2013 Fall Medium Range Discussion

[scottmartin49]

"There's a decent pool of very cold air over Alaska and NW Canada, so the potential is there and this has nothing to do with climo."

Heat anomalies over the pole will continue to place a demand on sub-arctic cold, with predominantly zonal flows continuing beyond the solistice. Potential is not probable, but again, I'm an amateur. The Wooly Bears said the pattern doesn't change 'til mid- January.

[wxmx]

"There's a decent pool of very cold air over Alaska and NW Canada, so the potential is there and this has nothing to do with climo."

Heat anomalies over the pole will continue to place a demand on sub-arctic cold, with predominantly zonal flows continuing beyond the solistice. Potential is not probable, but again, I'm an amateur. The Wooly Bears said the pattern doesn't change 'til mid- January.

Heat anomalies over the arctic are mostly a function of the current -AO. Check out severe cold snaps from the past, warm anomalies in the arctic are almost a requirement. Yes, there has been a climatological warmth of the arctic in the last 30 years, but it's a small part of the equation when there's a favorable synoptic setup for cold. If we were talking in September about the prospects of winter versus climo, then yes, I would agree that I would set a little warmer bias to my guesstimate at the moment, but we are now talking about how things are right now, and how they could evolve into a severe cold snap. This remind me of the Adam (am19psu) and some other guy discussion (cant remember his handle) with Sandy. With no storm, Adam would put the probabilities of a very strong storm with a favorable extratropical phasing very low for the East coast any given year...but the storm was there, and the synoptic setup already showed signs of the potential...making something remotely possible into statistically probable.

[am19psu]

Hopefully, you don't get challenged to a fight.

[scottmartin49]

Heat anomalies over the arctic are mostly a function of the current -AO. Check out severe cold snaps from the past, warm anomalies in the arctic are almost a requirement. Yes, there has been a climatological warmth of the arctic in the last 30 years, but it's a small part of the equation when there's a favorable synoptic setup for cold. If we were talking in September about the prospects of winter versus climo, then yes, I would agree that I would set a little warmer bias to my guesstimate at the moment, but we are now talking about how things are right now, and how they could evolve into a severe cold snap. This remind me of the Adam (am19psu) and some other guy discussion (cant remember his handle) with Sandy. With no storm, Adam would put the probabilities of a very strong storm with a favorable extratropical phasing very low for the East coast any given year...but the storm was there, and the synoptic setup already showed signs of the potential...making something remotely possible into statistically probable.

Your call; hope it works out!

[Srain]

The Euro op has trended much weaker with the early week system for the Plains/Midwest. The GFS op has a strong system, but it's delayed and does not really start churning until it reached Indianapolis on Monday morning. The Euro ensemble actually looks closer to the GFS op than the Euro op. I still feel confident that there will a formidable storm next week, but there is high uncertainty as to where it ends up.

Different day...different solution via the OP GFS. I tend to believe a formidable Winter Storm is in the cards for portions of the Colorado Front Range into Kansas on NE into the MidWest. Lighter amounts still may be likely across Northern New Mexico/TX/OK Panhandle as well. I'm also a bit more interested today in the severe threat in the warm sector ahead of that potent front as well.

[icebreaker5221]

http://raleighwx.americanwx.com/models/00zecmwfensindices.html

Still searching for that negative west-based NAO / negative EPO / positive PNA combo. 2 out of 3 would be fine, yet we can't even get 1 out of 3.

[NJwinter23]

It will be interesting to watch the current warming events in the stratosphere, driven by the tropospheric blocking, fade through the next 2 weeks and watch the vortex strengthen up there. I'd think we should see the over all AO trend back towards neutral/positive after this next dip to ~ -3 stdev. But at the same time we definitely will see the cold dumping into southern/central Canada, the plains with transient shots heading east-northeast. The east-based NAO means these shots from sustaining and really affecting the mid-atl/southeast..Do we eventually get these to sustain further east even with a rising AO? A big part of that would lie in whether the east based nao ridging can trend west going forward. I want to see that trend inside the 11-15 day period before I get excited for anything like that for the latter part of dec

[tacoman25]

The national torch we have seen recently has begun its demise, and we should continue to see colder weather increase from West to East over the next 7-10 days.

[tacoman25]

Your right, Europe has seen some big cold snaps the last few Winters. But this was more in reference to severe cold. I doubt they are reaching wide spread huge deep cold anomaly's.

Many cities in the USA can't reach within 10-20F of there coldest winter temps since the mid 90s. That is what is mean't by depth of cold. Nor those huge monthly anomaly's.

Despite warming in the Arctic, what really drives severe cold is the pattern. If you don't have big -EPO and/or -AO/-NAO, you aren't going to see severe cold in the CONUS. And of course, the best time to achieve the coldest temps for most of the nation is Jan - mid Feb. The times in recent years that we have seen good patterns for getting very cold (Jan 2009, Dec 2009, Dec 2010, Feb 2011), we saw extreme cold in places throughout the lower 48. There is no reason to believe we can't see extreme cold now, and if the right pattern occurs in the heart of winter, we will still see lots of cold records fall.

[Isotherm]

It will be interesting to watch the current warming events in the stratosphere, driven by the tropospheric blocking, fade through the next 2 weeks and watch the vortex strengthen up there. I'd think we should see the over all AO trend back towards neutral/positive after this next dip to ~ -3 stdev. But at the same time we definitely will see the cold dumping into southern/central Canada, the plains with transient shots heading east-northeast. The east-based NAO means these shots from sustaining and really affecting the mid-atl/southeast..Do we eventually get these to sustain further east even with a rising AO? A big part of that would lie in whether the east based nao ridging can trend west going forward. I want to see that trend inside the 11-15 day period before I get excited for anything like that for the latter part of dec

I'm not sure I agree about it turning positive any time soon. Generally these -AO/mod-strong blocking periods last at least 30 days, with some events as long as 50-60 days depending upon the regime in place. My guess is we do rise but remain negative through the remainder of December and potentially the first half of January as well.

Latest stratospheric observarions show warming continuing for pretty much the entire 70mb-5mb layer, and the vortex shouldn't restregthen to where it was a couple weeks ago IMO, at least not strong enough to really induce a modality change in the tropospheric AO.

[Isotherm]

Despite warming in the Arctic, what really drives severe cold is the pattern. If you don't have big -EPO and/or -AO/-NAO, you aren't going to see severe cold in the CONUS. And of course, the best time to achieve the coldest temps for most of the nation is Jan - mid Feb. The times in recent years that we have seen good patterns for getting very cold (Jan 2009, Dec 2009, Dec 2010, Feb 2011), we saw extreme cold in places throughout the lower 48. There is no reason to believe we can't see extreme cold now, and if the right pattern occurs in the heart of winter, we will still see lots of cold records fall.

Agreed. If the pattern suggests that extreme cold is possible, I wouldn't mute that signal much based on arctic warming. We've seen some impressive outbreaks in the modern era.

[GaWx]

Agreed. If the pattern suggests that extreme cold is possible, I wouldn't mute that signal much based on arctic warming. We've seen some impressive outbreaks in the modern era.

I think about GW this way. As much as has occurred, it has still warmed only about 0.5 C or only about 1.0 F since the very cold late 70's U.S. winters on a global basis. So, in my mind, the same setup that brought frigid weather down into the E US in 1976-7 and 1977-8 would, perhaps, be only a mere 1.0 F warmer than those years, which would obviously still be just about as frigid. Anyone else feel similarly?

For example, the winter of 1976-7 was 7.6 F below normal at KATL, the coldest on record. Had it been

1.0 F warmer, it still would have been 6.6 F below normal and still the coldest on record.

I realize that it is in reality more complicated than that due to a nonuniform warming over the globe. So, for example, perhaps I should have used 2.0 F warmer instead of 1.0 F due to the ice melt and warmer Arctic. Regardless, even a winter that is 5.6 F below normal would be only barely warmer than our 3rd coldest on record. The general idea is that cold extremes would theoretically still be very cold...just probably not quite as cold with GW.

Then again, maybe that's the weenie in me talking lol.

[tacoman25]

I think about GW this way. As much as has occurred, it has still warmed only about 0.5 C or only about 1.0 F since the very cold late 70's U.S. winters on a global basis. So, in my mind, the same setup that brought frigid weather down into the E US in 1976-7 and 1977-8 would, perhaps, be only a mere 1.0 F warmer than those years, which would obviously still be just about as frigid. Anyone else feel similarly?

For example, the winter of 1976-7 was 7.6 F below normal at KATL, the coldest on record. Had it been

1.0 F warmer, it still would have been 6.6 F below normal and still the coldest on record.

I realize that it is in reality more complicated than that due to a nonuniform warming over the globe. So, for example, perhaps I should have used 2.0 F warmer instead of 1.0 F due to the ice melt and warmer Arctic. Regardless, even a winter that is 5.6 F below normal would be only barely warmer than our 3rd coldest on record. The general idea is that cold extremes would theoretically still be very cold...just probably not quite as cold with GW.

Then again, maybe that's the weenie in me talking lol.

Actually, I believe it's more like .5F or .6F since then...but that's for another forum.

I completely agree with your points, though.

[Bob Chill]

I posted this in the ma subforum. Having a -pna/ao/nao dominant combo at the same time isn't all that common. Dec of 61 and 96 featured it. Dec 61 flipped mid month to a cold pattern. I pulled NH 500 anoms for the first and second half of the month. It's a pretty close match to what is progged the first half of this month and the second half of 61 looks a lot like some of the recent GFS runs in the LR.

First half of Dec 61 looks really similar in the pac and greenland to what we are seeing right now:

The second half evolved to this setup:

The 0z gfs day 11-15 from last night:

It's going to be tough to flip from where we are now to the same look that is showing on the GFS and what happened in 61 but it would be very interesting if it followed along. The AO of 1961 was quite negative but there was also a big -pna to deal with that made the first half of the month warm.

We really need to root for a west based -nao to get the EC into a productive pattern if we continue to battle a -pna and there are no signs of the PNA going positive anytime soon.

Here is Nov-Dec 1961 PNA Graph:

Pretty close to what we are seeing now:

[Isotherm]

Good post Bob, strongly agree w/ your thoughts. 61 was an analog I looked at for this winter and it is indeed quite similar to our current regime/progged regime. I don't see the -PNA departing anytime soon given the moderately neg PDO forcing, which has a very good correlation to -PNA/PAC NW troughiness pattern. Thus as you noted we need the -NAO, preferrably west based in orientation, to deliver sustained colder than normal temp anomalies into the Northeastern/Eastern United States.

[Bob Chill]

Good post Bob, strongly agree w/ your thoughts. 61 was an analog I looked at for this winter and it is indeed quite similar to our current regime/progged regime. I don't see the -PNA departing anytime soon given the moderately neg PDO forcing, which has a very good correlation to -PNA/PAC NW troughiness pattern. Thus as you noted we need the -NAO, preferrably west based in orientation, to deliver sustained colder than normal temp anomalies into the Northeastern/Eastern United States.

I stumbled into 61 last night when I was looking for other Decembers with a -pna/ao/nao combo. I made a post in our subforum about -ao decembers and 61 was on that list too. Monthly was -1.6+/-. I was kinda surprised when I saw the pattern in the pac because it looked very similar to what we are seeing now.

Of course the million dollar question is whether or not the blocking establishes itself in the right place (and enough strength) to fight against an awful pac if you like winter weather in the east. It was nice to see the gfs go in that direction today but it's fantasyland range so who knows. Euro is thinking about it but the -nao is a little too far east so the trough in the west wins in the LR. Time will tell. I would like to at least see some sort of cold pattern set up in the east before Christmas. Walking the dog in shorts and flip flops yesterday just didn't seem right. lol

[scottmartin49]

Actually, I believe it's more like .5F or .6F since then...but that's for another forum.

I completely agree with your points, though.

Responses to changing variables are not linear when attempting to use analogous pattern data. Think of it as a probability question; going from a six sided die to an eight does not merely add to the data set, it is fundamentally changed.

Changing climatics fundamentally alter all prior probabilities. Variance between models and reality are becoming common enough to allow for speculation. Check out this pattern of variance between AO prediction and event;

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao.mrf.diff.shtml

Notice how the variance is trending? This becomes pertinent to forecasting.

[tacoman25]

I stumbled into 61 last night when I was looking for other Decembers with a -pna/ao/nao combo. I made a post in our subforum about -ao decembers and 61 was on that list too. Monthly was -1.6+/-. I was kinda surprised when I saw the pattern in the pac because it looked very similar to what we are seeing now.

Of course the million dollar question is whether or not the blocking establishes itself in the right place (and enough strength) to fight against an awful pac if you like winter weather in the east. It was nice to see the gfs go in that direction today but it's fantasyland range so who knows. Euro is thinking about it but the -nao is a little too far east so the trough in the west wins in the LR. Time will tell. I would like to at least see some sort of cold pattern set up in the east before Christmas. Walking the dog in shorts and flip flops yesterday just didn't seem right. lol

I looked at likely analogs for this winter about a month ago and made a post about it, and I got a decent signal for a west-based -NAO as December progressed, along with a -PNA Pacific for much of the month. I then got a signal for an even stronger -PNA for at least the first half of January (but still a -NAO/-AO overall), before then transitioning to a +PNA for February with strong -NAO blocking (though more east-based).

[Isotherm]

I think about GW this way. As much as has occurred, it has still warmed only about 0.5 C or only about 1.0 F since the very cold late 70's U.S. winters on a global basis. So, in my mind, the same setup that brought frigid weather down into the E US in 1976-7 and 1977-8 would, perhaps, be only a mere 1.0 F warmer than those years, which would obviously still be just about as frigid. Anyone else feel similarly?

For example, the winter of 1976-7 was 7.6 F below normal at KATL, the coldest on record. Had it been

1.0 F warmer, it still would have been 6.6 F below normal and still the coldest on record.

I realize that it is in reality more complicated than that due to a nonuniform warming over the globe. So, for example, perhaps I should have used 2.0 F warmer instead of 1.0 F due to the ice melt and warmer Arctic. Regardless, even a winter that is 5.6 F below normal would be only barely warmer than our 3rd coldest on record. The general idea is that cold extremes would theoretically still be very cold...just probably not quite as cold with GW.

Then again, maybe that's the weenie in me talking lol.

Your thoughts make sense to me. If I had the following group of analogs when preparing a winter forecast: 62-63, 76-77, and 68-69, all very cold winters from a cooler globe, I'd probably mute the resultant DJF departure by at least 2F. For example, those 3 winter seasons yield about a -5 to -6 temp departure for DJF in the NYC area. I'd probably go with -3 to -4 given those analogs in our climatic period right now. We've also got to keep in mind, years in the 60s and 70s happened when we were already 10+ yrs in the -PDO decadal phase, which had been helping to cool the planet for some time. We flipped the PDO phase fairly recently, around 07-08, so we're only several years into the -PDO cycle, and thus the globe is certainly warmer than even the late 50s/early 60s. There is likely anthropogenic contribution since then as well, but that's for another forum.

[NJwinter23]

I'm not sure I agree about it turning positive any time soon. Generally these -AO/mod-strong blocking periods last at least 30 days, with some events as long as 50-60 days depending upon the regime in place. My guess is we do rise but remain negative through the remainder of December and potentially the first half of January as well.

Latest stratospheric observarions show warming continuing for pretty much the entire 70mb-5mb layer, and the vortex shouldn't restregthen to where it was a couple weeks ago IMO, at least not strong enough to really induce a modality change in the tropospheric AO.

I kinda left the door open there by saying "trending towards neutral/positve", because I'm not sure either at this point if it goes into that + territory. But I'm basically going off of the stratosphere forecasts and from what I see on both ensembles for the next 2 weeks, they are strengthening/consolidating/cooling the hell out of the thing compared to the current state, and even bringing it nearer to the pole..That doesnt mean you cant get warmings/ridging on the atlantic/pacific side of things though favoring negative height anomalies in our area despite the rising AO...

This blocking episode didnt strike me as a major 30-40+ day memorable episode either, ala 2009, given the state of the upper stratosphere..seemed like a recovery at any time could be on the table. With that said I'm pretty bullish about blocking being a continued major player through jan/feb too, im just trying to time out the relaxation period between now and then...we also need to see better things out of the pacific

[kwt]

This whole talk about extreme cold reminds me of a topic we used to have on Netweather (UK based forum) where many (including myself) said we could never again get the periods of cold we once had say in the 60s-80s.

If you were to look at our average from 88-07 there was a decent increase in the average temps and we struggled to even get one noteable cold spell in many winters, yet alone any outbreak of severe cold (relative to the UK, of course)

Then we had the winter of 09-10 which was decently cold throughout and sorta dispelled the myth somewhat. Some still wondered though whether we could match the real legendary months.

Then December 2010 was got the 2nd coldest December EVER (in over 400 years of records) so it CLEARLY showed that we could still get extreme cold relative to what our average was.

I think its just one of those things. The cycle at the moment has favoured Eurasia big time, I can't really remember any decent west based -ve NAO's other than the odd transient session as it decays away. I'm sure that will once again switch at some point, just like out winters very suddenly did a few years ago.

[am19psu]

Disappointingly, models are converging on a solution that keeps the system in the Plains and Midwest weaker and unphased next week. Despite the strong baroclinic potential, most of the heavy snow appears limited to the Northern Tier and Interior Ontario and Quebec. Severe weather across the Southern Plains and Lower Mississippi Valley also looks unlikely.

[scottmartin49]

"I think its just one of those things. The cycle at the moment has favoured Eurasia big time, I can't really remember any decent west based -ve NAO's other than the odd transient session as it decays away. I'm sure that will once again switch at some point, just like out winters very suddenly did a few years ago."

Agreed- One Robin doesn't make a Spring, nor one Penguin an ice age.

As all of our recent data have trended warmer overall however, this should lead to a change in confidence levels for predictions utilizing current analagous pattern data. A nice short term patch might be to watch the variance between observation and prediction for established teleconnections and extrapolate the data out to a more accurate value for each one. Utilizing the received values to find older analagous pattern data should then lead to higher confidence level predictions, provided that the established relationships between teleconnections remain the same.

Unless (cue ominous music),

......the changing climatics affect existing patterns in new and heretofore unseen ways, but that really does belong in another forum.

[Srain]

The Ensembles are still suggesting a rather unsettled pattern across the Intermountain West into the Plains in the medium range. It is interesting to note that there continues to be hints that EPAC moisture over running the shallow cold air mass at the surface providing a rather damp period along the Southern US/Gulf Coast States with an active pattern spreading across the Northern Plains with Clipper action for the Upper Midwest/Great Lakes Region as well as the Central/Northern Rockies. I suspect that areas further N will begin to build some snow pack that may bode well for the late December time frame with less air mass modification for areas S into the Central/Southern Plains.

[beanskip]

12z runs still show gorgeous -NAO, but with nothing to show for it. NAO actually trending a little more west-based, it seems.

[donsutherland1]

Some morning thoughts...

1. The AO has now fallen below -3. It currently stands at -3.055.

2. The PNA has now had its 33rd consecutive negative reading. The guidance shows the PNA remaining negative through the 16-day forecast period. For those who are interested, the PNA once had 81 consecutive negative readings (February 28, 1967 through May 19, 1967).

3. The NAO remains negative and there is strong agreement among the ensemble members that it will fall below -1.000 around December 20.

It's probably around that time that a colder--not exceptionally cold--pattern could lock into a portion of eastern North America. The evolution toward a cooler pattern should start farther west.

Below are composite temperature anomalies for all December cases where the AO was -3.000 or below categorized by cases where the NAO was above -1.000 and those where it was -1.000 or below with ENSO R3.4 anomalies of 0.0°C to +0.7°C. In total, there were 136 days in December when the AO was -3.000 or below regardless of ENSO. Just 4 (2.9%) of those days saw the NAO above 0.000, therefore I didn't create a map for the tiny subset of days with a positive NAO. Nevertheless, that tiny handful of days saw warmth on both the West and East Coasts with cold in the Plains States and across much of Canada.

Finally, below are again the maps for PNA <0 and PNA of -1.000 or below for AO cases where the AO was -3.000 or below:

[Ottawa Blizzard]

Excellent write up Don.

DT posted an excellent video on youtube last night about the upcoming pattern. Strangely, he comes across as a jerk on social media, being tactless, but is actually fairly calm and devoid of hype in his videos.

[usedtobe]

Don,

Here are the analogs based on today's D+11. It shows cold over the northeast but according to the analogs which are based strictly on the 500h composite, the cold does not last at least for the mid atlantic (DC and Phl parts). 1st the D+11

Then the composite of the 10 analogs which would be centered on the 19th.

Then the composite for 2 days later (the equivalent of Dec 21).

Note how the warmth expands because of all the pac air flooding the country with D+3 being warm

The good news is that the analogs show the warm shot being short lived and two actually give DC snow, one at D+4 and another D+5. The bad news for Dcers is 7 didn't have any snow anytime near the centered mean so this still doesn't look to be a snowy pattern in the southern Mid Atlantic even though the D+11 is the best so far this Dec.

[donsutherland1]

Don,

Here are the analogs based on today's D+11. It shows cold over the northeast but according to the analogs which are based strictly on the 500h composite, the cold does not last at least for the mid atlantic (DC and Phl parts). 1st the D+11

...The good news is that the analogs show the warm shot being short lived and two actually give DC snow, one at D+4 and another D+5. The bad news for Dcers is 7 didn't have any snow anytime near the centered mean so this still doesn't look to be a snowy pattern in the southern Mid Atlantic even though the D+11 is the best so far this Dec.

Wes,

I agree that it still doesn't look like a snowy pattern (New England might be an exception), even as it should be an improvement over the first half of December. If the NAO can gain a more westward orientation, opportunities might develop afterward. Also, some of the AO cases I mentioned with an NAO of -1 or below were ultimately followed by a snowy January.

Finally, it would be nice to see things improve over the Pacific.

[Ginx snewx]

Wes, I used the new 12Z GFS analogs and did the opposite of you and went back 4 days. Interesting result which indicates an Arctic outbreak and possible deep low pressure occur prior to the analog dates.

today's analog

Animated 5H and 1000mb surface