December 2012 Pattern Analysis

[earthlight]

There is definitely a storm signal around 10 days out. The better performing Euro ensembles

maintain enough of a ridge just off the East Coast to allow the low to cut very close to our

area with warm air spoiling the party.

The individual GFS ensemble members, in specific, are all over the place with this potential event which is to be expected at this range. But I think that retrogression being signaled in the high latitudes, and moving towards the NAO region by Days 7 and 10, increases confidence in a winter weather event occurring by the end of the month. There will be plenty of opportunities with an active pattern out west and plenty of shortwaves pushing east and eventually being forced underneath the blocking over Central Canada.

[Chris L]

Pretty strong blocking signal coming in Western Greenland, and extending into Hudson Bay, with troughs in the West and the East on the GFS ENS, nearly like an mini omega block?

[Isotherm]

Tom,

We can get a large storm with a negative to neutral PNA, but the pattern will probably breakdown right after. February 1969 which the PNA was negative, we still got quite a big snowstorm (The Lindsay storm) that month.

Chris -- I agree. I'm becoming more convinced w/ each passing day that we see the now east based NAO retrograde to Greenland, and then the Davis Straits, where it may sit and rot for a couple weeks before breaking down sometime week 4 in the second week January. At that point we may have a pattern relaxation.

However, the next 5-10 days will be very interesting as the global features shift around and the MJO potentially comes alive. We definitely need to monitor MJO progression into phase 1 and whether that can improve the NPAC pattern for us, maybe knocking the EPO back negative.

[Dsnowx53]

Definitely has the look of a stormy, but not cold pattern for us down the road.

[earthlight]

Chris -- I agree. I'm becoming more convinced w/ each passing day that we see the now east based NAO retrograde to Greenland, and then the Davis Straits, where it may sit and rot for a couple weeks before breaking down sometime week 4 in the second week January. At that point we may have a pattern relaxation.

However, the next 5-10 days will be very interesting as the global features shift around and the MJO potentially comes alive. We definitely need to monitor MJO progression into phase 1 and whether that can improve the NPAC pattern for us, maybe knocking the EPO back negative.

There's going to be a period -- and my confidence is increasing that it will be around Dec 20 and the week or two beyond that -- where the set up could potentially be ripe for a widespread winter weather event. These retrograding NAO ridges, when they get into Western Greenland the Davis Straight, have been historically friendly to us -- and although we have a -PNA the pacific is active and the blocking being in that position is exactly what we need.

A few concerns I have, though, going forward...include the low level cold air source, which could be a bit moderated especially with the core of it dumping down from Alaska into the Western US and then moving east....the MJO strength and forecasts which have been pretty horrid from ensembles so far this Autumn...and the potential for this block to never materialize and end up farther east based.

One thing I am not concerned about is this entire thing becoming a fallacy like it did last winter. It's just a matter of how it will materialize..and whether or not it will favor us getting snow.

[earthlight]

The other thing, and I touched on this above a bit, is the lack of cold...even despite having this west based NAO showing up on the models the big time cold air is just not there and I assume that's what NZucker was alluding to the other day. That said, this pattern as advertised can still deliver snow -- it just might be a little harder near the coast when you have a very modified airmass.

[Isotherm]

There's going to be a period -- and my confidence is increasing that it will be around Dec 20 and the week or two beyond that -- where the set up could potentially be ripe for a widespread winter weather event. These retrograding NAO ridges, when they get into Western Greenland the Davis Straight, have been historically friendly to us -- and although we have a -PNA the pacific is active and the blocking being in that position is exactly what we need.

A few concerns I have, though, going forward...include the low level cold air source, which could be a bit moderated especially with the core of it dumping down from Alaska into the Western US and then moving east....the MJO strength and forecasts which have been pretty horrid from ensembles so far this Autumn...and the potential for this block to never materialize and end up farther east based.

One thing I am not concerned about is this entire thing becoming a fallacy like it did last winter. It's just a matter of how it will materialize..and whether or not it will favor us getting snow.

Good points. The chance of last year happening is virtually nil given the AO has already tanked and we've got a vastly different nern hem pattern. To be honest the low level cold concerns me more than the NAO not working out. If the MJO dies and the NPAC is absolutely horrid, the cold air source may get cut-off in the nern plains/rockies, even with a big block to our north. This is partially why we could have a stormy pattern but not a very cold one, at least initially. If the EPO region can improve, but that likely won't happen (if it does) until very late dec, that's when the bitter cold can make it into our area. But I think most would be more than fine if the stormy pattern verifies w/ waves cutting underneath the west based block feature.

[earthlight]

Good points. The chance of last year happening is virtually nil given the AO has already tanked and we've got a vastly different nern hem pattern. To be honest the low level cold concerns me more than the NAO not working out. If the MJO dies and the NPAC is absolutely horrid, the cold air source may get cut-off in the nern plains/rockies, even with a big block to our north. This is partially why we could have a stormy pattern but not a very cold one, at least initially. If the EPO region can improve, but that likely won't happen (if it does) until very late dec, that's when the bitter cold can make it into our area. But I think most would be more than fine if the stormy pattern verifies w/ waves cutting underneath the west based block feature.

I would think that even if the forecast models are correct with the MJO, and we get a decent wave...we could have more trouble after the first week of January as well once it rounds the bend into Phases 2-3/etc. Although the MJO has had a tendency over the last 4-6 months to stay in 8-1/COD...if it starts venturing out of those areas the Dec/Jan composites offer the potential for big time above normal temperature spurts once again.

[SnoSki14]

Feb 2010 wasn't particularly cold if you're speaking arctic air but just enough of a cold airmass was available for us to benefit. I remember many of those snowstorms we were hovering near the freezing mark.

[Isotherm]

I would think that even if the forecast models are correct with the MJO, and we get a decent wave...we could have more trouble after the first week of January as well once it rounds the bend into Phases 2-3/etc. Although the MJO has had a tendency over the last 4-6 months to stay in 8-1/COD...if it starts venturing out of those areas the Dec/Jan composites offer the potential for big time above normal temperature spurts once again.

Yeah I'm not gonna lie - the MJO is something I've got very low confidence in forecasting, especially w/ how it's shown to have such low predictability this winter so far. If guidance from back in mid/late November was correct, we should have been going through phases 1-2 right now. So I'm not sure whether it will progress into p2-3+, stay in p1-2, or head back into the COD thereafter. Pattern persistence seems to work the best so I would agree that phases 8-2 seem to be favored this year which is another differentiating factor from last winter. Remember it was like pulling teeth to get the MJO near the favorable octants, and it spent most of the winter rounding through phases 3-6, i.e.. the death spiral phases.

[Isotherm]

Feb 2010 wasn't particularly cold if you're speaking arctic air but just enough of a cold airmass was available for us to benefit. I remember many of those snowstorms we were hovering near the freezing mark.

Yeah all three of those events I was barely 32F, in fact I think one event I spent most of the storm at 32.5-33F. Very little major cold due to the enormous blocking and warmth in the Arctic regions.

However 09-10 had a gorgeous Pacific pattern thanks to the PDO/PNA/Strong ENSO which this winter will lack.

[MJO812]

0z Nam is still so close . We just need it a little more west. Eastern LI and the Cape get hit with the Tuesday storm.

[nzucker]

The other thing, and I touched on this above a bit, is the lack of cold...even despite having this west based NAO showing up on the models the big time cold air is just not there and I assume that's what NZucker was alluding to the other day. That said, this pattern as advertised can still deliver snow -- it just might be a little harder near the coast when you have a very modified airmass.

A west-based NAO doesn't usually create big time cold unless we're talking about a mega-block like December 2010, which we're not in this case. We need help from the Pacific to bring arctic cold into the NYC metro region, for example the large-scale MJO wave that pumped up the PNA in January 2011 which helped bottom out temperatures around 1/24 just prior to the big Nor'easter...I reached 1F here with several nights dipping into the single digits.

I think the pattern coming will feature a significant storm, but we can't lock in any snow by any means. The 12/20 period has been signaled for a while, but I don't like how the models are retreating the PV to Asia, which leaves Canada on the milder side, sort of what we saw in Feb 2010 but with less extreme blocking.

[Isotherm]

A west-based NAO doesn't usually create big time cold unless we're talking about a mega-block like December 2010, which we're not in this case. We need help from the Pacific to bring arctic cold into the NYC metro region, for example the large-scale MJO wave that pumped up the PNA in January 2011 which helped bottom out temperatures around 1/24 just prior to the big Nor'easter...I reached 1F here with several nights dipping into the single digits.

I think the pattern coming will feature a significant storm, but we can't lock in any snow by any means. The 12/20 period has been signaled for a while, but I don't like how the models are retreating the PV to Asia, which leaves Canada on the milder side, sort of what we saw in Feb 2010 but with less extreme blocking.

There's a reason why virtually all of our major arctic outbreaks featured -EPO ridging into AK/NW Canada, as that feature sets-up the cross-polar flow from Siberia into Canada. With low heights over AK/NW Canada, there's not much of a mechanism to force that bitter air SE into the Lakes/northeast. The more west based and stronger we can get the -NAO blocking, the more likely it is we'll "grab" some of that NW Canadian air and send it SE.

We see a lot of modelling w/ the weird "split" look in temp anomalies over the US due to the pattern -- cold in the Northern plains, normal in the Lakes/Mid-west, and a bit below normal in the Northeast US thanks to the -NAO. In other words, there's no connection b/t the airmasses of W Canada and the Northeast as depicted in this upcoming pattern. This means we'll probably be reliant on storm generated cold air or marginal/stale airmasses for snowfall. Of course modelling could change over time and become more bullish w/ Western ridging if the MJO phase 1 does its dirty work. Would be nice to get some relaxation of the massive low height anomalies in the West.

[earthlight]

A west-based NAO doesn't usually create big time cold unless we're talking about a mega-block like December 2010, which we're not in this case. We need help from the Pacific to bring arctic cold into the NYC metro region, for example the large-scale MJO wave that pumped up the PNA in January 2011 which helped bottom out temperatures around 1/24 just prior to the big Nor'easter...I reached 1F here with several nights dipping into the single digits.

I think the pattern coming will feature a significant storm, but we can't lock in any snow by any means. The 12/20 period has been signaled for a while, but I don't like how the models are retreating the PV to Asia, which leaves Canada on the milder side, sort of what we saw in Feb 2010 but with less extreme blocking.

Correct, and the excitement from myself and others regarding the NAO block was never meant to signify the presence of arctic cold. That block is so ultra important, though, because it really changes the entire pattern to one that is more favorable than average for snow even with a not-so-hot Pacific. I also don't think we can say with certainty that these storms won't have cold air involved with them, because although the majority of it will be dumped from Alaska into Western Canada and then the Western US...as the storms propagate northeast the airmass modification won't be incredible to the point where we're constantly dealing with stale antecedent airmasses.

I tend to like the 12/18-12/20 storm as a threat especially away from the coast, but I think the period after that...falling coincidentally around Christmas similar to 2010...could offer potential for something bigger especially given the MJO response. There are some signals for a potential PNA spike and the forecast ensemble guidance has been consistent with showing a nicely positioned - albeit transient - 50/50 low from the storm system a few days earlier.

[earthlight]

0z Nam is still so close . We just need it a little more west. Eastern LI and the Cape get hit with the Tuesday storm.

Check out how much less amplified it has trended since 12z. The flow is way too fast and progressive and the storm has almost no chance to develop before it is kicked east rapidly. Throw this one in the trash bin.

http://www.meteo.psu.edu/~fxg1/WRF_12z/f78.gif

http://www.meteo.psu.edu/~fxg1/WRF_0z/f66.gif

[MJO812]

Check out how much less amplified it has trended since 12z. The flow is way too fast and progressive and the storm has almost no chance to develop before it is kicked east rapidly. Throw this one in the trash bin.

http://www.meteo.psu...WRF_12z/f78.gif

http://www.meteo.psu.../WRF_0z/f66.gif

Agree. I was just pointing the Nam out.

[Isotherm]

Here's what I'm talking about regarding the potential "lack of connection" from the airmass in the Plains. The cold over the Northeast US is entirely -NAO generated in the period 18th-24th. Here's the CFSv2 for that time frame:

Then by the end of the month it has the connection occuring, with most of the CONUS cold:

Peaks early January:

And here comes the pattern breakdown by mid Jan:

[Dsnowx53]

Great discussion in here, guys. The Dec 18-20 period definitely needs to be watched, but as I said before, I like the period just after that better. I think the blocking will be more west based at that point, and the PAC has a better chance of being shuffled more favorably with the MJO pulse.

[MJO812]

December 18th threat is shown on the GFS. OTS on this run.

http://mag.ncep.noaa.gov/NCOMAGWEB/appcontroller?prevPage=Model&MainPage=indexℑ=&page=Param&cycle=12%2F10%2F2012+00UTC&rname=SFC-LAYER+PARMS&pname=850_temp_mslp_precip&pdesc=&model=GFS&area=NAMER&cat=MODEL+GUIDANCE&fcast=216&areaDesc=North+America+-+US+Canada+and+northern+Mexico&prevArea=NAMER&currKey=model&returnToModel=&imageSize=M

[CooL]

GFS looks great for the 18th threat. Blocking is much more impressive early on which causes the first wave to go south of us reinforcing the cold and becoming a 50/50 low setting up the next wave

[earthlight]

Talk about walking a thin line on the GFS for the 12/18 threat...there is a big ridge already building into the Central US while the storm is occurring and the cold air is fleeting.

[Weathergun]

The 0z GEFS looks similar to the 0z GFS at 204hr. I think fast flow/progressive ridge out West along with the developing west based -NAO and 50/50 low, supports a later phase and SE track. But there are still many days to watch:

[earthlight]

Nice weenie solution at the end of the GEFS run with the block retrograding to Western Canada and hooking up with an Aleutian ridge, as well as a PNA spike and a cross polar flow...would be quite a Christmas.

[CooL]

Euro has an outrageous solution. However the west based blocking signal is getting stronger

[MJO812]

6z GFS is even further south with the next week's storm

[MJO812]

6z GEFS and the op agree on the storm for early next week. Way different than the Euro.

http://raleighwx.americanwx.com/models/gfsensemble/06zgfsensemblep12156.gif

[bluewave]

The models agree on the PV maxing out over the Arctic in about the next 5-8 days.

This could mean that the heights will rebound about 10-15 days later near Alaska

allowing colder weather to enter the U.S. than has been the case so far this month.

Any more seasonable to colder weather would arrive late this month or early in

January should this type of pattern change actually occur. We would need a

west based -NAO to link up with height rises near Alaska and bring the PNA

back closer to neutral of even positive to have a shot at normal or even

below normal temperatures here should a pattern change work out in

2 or more weeks.

[PB GFI]

This pattern should start to get interesting after the 20 th. Individual storms aside. I thought the PAC would start to reshuffle around this time frame. The change shouldnt be one of being dropped into siberia rather I think the change is gradual. But ask yourself if the first 20 days of garbage is followed by a nice xmas eve snowstorm what will you remember.

This pattern in week 4 shouldnt mimic europe or asia but it doesnt have too

[tombo82685]

6z GEFS and the op agree on the storm for early next week. Way different than the Euro.

http://raleighwx.ame...emblep12156.gif

On a situation like this you have to watch the low level cold air. Even though that may look like snow for you guys, the bl temps are pretty warm like the late november storm.