eduggs

That's how I see it.

Specific local impacts - 1-2 days. General signal for storm vs dry - 7-10 days. But obviously with increasing uncertainty as you move out in time. Other regions may have other characteristic lead times for reliable forecasts.

I think of it more like tugging on a buckled string. The impacts are continuous and simultaneous in all directions.

Well stated. As far as I know, CPC keeps things very general with broad brushed AN and BN for temp and precipitation. They avoid talking about specific patterns.

I don't agree. The climate indices are a snapshot representation of the atmosphere, not a driver of its state. The driver is global temperature gradients.

Snow melts so fast in March. And outside the hills, we're always battling marginal temps. You need intense snowfall rates in March. For me, Dec - Feb are the snow months.

If December ends up above normal temperature-wise, I'm hoping some of the long-term weeklies huggers and "pattern" obsessers start to appreciate the inherent uncertainty in long-term weather forecasting.

-4 SD AO is just a statistic; a number. It's a very crude way of characterizing the state of the pressure field/atmospheric circulation at a continental scale. Weather is a local phenomenon.

If we're in a "pattern" - which I argue we are not - then it's a terrible pattern for coastal plain snow.

ULL/PV near Hudson Bay at day 5 is not going to work. We need that in the Canadian Maritimes. Ensembles have been shifting the low heights further NW with time. Cutter City.

All the degreed or professional meteorologists who study 10+ day anomaly charts and climate indices have contributed nothing to local weather prediction so far this winter. We've experienced average to below average snowfall, mostly above average precipitation, and average temperatures with slightly more extreme highs than lows but no big extremes either way. Maybe this is a fruitful endeavor if you're forecasting drought in the western US and even if you're an energy trader... but if you're a medium range forecaster along the highly baroclinic east coast, I see very little utility studying the charts at day 10 and beyond. Maybe in the future, model skill will improve to the point of usefulness. But right now it only serves to create false expectations.

Climate indices aren't causally connected to weather. They are only loosely correlated to weather outcomes, particularly at the local level. So even if we could forecast their state 7 days in advance, we wouldn't know for sure if we were getting a coastal storm or cutter. But of course we can't forecast the state of climate indices that well 7 days out, especially the finer details like magnitude and orientation. So we are left using climate indices in hindsight to identify correlations instead of using them in advance for prediction. Everybody wants it to be so simple... That we move from one stable, definable weather regime to the next, and that we can see the discrete change coming. But instead of existing as a pattern, weather is characterized by a continuously changing set of features.

It's certainly not a classic blizzard, but it would be widespread snowfall across the east coast. Much colder in situ air and potentially two bouts of moderate-heavy snow. I'd sign on right now if I could.

That feels true in memory. I know all models occasionally do that and who knows if the CMC is more guilty. But I sure wish the CMC was on our side instead of the GFS.

Use ensemble means with caution. There are clusters broadly representing the extremes depicted in the recent op global runs. Clearly there is heightened sensitivity to a few key features that could shift this outcome significantly. Averaging these extreme camps creates a muted average unlikely to portend the final outcome.

Ooof, the CMC looks ugly again.

Heavy snow to mix to rain possibly back to snow on the GFS. Weaker trof keeps things wintry. Gonna be hard to avoid rain with a trof axis so far west.

Less explosive development. Weaker, less sharp trof. That could be good for us if we don't want rain and wind.

Well the follow up wave that ultimately carves out the big trof is noticably weaker as it moves through the Pac NW/intermountain west. That seems slightly good for us. The evolution is also delayed. But the ULL over Ontario looks likely less favorably positioned.

The 0z RGEM has lower heights over the Lakes at the end of its run. This looks improved over 18z and the 12z GEM. I expect the 0z Canadian to be at least a slightly less extreme cutter compared to 12z.

ICON has the upper level low feature in Ontario at day 5, just a bit too far north. Previous model runs that had east coast snowstorms had a strong antecedent ULL in this region. EC was really flat with this feature, and the CMC actually had a ridge. A stout ULL would force any follow up wave to divert south and possibly delay the negative tilting.

That's how it looks to me too. And the key features are only 4-5 days out from being in their critical locations, so there's not a ton of time for changes. But things could still evolve differently, so we'll all probably continue to track.

The blocking isn't helping and it won't last forever anyway. I don't believe in "patterns," but I will say from a snow perspective this early winter has been bleak outside the NW hills.

Nope, it's locked in now. Expect the GFS to trend further west and warmer. Could be severe storms.

Based on 144hr, it looks like the UK is in the CMC/ICON camp with high heights in Ontario mid-week and the follow up ULL moving eastward towards the lakes instead of diving south through the US. The 12z EC and 0z GFS are in the other camp, although both have a significant portion of ensemble members in the other camp.