December and a Hint of January Pattern Discussion

[mitchnick]

I hope things become clearer and that the high still is there tomorrow.    If so, the article will be fairly easy to write.

and I'll add, "and that the computers start picking up on a Great Lakes low of any sort that isn't there right now"

last week, it was sneaky energy coming down the back side of a fast moving u/l that formed a new u/l closed low over the northern GL; that was not there when that system was first ID'ed by the models

[aldie 22]

Hard to go against the regulars here and obviously their expectations are the correct way to go. I'll echo the concerns about warming above 850mb. We'll need good mid level frontogen to keep things cool over the area. As we get closer, models will hone-in on that and begin focusing QPF on these areas.

You on board for ice or do you think that might be a stretch? I feel like snow expectations are where they should be for this group...I prefer sleet though if ice is the choice over snow...freezing rain is boring

[usedtobe]

Hard to go against the regulars here and obviously their expectations are the correct way to go. I'll echo the concerns about warming above 850mb. We'll need good mid level frontogen to keep things cool over the area. As we get closer, models will hone-in on that and begin focusing QPF on these areas.

For snow lovers,  the temps around 800mb are going to be warmest in the column to they (we) will need to be looking closely at the soundings.  I wish Weatherbell or someone would come up with a graphic of the warmest temp in the 850 to 700 mb layer on a plane view.  That would be awesome and big help in cases like this one.

[DCAlexandria]

Thanks Wes. Any small chance we can stay all snow in a system like this? 30% maybe?

[mitchnick]

For snow lovers,  the temps around 800mb are going to be warmest in the column to they (we) will need to be looking closely at the soundings.  I wish Weatherbell or someone would come up with a graphic of the warmest temp in the 850 to 700 mb layer on a plane view.  That would be awesome and big help in cases like this one.

you can get text and skewts on the Ready site

http://www.ready.noaa.gov/READYcmetus.php

[usedtobe]

you can get text and skewts on the Ready site

http://www.ready.noaa.gov/READYcmetus.php

You can also get them from twister which is what I usually use.  The warmest layer on the progs at the start of the event was -1.8 at 800mb if I remember correctly (based on the 06Z GFS)

[usedtobe]

Thanks Wes. Any small chance we can stay all snow in a system like this? 30% maybe?

 

I think the chances of that are pretty small but....we're almost a week away from the event so I won't say it's impossible just unlikely.

[mitchnick]

You can also get them from twister which is what I usually use.  The warmest layer on the progs at the start of the event was -1.8 at 800mb if I remember correctly (based on the 06Z GFS)

I found the point and click was not that reliable as it seems to give you the same info from the closest airport even when you move the location around some]

click on a few different locations close to each other and you'll see the numbers are all the same; Ready isn't like that if you put in actual coordinates vs. the airport choices on their drop down list

[Yeoman]

DT was mentioning snow to ice even along the lower maryland eastern shore and I'm not sure what he's seeing. I'm new to living here in Salisbury and I know it can snow and ice but this storm looks like mainly rain here? Or am I missing something? It's easier to see the CAD for DC and all but we are much closer to the ocean here and honestly I'm not sure 100% sure of the CAD impacts here in Salisbury.

 

Why are you asking us? Aren't you the Met?

[usedtobe]

DT was mentioning snow to ice even along the lower maryland eastern shore and I'm not sure what he's seeing. I'm new to living here in Salisbury and I know it can snow and ice but this storm looks like mainly rain here? Or am I missing something? It's easier to see the CAD for DC and all but we are much closer to the ocean here and honestly I'm not sure 100% sure of the CAD impacts here in Salisbury.

I looked a little closer and think most oft the precip would be rain after maybe a quick shot of freezing rain or sleet so I think you probably are not missing anything at least based on the 06Z GFS. 

[WxMan1]

I haven't looked at the new runs for next Sun-Mon, but yesterday while at work I saw the broad, strong, deep SW flow aloft that as you all noted would no doubt lead to an elevated warm layer. It's definitely got that mix to freezing rain look, considering the strength of the low level high and CAD wedge, something we haven't seen in a long time, but certainly would make since given (1) the availability of arctic air to our north which continues to be re-enforced, and (2) the lack of blocking over the northern Atlantic which would allow for a more confluent, frontogenetic look at mid levels and thus deeper cold (sub 0C) air.

As Wes and others have noted, model soundings are the way to go when attempting to diagnose where exactly that elevated warm layer will be. However, this far out, I like to look at critical 850-700 mb thicknesses, since I can view it over an area rather than at a point (as with a sounding). For the most part any 850-700 mb thicknesses below 1540m is good enough for snow, i.e. approximate to the layer average temperature below 0C. 850-700 mb thicknesses bove 1550 m would favor rain or freezing rain depending on the surface temp. In between 1540 and 1550 m is where it gets messy, though typically in such events with mid level SW flow aloft extending well to our north (i.e. no confluence or frontogenesis over the northeast), we don't stay there very long. We may start out at snow/sleet, but then switch to fzra or rain at some point -- because we just don't have the frontogenesis above 850mb to our north to keep that layer cold.

Either way, I'd be excited just to have an event. An event that looks like this one used to happen with more regularity in the '80s and '90s around here...just not lately. Again, it has everything to do with the fact that, for a change, we actually have bona-fide arctic air to work with not too far north of us.

[snow.]

we just need a thump..even if it is .20" QPF..Just to get on the board and get some slop on the ground

[BTRWx]

I haven't looked at the new runs for next Sun-Mon, but yesterday while at work I saw the broad, strong, deep SW flow aloft that as you all noted would no doubt lead to an elevated warm layer. It's definitely got that mix to freezing rain look, considering the strength of the low level high and CAD wedge, something we haven't seen in a long time, but certainly would make since given (1) the availability of arctic air to our north which continues to be re-enforced, and (2) the lack of blocking over the northern Atlantic which would allow for a more confluent, frontogenetic look at mid levels and thus deeper cold (sub 0C) air.

As Wes and others have noted, model soundings are the way to go when attempting to diagnose where exactly that elevated warm layer will be. However, this far out, I like to look at critical 850-700 mb thicknesses, since I can view it over an area rather than at a point (as with a sounding). For the most part any 850-700 mb thicknesses below 1540m is good enough for snow, i.e. approximate to the layer average temperature below 0C. 850-700 mb thicknesses bove 1550 m would favor rain or freezing rain depending on the surface temp. In between 1540 and 1550 m is where it gets messy, though typically in such events with mid level SW flow aloft extending well to our north (i.e. no confluence or frontogenesis over the northeast), we don't stay there very long. We may start out at snow/sleet, but then switch to fzra or rain at some point -- because we just don't have the frontogenesis above 850mb to our north to keep that layer cold.

Either way, I'd be excited just to have an event. An event that looks like this one used to happen with more regularity in the '80s and '90s around here...just not lately. Again, it has everything to do with the fact that, for a change, we actually have bona-fide arctic air to work with not too far north of us.

great explanation!

[Bob Chill]

we just need a thump..even if it is .20" QPF..Just to get on the board and get some slop on the ground

 

I think we're all on board there. Heck, I don't think anyone has raised the bar any higher than that yet and that's impressive considering the pent up weenieism. 

 

The globals are quite focused and steady with the overall setup. I hope that continues and my hunch is that it will. This isn't a modeling nightmare irt to precip and general setup. There are plenty of encouraging signs that the airmass will support a period of snow changing to mess. Stating the obvious but how long of a snow period vs mess period is pretty much where we are now. I can live with that. Heck, I love that. IMO- we all have better than a 50% chance at accum snow. 

[snow.]

I think we're all on board there. Heck, I don't think anyone has raised the bar any higher than that yet and that's impressive considering the pent up weenieism. 

 

The globals are quite focused and steady with the overall setup. I hope that continues and my hunch is that it will. This isn't a modeling nightmare irt to precip and general setup. There are plenty of encouraging signs that the airmass will support a period of snow changing to mess. Stating the obvious but how long of a snow period vs mess period is pretty much where we are now. I can live with that. Heck, I love that. IMO- we all have better than a 50% chance at accum snow. 

 

I think on 12/2 we are still rational.  Usually the despondency and anger doesn't full surface until after Christmas

 

Obligatory content - the ensemble mean is not as bullish as the op but certainly exhibits a trackable event

[TSSN+]

I think we're all on board there. Heck, I don't think anyone has raised the bar any higher than that yet and that's impressive considering the pent up weenieism. 

 

The globals are quite focused and steady with the overall setup. I hope that continues and my hunch is that it will. This isn't a modeling nightmare irt to precip and general setup. There are plenty of encouraging signs that the airmass will support a period of snow changing to mess. Stating the obvious but how long of a snow period vs mess period is pretty much where we are now. I can live with that. Heck, I love that. IMO- we all have better than a 50% chance at accum snow. 

 

After the past couple of winters, we'll take what we can get. I agree it is looking decent for some wintry precipitation from this event. Just depends how much. Hope the ridging stays weaker and gives us just enough precipitation and cold air for this to work and not for the ridge to build too much and send a low into the lakes and flood the area with warm air too fast. 

[Bob Chill]

Looking beyond the sun-mon event, there definitely appears to be a shift towards a new type of pattern. Our favorable -epo is looking to lose its grip and the ridging is being modeled by both the euro ens and gefs to retro westward towards the dateline. The byproduct over the mid term is not all that great in our parts because lower heights build in the goa and the flow flattens across the conus. Generally mild and boring for a time for the east half of the country if it verifies. Hardly unexpected. 

 

This is the 6z gefs (the file is mislabeled as 12z). Both the 12z euro ens and gefs have similar looks as well:

 

 

One of the things I've been keeping my eye on is the ridging building poleward from scandanavia. This can put the squeeze on at the pole and pin the pv in canada. This possibility is causing a great deal of spread in the ensembles with the state of the AO:

 

 

The models are just now catching on to this shift but it's becoming consistent. We'll see if the look continue to show up and not keep getting pushed back to the end of every run. 

 

What does this mean for us? Not sure. Hopefully Wes can shed some light.

 

My thought are this:

 

Looks like we battle the -pna for a time and cold delivery is shut off but I doubt very much that is a long term pattern. I think there is some potential here to shift back to an amplified pattern with a -ao/-nao towards the end of the month. Not sure we get a favorable pna but transient ridging is possible. I'm just hoping for some blocking to set up and there are signs we are moving towards that. IF it happens it will take some time resulting in a not so fun period for winter wx. I hope variability keeps up. A -pna/-ao/-nao isn't a bad setup for mixed events. Fine with me. 

[wxmeddler]

As I said last night... it's hard to get a solid ice storm around here. Usually it's an overrunning and transition event or just plain too warm somewhere above our heads. That being said.. I will gladly take a overrunning event with 2" on the front end this time of year.

[Fozz]

I think we're all on board there. Heck, I don't think anyone has raised the bar any higher than that yet and that's impressive considering the pent up weenieism. 

 

The globals are quite focused and steady with the overall setup. I hope that continues and my hunch is that it will. This isn't a modeling nightmare irt to precip and general setup. There are plenty of encouraging signs that the airmass will support a period of snow changing to mess. Stating the obvious but how long of a snow period vs mess period is pretty much where we are now. I can live with that. Heck, I love that. IMO- we all have better than a 50% chance at accum snow. 

 

It's pretty incredible to confidently say that for a storm that's almost a week away.

[Bob Chill]

It's pretty incredible to confidently say that for a storm that's almost a week away.

 

I'm a weenie so I get a magic pass. 

 

Honestly, it's how I feel. If it was a timing / phasing thing I would never say such a thing. It's more of placement of a boundary and hp and models have been unusually consistent so far. That means something. And 51% is still coin flip odds . 

[snow.]

Looking beyond the sun-mon event, there definitely appears to be a shift towards a new type of pattern. Our favorable -epo is looking to lose its grip and the ridging is being modeled by both the euro ens and gefs to retro westward towards the dateline. The byproduct over the mid term is not all that great in our parts because lower heights build in the goa and the flow flattens across the conus. Generally mild and boring for a time for the east half of the country if it verifies. Hardly unexpected. 

 

This is the 6z gefs (the file is mislabeled as 12z). Both the 12z euro ens and gefs have similar looks as well:

 

gefs12z336.JPG

 

One of the things I've been keeping my eye on is the ridging building poleward from scandanavia. This can put the squeeze on at the pole and pin the pv in canada. This possibility is causing a great deal of spread in the ensembles with the state of the AO:

 

aoens.JPG

 

The models are just now catching on to this shift but it's becoming consistent. We'll see if the look continue to show up and not keep getting pushed back to the end of every run. 

 

What does this mean for us? Not sure. Hopefully Wes can shed some light.

 

My thought are this:

 

Looks like we battle the -pna for a time and cold delivery is shut off but I doubt very much that is a long term pattern. I think there is some potential here to shift back to an amplified pattern with a -ao/-nao towards the end of the month. Not sure we get a favorable pna but transient ridging is possible. I'm just hoping for some blocking to set up and there are signs we are moving towards that. IF it happens it will take some time resulting in a not so fun period for winter wx. I hope variability keeps up. A -pna/-ao/-nao isn't a bad setup for mixed events. Fine with me. 

good post....We are probably screwed for a while if/when the EPO relaxes....a lot of cold air locked up in Canada and the west, and a sharp gradient pattern from N to S...probably a good SWFE pattern...I'm still very very cautiously optimistic about a cold/snowy regime from just after Christmas through about 1/10

[yoda]

Nice CAD signature at 138... now we await the precip

[usedtobe]

Looking beyond the sun-mon event, there definitely appears to be a shift towards a new type of pattern. Our favorable -epo is looking to lose its grip and the ridging is being modeled by both the euro ens and gefs to retro westward towards the dateline. The byproduct over the mid term is not all that great in our parts because lower heights build in the goa and the flow flattens across the conus. Generally mild and boring for a time for the east half of the country if it verifies. Hardly unexpected. 

 

This is the 6z gefs (the file is mislabeled as 12z). Both the 12z euro ens and gefs have similar looks as well:

 

gefs12z336.JPG

 

One of the things I've been keeping my eye on is the ridging building poleward from scandanavia. This can put the squeeze on at the pole and pin the pv in canada. This possibility is causing a great deal of spread in the ensembles with the state of the AO:

 

aoens.JPG

 

The models are just now catching on to this shift but it's becoming consistent. We'll see if the look continue to show up and not keep getting pushed back to the end of every run. 

 

What does this mean for us? Not sure. Hopefully Wes can shed some light.

 

My thought are this:

 

Looks like we battle the -pna for a time and cold delivery is shut off but I doubt very much that is a long term pattern. I think there is some potential here to shift back to an amplified pattern with a -ao/-nao towards the end of the month. Not sure we get a favorable pna but transient ridging is possible. I'm just hoping for some blocking to set up and there are signs we are moving towards that. IF it happens it will take some time resulting in a not so fun period for winter wx. I hope variability keeps up. A -pna/-ao/-nao isn't a bad setup for mixed events. Fine with me. 

That isn't a cold pattern for us.  There is too much flow across the country plus most lows would probably track to our north.  I'd prefer to see high heights over Baffin bay.  I don't like a big super strong low north of hudson bay but your map is only a snap shot and might be different tomorrow.  Usually a cold AK teleconnects to a warm east.  The big positive anomaly near the Aluetians often is precursor of a pretty wet period somewhere along the west coast.  If that map verifies, Don's switch to a warmer than normal Dec for our area would be a pretty good bet.  I did look at the extended Euro and it has the biggest uncertainty in temps that I've seen in the short time I've had access to it so I don't think we can say anything definitive beyond it will get cold after our warm spell this week and we might see winter weather in some mixed up form. 

[TSSN+]

Nice CAD signature at 138... now we await the precip

 

Hr 147 is looking snowy. Looks much improved over 6Z. CAD really locking in. 

[snow.]

12z GFS came in a bit warmer but very wet...nice hit for the western burbs

[snow.]

Nice CAD signature at 138... now we await the precip

 

 

Hr 147 is looking snowy. Looks much improved over 6Z. CAD really locking in. 

 

 

It is ridiculously wet...but changes over sooner...

 

I'll let you guys see the panels 1st instead of doing more play by play..

[Bob Chill]

I agree Wes. It's not a good pattern as is. I'm just grinding on where we could go from there. The 0z gefs looked better in the east late in the run but that would be cherry picking. If you run the loop the ridging in AK is migrating back eastward. All way out there speculation but I seem to have a problem with doing that. lol

[wxmeddler]

Nice. CAD holds.

[yoda]

It is ridiculously wet...but changes over sooner...

 

I'll let you guys see the panels 1st instead of doing more play by play..

 

True, but looks like anything before 153 is snow... 153 is borderline snow/sleet

[TSSN+]

It is ridiculously wet...but changes over sooner...

 

I'll let you guys see the panels 1st instead of doing more play by play..

 

Yes for the city changes quicker. NW burbs locked into cold through 156. Heavy front end thump for the cities. Sure you guys won't mind that.