eduggs

Pretty well advertised quick hard hitting event. Just a wonderful daytime weekend snow event! Trust the models.

I meant the GFS & ECMWF vs. the AI models. Considering the size of the model domain, the camps aren't that far apart. The difference just feels really big considering the local sensible weather outcome. I feel like there have been many 75 mile shifts in precip. shields over the past 20 years with coastal storms within 48 hours.

They (GFS/ECMWF) aren't that far apart at this point, are they? What, maybe 50-75 miles with the heavy stuff offshore? The ECMWF OP in particular has shifted NW with the heavier stuff. As many people have mentioned, these are the kinds of setups that can and sometimes do shift NW in the last 48 hours. The outcome is extremely sensitive to minor changes in the shortwaves near the Gulf and also the Lakes. Presumably the AI models are correcting for those cases somehow. But that sensitivity is a double edged sword. I can also see how the AI models might overcorrect if their training datasets aren't perfectly representative or well matched to the current setup.

It looks like it comes is 2 waves, with the front buckling north and then back south. Most of the predawn stuff should be snow. If precip. shuts off - and esp if the sun comes out briefly, surface temperatures are likely to spike. Whoever get into the banding the longest could get some decent snow.

I'm not sure what you mean. I'm interested - fascinated really - why the AI models have been consistently west of their parent models for the past few days. I have not seen that behavior consistently or persistently earlier this season. And I offered one potential explanation for this specific situation. I reflexively tend to think the least snowy model will be correct, even if that's not scientifically sound.

A theory to explain the AI vs GFS/ECMWF battle could be the latent heat release - wave development feedback loop that Eric Webb mentioned a day or two ago. Shortwaves that tap Gulf moisture are susceptible to this effect. If this is biasing the global models too flat aloft, it could explain why the AIs are further west since they can bias-correct based on historical outcomes.

I agree with most of this. And I don't expect much if any accumulation in the asphalted area of NYC. But I don't think ensembles have the resolution to capture this partly mesoscale feature. The high QPF - short duration signature is prevalent across multiple models, so I'm inclined to think it's real. The question is where does it set up. Right now it looks north or west of NYC. But if the banding materializes and it impacts NYC, with a little dynamic cooling, I think there could be accumulations even in parts of the City. I really enjoy these low expectation localized events because they make for fun nowcasting.

Rates (precipitation per hour) are actually modeled to be fairly high. Modeled FGEN is significant across several models. But total precipitation is relatively light due to the short duration. Several models including the GFS deliver over 0.3" liquid over 4-6 hours in or near our region. A few models even have greater than 0.5" liquid nearby. That's a fairly significant QPF signal for short-duration frontogenic banding. The forecast difficulty is that the modeled placement of this banded feature (CT, LHV, CNJ) is highly variable. Forecast temperatures range from the upper 20s to mid 30s across our region with NYC roughly 31F to 35F depending on model during precipitation. Wetbulb temperatures are a little lower and modeled surface temperatures dropping during precipitation. Notably the HRRR is warmest, particularly after precipitation ends Saturday afternoon. NYC will probably record a minimum temperature below 33F on Saturday.

Saturday only (10:1)

Don't sleep on Sat. It's basically a mesoscale event. Could be nothing or a fast 3". Pretty significant FGEN values across multiple models. And it could come in multiple bursts predawn or daytime. My guess is CT or the HV is the winner, but a few runs have targeted CNJ to NYC. Could be a fun nowcast with low expectations. Contrary to what some say, this would have no trouble accumulating with 0.1" liquid per hour at 33F. Most will probably miss, but if you have the rates it will accumulate.

It's wild how good the AIGFS looks at 500mb. NYC is again over 0.5 liquid from just the Sunday event and the precip. shield ticked slightly NW.

0.4" liquid in 6 hours showing up on globals and mesos. It's very isolated and variable in placement. But someone could get a surprise with some intense frontogenic banding on Saturday!

Long range HRRR for Saturday.

I'm hoping for more than mood flakes on Sat as I expect that to be the snowier day for me. I think LI and southern NJ has a decent shot of accumulating snow on Sun. But I'm not closing the door on a significant west trend.

Lovely write up. For a change I don't think it's all hype and BS. I seem to remember this feedback loop being enhanced when PVA tracked close to the Gulf states and picked up additional moisture inflow... which is what is forecast by most models to occur.

I love how it's snowier than 12z. Lovely model battle

I'm in a similar situation both this year and in recent years. And I agree about the anecdotal observation. The RRFS is prone to wild swings (i.e. errors), especially beyond 48 hours. But it's still better to see it shift west than east. It's showing a significant snowstorm for NYC east and south on Sunday after an appetizer for some on Saturday.

The RRFS is very expansive with the precip. shield to the NW of the SLP. It's probably too expansive. I'm guessing a lot of that would end up as virga with that surface depiction combined with a weak 700mb low. The RRFS, NAM12km and NAM3km have a frontogenic banding signature on Saturday.

Where I agree is that meteorologists can use local knowledge combined with model output to occasionally outforecast a global model locally, in the short range, and for limited parameters like surface temperature. But forecasters who think they can outforecast a global weather model at the synoptic scale or in the mid-range are deluding themselves. They are susceptible to all sorts of biases that convince them that their gut feelings are superior (confirmation bias, availability heuristic, confidence bias etc).

I don't agree with this at all. I think it leads many people off a cliff. People think their intuition regarding loosely defined concepts like "pattern" is superior to supercomputers developed specifically to model exactly what's possible in the atmosphere. It's pure ego.

Where I agree with you is that if you pre-define a synoptic setup as simple (moist southerly flow into a cold dome), then it is comparatively simple. We do get hung up on semantics. But I also think we oversimplify and broad-brush weather events with terms that are too general.

I disagree with this. ECMWF and NOAA/NWS should be the baseline. AI can use verification to improve modeling beyond the current state of physics-equations-based modeling, which is limited by its programming and unable to quickly iteratively improve.

Thanks. I'm not saying it's an analogue. NYC isn't going to break its all-time snowfall record Sunday night. Yes the synoptics are broadly similar, but the similarity I want to highlight is that 3 days before that event, it was written off as an OTC solution.

The UK is at or below freezing for all except LI during Saturday's snow. It looks nice actually. A proper snowy weekend day. Surface temperatures near the City warm slightly above freezing after the precipitation ends.

I like the EC-AIFS too. I think it has done well this winter. Under 48hrs I'll be looking at the NAM. That's probably an unpopular opinion, but I think it does well with these trofs that touch the Gulf when the height field along the upstream trof flank is questionable. It often signals how much room there is to come NW. It the NAM stays east in the short term, that usually ends it.