December 2014 Observations for the Pacific Northwest

[Poulsbo Snowman]

Me!!!!!! :wub:

[Gradient Keeper]

Me

Same here getting excited, adrenaline pumping, almost peed a little, just slightly, few drips really, and I usually only do that during thunderstorms!

[Snow]

Last winter I derived an index I call "Pacific Northwest-Alaska Index" to aid in forecasting arctic blasts in the PNW. It is fairly simple and takes 500 mb height in decameters (dam) as inputs. Both the forecast (or historical) plus climatological 500 mb heights are required. The model then takes the modeled/historical 500 mb heights for Salem and Anchorage, normalizes them and adjusts them based on climatology (both at each station and the mean) with an output of an index value generally between +3.0 and -4.0. This value is a measure of the longwave pattern between Anchorage and Salem, whether it is zonal, meridional or somewhere in between as well as how anomalous it is. High heights at ANC and low heights at SLE (relatively speaking) are indicated by negative PAI values, however these can be either muted or intensified based on how the pattern is relative to climatology. For instance Anchorage can have a lower height than Salem and still return a negative PAI.

 

Historical minimum PAI values for recent "arctic blasts":

 

Dec 2008: -3.6

Dec 2009: -3.3

Nov 2010: -3.1

Dec 2013: -3.3

Feb 2014: -1.7 (this wasn't too impressive in WA as we know...interesting event)

 

Here is a visual showing the steps in calculating the PAI:

 

http://oi57.tinypic.com/nbw1ec.jpg

Thanks for sharing, looks awesome!

[gsax]

I think this is the first time of the year the NWS is saying colder than normal on their 8-14 day outlook. They've been very warm biased.

[Gradient Keeper]

Last winter I derived an index I call "Pacific Northwest-Alaska Index" to aid in forecasting arctic blasts in the PNW. It is fairly simple and takes 500 mb height in decameters (dam) as inputs. Both the forecast (or historical) plus climatological 500 mb heights are required. The model then takes the modeled/historical 500 mb heights for Salem and Anchorage, normalizes them and adjusts them based on climatology (both at each station and the mean) with an output of an index value generally between +3.0 and -4.0. This value is a measure of the longwave pattern between Anchorage and Salem, whether it is zonal, meridional or somewhere in between as well as how anomalous it is. High heights at ANC and low heights at SLE (relatively speaking) are indicated by negative PAI values, however these can be either muted or intensified based on how the pattern is relative to climatology. For instance Anchorage can have a lower height than Salem and still return a negative PAI.

 

Historical minimum PAI values for recent "arctic blasts":

 

Dec 2008: -3.6

Dec 2009: -3.3

Nov 2010: -3.1

Dec 2013: -3.3

Feb 2014: -1.7 (this wasn't too impressive in WA as we know...interesting event)

 

Here is a visual showing the steps in calculating the PAI:

 

http://oi57.tinypic.com/nbw1ec.jpg

 

 

One thing about the PAI is that it generally bottoms out a couple days BEFORE the really cold stuff hits us here in Oregon. The neat thing about it is you can sorta see the arctic air moving S through western Canada using the index values as you see heights rise over AK and fall over western Canada and the PNW.

 

The values shown are the legit ones for the early Dec 2013 event (00z sounding analysis for SLE and ANC). Notice in Dec 2013 PAI bottomed out on Dec 7th (00z, so actually on evening of Dec 6th) while coldest temps were felt across OR on Dec 8th.

Very nice. This had to take some time putting together. I for one really like your PAI Index. It's easy to understand, to apply, and it's accurate. It helps resolve how strong an arctic blast is and upper level support may be. One of the best indexes/indices ever made. Period

[SilverFallsAndrew]

Since Chris mentioned the Feb 2014 event, here is an insane temp gradient I found from February 8th.

 

Eugene 32/29

 

50 miles S at Roseburg 61/45

 

Eugene's coldest day was an astounding 25/20 on the 6th. Roseburg was 45/39. Bet the kids in R-burg were jelly.

[SilverFallsAndrew]

I think this is the first time of the year the NWS is saying colder than normal on their 8-14 day outlook. They've been very warm biased.

 

Well since early February we've been above normal about 90% of the time. 

[Gradient Keeper]

 

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All waiting for a jaw-dropping EURO run

 

[Gradient Keeper]

Here we go !

http://www.tropicaltidbits.com/analysis/models/ecmwf/2014121700/

[BLI snowman]

11 years ago right now the models didn't look very impressive. I remember that due to some impending travel we had coming up.

 

That late December through New Year's sequence surpassed most expectations. Both the snow amounts and the actual temps were impressive, given the forecasts. 

[Jesse]

Yup, already affecting the BDC.

So...we're screwed?

[TT-SEA]

Seems like the last 2 events looked like this at a week out and then became sharply colder in the home stretch.

[Deweydog]

That late December through New Year's sequence surpassed most expectations. Both the snow amounts and the actual temps were impressive, given the forecasts.

A lot of needles got threaded over that 10 days or so. 12-30 was most impressive to me, born of such a ridiculously innocuous set up.

[stuffradio]

The 00z Euro still going with highs below 32F for Abbotsford on Boxing day. It has maybe only traces of snow too.

[SilverFallsAndrew]

A lot of needles got threaded over that 10 days or so. 12-30 was most impressive to me, born of such a ridiculously innocuous set up.

 

One of my all-time favorite stretches of winter in the mid-valley. The 12/29 and 1/1 snow events were so under forecasted. The 2nd snow event was a solid 3-6" from Eug to PDX though if I remember it was heavier E of I-5 because it was a wrap around band. The first snow event was really a mid-valley show. We got about 4" in Silverton. SLE had about 6" and places west of Salem toward Dallas had almost 10". 

[BLI snowman]

A lot of needles got threaded over that 10 days or so. 12-30 was most impressive to me, born of such a ridiculously innocuous set up.

 

I had a high of 32 that day with 3+" of snow that night. That felt like January 1950 after the five year stretch we had had!

[Gradient Keeper]

HR 72

http://www.tropicaltidbits.com/analysis/models/ecmwf/2014121700/ecmwf_z500_mslp_namer_4.png

[IbrChris]

If anyone is utilizing the PAI they will need 500 mb height climatology for SLE and ANC...while the values don't change a lot (about 10 dam from early Nov-late Feb at SLE) they will have an effect on the output if not used properly. You could probably get away with a mean value for each month but when I built this I grabbed values for each calendar day.

500 mb height Climatology (dam)
Date SLE ANC
1-Nov 563 530
2-Nov 563 530
3-Nov 562 530
4-Nov 562 529
5-Nov 562 529
6-Nov 562 529
7-Nov 561 529
8-Nov 561 528
9-Nov 561 528
10-Nov 561 528
11-Nov 560 528
12-Nov 560 528
13-Nov 560 528
14-Nov 560 527
15-Nov 560 527
16-Nov 560 527
17-Nov 559 527
18-Nov 559 527
19-Nov 559 526
20-Nov 559 526
21-Nov 559 526
22-Nov 559 526
23-Nov 559 526
24-Nov 559 526
25-Nov 559 526
26-Nov 558 526
27-Nov 558 525
28-Nov 558 525
29-Nov 558 525
30-Nov 558 525
1-Dec 558 525
2-Dec 558 525
3-Dec 558 525
4-Dec 558 525
5-Dec 558 525
6-Dec 558 525
7-Dec 558 525
8-Dec 558 525
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11-Dec 558 525
12-Dec 558 525
13-Dec 558 525
14-Dec 558 525
15-Dec 558 525
16-Dec 558 525
17-Dec 558 525
18-Dec 558 525
19-Dec 557 525
20-Dec 557 525
21-Dec 557 525
22-Dec 557 525
23-Dec 557 525
24-Dec 557 525
25-Dec 557 525
26-Dec 557 525
27-Dec 557 525
28-Dec 556 525
29-Dec 556 525
30-Dec 556 525
31-Dec 556 525
1-Jan 556 525
2-Jan 556 525
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30-Jan 554 526
31-Jan 554 526
1-Feb 554 526
2-Feb 554 526
3-Feb 554 526
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29-Feb 553 527

[TT-SEA]

The 00z Euro still going with highs below 32F for Abbotsford on Boxing day. It has maybe only traces of snow too.

 

 

Boxing Day is such a rarely used term down here.    Strange how an imaginary line divides speech and terminology so perfectly.

 

Aboot.   Eh?

[stuffradio]

Boxing Day is such a rarely used term down here.    So strange how an imaginary line has such differences in speech.

 

Aboot.   Eh?

Only a few people say Eh here. I'll climb on my ruff to look for the Arctic air.

[Deweydog]

HR 72

http://www.tropicaltidbits.com/analysis/models/ecmwf/2014121700/ecmwf_z500_mslp_namer_4.png

Too warm for snow at my house.

[gsax]

HR 72

ohttp://www.tropicaltidbits.com/analysis/models/ecmwf/2014121700/ecmwf_z500_mslp_namer_4.png

Correct me if I'm wrong, but that's a lot of the good stuff that looks to slide down.

[Bryant]

The 00z Euro still going with highs below 32F for Abbotsford on Boxing day. It has maybe only traces of snow too.

 

You posted that at 10:05... Euro isn't out 

[Gradient Keeper]

HR 120

 

http://www.tropicaltidbits.com/analysis/models/ecmwf/2014121700/ecmwf_z500_mslp_namer_6.png

[FroYoBro]

I'm calling it here right now. There will not be an arctic outbreak before New Years.

Seems like a pretty easy call at this point. 

[stuffradio]

You posted that at 10:05... Euro isn't out 

It is on Weatherbell.

[SilverFallsAndrew]

Seems like a pretty easy call at this point. 

 

Not everyone agrees with us.

[Bryant]

It is on Weatherbell.

 

My apologies... been working long hours

[whitechristmas]

Oh, sorry I should have mentioned that. Buehner is from the Seattle NWS.

 

 

Thanks! Buehner's name didn't ring a bell.

[Gradient Keeper]

00z ECMWF is FANTASTIC !!!!!!!!! WOW

 

Ideal 500mb pattern!

[luvssnow_spokane]

00z...         

[Snow]

[Gradient Keeper]

Nice amplification and a pretty SW digging trough on the Euro. Looks nice. And this is just hour 192.

 

And still digging southwestward after.... then a southeast US ridge develops before day 10.... beautiful

[snow_wizard]

Seems like a pretty easy call at this point. 

 

Really?

[snow_wizard]

Nice amplification and a pretty SW digging trough on the Euro. Looks nice. And this is just hour 192.

 

 

Looks Arctic to me.

[Gradient Keeper]

Progression from 226 to 240 almost looks odd, looks like an error in data. Pattern change now begins upstream/offshore by day 6 guys(and gals) ....

[Guest Winterdog]

Looks Arctic to me.

Not so much at hour 240 though.

[Gradient Keeper]

Looks Arctic to me.

Kind of chilly yes.

[Gradient Keeper]

Not so much at hour 240 though.

I'm not buying the pattern breaking down that quickly from HR 216 - 240. No way

[Phil]

So...we're screwed?

Wouldn't say that at all..just something to keep in mind. The Midwest/East should be slammed regardless of what happens, in my opinion.