purduewx80

it was safe to operate, just much slower than normal.

Look like the coastal front is actually retreating a bit now, could be an icy few hours in Boston.

If the NAM verifies, conditions will become favorable late tomorrow afternoon and evening for scattered snow squalls ahead of our Arctic frontal passage. 8C/km lapse rates and best lift in the DGZ. This suggests some brief whiteout conditions are possible.

This is a good signature for significant turbulence and compression on the JFK TWDR. NE winds near 10KT at the surface and SW winds 50KT+ at 4000 feet. This wind difference often slows down air traffic into the NY metro airports. A 767 reported severe turbulence coming into JFK earlier this morning. RGEM forecast soundings valid at 15Z show what would be a nice hodograph if there were surface based instability.

I was surprised to see JFK hang onto freezing rain longer than LGA and EWR. I think the high may have been placed just right to drain cold air down the island. Most of the UHI had a wind off the relatively warmer sound. Subtle trajectory differences and terrain obviously played a factor, too. SPECI KJFK 170943Z 04010KT 7SM -RA BKN009 OVC023 01/00 A3000 RMK RAB42FZRAE42 P0004 T00060000 METAR KJFK 170851Z 05010KT 7SM -FZRA BKN009 OVC023 00/00 A3003 RMK SLP169 P0005 60023 T00000000 56031 SPECI KJFK 170843Z 06009KT 7SM -FZRA BKN009 OVC025 00/00 A3004 RMK P0005 T00000000 KJFK 170751Z 06013KT 7SM -FZRA FEW005 OVC019 00/M01 A3005 RMK SLP174 P0011 T00001006 KJFK 170651Z COR 06011KT 6SM -FZRA BR FEW006 BKN025 OVC075 00/M01 A3010 RMK RAE30FZRAB30 SLP191 P0007 T00001006 SPECI KJFK 170630Z 07008KT 6SM -FZRA BR FEW006 OVC022 00/M01 A3012 RMK RAE30FZRAB30 P0003 T00001006 METAR KJFK 170551Z 06006KT 6SM -RA BR FEW006 BKN023 OVC035 01/00 A3012 RMK RAE11B49FZRAB11E49 SLP200 931000 P0008 60030 T00060000 10022 20000 58024 SPECI KJFK 170511Z 04005KT 6SM -FZRA BR FEW006 OVC024 00/M01 A3015 RMK RAE11FZRAB11 P0001 T00001006 METAR KJFK 170451Z 06006KT 6SM RA BR FEW009 OVC026 01/M01 A3015 RMK RAB36FZRAE36PLE50 SLP210 P0011 T00061011 401220000 SPECI KJFK 170437Z 07005KT 6SM RAPL BR FEW009 OVC028 01/M01 A3016 RMK RAB36FZRAE36 P0007 T00061011 METAR KJFK 170430Z AUTO 08005KT 8SM -FZRA -PL OVC036 01/M01 A3017 RMK P0006 METAR KJFK 170425Z AUTO 07005KT 8SM -FZRA -PL OVC036 01/M01 A3017 RMK P0005 METAR KJFK 170351Z 07004KT 9SM -FZRAPL OVC034 01/M01 A3018 RMK AO2 RAE51FZRAB51 SLP219 P0004 T00061011 METAR KJFK 170350Z AUTO 07004KT 9SM -RA -PL OVC034 01/M01 A3018 RMK P0004

This one is definitely going in the UHI folder.

It does look like precip in the area will become convective at times late tonight into midday tomorrow, so heavy rain is a given for the immediate NYC metro. The 18Z RPM and new HRRRv4 are showing some ice accretion amounts of 0.5-0.75" in the same general areas as the NAM:

NWS just updated to expand the winter weather advisories a bit closer to the 5 boroughs. I suspect they may need a winter storm warning for the combo of snow, pellets and freezing rain accretion for the areas you mentioned.

This is probably going to factor in to precip types later - 850 mb dew points were ~20C drier than modeled.

I feel like this may be tied to the amount of convection in the warm sector. 850 and 700 trajectories suggest to me RH will be a problem farther north.

There may be some dynamic cooling as frontogenesis increases late tomorrow evening, but with the SE ridge amped up like it is on the EPS below, it will be hard to avoid torching the layer just above the surface. This could be a fairly bad ice storm near White Plains, NNJ, southern CT imo.

The Euro suite of products has been trending deeper with the wave up over Alberta and Manitoba, which feeds into the 50/50 low and places confluence farther south in the Northeast. I'm not sure most of the guidance is initializing all the shortwaves correctly looking at WV imagery this morning. 00Z EPS trends valid at 00Z this evening below, the 06Z was even stronger w/ that low in central Canada.

It shows a quarter to half inch of ice for a lot of CT/RI.

Speaking of the raging Pacific jet - Boise, ID set a new 250mb wind speed record today - 173KT at 12Z vs. the previous record of 169KT. Records there go back to 1948.

can't share our internal graphics.

There's a lot of convection with this system over the Southeast today that will be contributing to this. Some of the hi-res guidance suggests we could see a thunderstorm in the region tomorrow afternoon as the 500mb jet max punches in.

06Z Euro looks like a nice front-end thump Monday evening. Nearly 0.2" liquid equivalent and 700, 850, 925 and sfc temps are at/below freezing for all of us through 00Z.

Yes, thanks for pointing this out. We do also have a comparison/trend series of EPS/GEFS/GEPS using the same methodology - can't post it but the differences are less stark. EPS has the NAO bottoming out at -0.68, the GEFS at -0.56 and the GEPS at -0.42, all on Dec 19th.

EPS is still trending more negative next week with the NAO, while the GEFS and GEPS are ~neutral. The 06Z EPS shows a low tracking from the Delmarva to the benchmark. As long as we don't see a reversal of these EPS trends over the next ~48h, I think a front-end thump to ice pellets scenario is on the table for the city proper early next week. Far northern and western parts of the metro could be in for a sizeable snow as well.

No surprise, but there's still quite the range of solutions so far on the 12Z runs for next week. GFS is still a Lakes cutter, while the UKMET (below) is suppressed/dry, and the Canadian somewhere in between.

I like the trends on the ensembles for the ~Tuesday possible Miller B event. Both the GEFS and EPS have Davis Strait blocking for a time. That dreaded E Asian/W Pac jet looks to get roaring past this period, but we'll see.

Model analyses and short-term forecasts of vertical velocities are one way (RAP/HRRR especially), but they're subject to model depictions being correct. RAP analyses are used in the SPC meso products - check out the winter weather and upper air sections for the relevant info. The 12Z OKX sounding showed no dry air issues and had the dendritic growth zone centered near 500mb. So any parcels lifted from below into that layer will give you the better snow growth. 700mb (or likely just above this) frontogenesis is doing the trick now.

Any of the brighter echoes moving through the city now are indicative of the better snow growth with forcing near 500mb. We went from white rain to large dendrites and moderate snow here in Bed-Stuy over the past 15 minutes. Moderate snow at Central Park now too.

There are some ocean/bay effect snow showers moving S/SW into Sandy Hook and coastal NNJ now. Low-level lapse rates plus seeding from the synoptic event are helping these out. The north shore of LI will probably get a boost from these, as well.

haven't seen theirs yet either.