Carvers Gap

Jax has a great map. I had this post on deck as he posted. Apologies for the repeat. Here is the comparison to the full run at 15z. Most short run modeling will release a longer run every six hours. So, one trend we are noticing is model totals going up and the precip shield expanding northward. We are probably at the point were 18z is the last run which will have full maps of the event. I am also attaching the set-up so that we can look back for similar looks in the future. Looks like we managed a storm setup w/ a high in the Aleutians but a -EPO and strongly negative AO and NAO. Trough/storm is easy of Hawaii.

Never been my strong point!!!! LOL.

Yeah, it does. Chattanooga is in the mix as well.

@tnweathernutor @TellicoWxor @John1122 or @BNAwx.......I would think there is very little mechanism to bring WAA northward. Time of day could be an issue if it falls during daylight hours and the front stalls. Dynamic cooling would likely play some part as water evaporates and cools the column. It might be less with this set-up, but not absent. Just a layman's guess.....

18z GFS comparison run to 12z for trends...new is on the left.

The 18z GFS manages to keep Chattanooga on the books. Very, very slight NW jog but massive expansion of precip shield and amounts increased decently.

You know your stuff. It is great to have the board grow. When we started, there were just a handful of us. Now, it is a pretty formidable gathering of people teaching/learning/enjoying a great hobby. It took a bit longer than we expected to grow the place, but it is rocking now.

Some of it is an algorithm issue. Some of it is general precip shield shifted about a county northwest for that model. I don't know what trends on the ground are, so it is going to be super important for folks west of us to post their observations. For now, I am going to ride w/ the NBM - I think. But the NBM will be late to the table if this trends sharply.

Yep. Very true. Also, a northwest jog has been discussed for several days. It is one reason I try not to be too emotional about modeling. The wx is gonna do what it is gonna do...and not a thing I can do about it but observe, predict, and revise...and enjoy the process. This is a fun hobby for the most part.

Good deal. After so many years of Memphis having to sit and watch others get snow, you all are on the books with yet another one! It has been a good 4 years for you all generally.

18z RGEM...surface temps are an issue for Chattanooga as is decreased overall precip. Sleet and ZR mixed w/ rain and snow. Not sure I buy that, but the WxBell algorithm has it.

Kuchera for 18z RGEM (left) and for side-by-side comparison w/ 12z. Slight jog northwest, but pretty massive expansion of precip field which we are seeing across modeling.

The RGEM really beefed up amounts. The 18z RGEM brings the entry point in the forum area slightly north of 12z. It still flattens the system as it heads eastward. That slight changes increases amounts over middle TN. Last minute northwest trends are not uncommon. We actually "stole" a system many years ago from North Carolina on a 48 hour trend at the last minute. If the cold in middle TN is stronger than expected, there will be a likely limit as to how far it can trend northward. More than anything we are seeing an expansion of the northern precip shield vs a major movement of the snow demarcation line to the south. About a one county jog northwestward for the southern extent of snow. Also to account, there is a certain amount of ebb and flow noise in modeling.

Awesome, man! How much are the predicting for your area, AMZ?

The 20z RAP at 21h looks nearly identical to the 18z RGEM at the equivalent time.

So, my pessimism aside, if modeling bumps up totals at 18z, it likely means they are playing catch-up. If you like lots of snow, that is a good thing...wherever this sets up. The best winter storms rarely stop increasing totals, even during the last run prior to the event. The 18z ICON is a good trend it appears. Also, of note, El Nino systems tend to overperform at times.

We were 7 degrees over projected highs at TRI today.

At first glance, that looks too high for most of TRI. They must be banking on good rates and the bigger model runs. There is certainly some model support for that. The NBM is around 3-5" of snow here. I admire their courage. Without the NAM on board, I am still holding my cards on amounts. I honestly don't know for TRI.

Actually, I hadn't looked at the RAP. Its recent run looks like the RGEM from 12z w/ slightly more precip on the northern edge. Are you saying that models may be underestimating totals since cold air is already in place? Just trying to make sure I understand. Thanks, man.

The RAP over the eastern valley is usually pretty poor, but we'll see. A system trending northwest is not out of the question at the last minute. OTH, the RAP and NAM being over amped is also not out of the question at this range.

The 18z NAM again looks like it is experiencing feedback issues. And that is a known bias of that model. It turns the line of precip well north and much earlier over the eastern valley. It could score a coup and certainly has before, but big totals(which aren't on other models) are usually indicative of feedback. We'll see. I also have seen the NAM overestimate my totals by 3-4x the actual amount in reality.

3k NAM trended SE and expanded northern precip shield.

The wind in combinations with temps in the 30s has been very cold. I know some out and back runners who had it good on the way out, and then had an 18 degree WC headwind on the way back.

Advanced teleconnections.

That is awesome. Didn’t u also have the fully black wooly worm?