high risk

I appreciate that, but I honestly wasn't offended by your post. It has definitely been a rough period lately in the extended range. To me, the fact that we have higher expectations now for Week 2 forecasts speaks highly to the progress that has been made. We just have to remember that certain patterns / transitions still give the models fits, and identifying those in advance is not trivial.

I think that recent longer-range forecasting successes, part of the ever-improving state of NWP, have raised our expectations a bit too high. We're not yet at the point where we can expect the Week 2 period to always be forecasted with skill, even for ensemble systems.

Some HRRR runs do maintain it, but some are like several other CAMS in weakening the line as it moves into northern MD/VA. Even the previously bullish HiResW FV3 has backed off quite a bit.

THIS. Even though our resident third graders want to moan that poor forecasts show that NWP is useless, there are certain patterns that for whatever reason just aren't predictable. The fact that all of the major world modeling ensemble systems showed something very encouraging for the end of the first week of January makes it clear that something about those forecasts (initial conditions generally driven by lack of observations or observational errors, the actual equations and parameterizations, numerical methods, or some combo of those) made skillful predictions impossible. But there are plenty of periods where guidance shows remarkable skill even at extended ranges. Here are the 500 mb anomaly correlation scores (the best measure of synoptic pattern success) for 10 day forecasts over the past 3 months for the 3 major ensemble systems (and yes, it only makes sense to verify ensembles at this range). A score of 1 is a perfect score, and the dates on the bottom are the days on which the forecasts verify, not when they're made. There were periods of poor performance by all 3 systems (early October and around November 9), periods of poor GEFS and GEPS performance but with the Euro doing fine (around November 12 and at the very end of December), periods of fair performance by all 3 (mid October), and periods of fantastic performance by all 3 (third week of November and especially the third week of December). Those scores between December 18 and Christmas are remarkable for 10-day forecasts and are numbers we could have only dreamed of 20 years ago. Advances in data assimilation and coupling of the ocean to the atmosphere in models will lead to even bigger improvements, and AI offers tremendous opportunities to run the massive size of ensembles needed to truly represent the uncertainty and potential for extreme events with more lead time. That doesn't mean that frustrations like those with the upcoming pattern will completely disappear, and it REALLY doesn't mean that we should soon expect models to lock in on a snowstorm 12 days out and never waver up until the day it happens. We just need to remember the current limitations and focus on consistency in patterns (and not details of deterministic runs at extended ranges) in ensembles, understanding that progress in forecasting the extended ranges doesn't preclude huge busts. I'll end with this plot of Day 5 anomaly correlation by year over the past 40 years (apologies for not having the values for Day 10). While the lines have flattened more than we'd like in the past 10 years (I think that AI is the way we'll see these rise again), and the GFS needs to catch up to the Euro, the progress is undeniable. Thanks for coming to my TED talk, and Happy New Year! pa

I know that we're all chasing big dogs, but this would be a nice start to 2026 if it happens. NAM Nest and RGEM aren't as tasty as the HiRes FV3, but they all have the idea of some sort of quick-hitting band right on the front.

Understood, but while that means that it wasn't an issue with the processing on those sites, it's a dissemination issue with the data. The model chugged along just fine; issues with the actual runs are extremely rare.

Friendly reminder that graphics updating slowly on someone's website does not mean that there is anything wrong with the actual mode run.

Fascinating late evening radar on Long Island, with synoptic snow moving west-northwest to east-southeast, while ocean-effect snow streams from south to north across Long Island.

Same here! As for the overnight rainfall, a bunch of HRRR cycles late yesterday showed a significant minimum in the precip for most of the area. I dismissed it, because it really didn't fit the narrative, but it was spot on.

It's remarkable that every CAM has a forced line of convection tomorrow morning arriving on the west side of DC around 7AM and hitting the eastern side around 8. I'm also very intrigued by all CAMs showing a broken line on the secondary front in the early afternoon. This environment will have some CAPE and some low freezing levels, so I suspect that these could be accompanied by small hail or graupel.

It is indeed remarkable how fast these AI-based models run. It really opens the door to running larger ensembles than ever thought possible, although getting meaningful spread still needs research

All of the new AI NOAA global model products are using Graphcast. Tropical Tidbits is displaying the deterministic GFS, called the AIGFS. There is also an AIGEFS, but it's not yet displayed here. The HGEFS is the hybrid GEFS, which combines the 31 members of the "regular" GEFS with the 31 members of the AIGEFS. Note that the AIGEFS has been shown to be somewhat underdispersive, so treat high probabilities with caution. https://www.noaa.gov/news-release/noaa-deploys-new-generation-of-ai-driven-global-weather-models

This is the Round 2 for midday / early afternoon tomorrow that I referenced in the above post. Interesting to see some impressive modeled reflectivities with that.

Every CAM has a nice forced line just ahead of the front, with consensus showing it passing through DC around 6 or maybe 7AM. Most of these events end up being just heavy rain, but they do occasionally surprise us with more. Another thing to watch is that all of the guidance has another round of scattered heavy showers around midday in a well-mixed environment with a bit of low-level CAPE and low freezing levels. Would not be surprised to see some graupel out of those.

The NAM Nest and HiRes Window FV3 both have a similar idea of initial rain turning to snow, with a nice band moving to the southeast in the late night hours. Surface temperatures are VERY marginal, but most of the column is "cold" other than right near the ground, so it should be mostly snow after initial rain for some. It's a good thing that this will fall at night, or else stickage would be completely dependent on rates.

Probably this spring. But what about this run is so clearly awful?

Actually, there are a few SREF and GEFS members that (no surprise) are super wet. Those inputs are driving those high percentile values.

Honestly, I usually start with the 10:1 maps and make some modest mental adjustments (up or down, depending on whether temperatures are marginal or solidly cold). The concept of Kuchera is good, but it's not as simple as a colder profile means better ratios, and I find that Kuchera runs outrageously hot in many cases when the snow falls at temperatures well below 32.

This thread is reminding me why I love summer: the long hours of daylight, the warm breezes, and not have to look at a stupidly-inflated Kuchera plot for 8 months.

I think this is a great point - social science is really going to be a factor here. Tomorrow's decision will be made with Tuesday's decision fresh in their minds, and they'll absolutely be scared to death of another delay or closing that ends up not needed. And it seems like a 2h delay wouldn't accomplish much tomorrow, as it will be cold and snowing 2 hours later. It's probably either a "normal day" or "closure" decision.

What stands out to me is that even if the totals are very light, temperatures at onset are in the mid to upper 20s for most of us (except maybe for the far southern crew). With the earlier onset, as others have noted, the morning rush hour could be very tricky, and school systems are going to have some very challenging decisions to make.

This is bothering me a lot, as the NAMs are usually the colder solutions. I think we're still in the range where the NAM could be having synoptic issues, but if it continues on Monday to keep the accumulations further northwest of the I-95 corridor, I'm going to guess it's right. The faster onset, shown by the GFS and its hi-res HiResW FV3, would help a ton here, although even where it shows snow, the thermal profile has pretty much zero margin for error.

NAMs will around through at least the rest of this winter.

Incredibly tricky temperature forecasts this weekend. Warm air will be lurking just our south and southwest, but there is increasing concern now that we'll end up on the cooler side of the boundary each day.

While we'll be freezing tomorrow, there is very good model agreement that we get quite warm on Sunday.