December Medium/Long Range Discussion

[MN Transplant]

19 minutes ago, SnowenOutThere said:

Wonder if 18z gfs can do something. It’s a more progressive look out west so I doubt we get enough cold air push  

I like the massive day 9 trough in CA that was completely absent from 12z.  Really makes me believe in these solutions.

[CAPE]

This is a pretty decent H5 look for ejecting a modest wave from the SW towards the MA with cold air pressing southward. Biggest negative is its a bit early in the season.

[Stormchaserchuck1]

8 minutes ago, CAPE said:

This is a pretty decent H5 look for ejecting a modest wave from the SW towards the MA with cold air pressing southward. Biggest negative is its a bit early in the season.

We've gotten snow when there is +300dm over the Aleutian islands and -250dm just south of Greenland on Dec 5.. like never. I look at that map and say the opposite is what we want. Look how there's even 4 cold waves around the N. Pacific RNA (established). 

[CAPE]

1 minute ago, Stormchaserchuck1 said:

We've gotten snow when there is +300dm over the Aleutian islands and -250dm just south of Greenland on Dec 5.. like never

Like I said, a bit too early. That said, both the Euro and GFS are hinting at a little something.

[Stormchaserchuck1]

2 minutes ago, CAPE said:

Like I said, a bit too early. That said, both the Euro and GFS are hinting at a little something.

I think that's because there's a -EPO a few days before. It takes the US pattern a few days to change after the Pacific changes, but that pattern is going warm. I guess the N. Pacific ridge heading a little polar could keep it cool enough near the Great Lakes. The longer that storm takes to get here, the more likely it is for rain. We want it early while there's still a -EPO in place pushing down a strong High pressure. 

[mitchnick]

32 minutes ago, Stormchaserchuck1 said:

I think that's because there's a -EPO a few days before. It takes the US pattern a few days to change after the Pacific changes, but that pattern is going warm. I guess the N. Pacific ridge heading a little polar could keep it cool enough near the Great Lakes. The longer that storm takes to get here, the more likely it is for rain. We want it early while there's still a -EPO in place pushing down a strong High pressure. 

Reality will be nothing like that map, so no need to fret. 

[Jebman]

9 hours ago, Daniel Boone said:

All we need is an Arctic Front for it to hookup with and run to the Benchmark 

That happens I am flyin back to DCA just to see that once in a million year hyper blizzard!

[Jebman]

6 hours ago, MillvilleWx said:

It feels good to be back 

I'm ready to be hurt again!! 

Don't forget Lucy...

[mitchnick]

18z Eps AI sorely lacking warm temps over the period once past Thanksgiving Eve.

https://www.pivotalweather.com/model.php?m=eps_aifsens&p=sfct_anom-p105090-imp&fh=loop&dpdt=&mc=

[Eskimo Joe]

19 minutes ago, donsutherland1 said:

Continuing the illustration showing how I'm thinking about December 1-10 and December 11-25. Here's the framework I am using.

The CPC 8-14 day forecast is a good illustration of how I think things will evolve during the December 1-10 period:

The risks of a faster turn to a warmer pattern in much of the eastern U.S. (not the Great Lakes, northern New England, eastern Canada) have increased with growing ensemble consensus for a predominantly AO+ pattern.

Composite WPO-/EPO-/AO+/PNA- 500 mb Height Anomalies:

ECMWF Weekly 500 mb Forecast for December 8-15:

Composite WPO-/EPO-/AO+/PNA- Temperature Anomalies:

ECMWF Weekly 500 mb 2m Temperature Anomaly Forecast for December 8-15:

Right now, the guidance is still in a low-skill timeframe. What's noteworthy is the change that has taken place in the past few days. For example, this was the ECMWF weekly forecast for the December 18-15 period from three days earlier:

If the guidance holds or strengthens the forecast AO+ beyond December 10, the warmer outcome could become the baseline for that period with perhaps a mid-month shift to the milder pattern. The 18z GEFS is also suggesting that the EPO could go positive. If so, that would further increase the risks for a turn toward milder conditions. 

In sum, December 1-10 still remains on track. One should see cold move into the Upper Midwest and Great Lakes and then spread eastward. The Southeast will remain warm due to the resilient SE Ridge. Uncertainty beyond December 10 has increased and the risk of a shift toward a warmer pattern has increased. The guidance will need to be watched closely to see if its turn toward an AO+ persists.