October 2016 Observations and Model Discussion for the Pacific Northwest

[Phil]

Also, "frozen dew" is not frost. Frost arises via direct conversion from gaseous H^2O. Frozen dew is just ice.

[westcoastexpat]

I think you're probably making this much more complicated than the answer he was looking for.

 

Agreed... the answer I gave him was entirely sufficient for stuffradio's purposes, lol...

[westcoastexpat]

Also, "frozen dew" is not frost. Frost arises via direct conversion from gaseous H^2O. Frozen dew is just ice.

 

Yes, but frozen dew will still result in a frost advisory--same effect on crops. It also looks just like frost to a human observer.

[snow_wizard]

Too bad there are so few people on here tonight.  Some really good reading instead of the usual bickering.

[Phil]

Yes, but frozen dew will still result in a frost advisory--same effect on crops. It also looks just like frost to a human observer.

They're totally different, both visually and physically speaking.

 

- "Frozen dew" requires sub-freezing temperatures and looks glassy/translucent, like your typical ice accretion via freezing rain. Hence if anything you'd be looking at a freeze warning, not a frost advisory, and really it's not something that occurs very often anyway given sublimation rates.

 

- "Frost" forms at the frost point, with temperatures/dewpoints often above 32 degrees. It has an obvious, "snowy" look to it, and isn't related whatsoever.

 

Freezing dew is basically like freezing a puddle of water.

[HighlandExperience]

Too bad there are so few people on here tonight. Some really good reading instead of the usual bickering.

Joe Bastardi scared them away with his pro trump, anti west coast tweets

[TT-SEA]

Next couple days look nice... I wish we were going to get some more clear and cool weather.

[SilverFallsAndrew]

Too bad there are so few people on here tonight.  Some really good reading instead of the usual bickering.

 

It is a Sunday evening. People retire early for the night this time of year too. 

[Phil]

Nice end on the 0z. Exactly what we want to see in October.

Yeah, 00z is back to the blocky solution w/ a weak PV. Good ensemble agreement too.

[westcoastexpat]

They're totally different, both visually and physically speaking.

 

- "Frozen dew" requires sub-freezing temperatures and looks glassy/translucent, like your typical ice accretion via freezing rain. Hence if anything you'd be looking at a freeze warning, not a frost advisory, and really it's not something that occurs very often anyway given sublimation rates.

 

- "Frost" forms at the frost point, with temperatures/dewpoints often above 32 degrees. It has an obvious, "snowy" look to it, and isn't related whatsoever.

 

Freezing dew is basically like freezing a puddle of water.

 

Gonna have to agree to disagree on this one!

[snow_wizard]

Joe Bastardi scared them away with his pro trump, anti west coast tweets

 

He's for Trump?  I guess he isn't all bad.

[snow_wizard]

The ensemble is indeed looking good for the final week of the month.  Everything seems to be on track for us.

[stuffradio]

Thanks for the responses!

[SilverFallsAndrew]

Up to 4.18" of rain on the month so far. 

[Jbolin]

Too bad there are so few people on here tonight.  Some really good reading instead of the usual bickering.

A lot of great reading tonight, 'tis been refreshing to say the very least

[westcoastexpat]

Are you honestly a meteorologist? Don't take my word for it, just grab a highschool chemistry textbook or something.

 

You're denying elementary laws of physics here. If water behaved the way you seem to think it does, life couldn't possibly exist.

 

Phil, please stop.

[BLI snowman]

The ensemble is indeed looking good for the final week of the month.  Everything seems to be on track for us.

 

Persistent cool northerly flow at this stage would be nice to see. 1984-like. Big brother is watching us.

[crf450ish]

Blue skies and sunny @ 39 degrees here this morning. 

[Abbotsford_wx]

On a clear night I start looking for frost at about 39F. You'll usually find some if you look in the right places. Roof shingles cool very effectively by radiation, so they tend to be one of the first places to show frost.

 

Yeah, there's a difference between frozen dew and frost, but to the layman they're the same thing. I've never heard a forecaster predict frozen dew, despite the fact it's probably just as common as "real" frost in the Pac NW because dew points usually start out above freezing and may not reach freezing until early morning. You can sure tell the difference when you're scraping your car windows - frozen dew is far more difficult to remove.

[stuffradio]

Happy Thanksgiving to us! Here's hoping in 4 weeks after the depressing event of having to lose an hour of light, we are tracking really exciting things.

[TT-SEA]

Happy Thanksgiving to us! Here's hoping in 4 weeks after the depressing event of having to lose an hour of light, we are tracking really exciting things.

 

 

We don't lose the light... its just shifted around.   

 

And then the models come out earlier!   

[TT-SEA]

Sunny here this morning... of course it comes on Monday after a cloudy weekend.

[stuffradio]

We don't lose the light... its just shifted around.   

 

And then the models come out earlier!   

Fine, let me be technical by saying we lose an hour of useful light, meaning we aren't getting up an hour earlier just so we can still use it.

[Parksvillewx]

White roofs in my neighbourhood this AM. Cars and grass just stayed wet though.

[TT-SEA]

Thursday and Saturday look stormy.

[MossMan]

Thursday and Saturday look stormy.

I need to get the boat out of the water it looks like before Thursday.

[IbrChris]

Well, it's the surfaces accreting frost that cool below 32F, not necessarily the air itself.

 

That's why you don't usually see frost on cloudy nights (radiative exchange between the clouds/nucleated aerosols and the surface prevents the surface from cooling below the LTE threshold).

 

This is also why you'll often see frost on open fields but not under trees, thanks to backradiation preventing the ground from radiating efficiently.

 

If it were just the temperature cooling to the dewpoint below 32F, you'd have freezing fog, or just regular fog. There's a difference here. The dewpoint doesn't have to drop below 32F.

Also why a car parked under an open sky will often get roof frost while a car parked in a carport won't.

[ShawniganLake]

GFS is trying to bring back the GOA ridge for the end of October.

[IbrChris]

So much for Westerners who think negative NAO is bad for us.

-NAO can be good, bad or neither in terms of arctic air potential in the PNW...ridge position in the NE Pacific is more important, and I'd say -AO is also more important along with -PNA as teleconnection indices to watch.

 

For instance a -NAO with a fairly high NH wave number is going to have a much different longwave pattern upstream than a -NAO with a low hemispheric wave number.

 

I built a predictor index awhile back (think of it as a homemade teleconnection index) using model forecast 500 mb heights at ANC (Anchorage) and SLE (Salem). The values were normalized so that in most cases they fell between -2 and +2...anything below -2 hinted at PNW arctic blast potential. Using historical data I derived index values for past events using sounding data for Anchorage and Salem. The more extreme events were in the -3 to -4 range. There were no arctic blasts that didn't feature a decent signal on the index, with mean values generally -2.5 to -3.

[Brennan]

Temperature got down to 39 here last night and will probably hit mid 30’s the next couple nights. May be the first and last chance at frost this month!

[Front Ranger]

-NAO can be good, bad or neither in terms of arctic air potential in the PNW...ridge position in the NE Pacific is more important, and I'd say -AO is also more important along with -PNA as teleconnection indices to watch.

 

For instance a -NAO with a fairly high NH wave number is going to have a much different longwave pattern upstream than a -NAO with a low hemispheric wave number.

 

I built a predictor index awhile back (think of it as a homemade teleconnection index) using model forecast 500 mb heights at ANC (Anchorage) and SLE (Salem). The values were normalized so that in most cases they fell between -2 and +2...anything below -2 hinted at PNW arctic blast potential. Using historical data I derived index values for past events using sounding data for Anchorage and Salem. The more extreme events were in the -3 to -4 range. There were no arctic blasts that didn't feature a decent signal on the index, with mean values generally -2.5 to -3.

 

Very cool. I think you've mentioned this before.

 

Where did Feb 2011 fall on that scale?

[stuffradio]

What was the setup in Jan 2012 that allowed us up here to get a deep freeze for a week or so and lots of snow?

[IbrChris]

Here are some past values (minimum for each event):

 

Dec 2013: -3.3
Nov 2010: -3.1
Dec 2009: -3.3
Dec 2008: -3.6

Found an interesting post on Facebook re: this index from 11/10/2013:

"An interesting development. In running some recent months with arctic events in the PNW it appears the index is ahead of the cold air by 1-3 days. In other words the index goes sharply negative as the ridge amplifies over AK and downstream development leads to an amplifying/digging trough over the PNW. Some lag time for the cold air to make it here at the surface however, although the index generally stays below -1 during the entire arctic event, occasionally below -2."

A Jan 2013 example:

Lowest index value -1.9 on the 9th and -1.7 on the 10th. Cold hits PDX on 12th with 34/28, same on 13th. Salem stays in 20s.

Dec 2008:

Lowest index value -3.6 on 14th. Coldest day in initial blast was the 15th (mean temp 25 at PDX). Secondary index minimum of -3.2 on the 18th (reload signature). Coldest day in 2nd blast was the 21st with mean temp of 22 at PDX.

Dec 2009:

Lowest index value -3.3 on the 6th. Coldest day was the 9th (mean temp 21 at PDX).

I have more examples but I'm at work currently and my historical file is at home. I calculated the Dec 1990 blast and it was nearly -4 at the lowest.

[IbrChris]

The 18z GFS threw out a arctic blast lover's dream on Dec 18, 2014 and I calculated a minimum index value of -3.2 on day 16, although the initial drop to -1.5 occurred on day 9 (Dec 27) then a reload/intensification to -2.5 on day 14 (Jan 2).

There WAS a western US arctic blast around New Years 2015 though it was focused mainly on the Rockies and Plains...in this event Peter Sinks in northern UT recorded it's coldest low of -51 (Dec 31, 2014) in the Campbell Scientific era (2010-present). Later model runs backed off considerably for the PNW and the index value rose on those runs.

PDX saw 35/26 and 37/21 on Dec 30 and 31, 2014 respectively...so we did get a hint of the blast as well, pretty respectable lows for PDX. Three days below 40 for a high as Jan 1st was 39/24.

As a predictor of cold weather (though not always a true arctic blast) the index seems to hold some promise, especially when considering ensemble mean output.

[ShawniganLake]

The 12Z euro has a 963mb low to the west of Washington state on Saturday morning.  Someone on the Canadian forum noticed Typhoon Songda may get swept into the westerlies, and this does indeed look to be the remnants of the typhoon.  Should be a little extra juice in the storm track later this week. 

[IbrChris]

In the lead-up to the impressive Dec 2013 blast, on Nov 24th I posted the following:

"12z Euro Op...the index drops to -3.4!"

Nov 25th:

"Working on 12z runs...GFS Op dips down to -3.5 (index) on Dec 5th with FIVE days below -2.7 from Dec 2nd through 6th. 12z Euro Op also hits -3.5 on the 4th with -3.3 on 3rd and -3.5 on the 5th...great agreement between GFS and Euro. On the operational runs there is a 4-5 day period that is very low."

As we know it got chilly with highs at or below freezing at PDX from Dec 5 to Dec 9 along with four nights in the teens. Using this index an arctic event could be reasonably foreseen 10-12 days in advance in the case of Dec 2013. Of course this isn't always the case and there are false positives in the models even when there's decent agreement in the longer range. One neat thing about this index is you can see the pattern becoming supportive well before the arctic air is shown diving through BC into the PNW on the models.

[ShawniganLake]

Noticeable outflow going in the Fraser Valley in the last couple of hours.  NNE winds 15-25mph, and the radar indicates that the rain showers are being pushed to the SW as they cross the strait of Georgia. 

[BLI snowman]

Noticeable outflow going in the Fraser Valley in the last couple of hours.  NNE winds 15-25mph, and the radar indicates that the rain showers are being pushed to the SW as they cross the strait of Georgia. 

 

Yup, a little "arctic front" ahead of the switch to NE winds at BLI.

[IbrChris]

Yup, a little "arctic front" ahead of the switch to NE winds at BLI.

Yeah this would be a decent little blast with a potential overrunning event late Wed if this were Dec-Jan-Feb timeframe. The classic "garden hose" atmospheric river event afterward.

[Bryant]

People are noticing...