December 2020 Medium/Long Term Pattern Discussion.

[John1122]

Unfortunately by h54 it runs due north instead of more northeast like it did at 12z. 

[John1122]

Through 60 it's weaker, more west and warmer vs 12z. 

[John1122]

Marginal differences towards the 72 timeframe vs 84 at 12z.  Low is in western New York, 992 vs 990 at 12z. Overall snow showers across the eastern 2/3rds of the state. The low moves slower this run and the change to frozen happens later across our area. The low does a loop in New York this run instead of moving into SW Ontario like it did at 12z. This keeps the upslope more towards SW Virginia a little longer than 12z did. 

Looks like it's going to be Plateau and mountains getting 1+ inch accumulations with less in most lower elevations. Overall it backed off a little in both areas vs 12z. 

[John1122]

What an odd run of the Euro. 138 there's a southern system running along the Gulf coast. The primary goes from the Texas coast to the Florida coast then seems to jump from Panama City to Arkansas where it sits for 18 hours pounding Oklahoma. 

[Carvers Gap]

6z GFS is now a Miller A.  As John notes, the Euro operational is not budging.  

[fountainguy97]

Hope this look holds! Of course it’s the LONG range NAM and loves to over amp.

 

[Carvers Gap]

The 12z WRF-ARW is southeast of its 0z run.  Not a ton of difference in track, but if the storm consolidates on either side of the Apps(not as confident as yesterday that happens west of the Apps), this storm may be stronger.  Right now, it may well be missing the phase until later - just guessing as I have not seen the vort maps.  Just seems like there is less of a mechanism to pull it Northwest which is why some modeling is sliding it further eastward before turning it.   Just giving the ARW one last look, it is now basically a Miller A.

[Carvers Gap]

There are actually two lows present at 51z on the 3K NAM for TT (national view).  Either energy handoff or a lee side low develops.  Not sure the slp placement changes the solution(outside chance it might) much, but really watching this for future reference.  I have thought the Euro was over-amped...just wanting to see if that hypothesis is correct for this circumstance.  

[Holston_River_Rambler]

12z RGEM looks like it will come in a bit east as of around 40 hours into the run. Looks like more N stream interaction sooner on this run compared to 6z. 

[BhamParker]

RGEM looks pretty juicy. 

[Holston_River_Rambler]

 

It is really bullish on the n stream upper low as it swings through 

[Carvers Gap]

Seems like the differences go back to when the storm comes north from Louisiana.  Recent solutions get the storm further East before turning.  The 12z RGEM pivots the bottom of the total precip shield eastward and the precip shield in Indiana and Illinois westward.  Was a bit later with the turn but sharper turn north once it turned.  As Holston notes, once the northern stream energy grabs it, it goes almost due northward.  It is worth noting that the RGEM shifted eastward in regards to when it arrived in the TN Valley.  May well be that the trend is a later phase.

[Holston_River_Rambler]

There is moisture over E TN up to 700 mb and even 500 mb over parts of eastern KY, so the upper low backing the flow could provide lift for it:

700 mb relative humidity 

 

[Carvers Gap]

Some decent differences in the RGEM in SLP placement and strengthening immediately after hour 40.  

[Holston_River_Rambler]

Just now, Carvers Gap said:

Some decent differences in the RGEM in SLP placement and strengthening immediately after hour 40.  

It gets really close to jumping it up the eastern slope of the Apps. 

The surface front has made it to around 100 miles (maybe) off the Gulf Coast, it will be interesting to see exactly where the SLP forms on that front

[Carvers Gap]

12z GFS is rolling now....

 

[Carvers Gap]

12z GFS is way eastward with the slp....phase is just later.  There are two lobes of precip with the southern system - one over northern MS and the other sliding along the GOM.  When the lobe over norther MS is weaker, the primary low/energy shifts to the GOM.  I am guessing that is due to a later phase.  Pretty much can see that on all modeling.  When the lobe over MS is stronger, system and slp are west which indicates an earlier phase.  Finesse stuff.

[Holston_River_Rambler]

Not looking at any other aspect of what the GFS is showing for now, that is some upslope heaven at 60 hours:

 

a fetch at 850 right off of lakes Superior and Michigan 

[Carvers Gap]

The 12z GFS is just weaker by a few mb.  One can go to TT and toggle back about 5 runs from that point.  You can see the system slide eastward every so slightly.  Could it be a more progressive bias from the GFS?  Maybe.   That weaker solution is likely due to a later phase.  This could still trend into a stronger system east of the Apps or it could just run the Apps.  Lots of moving parts and interesting to watch.

[Carvers Gap]

1 minute ago, Holston_River_Rambler said:

Not looking at any other aspect of what the GFS is showing for now, that is some upslope heaven at 60 hours:

 

a fetch at 850 right off of lakes Superior and Michigan 

Pretty much a great angle in terms of winds.

[Carvers Gap]

Going to be a really good test of modeling with this system.  Getting the phase right seems to be the hurdle.

[Carvers Gap]

15 minutes ago, Holston_River_Rambler said:

It gets really close to jumping it up the eastern slope of the Apps. 

The surface front has made it to around 100 miles (maybe) off the Gulf Coast, it will be interesting to see exactly where the SLP forms on that front

Which model has that modeled the best?

[Carvers Gap]

12z CMC is now rolling.

[Carvers Gap]

Can already tell the 12z CMC has initialed slightly quicker with the northern low in Alberta when compared to 0z.

Edit:  but the Holston's front is a hair further south.

[Carvers Gap]

CMC at 24 is further south but looks like it has the ability to come north quite quickly from the Louisiana/TX border.  

[Holston_River_Rambler]

6 minutes ago, Carvers Gap said:

hich model has that modeled the best?

Good question, but I'm not sure how I could figure that out. I think it would have to be a mesoscale model. 

I'm looking at the RGEM and NAM and WRF on TT, but having trouble seeing it in enough detail on the simulated satellite. 

Here are the gifs with a fresh satellite. See what you think:

3km NAM:

 

RGEM:

 

WRF:

 

Maybe there is a better parameter to figure out where the front is now? I'm not sure those cloud depictions are all that helpful since they seem pretty course.

Current satellite (sandwich depiction with visible and IR)

 

 

 

[BhamParker]

GFS goes pretty wild with the snowfall compared to the latest nam. It’s been fairly bullish with snowfall amounts in the mountains area. 

[Carvers Gap]

At 42 the 12z CMC is south and east of its 0z run and slight weaker.  Last comment on that model so as not to gum up the thread...trend south and east with it as well. 

[Holston_River_Rambler]

Here is where it looks like the front is on the latest SPC mesoscale analysis's windbarbs: 

[Holston_River_Rambler]

Maybe I answered my own question lol.
Interesting to look at 10m wind on the same three mesoscale models:

Nam 3k:

 

WRF:

 

RGEM:

 

It does seem like there is a correlation between how far south the front makes it and how eastward the SLP moves. The WRF-ARW gets it a little further south and has the most easterly of tracks:

 

It also gives a little more umphh to a surface low off the GA coast which tugs on the Gulf low a bit. Could be a question of how the convection impacts the SLP formation?