December Forecast Discussion

[andyhb]

Yawn... severe weather in December climo wise usually doesn't deliver.

To add on to/simplify what I said, climo actually favors severe weather in the SE during winter months, and if the models are on to something, there certainly won't a be a winter-like air mass in place here by next weekend.

[Disc]

To add on to/simplify what I said, climo actually favors severe weather in the SE during winter months, and if the models are on to something, there certainly won't a be a winter-like air mass in place here by next weekend.

It sure would be nice to have some severe weather to track. GFS has some fairly warm temps into the 60-70's and some nice DPs in the 60 range across the SE. I suppose this is what you're looking at:

[andyhb]

It sure would be nice to have some severe weather to track. GFS has some fairly warm temps into the 60-70's and some nice DPs in the 60 range across the SE. I suppose this is what you're looking at:

Yeah, that's the ticket, the 12z Euro is quite similar to this and some of the 12z/18z GFS ensemble members really go off.

[LithiaWx]

To add on to/simplify what I said, climo actually favors severe weather in the SE during winter months, and if the models are on to something, there certainly won't a be a winter-like air mass in place here by next weekend.

Its hard to get strong supercells this time of year anywhere in the US. December is probably one of the least active months for severe wether in the southeast. If we can pop some good storms so be it but the time of year still is a big negative for the noteworthy supercells. It can happen it just usually doesn't.

[Disc]

Its hard to get strong supercells this time of year anywhere in the US. December is probably one of the least active months for severe wether in the southeast. If we can pop some good storms so be it but the time of year still is a big negative for the noteworthy supercells. It can happen it just usually doesn't.

Where did you get supercells from? We were just noting that the models were hinting at some sort of severe risk, but probably nothing really noteworthy.

[andyhb]

Its hard to get strong supercells this time of year anywhere in the US. December is probably one of the least active months for severe wether in the southeast. If we can pop some good storms so be it but the time of year still is a big negative for the noteworthy supercells. It can happen it just usually doesn't.

What?

June to September (discounting tropical systems) are almost always the least active months for severe in the SE.

[Jon]

Alright, no more 300+ hr GFS storm reports.

I'm glad someone with some authority has finally noticed.

Where did you get supercells from? We were just noting that the models were hinting at some sort of severe risk, but probably nothing really noteworthy.

Yep. I'm sure every betting man would agree with that. Even during severe wx season we had trouble getting a good setup going even with pretty good support on the models. Once it got here, atmosphere got more and more stable and nothing popped off...don't expect it to in December that's for sure.

[andyhb]

Yep. I'm sure every betting man would agree with that. Even during severe wx season we had trouble getting a good setup going even with pretty good support on the models. Once it got here, atmosphere got more and more stable and nothing popped off...don't expect it to in December that's for sure.

That's mainly due to the sub-tropical ridge being in a rather unfavorable position for the better part of the season, with the added problem of the strong central US omega block preventing systems getting east of the Plains. This time, that doesn't look to be a problem, at least from the position currently across the model spectrum.

[NCsandhills]

so y'all are saying there might be a severe weather event in a few days in the SE? what part of the SE? sorry, i'm not good yet at reading those maps. i'll look at them every single day and try to make sense of them but i cant. halfway through ahrens essentials to meteorology and another library book entitled climate and weather, but so far nothing on reading GFS NAM or euro models. kinda annoying.

[andyhb]

Too far out to be certain of that yet.

[Jon]

so y'all are saying there might be a severe weather event in a few days in the SE? what part of the SE? sorry, i'm not good yet at reading those maps. i'll look at them every single day and try to make sense of them but i cant. halfway through ahrens essentials to meteorology and another library book entitled climate and weather, but so far nothing on reading GFS NAM or euro models. kinda annoying.

The possibility is being advertised in the models, yes. I will let some of the severe weather experts (in my opinion) answer your question (maybe Disc or andyhb)...But for now, this is a good resource for learning also the website http://www.theweatherprediction.com is an excellent website for model charts specifically. For instance, the above map was the wind at the 500mb level, here is the page from that website discussing why 500mb maps are of interest in severe weather http://www.theweatherprediction.com/charts/500/basics/ Just try to learn as much as you can by reading the posts from users, might have to sit out a winter season and severe weather season to really learn enough to understand! All of us non-meteorology majors all go through this Enjoy!

[andyhb]

Generally when you look for a severe threat, you look at the Eastern/Southeastern portion of the 500 mb trough (the warm sector, ahead of the cold front, when you have winds throughout different altitudes in the troposphere from, say, south near the surface and more southwesterly to westerly at 500 mb, overlapping the warm sector, otherwise known as vertical shear, you have the potential for severe thunderstorms, and in some cases, tornadoes).

You also want moisture in the low levels to help facilitate low cloud bases, and dryer air in the mid levels to help increase instability to create a more volatile environment, such as when the cap (a layer of warm air in the low/mid levels) is broken, thunderstorms will develop explosively (ala 4/27/11 last year).

[Jon]

There's that arctic air we've been missing coming into the 0z Euro...Also taking a look at the 0z model suite, there's some consensus on a +PNA developing, -AO and -NAO...dare I say it?

[Aubighitter]

Glad there is finally some cold looking to come our way.

[WilkesboroDude]

By hour 192 GFS begins to lay down snow cover from Texas to Michigan.

[mackerel_sky]

That's not good for most of the SE that want cold and snow!

By hour 192 GFS begins to lay down snow cover from Texas to Michigan.

[packbacker]

That's not good for most of the SE that want cold and snow!

I think that may be the pattern this year, with ENSO going negative today we will be battling a neutral/negative ENSO and thus that pesky SE rigde. I know it's only Dec 3rd but I feel like we are going to be above normal this entire winter. I still think we will get lucky and have a chance or two this wintering we can get some extreme blocking , but there won't be any extended periods of cold...all due to the pacific.

[burgertime]

I think that may be the pattern this year, with ENSO going negative today we will be battling a neutral/negative ENSO and thus that pesky SE rigde. I know it's only Dec 3rd but I feel like we are going to be above normal this entire winter. I still think we will get lucky and have a chance or two this wintering we can get some extreme blocking , but there won't be any extended periods of cold...all due to the pacific.

While the Euro does hold the cold at the SE doorstep for it's run last night, I think it's slowly moving towards the GFS long range with major cold coming to the US as many other mets have said in the latter part of Dec. We shall see what the pacific does, but for now it might be a little extremist to feel that way this early. Given last year though it's understandable.

[HKY_WX]

The GFS ensembles show something important by day 10. Something I mentioned in my winter forecast. THey both start to show warming at 500mb's over the Davis Straight area and eventually a block pinches off in this area and sets up. This is also showing now on the euro Ensembles around the same time. What this does is dislodges the PV over Alaska and sends it SE into central Canada and eventually the Plains. The euroENS has < -30 850's over the Dakotas by Day 14. So if we see run-run consistency on this, there is a good chance we'll see a pattern change around the 20th.

[packbacker]

While the Euro does hold the cold at the SE doorstep for it's run last night, I think it's slowly moving towards the GFS long range with major cold coming to the US as many other mets have said in the latter part of Dec. We shall see what the pacific does, but for now it might be a little extremist to feel that way this early. Given last year though it's understandable.

I know I probably came off as super negative but really all I am saying is Dec-Feb will average warmer than normal, assuming we get blocking we should see a few periods of cold but overall with everything we are seeing and everything we know we I think we will be warmer than normal.

[SnowNiner]

The GFS ensembles show something important by day 10. Something I mentioned in my winter forecast. THey both start to show warming at 500mb's over the Davis Straight area and eventually a block pinches off in this area and sets up. This is also showing now on the euro Ensembles around the same time. What this does is dislodges the PV over Alaska and sends it SE into central Canada and eventually the Plains. The euroENS has < -30 850's over the Dakotas by Day 14. So if we see run-run consistency on this, there is a good chance we'll see a pattern change around the 20th.

Weren't we in this exact same scenerio 2 weeks ago thinking the cold was coming per the GFS? The EURO wasn't on board and of course it didn't happen. So now we're thinking it's going to happen because the GFS is calling for it again? Fool me once shame on you. Fool me twice, shame on me. I'm with others on the pattern change; show me a consistent EURO showing the same thing and I'll start to believe.

I'm still very positive about Jan and Feb but in the back of my mind the whole pacific discussion is starting to worry me.

[burgertime]

Weren't we in this exact same scenerio 2 weeks ago thinking the cold was coming per the GFS? The EURO wasn't on board and of course it didn't happen. So now we're thinking it's going to happen because the GFS is calling for it again? Fool me once shame on you. Fool me twice, shame on me. I'm with others on the pattern change; show me a consistent EURO showing the same thing and I'll start to believe.

I'm still very positive about Jan and Feb but in the back of my mind the whole pacific discussion is starting to worry me.

Two weeks ago I believe GFS OP runs were the only ones really hinting at big cold. Big diff when you have ENS runs on board of both the majors as well. Also he didn't say it would def. happen, just that basically confidence is growing. He also pointed out that more run to run consistency is needed. If you have reasons why you disagree with him then by all means spell it out for us.

[packbacker]

Weren't we in this exact same scenerio 2 weeks ago thinking the cold was coming per the GFS? The EURO wasn't on board and of course it didn't happen. So now we're thinking it's going to happen because the GFS is calling for it again? Fool me once shame on you. Fool me twice, shame on me. I'm with others on the pattern change; show me a consistent EURO showing the same thing and I'll start to believe.

I'm still very positive about Jan and Feb but in the back of my mind the whole pacific discussion is starting to worry me.

He did day it's showing on the Euro ENS. Hopefully it pans out, that could do the trick with a not so great PAC.

[SnowNiner]

Two weeks ago I believe GFS OP runs were the only ones really hinting at big cold. Big diff when you have ENS runs on board of both the majors as well. Also he didn't say it would def. happen, just that basically confidence is growing. He also pointed out that more run to run consistency is needed. If you have reasons why you disagree with him then by all means spell it out for us.

Sorry, no I'm just asking the question. I didn't mean to single out HKY. It just seemed like "we" (all of us here) were at the same place a couple of weeks ago.

[Brick Tamland]

I saw over the weekend that Raleigh has hit at least 70 degrees every December since 2007. So, even though things look bad now, we shouldn't give up hope for the rest of winter. I just looked at Matthew East's blog for today, and he said the pattern change looks like it is coming later this month. I am still worried about the pacific trough, but if the recent past has taught us anything is that things can change quickly. I am sure back in December 2010 when it hit 70 that no one thought we would have snow on Christmas night.

[Bevo]

I think that may be the pattern this year, with ENSO going negative today we will be battling a neutral/negative ENSO and thus that pesky SE rigde. I know it's only Dec 3rd but I feel like we are going to be above normal this entire winter. I still think we will get lucky and have a chance or two this wintering we can get some extreme blocking , but there won't be any extended periods of cold...all due to the pacific.

At least you qualified that statement as an opinion and not fact. I can live with that. I disagree with it, but mine too is an opinion. I haven't been above normal since April - I see no reason to believe things will pull a dramatic 180 here.

The second part on the other hand...

While the Euro does hold the cold at the SE doorstep for it's run last night, I think it's slowly moving towards the GFS long range with major cold coming to the US as many other mets have said in the latter part of Dec. We shall see what the pacific does, but for now it might be a little extremist to feel that way this early. Given last year though it's understandable.

This is why I disagree with packbacker at this point. I'm not saying he's wrong - it's too early to know either way. And in my opinion, the Euro garners too much praise outside of split flow situations. My confidence does get a boost whenever the king agrees somewhat with the other models, but I'll never hang my hat on the Euro hook alone.

[Bevo]

I saw over the weekend that Raleigh has hit at least 70 degrees every December since 2007. So, even though things look bad now, we shouldn't give up hope for the rest of winter. I just looked at Matthew East's blog for today, and he said the pattern change looks like it is coming later this month. I am still worried about the pacific trough, but if the recent past has taught us anything is that things can change quickly. I am sure back in December 2010 when it hit 70 that no one thought we would have snow on Christmas Eve.

I think you're actually pointing to the bigger picture here (as strange as that felt to type). Two weeks ago, and even to this day, so many SE residents seemed to be expecting a cold December, and are anxious that it probably won't be (at least for the entire month). But it generally never is. As of right now, the concern over the Pacific - in my opinion - is like driving for the first couple of weeks after an auto accident. You still remember the experience and become jumpy behind the wheel. But the reality is that the Pacific monster is not positioned in the same beastly mode it was last year (yes, I understand that it could take a turn for the worse - but right now it isn't). We also had no support from the AO/NAO so everything was sent speeding along the northern route. That now looks to be different as well. It probably won't be a record setting winter in the SE. But I certainly believe we will actually experience a winter season this year.

[FoothillsNC]

I began to talk about the coming change around November 27 but was using a blend of the models and ensembles out at day 10 and into day 15, so that puts us about on target for the change to begin. Remember that there's a week or even 2 of lag time to feel the effects of change, so all along that would put us around mid December to really start to notice the changes . You can see the models are still steadfast with it, so are ensembles. You can see operational ECMWF on days 8, 9 and 10, showing the Gulf of Alaska trough being replaced with more ridging...and on the eastern side, around Greenland it shows a building (slowly) of the heights there, so in essence this will force the jet to sag south with time, maybe not in one lump sum, but in step down process.

We've had a relatively coolish Fall in many parts of eastern Plains to Ohio Valley and part of the Southeast, so the current warm up is expected and was shown nicely, but now things are about to begin changing again.

The current slightly pos. NAO will begin going down, but this won't be a sudden drop and I don't think we're heading straight to the Arctic yet. If you look at the 850 temp anomalies, they're not all that strongly negative through days 15, but just keep on slowly sagging more and more into the negative territory as time goes on through mid month, thanks to the models keeping some PNA + ridging and some -NAO. In fact on Allans site you can see the Ensembles from GFS really show that Greenland blocking works slowly west to cover central and eastern Canada later on and tha'ts probably when it turns more cold down here (and stormy) Of course not many folks would trust GFS beyond the 240 but so far it lines up closely with the progression seen on ECMWF and the other Globals now that go out for a month, so I think the odds are the blocking does work around Greenland but at first it's going to be a slow process, and won't be all that cold down here even in mid December, relative to normals.

If the GFS is right beyond 240, same thing for CFSv2 and the globals like China and Korean, then the North American sector will have a pretty stout +PNA pattern with Greenland or some kind of Canada blocking up north, which will translate to a supressed storm track and colder air forced south. So far I don't think that will be super cold though like 2010 or 2011 yet, but it's worth watching later on. You wouldn't want a really cold pattern , otherwise high pressure rules. Instead a flow like I described above would feature a storm track from the Gulf of Alaska down into the West Coast then across the Plains and to the East, and one of those could take a far south track nearer the Gulf Coast. Also, overrunning could occur if any front can lay down far enough south following an amplified storm, and those amplified storms can't be seen too far out. Overall I like how things are looking esp. for the TN Valley to MidAtlantic section at first (probably first chance at snow/ice).

[Cold Rain]

I saw over the weekend that Raleigh has hit at least 70 degrees every December since 2007. So, even though things look bad now, we shouldn't give up hope for the rest of winter. I just looked at Matthew East's blog for today, and he said the pattern change looks like it is coming later this month. I am still worried about the pacific trough, but if the recent past has taught us anything is that things can change quickly. I am sure back in December 2010 when it hit 70 that no one thought we would have snow on Christmas night.

Good post. I agree. By the way, it's a little early for a New Year's resolution on posting reform isn't it?

[Cold Rain]

^^ Good info, Robert. Great to see you posting and certainly appreciate the thoughts. As I have said, I'm certainly content to slowly work colder through the month and the signs are ther that this is indeed likely now. It's good to see it being corroborated by many different sources.