December 2021 Weather Discussion

[tron777]

Long Term guidance is showing a more robust -NAO as we get closer to Christmas. You can see it on the 12Z EPS. Last 4 12Z EPS runs below starting on 12/10 and ending on 12/13. All valid for 12/25. See how the SE ridge starts out as being pretty stout but it keeps getting flattened thanks to the blocking developing, if correct. Hoping it is... we need something to help offset the -PNA that refuses to change. (Why would it, we're in a Nina)

Dec10-13_EPS_trend.thumb.gif.3343bf27425f52a4380315bf31c9b1a0.gif

[Bgoney]

That should help get some arctic air for the Northern plains around Christmas. Right now I'm just hope we can muster seasonal temperatures for the OV

[MVWxObserver]

Looks like a wet one for family celebration of my folks 60th Anniversary in Richmond on Fri evening, but will take liquid variety over frozen for travel.

Currently 41 here in G'ville and progged for around 30 Tues morning.

[Bgoney]

Wet Thursday/Friday with front coming through and stalling with a wave then moving up the boundary. Going with 1"-2.5" for now, with amounts depending on where the front stalls. Dont think flooding issues will be a concern atm.. Saturday starts out mild bit cools down all day and possible light showers first part of day. Beginning of next week starts near normal

[tron777]

1-2" is a great call with locally higher amounts. GFS and Euro both have Sat as being the day when the heaviest rains come in. I'd probably back that up to Fri night into Sat myself. Still will see high chances for rain as discussed on Thurs / Fri also. Get done what you need to get done outside now for sure. I think we're on the same page here Bgoney.

[tpweather]

Good Morning guys. Great forecasts and the only thing I will add is rainfall totals. I agree 1 inch looks good for most locally and yes higher amounts very possible but also a cutoff of the heavier amounts will happen as well. At the moment models are pointing somewhere near Indy and that could lead to very little rainfall somewhere northwest of here. How far south the front goes will determine exact location of the heavier amounts. Alaska going to get hit with several days of snow over the next week to add to the already heavy snow on the ground. Last time a big storm went further northwest and this brought of course a blizzard to many parts but only a quick warm up for them. This time and we will see as patterns are hard to break but after the next 5 days or so it looks like some higher heights will try and move into Alaska and hopefully this can kick the cold air further east into Canada. This happened last time but we were unable to get the transport of cold air to last more than a day or two. Like Bgoney mentioned the northern plains will get cold but just slightly below normal so temps near 10 for highs and lows maybe -10 so cold but nothing unusual in that part of the world. We should be more seasonal next week and yes this at least gives us a shot at some winter weather but way to early to get in much detail at this moment. I agree about the flooding and with 1 inch over a period of time no problem but if you get in the area where the front stalls and get involved with some of the heavier rains then localized flooding is possible. Making up for lost time in terms of rainfall after a calm November.

[tron777]

In the extended range... I am seeing more support for a -EPO -AO and -NAO however the persistent -PNA is going nowhere for a while. This will keep us active with numerous slow moving frontal boundaries but how negative do the EPO, AO and NAO get, will determine how far south the cold air can get. Def looking like a gradient pattern setting up which is very typical of La Nina's. Again... patience is going to be needed for sure. Certainly looking like an MJO Phase 7 pattern to me over the CONUS where we are in the battle ground zone between the warmth and the cold which is usually the case for the OV most winters anyway.

[tpweather]

In the extended range... I am seeing more support for a -EPO -AO and -NAO however the persistent -PNA is going nowhere for a while. This will keep us active with numerous slow moving frontal boundaries but how negative do the EPO, AO and NAO get, will determine how far south the cold air can get. Def looking like a gradient pattern setting up which is very typical of La Nina's. Again... patience is going to be needed for sure. Certainly looking like an MJO Phase 7 pattern to me over the CONUS where we are in the battle ground zone between the warmth and the cold which is usually the case for the OV most winters anyway.

Good Morning Les and I agree but we need to get the mjo to travel into phase 8. Once you get into the second half of December phase 7 becomes much milder and the colder phases are 8,1 and moving into 2. If we see this stall in 7 then mild will continue and if it moves into 8 then cold should head this way. Usually when the QBO is in the easterly winds this allows more blocking which we had earlier in the fall so hopefully this will return in the next few weeks. Plenty of cold to grab hold of so that is not the problem.

[tron777]

In the extended range... I am seeing more support for a -EPO -AO and -NAO however the persistent -PNA is going nowhere for a while. This will keep us active with numerous slow moving frontal boundaries but how negative do the EPO, AO and NAO get, will determine how far south the cold air can get. Def looking like a gradient pattern setting up which is very typical of La Nina's. Again... patience is going to be needed for sure. Certainly looking like an MJO Phase 7 pattern to me over the CONUS where we are in the battle ground zone between the warmth and the cold which is usually the case for the OV most winters anyway.

Good Morning Les and I agree but we need to get the mjo to travel into phase 8. Once you get into the second half of December phase 7 becomes much milder and the colder phases are 8,1 and moving into 2. If we see this stall in 7 then mild will continue and if it moves into 8 then cold should head this way. Usually when the QBO is in the easterly winds this allows more blocking which we had earlier in the fall so hopefully this will return in the next few weeks. Plenty of cold to grab hold of so that is not the problem.

It's nice to see the blocking showing up in the guidance again. Without it, we would have little chance of getting the cold to come this far south. It's the only positive that I see right now with the effects TBD. I don't think we'll see Phase 8 until January as far as the MJO is concerned.

[Bgoney]

Big step in the pattern change process is in progress with the consolidated PAC jet running into a MAGA wall of high pressure at the dateline and for all intensive purposes splitting . Instead of ramming the PNW from the west , the polar jet drops in for colder systems.

gfs_uv250_npac_fh-12-240.gif

[tron777]

I agree that the changes have begun and I'm waiting to see what correction we see in the MJO plots and modeling once the West PAC convection stops screwing with everything as I mentioned the other day. So in short, we will probably see some good model swings for the next week or so. Whether or not that is good or bad news for us remains to be seen.

[Bgoney]

I'd like it to stay stronger in 7 to build momentum it needs to fight the easterlies near the dateline, I'm afraid if it stays on the weak side, the wave could collapse

[tron777]

I'd like it to stay stronger in 7 to build momentum it needs to fight the easterlies near the dateline, I'm afraid if it stays on the weak side, the wave could collapse

Agreed. As of 12/13 on the Aussie site, we're just barely into Phase 7. I'd say about a medium amplitude at this time.

[tpweather]

I'd like it to stay stronger in 7 to build momentum it needs to fight the easterlies near the dateline, I'm afraid if it stays on the weak side, the wave could collapse

I agree 100p/c. Took about 10 days to go through phase 6 which is a good clip. Many times you see the mjo of course stay put for a day or two and then rocket itself through a phase. Lets see if that happens with the current wave. I agree if the wave collapses then this could leave us with a pattern that would not support a great deal of cold making it to far south. Sure it would be late December and even a normal pattern can give us some winter weather but even harder to get than normal lol.

[tron777]

Also guys.... and I am sure you know this... but there is also a lag too. So no matter what phase the MJO is in, there is usually a lag until we see the atmosphere respond. Thus, I am thinking the pattern won't get very favorable until January. We can still see changes for the rest of December but the better pattern and more cold air for us to work with may not come until January.

[tron777]

12Z GFS has 1.48" of rain for CVG with the highest chances Fri night and Sat. Not much change really from the last few runs.

[airwolf76]

my 10 day forecast isnt showing anything. i am thinking from Christmas to New years . i cant see going through all of Nov and Dec with only a half inch of snow but it has happened before.

[tron777]

my 10 day forecast isnt showing anything. i am thinking from Christmas to New years . i cant see going through all of Nov and Dec with only a half inch of snow but it has happened before.

It's happened here more times then I can count.

[westharrisonwx]

Also guys.... and I am sure you know this... but there is also a lag too. So no matter what phase the MJO is in, there is usually a lag until we see the atmosphere respond. Thus, I am thinking the pattern won't get very favorable until January. We can still see changes for the rest of December but the better pattern and more cold air for us to work with may not come until January.

It would just be nice to get some seasonable weather around here in December. I'm not even asking for a December 2010 redux.

Just your typical 40s/20s type of pattern with a few light snow events sprinkled in. It's been pretty hard to come by over the last decade in the tri-state area.

[tron777]

Also guys.... and I am sure you know this... but there is also a lag too. So no matter what phase the MJO is in, there is usually a lag until we see the atmosphere respond. Thus, I am thinking the pattern won't get very favorable until January. We can still see changes for the rest of December but the better pattern and more cold air for us to work with may not come until January.

It would just be nice to get some seasonable weather around here in December. I'm not even asking for a December 2010 redux.

Just your typical 40s/20s type of pattern with a few light snow events sprinkled in. It's been pretty hard to come by over the last decade in the tri-state area.

I do see temps more seasonal starting on Sunday but any snow prospects right now to me are low. I'm not yet seeing the cold being able to pernitrate far enough south as of yet. That -PNA is going to want to continue to dominate the pattern but I do think some blocking in the EPO and NAO domain should help try and reduce the -PNA's effects some. What would really be nice to see, is the -EPO and -NAO ridges to connect to each other over the top. Then the AO would plunge negative and it would also cause a major disruption in the PV. You'd see a split and a good chunk of it be forced south. You'd get a nice arctic outbreak then to go along with the active pattern the -PNA provides. That would be an awesome pattern for many in the country should it occur. I don't see it happening right now but it is something that needs to be watched once the blocking gets established. I think the cold shots are transient for the rest of December but come early January, I think we've got a better chance of it staying for a while. Just some early thoughts. Watching the MJO phase too for help with the longer term. Phase 7 is not going to get the job done. Need it in Phase 8 which I do think has a shot come January.

[tron777]

Waiting to see how the West PAC tropics are impacting the MJO wave progression. That is my concern on the MJO not going where we want it to go. We've got 2 tropical systems in the West PAC currently. TS Rai which looks to become a typhoon and then track thru the Philippines then eventually towards Vietnam. We've also got Tropical Cyclone Ruby that has developed moving SE. It looks to stay a TS and miss New Zealand to the NE. So we'll have to wait and see if this activity weakens the MJO wave or if it delays the progression thru Phase 7 a little bit. This is why I am not very excited for us yet until January. Not saying December snows are completely dead, but IMO the chances are currently on the lower side at this time. All we can do is watch and wait and keep tracking things around the globe like we always do.

[Bgoney]

12Z runs are much the same (pattern)unfortunately . Things may be starting to transition at the 500mb levels , but in its infancy. So we go through more of the same through Christmas, at least ,with wet periods mixed in. A huge chunk of the lower 48 is well above normal and will finish the month as a whole , well above normal . Not the fast start that so many signs seemingly suggested

[tron777]

12Z Euro coming in with 2.31" of rain at CVG. We get some light rain Thurs with the bulk of it coming Fri afternoon thru around midday Saturday give or take.

[tron777]

12Z runs are much the same (pattern)unfortunately . Things may be starting to transition at the 500mb levels , but in its infancy. So we go through more of the same through Christmas, at least ,with wet periods mixed in. A huge chunk of the lower 48 is well above normal and will finish the month as a whole , well above normal . Not the fast start that so many signs seemingly suggested

Exactly... we are on the same page with this for sure. It looks to be a slow transition for sure at this time and that is largely because of the MJO moving slowly as well through its phases. Like I mentioned last week, if we can get to Phase 8 and keep the slow movement going, the colder pattern would likely have some staying power. When is the part that we just don't yet know.

[tron777]

12Z GEFS is an improvement if you look at the North American View on Tropical Tidbits and use 500 MB anomalies. If you look at the entire run, you can see the -EPO and -NAO develop. -NAO looks very nice but the -EPO is a little too far west still. Pretty much an Aleutian Ridge. But you can see the cold is over most of Canada and into the Lakes and NE states. The SE ridge retrogrades towards Texas. This is not a classic wintry pattern for us but it is an improvement over what is going on right now. This would be a gradient pattern for the OV with all modes of precip possible depending on where the baroclinic boundary sets up and how far south the cold air can get with each passing wave of low pressure. Again not ideal but not a shut out pattern either IMO.