Carvers Gap

Euro Weeklies Control is picking up another sharp cold shot during week 3. That is just beyond the reach of deterministic modeling right now. But you can kind of see it on most 12z modeling...push south of cold air.

This kind of puts in perspective the month so far. And honestly, I might not mind a 7-10 day warmup. Right now as I type the wind chill is 10F. TRI has recorded a trace or more of snow at the airport 10 out 20 days this month so far. Yesterday was 19 degrees below normal. During December, all of those LR ext models which called for January cold weren't too far off the mark. When it snows all the way to the Gulf Coast, that is a pretty amazing cold snap and one which leaves me a bit in awe. Look at those departures from normal. Only three days AN so far for the month.

Lastly, the 6z EURO AIFS really wants to leave the EPO in place but squashed. That would allow for periodic cold shots into the east. That might well be a direct result of the PDO being less hostile. The AIFS has been uncanny and rightfully stubborn in the long range. The AIFS is probably our best chance going forward. I give it a lot of weight. It is basically the zonal/chinook outcome that mention in the first of these four posts(this being the fourth). If the cold air supply is strong enough over NA, the MJO can do weird stuff(like the complete opposite of what the temp phase should be). That said, we are due for a pattern change if you go by the 4-6 week rule for patterns. So, I lean warm for the new pattern...but with great caution for Feb. This is one where I look over my shoulder on every run for modeling to flip cold in the East.

I do think a western Atlantic ridge (WAR) could fire later in the d10-15. That brings very warm temps to the area. But what do we remember about that feature during winter? It often shreads the TPV. If the TPV splits, we might not have to worry about the cold going to Asia. Why? It is already here. Wouldn't surprise me to see a legit strat split during early Feb which sends us into the icebox later in Feb. That is probably part of the reason why so many analogs are cold for March.

Below is why we have to tread carefully. The first slide is basically right now. The second slide is 384(looks quite similar to the ensemble BTW). See how much cold is in Canada. That is coming south at some point. My guess is the West will benefit, but any cutter through the Plains could bring part or all of that air mass southward. The 12z Euro has a strong SER, but that might be a buckle before the next air mass. IF....IF the Euro MJO is correct, that air mass is heading SE. If the American MJO plot is correct....that air mass goes west, and we have the SER. But that is a crap ton of cold in Canada to start February. Right now the cold is just rotating west to east along the Canadian/US border with zonal under it. It is rare to be dealing with so much cold in NA late in that run(common theme and likely correct even at that range). I am having to adjust a bit to having that much cold which could drop into the pattern very quickly. Normally, I would just go torch for Feb....but that air mass is going to have to reckoned with I think....guessing it will modify and the last 10 days of Feb is when we see it move east. But that is a guess only.

Looks like we are about to enter a time frame around Jan 30th when cold air delivery mechanisms will be largely absent, and zonal flow over most of NA will be present. There are still very divergent outcomes when we look at the MJO progression(both amplitude and speed) on several models. The Euro gets it rapidly through the warm phases. American modeling take it to 6 and leaves it there the rest of winter. During Feb, I suspect we see very small windows where it can snow. The cold air supply to our north is substantial, but with zonal...it is stuck there. I think we will still see strong cold fronts, but they will likely lack staying power. So, an precip(if we want snow) is going to have to be timed nearly perfectly. I continue to think March(and the latter half of Feb if we are lucky) will feature a final return to cold. We have seen two bouts(early-mid Dec and almost all of Jan) of cold already. One more appears likely. It wouldn't surprise me if it is the coldest against the norms. A word of caution...as long as that substantial pool of cold air lurks in Canada, any warm forecast is in substantial danger. Warmth could/should rule the day for February, but cold lurks behind any cutter which could flip the pattern on a dime. One thing we have seen with cold this winter, when we get it...it isn't halfway. For now, February looks base warm with some cold intrusions which could provide wintry weather if timing is precise. Otherwise, we wait until late Feb and early March. I suspect the modeled zonal pattern (beginning late next week) is likely the "new" pattern. However, zonal can be tough to maintain during February as wavelengths shorten up. I would suspect some of the Feb cold shots will not be seen until the last minute on modeling. That's about it. Pretty boring pattern on tap for a few days, but the pattern is capable of snow...so it is worth keeping an eye on. There are a few chances on either side of Jan 30th. Again, it would not surprise me to see a mix of severe and winter weather tracking for the next couple of months. Sidenote: Analog packages have been pretty stellar so far this winter. They picked up the conflicting signal for January. They had the cold end to November and cold start to Dec. Most are very warm for February. Many are very cold for March. 2017-2018 has been a great analog this winter.

it used to be that spring snow IMBY was not uncommon, and that snow during late November and early December was very unusual. That has flipped since about December 2009. Winter finds a way to get going early in NE TN more times than not lately. We can have cold/rainy springs..... Also, I am thinking what I looked at was snow and not temps now that I think about it. Though, there is prob some correlation there. Snowier falls and early winters. Less snow springs.

Just looking at photos from Bristol, TN/VA, it looks like they go 2-4". We have a dusting IMBY. Upslope is not my game. Pretty good thump in eastern Sullivan though. They have been scoring all winter. RGEM with the score yet again. The GFS at very short range wasn't bad. Portions of extreme NE TN and SW VA have been hammered.

Just looking at the Euro Weeklies tonight...after a warmup during a TBD portion of February(edit), it sure looks like March might be an extension of winter for the usual places which can have winter during March.

This seems to be a very common look around or just after 240. I am watching this time frame. The CMC and GFS have something similar. Possible reload after this rotates through. That is begging or a winter storm. Cold air supply is stellar and the SER should flex right into that.

18z GFS.....make stationary fronts fun again.

Also, next Sunday, ensembles and now the 18z GFS are picking up on a WAA system. Something to watch for NE TN and northern Cumberland Plateau folks.

This is pretty awesome. Want to watch the PDO flip? Watch the water right along the northern Canada and Alaska coast. Starts off below normal. The water in the GOA is above normal. Then watch as the water directly along the Alaska coast goes AN and the water west of it in the central Pacific - BN. That is a flip from a -PDO to a +PDO. Could be temporary or permanent. This is likely what is causing the EPO to lock in. That change matches the current cold shot almost perfectly. The atmosphere responded almost immediately. Link for PDO phase maps for reference...

Warmer patterns with cold lurking are not always bad.

I saw some data where late fall and early winter have gotten colder. Spring has gotten warmer. But until this cold pool loses its supply, could be a slog. Many March analogs are cold. This winter we are bucking the majority analogs though. I said up front this winter might not play nice. It has lived up to that. From the word go, this winter just seemed to have a different look on long range modeling. Not sure I can put my finger on exactly what…just seemed like it would buck the trends. All those warm weeklies looks have been can kicked almost 2-3 weeks so far.

Again, the big difference between this and other winters is our cold source is old-school legit. The other thing is the EPO seems to want to fire regardless of the MJO. That tells me the PDO has flipped or is flipping. The PDO will be in direct conflict with the MJO signal. That is going to wreck havoc on modeling. Don't think so. BN heights in Alaska with a ridge on the West Coast....that has not happened a lot recently. It can happen, but that isn't a recent staple. The playing field has changed....let's see if the surface responds. This is one of these deals where we could have severe one week and a winter storm the next.

Welcome to thread-the-needle time. That should last for about the next 4-6 weeks. The MJO is all over the place, and that fits with LR modeling - all over the place. North America is cold, folks. During previous winters, we would throw in the tall after this next cold shot. The problem with that is that any cutter can driver wickedly cold air all the way to the coast right now. Chinooks will be short lived. I kind of felt like this winter wasn't gonna be an easy call, and nothing looks easy about the next 4-6 weeks in terms of any kind of generalization. I don't think we will have a locked in cold pattern, but we may well have very sharp shots of cold air. If we can get a shortwave to interact with the northern stream(phase), the ingredients are on the table for a big storm. But....it will be thread the needle stuff where we will like depend on cold rushing into the backside of a storm.

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Reading on scannerfood that some ice has developed in the mountains with the onset of this rain. ZR has caused multiple wrecks. Wise, VA, has reported ice as maybe some areas in W NC.

I got about 25% of the RAP snow forecast last weekend. LOL. Maybe not even that. Looks like the RGEM though!

The 12z GEFS has a trailing system like the 12z Euro deterministic does later in the week....something to watch and makes a lot of sense.

The 12z GEFS has flipped cold after brief warmup d10-15. What if this pattern is just starting and not ending? Worth asking. Need to watch for a trailer to the Deep South system. @Daniel Boone, we have seen that many, many times. Jeff mentioned it as well. The cold pulls back north and stalls. That creates a boundary for the next storm. Just have to time it right. The 12z GEFS oddly supports the Euro operational at 12z - just quicker.

The 12z GEFS has a trailer system (similar to the EURO) to the SE mauler. It is showing up on ensembles about 36 hours later. Decent hits.

The CMC is on the west side of guidance, and its ensemble is west of that at 12z. Decent jog west on ensembles. GFS and its ensemble are still buried. The GEPS came in west of the operational at 12z. I noticed the ensemble mean was up (GEPS), and decided to look at the individuals. Most of the bigger solutions get portions of E TN.