purduewx80

12Z obs showing 0.5" for EWR and JFK, with 0.6" at LGA. Still some banding from the higher-based forcing working in, but it's battling dry air in NJ; should snow on/off through late morning for most of us. LI will do well.

I didn't really say that - it will be a factor on the back edge of the precip shield and could provide a sharp cutoff in snowfall on the northwestern fringes.

The EPS has been trending to a -NAO but the 12Z Euro is considerably more blocky up there than its ensemble and is snowier here as a result. GEFS is closer to the ECMWF products with the blocking potential than the FV3 is, at least on today's runs.

There is a lot of dry air leading to virga on the northern fringes of what you see on composite radar imagery. The 12Z Little Rock sounding (below) revealed the dry air layer. No models caught on to the -21C dew point just below 850mb. SGF to its northwest was considerably drier and explains why Memphis and Nashville are currently not observing precipitation.

Makes sense. The city obs were all dry between ~midnight and ~noon.

Big bust for the GFS in terms of precipitation placement.

Certainly what the 12Z HREF is showing.

I'm not totally sold on the warm day = no accumulation argument. Cloud cover is going to be thick all day today. You can also tell the roads/sidewalks are cold based on everything still being wet - they're "sweating" due to the dew point being warmer than pavement temps. That said, despite the potential for a 1-3h burst of snow in the AM, reeling in expectations for more than an inch or two is wise in the city. Local areas could cash in, but this will be the exception rather than the rule. The mesoscale nature of these snowfall bands will be another nowcasting deal. We know large-scale conditions are favorable, but precisely where they develop is yet to be hashed out. You think our forecast is hard? Check out the day-of spread in the MS/TN Valleys - they're in the right-rear quad today: Currently, there are reports of sleet in the Memphis area...would not want to be a met at FedEx today.

I like using the trend gif option on the freely available sites. You can see how the northern stream wave was farther west over the Great Lakes on the NAM runs that had a stripe of heavy snow farther north. This allowed more of the southern stream wave over TX to edge in front of it. The OH Valley vort (now over WI/IA on WV loops) has trended a bit stronger too which flattened the ridge and shoved everything farther S/E.

It has everything to do with it. That shallow wedge of dry air on a few models at 850 mb has nothing to do with why most guidance shifted southeast in the past 24 hours.

Yeah, and the DGZ is right at 500 mb. Still time for this to wiggle around but wherever that sets up will see a brief burst of mod/heavy snow during rush hour.

QPF queens will get burned with this one.

There's a thread for Wednesday so we aren't talking about it in multiple places.

Nice sounding from the 18Z NAM valid at 12Z Wednesday. Not sure why the best guess precip type guess is rain here, maps show snow and that sounding would also be (very wet) snow. Best lift is centered *just* below the DGZ (near 500mb), and there's an ~isothermal layer below that, so at least moderate snow is supported.

Averaged frontogenesis from 800-600mb on the 12Z NAM is impressive Wednesday morning. That's how you get bands of +SN to develop.

Not stupid at all, it's quite complicated. See https://www.weather.gov/source/zhu/ZHU_Training_Page/winds/JetStream_Stuff/300_200_chart.htm for some in-depth descriptions behind the fluid dynamics. The image below is a simple model of a straight jet, things get more complicated when the jet streak is curved cyclonically vs anti-cyclonically. In the right entrance region (or right-rear quad) of the jet streak (where we are in the 250mb map I posted), you have extreme divergence aloft. That rapidly evacuating air aloft has to be replaced, so you get strong ascent from below, lowering pressures, etc - all this creates areas of convergence/frontogenesis in the low and mid levels (specifically near 700mb in this instance). Basically the upper jet helps strengthen any lower level baroclinic zone, creates strong lift and enhances/creates banded precipitation.

There is consensus on the surface front passing by 8-9PM Tuesday evening, but the 925-850-700 fronts lag well behind (i.e. anafront), hence the rain to mix to snow scenario. The high placement and shallow nature of the Arctic air mass is not supportive of the cold air plowing over the Appalachians, so we'll have to rely on dynamic cooling from the jet max and stretched 500 vort to get anything that will stick.

The battle between Tuesday's near-record warmth and the influx of Arctic air from the Lakes Wednesday will lead to an impressive jet streak across the Northeast. This kind of jet structure can lead to a band of moderate-heavy precipitation that would be our best bet for a few inches of wet snow Wednesday morning. NAM and GFS both showing a 170-190KT wind max between 200-300mb: Most of the forecast soundings suggest we go from rain to a wintry mix (IP and FZRA) over to snow, but we may not know exactly what transpires for another day or two.

the weather coming monday-tuesday will melt snow in a lot of the northeast. dewpoints are forecast well into the 50s with this airmass, likely for over 24 hours. classic snow eater.

4.3" as of 12Z today.

Yes, NYC's observations are also available in METAR form. The 931 groups are usually only done for the 3 major airports: JFK, EWR and LGA, and even that isn't consistent. ISP did not report a 931 group at 12Z.

There are snowfall reports in the 12Z METARs: KJFK 031151Z 35013KT 7SM -SN BKN024 BKN043 OVC065 M01/M03 A2954 RMK AO2 SLP003 BKN024 V SCT 931002 4/001 6//// 7//// T10061033 11006 21006 50004 KLGA 031151Z 33013KT 10SM BKN055 OVC110 00/M04 A2953 RMK AO2 PK WND 32027/1104 SNE1059 SLP999 931001 P0000 60000 70034 T00001039 10011 20000 53001 KEWR 031151Z 33010G19KT 9SM -SN FEW007 SCT018 OVC130 01/M02 A2954 RMK AO2 SLP003 931002 4/001 P0000 60001 70031 T00061017 10011 20000 51002 The 931 group is snowfall in the past 6 hours. So JFK/EWR saw an additional 0.2" and LGA had 0.1" from 06-12Z.

Several strikes already showing up with those cells off the Jersey Shore.

-PLRA at EWR now and here in LIC too.

we good