purduewx80

Certainly not a bad look on the UKMET.

No bueno. LI and SE MA get some light snow, but the Gulf low amplifies over the Gulf Stream and then loses its oomph as the trough digging into the Rockies/Midwest launches it out to sea.

Will be interesting to see how quickly precip moves into the area Wednesday. Some guidance hinting that if it's early enough, it may begin as freezing rain. Highest probs for this currently just W and N of the city. Even with the southerly flow forecast, it will take some time to erode this air mass. Then it's game on for another heavy rain/ring of fire/southerly flow event Wed night - Thu AM.

Varies depending on the model/run but the EPS shows a shift in the PNA and AO around that time, with near-neutral values on the 27th. NAO had been forecast to go negative this week but that appears to be a failure on its part. We'll see if it does by the end of the month. To me, pattern change = lower predictability than 'normal', so this one could be all over the place until energy is better sampled Thu-Fri.

Will be interesting to see how this evolves the next couple days, but the majority of ensembles at 00z favored something closer to the Euro w/ the 500 wave cutting off somewhere over the Gulf Coast/Southeast. We saw this with the system a few days before Christmas where parts of the Gulf Coast/SE set new record low 500 heights. If something like that verifies (high heights Canadian maritimes, low in the SE CONUS), obviously this will be another high precip event for the region. Some hints of an east-based -NAO which would favor inland areas seeing highest risk for +SN. At least there is good agreement the EPO is in better shape. Clusters of 500mb anomalies valid Sunday evening below.

There are indications of a ~1040mb high in SE Canada on most of the guidance, but the timing is variable due to the northern/southern stream differences. On the Euro, the Gulf low attacks the high from the S. Looking back at bluewave's initial post - the GEFS and EPS have a stronger high there than the Canadian ensembles.

I don't quite understand why they weren't issued for the city, other than perhaps because it's a holiday? Wind chills have met the advisory criteria of -15F or colder for JFK, LGA, EWR for most of the past 3-4 hours.

Sure is. Low is directly over the city now and will probably hug the coast into far SE New England.

yep.

I've seen drizzle and a few pellets mixed in now too.

light snow in bed stuy now. at least it didn't start as rain.

walt started an obs thread, btw.

was just noticing this about the HRRR too; correcting colder/drier the past 5 runs in nearly the entire cold sector and in damming areas east of the appalachians.

A surface low with pressure near 1000 mb is currently located near Memphis. Noted by the arrow on the COD pressure fall analysis below is the area of strongest 850mb warm-air advection (see SPC analysis page). It's no coincidence max pressure falls are occurring in the same area over eastern KY. There is also a secondary max associated with latent heat release in western AL, just north of numerous strong to severe thunderstorms.

Much like the November event, there is a layer of extremely dry air in the lower levels. It's a thinner layer at OKX than ALB or CHH. -50.5 Td at 812mb below:

Yes, there are a number of tools and in-house models available to both private sector and NWS mets that the public doesn't have access to. Local knowledge is important, but understanding model biases is just as important. Probabilistic guidance is becoming an increasingly used tool to support decision making.

fair point. if you apply that bias and assume it holds for the event, northern and western parts of the metro still would see predominantly pellets and then freezing rain (after the evening snow) before precip ends. again it's important to watch trends w/ that air mass once it comes into the NE tonight/tomorrow. even today no one model has this pegged.

It's doing well with the incoming air mass, currently located N of the Great Lakes.

The NSSL convection-allowing models and some other hi-res guidance show the potential for icing throughout most of the city even if the warm front makes it to central NJ. This is not necessarily in their wheelhouse yet, but I think it's a good illustration of how low-level cold hangs tough directly north of the surface front. This is the warmest panel on the 12Z NSSL WRF, which gets the freezing line to JFK for an hour and then rapidly brings temps down into the 20s by 12Z Sunday. Given that the heaviest precip will be around during this period, it will be important to see if the globals correct S/E in the next 24 hours or if the CAMs trend north.

Everyone should understand there are still going to be changes in the modeling up through the event due primarily to three things: While some of the Pacific energy was sampled on the West Coast this morning, the backside jet (500-250mb) will be better sampled on the 00z soundings. I've seen this matter countless times for storms in the Midwest, specifically with the GFS and NAM, no matter how good the ingestion of satellite data is these days. The subtleties of its phasing with an arm of the polar vortex - timing and location of this still isn't ironed out, as many have pointed out. Convection will play havoc with surface low and low-level jet development. This system will be highly convective through the mid-south due to warmth and moisture from the Gulf meeting up with the Arctic air mass, in addition to all the jet dynamics. More often than not, convection may "drag" surface features (including the sfc low) towards the higher instability/waa until jet dynamics and vorticity advection take over (which is what causes the low to bomb out well NE of here). Even the hi-res models miss this all the time. There is at least some model evidence now to support the idea that even if the surface low(s) pass just south of the region, surface temps could stay sub-freezing throughout the city and most of LI as ageostrophic flow out of the high to our north outperforms. It's not just the RPM showing this. I see no reason to doubt a front-end thump here followed by a brief transition to sleet before primarily liquid precip falls. I wouldn't count out some back side pellets or snow either, although for now that looks light.

that's a given

Pretty much what I'm expecting unless there are major changes in the modeling today.

wind chills may be as cold as -15 monday.

only thing that may "close" it is >2"/hr snow rates, which is possible in this storm but who knows where. typically hard for crews to keep up with that.

this is all due to that polar vortex extension phasing with the southern vort much later than modeling had a day or two ago. i'm not sure this trend has ended though, we need to see some stability on that before any of this can be trusted.