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Jan Medium/Long Range Disco: Winter is coming


stormtracker
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31 minutes ago, Ji said:

Cmc looks like it may deliver

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I liked the 12z CMC a little better, but both the 12z and 0z CMC are pretty decent... much more threatening than the GFS. I don't love the trof along the west coast at the end of the run, however.

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Anybody know the history of this kind of west meandering cut-off low in late December? Feels extremely rare, but I don’t really know.

I suppose we’ve had tons of big low pressure systems delivering warm temps in dc and blizzards in the Midwest around Christmas time. Remember Santabomb? But I can’t remember a cutoff low that drifted.

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2 hours ago, eduggs said:

I think you've hit on why it has a poor track record in terms of assessing storm threats in the LR. There are a couple problems:

1. "Longwave pattern" is a very general concept. It's continental-scale - meaning correlations with regional weather are weak - particularly in a predictive sense. Yes significant snow is well correlated to characteristic "patterns," but since there are far more of these "patterns" than significant snowstorms, we know that these features are necessary but not sufficient for big snowfall.

2. Significant uncertainty exists in ensemble modeling forecasts beyond 10 days. Even if aspects of a 500mb height field are well predicted over parts of the globe, other areas are poorly predicted. It's usually not possible to know which regions will be well modeled. This keeps overall confidence in LR pattern recognition relatively low.

3. The sub-continental scale details only resolvable inside 10 days largely determine whether a global scale longwave pattern can be productive for regional wintry precipitation or not. This would be true even if you knew the precise longwave pattern in advance.

Add these up and the argument is that using low confidence LR anomaly charts to try to identify general "patterns" is not very effective for LR regional storm threat identification. At the very same time you are able to start determining if a nearing "pattern" is a head-fake or not you are just starting to pick out the finer scale mid-and upper level details. Some of the same models are used for both objectives (pattern ID and details), and they both start to clarify at the far end of the mid-range simultaneously. That's why I believe multi-model ensemble QPF and 850mb temperature charts inside 10 days are the better starting point for threat identification. Followed by looping the raw 500mb heights with vorticity of both the ensembles and operational models inside about 8 days.

It's funny how people are so quick to come up with excuses for why a sure-fire pattern change advertised on the models failed to materialize. It's usually something random like a bridging ridge, west or east-based something, one of the indices... AO, EPA, NAO offset ENSO. What those excuses are really a reflection of is that modeled LR "patterns" are not causally connected to future outcomes. One does not cause the other. They are both simultaneous reflections of the state of the atmosphere-ocean system at a given time.

You aren’t saying anything we don’t already know. A bad pattern might yield a 5% chance of snow in a given week. A good one maybe 30%.  A good long wave pattern doesn’t guarantee snow it just increases the probabilities. 
 

Everything you said about threat identification is also great, except it only works out to about day 7-10.  If we are looking at stuff day 12 or 15 or 20 that won’t work. The best we can do it identify the long wave pattern then wait until inside 10 days to identify a specific threat. 

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Both the 0z GEFS and EPS continue to signal potential storms for the 4th, 7th, and the 10-11th timeframe. The first 2 look like lows that track underneath and off the coast of VA/NC. The potential for the 10th looks more complicated, with a possible primary tracking to our west. For now I think the 7th looks the most promising for some sort of a moderate frozen/mixed event across the region given the h5 look, track, and cold air availability. 

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The 10-11th potential looks to involve a significant piece of NS energy, so our area may be on the milder side with the focus for frozen further NW. Still a long way out so plenty can change. Behind that the central and eastern US may see more impressive cold. Advertised h5 look on the GEFS is favorable with indications of a ridge building over AK, and a west based -NAO. Hints of another wave at the end of the run but that's way out there.

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10 minutes ago, CAPE said:

6z GEFS is even more impressive for the 7th wrt the surface low strength and frozen potential. Looks especially good along/west of the Fall line. 

I noticed that as well. Decent interaction with NS/part of the TPV with decent timing location. There have certainly been hints of this but this run has been best with this feature thus far.

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16 minutes ago, Ralph Wiggum said:

I noticed that as well. Decent interaction with NS/part of the TPV with decent timing location. There have certainly been hints of this but this run has been best with this feature thus far.

Yeah the timing and degree of interaction with any NS energy is going to be critical for determining the exact outcome. That was absent last run.

We just cant know yet lol.

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8&11 day GEFS analogs look pretty good for winter wx. No big storms in the top part of list but majority have winter wx events within a few days either way. Nearly all have precipitation so rain is certainly part of the analog set. Top ones look pretty good though and worth mentioning as we're now at the d8-11  lead time for what still appears to be whiter pastures. 

These are a day old. I'll check l8r and if see if anything changes. I dont expect much new information as guidance has been semi locked in in the extended. 

Eta: Jan 1964 analog was actually a decent storm. Bwi looks like they got 6". Can't tell at IAD but it snowed. DC snowed too but more mixing there. 

 

 

image.png.ee6ceca57efea0d6e01528094c3bb275.pngimage.png.7945d3118b24f578c67e21dae10fd19a.png

 

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54 minutes ago, CAPE said:

6z GEFS is even more impressive for the 7th wrt the surface low strength and frozen potential. Looks especially good along/west of the Fall line. 

not bad at all. 50/50-ish feature from the departing 1/3-4 LP, nice southern stream vort, PV in Canada, brief ridge over the southwest, and blocking over the top. looks more like the EPS and GEPS at this point, but there are differences in how they handle the TPV, which is expected at this range. either way, this looks like our first legit threat

673712717_gfs-ensemble-all-avg-namer-z500_anom-4542400(1).thumb.png.a414301951818ddaf3f084b4f3b5c41b.png

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1 hour ago, CAPE said:

6z GEFS is even more impressive for the 7th wrt the surface low strength and frozen potential. Looks especially good along/west of the Fall line. 

24 hr precip maps really juicing up in the south east. Hopefully we see some OP runs that show the potential also.

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1 hour ago, Bob Chill said:

8&11 day GEFS analogs look pretty good for winter wx. No big storms in the top part of list but majority have winter wx events within a few days either way. Nearly all have precipitation so rain is certainly part of the analog set. Top ones look pretty good though and worth mentioning as we're now at the d8-11  lead time for what still appears to be whiter pastures. 

These are a day old. I'll check l8r and if see if anything changes. I dont expect much new information as guidance has been semi locked in in the extended. 

Eta: Jan 1964 analog was actually a decent storm. Bwi looks like they got 6". Can't tell at IAD but it snowed. DC snowed too but more mixing there. 

 

 

image.png.ee6ceca57efea0d6e01528094c3bb275.pngimage.png.7945d3118b24f578c67e21dae10fd19a.png

 

IAD got 10” with that Jan 1964 storm

Mood in this thread seems a little better now. I was afraid to open it this morning!

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13 hours ago, RIC_WX said:

Being conscious of my tone, we should probably be very cautious when referencing analogs from what was objectively the coldest decade of the entire 20th century and attempting to apply them to modern times.  

Comparing modern times to the 60's can be risky.    My detailed records reveal a high of 65 for Christmas day of 1964 and 63 for Christmas day of 1965.  January of 1966 began with a cloudy, showery Jan 1 with a high of 56.

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Guys stop panicking CFS just had its best run of the season! Seriously if anyone needs their digital snowfall/cold I'd highly recommend checking this run out, instead of crapping up the thread with negativity *cough* Ji. Its got a snowstorm with temps in the single digits and qdf of .7 then lows in the negative teens across the area.

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Guys stop panicking CFS just had its best run of the season! Seriously if anyone needs their digital snowfall/cold I'd highly recommend checking this run out, instead of crapping up the thread with negativity *cough* Ji. Its got a snowstorm with temps in the single digits and qdf of .7 then lows in the negative teens across the area.
500h_anom.nh.png
sfct-met.nh.png

Are you actually Mark Margavage?
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