RU848789

Wasn't sure where to post this HRRR comparison of 18Z and 0Z for tomorrow's little storm in SNJ/SEPA/DE, but in the vein of model mayhem, here's reason #993 to not trust the HRRR beyond 24 hours, lol...

Every pro here and on 33andrain and elsewhere is scratching their heads over what to make of all of this now that the Euro joined the UK as misses for our forum, meaning I have no shot of figuring anything useful out at this time. Even using the NBM Model Blend is probably a bad idea when there are two very distinct camps like this. One can blend them and get a moderate snowfall for our area, but the outcome is just as likely now to be one camp or the other. FWIW, the NBM is about the same as it was at 18Z. I don't envy forecasters for this one. At this point I would probably just punt and wait for better model consensus and use the NBM which still says 1-3"/2-4" for CNJ (less north and more south), but I'd note that <1" (or even nada) and 3-6" are still on the table. Crazy.

I still like 1-3/2-4" for CNJ, which is what we're still seeing for the NBM, which actually got a little snowier for CNJ at 01Z vs. 19Z. Of course, a blend will miss if one of the outliers is on to something and can be terribly wrong, but major outliers rarely verify, so it'll usually at least be in the ballpark, unless we see some huge shift by all the models, which has never happened before 3+ days before an event, lol.

Reason #993 to not trust the HRRR beyond 24 hours, lol..

Just when I thought we were going to have consensus on a snow party with the ICON/GFS, the CMC brings us back to reality and then the UK impersonates Dr. No.

Holy crap, we just got NAM-ed by the 0Z GFS, lol. Stepped away for 30 min and boom!

Why? It was an outlier at 18Z north, so coming back a little bit south is no surprise; it's still likely going to be the furthest north of the 0Z models.

I'll take that, thanks for guaranteeing that outcome, lol.

11.25" - not a top 10 storm, accumulation-wise, but a top 5 storm, experience-wise, partly because of the surprise element and partly because of the incredible 3-4" per hour rates for most of 2 hours. Different setup and I doubt we'll see that kind of gradient on both sides of a very narrow band.

Very nice for our area to see the 18Z GFS, ICON and Euro continuing to move the snow/precip shield further north putting CNJ potentially in line for 2-4" and NYC for 1-3" (or possibly more...or less)...and to see the NBM do a further increase for northern areas. Still 3+ days to sweat it though and we know what can happen in 3 days. Here's the Euro and NBM at 12/18Z.

While the ICON is just nuts, gotta like the snow shield shift north again on the 18Z GFS, with a 3" line along 78 now and 2" in NYC...

Just closing the loop on this. Thankfully, the NWS-Philly has finally come around to the reality of what the models are showing, as I figured they had to - and they're quoting the NBM (National Blend of Models) and noted the northward shift of the snow shield/accumulations mentioning that further northward shifts are possible; full discussion on Monday's storm is below. Too early for snowfall maps yet (they'll come Friday night), but their comments are fairly well in line with the NBM (and what I posted earlier): they have their 4" line from Philly to Toms River (the NBM is closer to 276/195) and they say more is likely south of that line and then snowfall amounts will decrease north of that line, with areas N of 78 likely well below advisory criterion (which is 3", so reading between the lines, maybe 1-2" along 78 and 2-3" for most of CNJ. Area Forecast Discussion National Weather Service Mount Holly NJ 304 PM EST Thu Jan 2 2025 .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... The synoptic pattern starts out with a flattening ridge shifting offshore Sunday night, followed by a flattening trough approaching from the west on Monday. A low pressure system associated with the trough will approach from the west beginning Sunday night while weakening as it crosses the Appalachians. The low will then cross the Mid-Atlantic and strengthen again as it passes offshore. Following the wintry system, conditions will turn colder and drier as a phased deep trough across the eastern CONUS supports shots of reinforcement for the arctic airmass persist through the end of the week. Confidence is increasing that widespread snowfall accumulations will impact the region Sunday night into Monday, with potential for significant amounts within a relatively narrow band roughly 30-50 miles wide. The exact track of the low pressure system and frontogenetic forcing will dictate where exactly this heavier snowfall band develops. This will depend on the strength of the high to the north and the evolution of the surface low, which will likely wobble a bit in the guidance from run to run and from model to model for the next 36-48 hours or so. Current indications from a consensus of deterministic guidance places this band somewhere between central Delaware and adjacent areas of eastern Maryland and far southern New Jersey, to potentially as far north as the Philadelphia metro area. There has been a slight north trend evident in the latest guidance alone, however I`m a little worried even this may not be quite far enough north. There will almost certainly be frontogenetic forcing and other mesoscale factors involved, which models have progged to be maximized somewhere between a line from DC to Delaware Bay, to perhaps as far north as northern Delaware near I-95. This would put the heaviest QPF/snow axis potentially as far north as the Philly metro. The 850 mb low center looks to cross the Appalachians around WV and east into northern VA and MD into Delmarva. The derterminisitc guidance seems a little too far south with the surface low given the jet dynamics aloft. This along with the warm advection aloft could easily spell mixing issues in the far south of the forecast area, such as southern DE and Cape May. This mixing area could include a mix with sleet, freezing rain, or even all rain for a time. PoPs were increased slightly across the board given the growing confidence in a potentially significant system. Current NBM probabilities support a 60-70% chance of snowfall exceeding 4" across much of Delmarva and southern New Jersey south of Philadelphia. Around Philadelphia proper and along a line east and west of there, the probability of 4" or more is near 50%, then lessens quickly farther to the north. The exact totals remain unclear, and we do not currently have an official snowfall forecast for this event yet. That won`t come until Friday afternoon`s update, but initial probabilities suggest *at least* advisory level snowfall (2-4") from around the Philadelphia metro and south, potentially low end warning snowfall (5"+) where ever the heavier band of snow sets up. Farther north of Philly, amounts are likely to lessen considerably to below advisory levels, especially along and north of I-78.

the latest from the NWS on tomorrow's little shortwave that could...advisories are actually up for 1-2" from Philly metro to about AC and SW of there in PA/DE/MD/NJ.

I know this is the 1/6 thread, but didn't know where to put the latest on tomorrow's little shortwave that could...advisories are actually up for 1-2" from Philly metro to about AC and SW of there in PA/DE/MD/NJ.

I get the confluence concerns, but I think you're underdoing it for CNJ. I would be surprised if the 1" line isn't at least as far north as 78, meaning most of CNJ south of there would get 1-3" with ~3" being down towards Trenton to Belmar. Most models are showing that and the NBM is showing more, including 1-2" for NYC.

3" line moved ~30 miles N and the ~1" line moved 10-15 miles N. Progress.

A small uptick on the CMC and later precip too...warning snows south of 276/195 and advisory snows from there up to 78, i.e., all of CNJ.

Yessiree! That along with the ICON getting much snowier for areas N of 276/195 are good signs...

Enough said, thanks. My one comment for the author of that AFD would be to perhaps address the NBM/precip inconsistency, especially given how often the NBM is invoked by the NWS as a major aid in forecasts.

A bit off topic, but below was my recap for the 1/19 event (for my email lists/FB/other non-weather forums - I post a lot more in those places than here, since most posters here are pretty knowledgeable), discussing that sharp cutoff and the graphic that showed it pretty clearly. We got very lucky in Metuchen for this one. Brief Recap of 1/19 Event: The NWS forecast was excellent for everyone about 5-10 miles south of 78 and south of there, with 2-4” from there down to about 276/195 and a general 4-6” from along 276/195 down through the rest of SEPA, SNJ, DE, MD, etc., as that’s where the Norlun Trough set up. As I feared from just south of 78 northward, the NWS forecast busted, as snowfall was 1-2” near 78 and generally <1.5” N of 78, including <1” for almost all of NENJ, NYC, SENY and LI; the exception was Sussex/Poconos where 2-3” fell. We got very lucky in Metuchen, where we got 2.9” vs. my forecast of 3.3” at my house, as the radar showed the moderate to heavy echoes including us, but slammed shut just a few miles north of me (too much dry air to the north), which is why Clark, just 6 miles north of me only got about 1”. So, NYC continues its snow futility, but Trenton, Philly, Wilmington, Baltimore and DC all got 4” or more, breaking their snow futility streaks, as per the 2nd graphic below.

Thanks for the insights. Unfortunately, if certain folks in the incoming administration have their way, we might not have a NWS any more or at least not one that makes forecasts - perhaps they'll only be the collector/provider of data for private firms to use for their paid forecasts. I hope it doesn't come to that as I've always liked having professional mets at the NWS offices with great general meteorological knowledge paired with strong local knowledge of the area's weather.

Yes, I noticed that - they actually upgraded their probabilities of snow from yesterday at 4 pm to today at 4 am in the AFD, but they're still "conservative" from a prediction perspective wanting to maintain continuity with previous forecasts, but the problem is that they're not being "conservative" at all with regard to alerting the public - a conservative approach there would be to play up the threat at least a bit so people aren't surprised on Monday if there's 1-2" in NNJ/NYC and 2-3" in CNJ.

Well, CPK got 2.3" last Jan, while we got 7.3" (2.0" on 1/2, 2.4" on 1/15 and 2.9" on 1/19) and they only got 7.5" all winter while we got 24.6" in Metuchen, which was an insane difference.

Look at the two maps I just posted above - significant disconnect, clearly, especially since it's the National Weather Service Blend of Models. I'm glad I'm not the one having to make this forecast, lol.

Interesting that the NBM snowfall forecast bumped up for 07Z vs 01Z last night and yet the NWS-Philly is clearly downplaying the event potential north of Philly, as per the part I bolded below, when they often follow the NBM for snow events. Maybe they're going by the WPC precip forecast and not the NBM snowfall forecast... @MGorse- any comments on this apparent disconnect? Just trying to figure out what you guys are thinking, thanks... National Weather Service Mount Holly NJ 401 AM EST Thu Jan 2 2025 LONG TERM /SUNDAY THROUGH WEDNESDAY/... Guidance from a synoptic standpoint is depicting a Miller B nor`easter to develop with an upper level trough swinging a surface low from west to east across the KY/TN area before redeveloping as a low pressure system offshore Monday. Ensemble guidance is split into 2 different clusters with the variance generally explained by how strong the upper level ridge will be over Quebec. This boils down into two scenarios, one with a more northern track bringing snow towards the RDG/TTN/PHL, and one with a more southern track keeping the snow more over the DC area. The more northern stream track relies on a weaker high and thus develops a bit more cyclogensis over our region thus lifting the band of 2-4 inches of snow further north, whereas in the southern track, the high is stronger and displaces the surface low to the south more leading to most of the area seeing little in the way of snow. 01Z/02 NBM generally is taking a blend of the two scenarios thus leads to probabilities similar to the 13z/01 NBM with snowfall greater than 1 inch is 60 to 80 percent across southern New Jersey, the Delaware Valley including Philadelphia, and the eastern shores of Maryland and Delaware while the probability of snowfall greater than 3 inches is 40 to 50 percent. North of Philadelphia, probabilities lower to 30 to 50 percent for greater than 1 inch of snow and 20 to 30 percent for greater than 3 inches of snow. For the time behind will continue to show a blend of the two tracks but anticipate that the gradient of snowfall will sharpen quickly somewhere north of Philadelphia over the coming runs depending on how guidance handles the upper level ridge. While it is still too soon to tell how much snow will fall, the trend looks to be for advisory level snowfall for Delmarva, sub- advisory amounts for southeast New Jersey and the Delaware Valley, and minimal amounts north of Philadelphia.