps7aodmmbc.png

[Phil]

Removing AAM. That's an interesting way of putting it. So it's essentialy slowing down the jet? Or at least helping put kinks in it in a spot that teleconnects favorably for western troughing/-PNA downstream.

Yeah, simply put, westerly flow under the Eurasian trough is deflected by the Himalayan mountains (transfer of angular momentum from the atmosphere to the Earth's surface), which builds mass downstream over the NPAC/slows the NPAC jet.

 

This can also play on the tropical forcing through alterations to static stability, usually reinforcing the +Jesse index style convective state.

 

Even if the immediate response is a (temporary) western ridge, the mass imbalance will almost always lead to a discontinuous westward retrogression of the ridge offshore, and a return to western troughing.

[Phil]

Doesn't get more classic than this. Scandinavian wavebreak builds poleward -> Eurasian trough activates the east-Asian mountain torque -> AAM removal -> builds NPAC high -> trough develops in western US.

 

The process takes ~ 2 weeks, so expect western troughing to develop between October 4-8th.

 

http://i724.photobucket.com/albums/ww243/phillywillie/Mobile%20Uploads/EC9A544B-1FFB-4D14-BD21-88A4CCDD0C82_zps7aodmmbc.png

Classic evolution..process completes during week two:

 

http://i724.photobucket.com/albums/ww243/phillywillie/Mobile%20Uploads/89C75A7C-BB92-4EFF-B0AF-D90C0A3B4ECA_zpsgwvkbnbq.png

[Jesse]

I checked out of curiosity. Definitely looking ridgy in Sweden the next 10 days.

 

https://www.wunderground.com/forecast/se/stockholm

[Jesse]

Classic evolution..process completes during week two:

 

http://i724.photobucket.com/albums/ww243/phillywillie/Mobile%20Uploads/89C75A7C-BB92-4EFF-B0AF-D90C0A3B4ECA_zpsgwvkbnbq.png

 

That last map looks a lot like the 00Z Euro in the long range. Maybe it isn't totally out to lunch.

[Phil]

I checked out of curiosity. Definitely looking ridgy in Sweden the next 10 days.

 

https://www.wunderground.com/forecast/se/stockholm

If you animate the GFS run here (500mb geopotential height anomalies), you can see how the Scandi ridge/Eurasian trough acts to build NPAC heights/slow the jet through Himalayan mountain torque. Throwback to the 1950s here:

 

https://www.tropicaltidbits.com/analysis/models/?model=gfs&region=nhem&pkg=z500a&runtime=2017092212&fh=192&xpos=0&ypos=0

[stuffradio]

That last map looks a lot like the 00Z Euro in the long range. Maybe it isn't totally out to lunch.

What's the earliest snow for you that you can remember in your lifetime? That October 21 or whatever in 2012 is the earliest for me. I think there have been times with snow here in September, but not in my lifetime.

[Jesse]

What's the earliest snow for you that you can remember in your lifetime? That October 21 or whatever in 2012 is the earliest for me. I think there have been times with snow here in September, but not in my lifetime.

The earliest snow I've seen falling here? Early November 2003. I believe on 11/2 or 11/3.

[Front Ranger]

What's the earliest snow for you that you can remember in your lifetime? That October 21 or whatever in 2012 is the earliest for me. I think there have been times with snow here in September, but not in my lifetime.

 

Aren't you at 500'? I can't imagine any place in the PNW at 500' that's seen snow in September.

[TT-SEA]

What's the earliest snow for you that you can remember in your lifetime? That October 21 or whatever in 2012 is the earliest for me. I think there have been times with snow here in September, but not in my lifetime.

 

The biggest snowstorm I ever experienced in Minnesota started on Halloween in 1991.    That was an incredible event.   How rare is it to have the biggest snowstorm ever in a fairly snowy climate start in October?   The event continued into November so the the storm total was split between two months.

 

 

 

Ended up with close to 40 inches of snow over 3 days at our house... and then it turned really cold.   I remember cars putting flags on their antennas so they could be seen better coming around corners with the massive snowbanks.  

[stuffradio]

Aren't you at 500'? I can't imagine any place in the PNW at 500' that's seen snow in September.

Not in the 50's or something?

[Phil]

The biggest snowstorm I ever experienced in Minnesota started on Halloween in 1991. That was an incredible event. How rare is it to have the biggest snowstorm ever in a fairly snowy climate start in October? The event continued into November so the the storm total was split between two months.

 

 

 

Ended up with close to 40 inches of snow over 3 days at our house... and then it turned really cold. I remember cars putting flags on their antennas so they could be seen better coming around corners with the massive snowbanks.

That's sick. The earliest I can remember was back on October 29th, 2011. Finished with about 1", which ironically ended up being the largest snowfall of that entire winter.

 

October snow is a curse here. I don't think we've ever had a snowier than average winter following snowfall in October.

[Geos]

Classic evolution..process completes during week two:

 

 

Wow, that's some low heights. 

[Jesse]

Not in the 50's or something?

You'd have to ask statman to be sure. But I've never heard of anyone in the western lowlands getting snow before mid-October or so. Even historically.

[epiceast]

Through day 6:

 

Looks like a lot less than GFS was showing

[TT-SEA]

Sun is coming out in Stevenson... looks much more socked in towards Portland though.  

[stuffradio]

Look how many members are at or below 0C 850 now.

 

[Jesse]

Sun is coming out in Stevenson... looks much more socked in towards Portland though.

Glad it's clearing out for you. The Gorge is a beautiful place.

[Phil]

Seasons are a' changin'.

 

http://i724.photobucket.com/albums/ww243/phillywillie/Mobile%20Uploads/61E82307-21C5-4136-8F35-A291AAD12DB1_zpsmsy0medi.jpg

[BLI snowman]

You'd have to ask statman to be sure. But I've never heard of anyone in the western lowlands getting snow before mid-October or so. Even historically.

 

Not aware of anything in September other than hail counted as snow traces.

 

The cold spell of mid October 1881 probably produced some sleet in areas on the 14th. Portland had a 45/32 day and Olympia was 42/28 as a warm front overtook an arctic airmass. That would be the earliest frozen precip that I'm aware of in the lowlands. October 2009 was similar of course, with the eastern gorge getting overrunning snow on the 13th and sleet in the western areas.

[TT-SEA]

Glad it's clearing out for you. The Gorge is a beautiful place.

 

The view from our room is spectacular...

 

[Jesse]

The view from our room is spectacular...

 

Nice pic. Hard to tell how much the fire affected Nick Eaton ridge and the Herman Creek valley. That's the ridge and the drainage at its base on the far right of the picture.

[TT-SEA]

Nice pic. Hard to tell how much the fire affected Nick Eaton ridge and the Herman Creek valley. That's the ridge and the drainage at its base on the far right of the picture.

 

You can definitely see smoke nestled in the hills over there. 

[TT-SEA]

Wow... the 12Z ECMWF is completely different than the 00Z run late next week.     

 

[Jesse]

12z Euro completely does away with any cool down on the 29th/30th. Record warm September looking pretty likely for PDX at this point.

[Farmboy]

Doesn't get more classic than this. Scandinavian wavebreak builds poleward -> Eurasian trough activates the east-Asian mountain torque -> AAM removal -> builds NPAC high -> trough develops in western US.

 

The process takes ~ 2 weeks, so expect western troughing to develop between October 4-8th.

 

http://i724.photobucket.com/albums/ww243/phillywillie/Mobile%20Uploads/EC9A544B-1FFB-4D14-BD21-88A4CCDD0C82_zps7aodmmbc.png

 

Wow that sure is a vastly differing forecast than what accuweather is calling for.  They think our first week of October is going to torch.  I guess they must be putting all their chips on the Euro...

[Farmboy]

Or they know something we don't...

[Front Ranger]

12z Euro completely does away with any cool down on the 29th/30th. Record warm September looking pretty likely for PDX at this point.

 

Nah. If the warm runs verify, you might be looking at three 85/50-ish days to close the month. That wouldn't be enough to push up the monthly average hardly at all, which will be below the record within a couple days.

 

Monthly departure for PDX is down to +2.6.

[Phil]

Wow that sure is a vastly differing forecast than what accuweather is calling for. They think our first week of October is going to torch. I guess they must be putting all their chips on the Euro...

The first few days of October might torch, but I doubt it even lasts a week.

 

That doesn't mean the month can't finish warm, but I'd lean against it. What happens after the next round of -PNA is still unclear, though.

[Jesse]

Nah. If the warm runs verify, you might be looking at three 85/50-ish days to close the month. That wouldn't be enough to push up the monthly average hardly at all, which will be below the record within a couple days.

 

Monthly departure for PDX is down to +2.6.

We'll see. You are banking on cool nights the rest of the way through, but after the warm front moves through on Monday they will trend warmer. Could see a run of lows in the mid-upper 50s at PDX next week.

[Jesse]

Or they know something we don't...

Accuweather knows all.

[Front Ranger]

We'll see. You are banking on cool nights the rest of the way through, but after the warm front moves through on Monday they will trend warmer. Could see a run of lows in the mid-upper 50s at PDX midweek next week.

It's now the time of year where if you have mild lows, the highs usually aren't that warm. But if you get warm highs, the lows are fairly cool.

 

You're not going to see an 86/59 day like you would have a few weeks ago. More like 86/51. Or if it's cloudier/moister, 74/56. Either way, it's very rare the last week of September to get average daily temps warmer than 67-68, and PDX will likely need to average around 70 the last 3-4 days of the month to pull it off.

[Jesse]

It's now the time of year where if you have mild lows, the highs usually aren't that warm. But if you get warm highs, the lows are fairly cool.

 

You're not going to see an 86/59 day like you would have a few weeks ago. More like 86/51. Or if it's cloudier/moister, 74/56. Either way, it's very rare the last week of September to get average daily temps warmer than 67-68, and PDX will likely need to average around 70 the last 3-4 days of the month to pull it off.

 

PDX says that sounds like a challenge.

[Front Ranger]

PDX UHI says that sounds like a challenge.

 

Fixed. 

 

I don't see it happening, but anything is possible.

[epiceast]

Wow... the 12Z ECMWF is completely different than the 00Z run late next week.     

 

Finally a ridge when we need it.

[Jesse]

EPS breaks the ridge down pretty quickly by day 9-10. The operational and ensemble seem to be more or less back in phase now.

 

I wonder if the 11-15 day range is still ridgy on the EPS?

[Phil]

I wonder if the 11-15 day range is still ridgy?

Nope. It's -PNA/-NAO/western trough.