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December Forecast Discussion


Wow

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Was just looking at the Euro Ens. The block looks excellent at hr120-144, before it weakens a bit. Some of that is natural I suppose with it being an ensemble, but that looks quite good if it holds longer. It's interesting that the best performing model output in the world at this amount of lead time (Euro Ens) looks the best.

Here's the overnight HPC Disco:

THE BULK OF GUIDANCE FROM MOST MODELS AND ENSEMBLES OFFER A

REASONABLY SIMILAR LARGER SCALE PATTERN EVOLUTION FOR THE NEXT

WEEK. THIS FLOW IS HIGHLIGHTED ALOFT THIS WEEKEND BY AN AMPLIFIED

TROUGH JUST OFF/ALONG THE WEST COAST...AN AMPLIFIED RIDGE OVER THE

W-CENTRAL US...AND ANOTHER AMPLIFIED TROUGH/CLOSED LOW CENTERED

OVER THE NORTHEAST. THE LEAD SYSTEM AND ASSOCIATED DEEP SURFACE

LOW/SYSTEM AND ASSOCIATED SENSIBLE WINTER WEATHER FOCUS SHOULD

PROVE SLOW TO EXIT INTO THE CANADIAN MARITIMES WORKING INTO

BLOCKED FLOW. THIS WILL LEAVE PLENTY OF ROOM FOR COOLING BACK

ACROSS THE ERN AND CENTRAL US DOWN THROUGH THE SRN TIER STATES

WELL IN ITS WAKE...INCLUDING PROTRACTED LAKE EFFECT SNOW

POTENTIAL. UPSTREAM...ERN PACIFIC TROUGH ENERGIES AND ASSOCIATED

UNSETTLED WEATHER/COOLING/PCPN ARE EXPECTED TO WORK INLAND ACROSS

THE WRN US BY SUN/MON BEFORE EMERGING INTO THE CENTRAL US NEXT TUE

WHERE SRN PLAINS CYCLOGENESIS/GULF INFLOW/DEVELOPING PCPN COULD

OCCUR TUCKED UNDERNEATH A MID-HIGHER LATITUDE DOME OF COLDER HIGH

PRESSURE.

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Here's my take on the situation...and if what I'm about to say is considered banter then my apologies...but I think it needs to be stated.

First off...I think we're all guilty of being the prisioner of the moment and taking a Day 6-7-8 forecast verbatim. I totally respect those who don't feel confident in the prospects of winter weather but I also think people like Brandon (HKY) and Burger, people who have seen these events evolve over the years, they have spotted the key ingredients that are needed for a winter storm...

1. 50/50 low which serves to block things

2. STJ interaction and its known biases in the models

To me, the pieces are there...and have to be respected. The next 2-3 days are going to be huge. For one reason, our first storm that is supposed to create the 50/50 will have already developed. And second, we're getting in that window where the models magically evaporate things.

If the signs of CAD and blocking are still in the models come Friday, then I would be ready to prepare for some sort of a winter weather event in parts of North Carolina.

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Here's my take on the situation...and if what I'm about to say is considered banter then my apologies...but I think it needs to be stated.

First off...I think we're all guilty of being the prisioner of the moment and taking a Day 6-7-8 forecast verbatim. I totally respect those who don't feel confident in the prospects of winter weather but I also think people like Brandon (HKY) and Burger others with more knowledge, people who have seen these events evolve over the years, they have spotted the key ingredients that are needed for a winter storm...

1. 50/50 low which serves to block things

2. STJ interaction and its known biases in the models

To me, the pieces are there...and have to be respected. The next 2-3 days are going to be huge. For one reason, our first storm that is supposed to create the 50/50 will have already developed. And second, we're getting in that window where the models magically evaporate things.

If the signs of CAD and blocking are still in the models come Friday, then I would be ready to prepare for some sort of a winter weather event in parts of North Carolina.

Fixed that for you! Seriously I'm only reporting what the models look like to me, I'm about as far from an expert as you can get. One thing that really perked me up is that the Euro just has such a defined CAD signal on the surface map...you don't see it that often. We shall see what the 12z has to say though.

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Where does it initiate the surface low burger? At 180 there is a low south of the TX border, but it looks like it wants to initiate a surface low in southern OK

looks to me like the main low is there then once it gets to around TN it breaks away and you get a low around northern GA...then a transfer to the coast.

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Well needless to say I was wrong about it being more suppressed this thing is a monster out in the plains and heading NE...CAD showing up on the GFS 1028 high sitting over NY @216

It was more suppressed through around 180'ish, the high pressure in central Canada was further south and than it everything lifts north. Sure does look like this is going to cut not matter what. Good news, is the LR forecasts are showing good signs for January....

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Nice to see something "brewing" this weekend. 10 pages since Friday afternoon.

Is there any chance this system evolves to Miller A scenerio? I would have to agree that the proposed Miller B's rarely work out for CLT and surrounding. Never say never but my enthusiam for anything frozen would greatly diminish if we're counting on something transfering to the coast. By that time either cold is not here yet or when it is, the moisture is gone. Man I know that sounds weenieish, but just my recollection from past experience....

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The GFS digs the southern shortwave much further south as it comes ashore, and out to 180 looks like a NC snowstorm sure enough. After 180, it doesn't dig the ULL enough, and it also has the surface low to far north according to fundamental meteorology and the position of the ULL to the surface. The surface low should be to the southeast of the ULL when it cuts off. Bottom line: this was a huge step towards us getting a major winter storm in the southeast!

See folks this is why you always wait for a pro to chime in. Thanks. With the surface low so far north is that why you get the split and another low spinning off?

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I wouldn't dwell on anything past GFS truncation at this point. I even have a hard time believing anything beyond days 2-3 actually. With that said, I wouldn't be surprised to see this be a heck of a snowstorm for the plains area into the midwest. I would think the trailer to this storm could actually be the one we should watch around the end of the year. JMO

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The GFS loses so much resolution after 192 hours it's hard to tell what it's doing. At 192 it should have continued to dig southward it appears, and then after that the model loses it's resolution so even the upper level pattern isn't modeled well enough to figure out much. Of course this system will begin to lift northward at some point, but right now it's difficult to pinpoint when that will be. That will probably still be the case days from now...but the trends appear to be for a stronger shortwave and more digging, which is what we want to see here in the southeast along with the PV holding in as long as possible in the northeast.

I do agree with the truncation problem, however, the Euro pulls this trick as well so I can't completely rule it out. While there is quite a bit of ridging going on in Canada, there's also not a lot a low heights either, so whatever Rex block does pop up, the height field across all of NA is quite fluid. If the 50/50 continues to trend stronger and hold in place longer, then without a doubt the southern ULL will dig farther south and trek east and will hold in a +/neutral tilt farther east due to closer proximity of the confluence zone.

On simple analyis: You'll notice how the GFS before truncation (prior to 204 hrs) the ULL was continuing to dig south and cut off from the main flow, then all of a sudden by 204 hrs the ULL opens up, turns neutral, and phases with energy hanging back in S Canada.

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I know this won't be popular but I think people need to give up on this thing heading south and east. It's pretty much a given the surface low will not take a favorable track for southern snow. The GFS has the trough beginning to cutoff in New Mexico we would want that to happen in Georgia if at all.. Not even the GFS will be wrong by that wide a margin. The key feature that everyone needs to focus on is the high pressure coming out of Canada and how it orients itself along the east coast. The GFS keeps the high center far removed from the east coast and has only an extension across the northeast. This would provide little to no CAD. The euro breaks off a piece of the main arctic high and places it over eastern Ontario. This is a much more favorable position and the only way this is anything but rain for the SE.

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I know this won't be popular but I think people need to give up on this thing heading south and east. It's pretty much a given the surface low will not take a favorable track for southern snow. The GFS has the trough beginning to cutoff in New Mexico we would want that to happen in Georgia if at all.. Not even the GFS will be wrong by that wide a margin. The key feature that everyone needs to focus on is the high pressure coming out of Canada and how it orients itself along the east coast. The GFS keeps the high center far removed from the east coast and has

I agree, although if the system was weaker and didn't strengthen so fast this would argue the possibility of some overrunning precip...

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Track of the low on the ENS mean takes the low from the middle of AL to the middle of TN due north then trucks it off the coast of VA :wacko: ...doesn't cut to the lakes though.

A wide array of scenarios between the ensemble members. Not much agreement yet. This is still 8+ days away people.

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Overall even though the exact solutions on the runs over the past day or so haven't been ideal the trends have been positive. While the op run of the gfs has consistently shown a lakes cutter, each run digs the s/w further south/east. It is still 7 days away and a lot will change, for better or for worse.

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I agree, although if the system was weaker and didn't strengthen so fast this would argue the possibility of some overrunning precip...

True a weaker system may not bring in as much warm air initially but this will eventually head too far north for snow. Already none of the models bring the 850 line much south of the VA/NC border, and this is in the day 5-6 range. I don't think that part will change much. My point is that as long as we have a strong surface high in a favorable CAD position it does not matter how far north and west the low tracks. We would still see sleet/freezing rain even if it tracks to Chicago.

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