bluewave

My guess is that the La Niña background is making the Northern Stream of the Pacific Jet faster than the models forecast back at the beginning of December. None of the models from three weeks ago had this big jet extension leading to the strong +EPO at the end of December. The other factor has been the +SOI spike in late November lead to the +PNA mismatch pattern for a La Niña background. So we get these ridges in the EPAC and WNA that keep getting weakened by the faster Pacific Jet than forecast.

Yeah, this is turning into a late blooming La Niña due to how warm the Pacific started out. The WWBs being forecast are only in the EPAC. Trades continue near the Dateline making this more a CP La Niña. We actually set a new CP OLR record for any La Niña back in November. https://www.climate.gov/news-features/blogs/enso/december-2024-enso-update-party-time-excellent In these graphs, higher numbers are more like La Niña). In fact, the OLR from November 2024 ranks higher than any previous La Niña!

Nice improvements away from Southern NJ with Providence recording their wettest winter day.

The delayed freeze up on Hudson Bay is probably contributing to the record warmth being forecast. https://nsidc.org/sea-ice-today/analyses/sluggish-freeze-warming-north

Yeah, no clean pass showing up going into January with the forcing shifting from the EPAC back to the IO and MC a few days later.

Yeah, it’s great to be in an area where there is such an active storm track and we don’t go years and years without much rainfall. All the summer rains and onshore flow have kept the 100° temperatures in check. If we ever got a drought like we had this fall during the summer with enough westerly flow, then the usual spots in NJ could top 110° and have their first summer with 10 days reaching 100°. Just a weaker short term dry pattern in NJ during 2022 resulted in over 5 days reaching 100°.

Parts of Long Island and CT have seen the greatest drought relief with 8-10” over the last month. Data for November 20, 2024 through December 19, 2024 Click column heading to sort ascending, click again to sort descending. NY SEAFORD 0.4 SE CoCoRaHS 10.10 CT PAWCATUCK 0.8 SE CoCoRaHS 8.65 NY MOUNT SINAI COOP 8.59 CT PUTNAM LAKE COOP 8.40 CT STONINGTON 1.4 NNW CoCoRaHS 8.39 CT PAWCATUCK 1.8 SSE CoCoRaHS 8.38 CT COLCHESTER 0.6 ENE CoCoRaHS 8.35 NY CENTER MORICHES 0.5 N CoCoRaHS 8.31 NY MANORVILLE 1.8 SSE CoCoRaHS 8.23 CT SALEM 3.6 SE CoCoRaHS 8.22 CT GUILFORD COOP 8.18 NY BAITING HOLLOW COOP 8.18 CT MYSTIC 1.6 W CoCoRaHS 8.17 CT OAKDALE 2.6 WNW CoCoRaHS 8.10 NY CENTERPORT COOP 8.09 NY RIDGE 1.8 SE CoCoRaHS 8.01

We haven’t had a legit +PNA with widespread double digit snows since January 2022 around the NYC Metro OKX forecast zones. As you mentioned, many of the +PNA winter months had lower heights over the SW US leading to cutter or coastal hugger tracks which wound up too warm for a nice KU event. Mostly smaller snow events since then. The once common denominator has been the very fast Northern Stream Pacific Jet. So the +PNA ridges in Canada get undercut frequently. This month the issue was the eastward drift due to the fast Pacific flow lowering heights from the west. Some localized areas from PA across to Central NJ were able to due well last February with the record jet streak snowband. But much of my area missed out on that event. The one positive for them was the record STJ was able to dominate over the NS due to such a strong El Niño. Both 22-23 and 23-24 were similarly both top 3 warmest around my area. But the STJ made the difference for a few spots while much of the area got very low snowfall totals both winters relative to the averages and rankings.

The issue is that the models are converging on a bootleg +PNA to at least start January with lower heights under the Canadian Ridge out West. Anytime we see lower heights in the Western US with a +PNA ridge in Canada it leaves room for storms to continue tracking to the Great Lakes. We get short term Southeast Ridge amplifications. The trough returns to the East after the storm has past. The EPS has been struggling the most showing too much of ridge beyond 10 days near EPAC and WNA. Same model bias since the beginning of December. New run Old run

Luckily, looks like the peak of the drought is behind us. As NYC will probably finish December over 3.00”. Still drier than what were before the fall. We’ll know we are back to the old wet pattern again when we get a month with over 5.00”. Monthly Total Precipitation for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. 2024 5.28 2.05 9.06 3.47 4.11 1.71 4.20 7.02 1.58 0.01 3.35 2.70 44.54 2023 4.38 1.28 3.32 7.70 1.28 1.62 5.34 6.56 14.25 3.90 2.95 6.71 59.29 2022 4.29 3.23 2.39 4.53 4.52 2.92 4.55 1.71 4.10 5.08 3.15 5.83 46.30 2021 2.31 5.13 3.41 2.69 4.36 2.62 11.09 10.32 10.03 5.26 1.12 1.39 59.73 2020 1.93 2.54 3.78 4.49 1.65 1.76 6.58 5.03 3.94 5.05 3.99 4.61 45.35

Getting 3” or more is all that most of us care about in NYC. So far that doesn’t look like it’s in the cards. But a light accumulation or no accumulation seems to be what’s on the menu now.

The only monthly temperatures which matter for snow are on the days that the precipitation falls.

The pattern coming up doesn’t equate to any one individual MJO phase. The forcing is split between the EPAC and WPAC. So it’s a bit like playing a chord with the forcing instead of an individual note. So the resultant pattern has features of several different MJO notes playing together.

December 2022 was the last time the 7 station average finished below average at -0.5. EWR….+0.3 NYC….-0.6 LGA…..-1.3 JFK…..-0.8 HPN…..-0.1 BDR….-0.9 ISP……-0.3 avg…-0.5

A very super El Niño look to the pattern close to close out the year.

The whole area averaged out will probably be not too far from normal by the end of the month as we are currently at -1.3 for the local station average. 3 cooler departure days coming up with 3 around average. Then the 26st to 31st will be back above average. EWR….-0.9 NYC….-1.9 HPN….-1.1 LGA….-1.9 JFK…..+0.2 ISP…..-1.5 BDR…..-1.8 AVG….-1.3

Don, I believe that forecast would represent near the top 3 warmest last weeks of December for the entire North American continent. The Hudson Bay Area would be ridiculously warm with the delayed freeze up from the marine heatwaves back in the summer and fall. My guess is that the North American snow cover extent would dip to near the lowest for late December.

While we won’t have the highest departures here, it will be one of the warmest last weeks of December on record for the North American continent.

While 23-24 and 22-23 were both in the top 3 for warmth, at least the El Niño driven STJ was able to improve the snowfall situation in 23-24. Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. 1 2001-2002 41.5 0 2 2022-2023 41.0 0 - 2015-2016 41.0 0 3 2023-2024 40.6 0 4 2011-2012 40.5 0 5 1931-1932 40.1 0 6 1997-1998 39.6 0 7 2016-2017 39.3 0 8 2019-2020 39.2 0 9 1990-1991 39.1 0 10 1998-1999 38.6 0

This is why I would much rather take my chances with a record STJ than a record Northern Stream.

This was probably the first time we saw such a narrow snowband track exactly due east from Illinois with the record jet streak.

December 89 was colder than all but 2 Januaries since 91. I can still remember the snow around Thanksgiving. Was thinking we may have been on a 76-77 track that December. Everyone was really surprised how quickly the pattern changed around New Years with one of the warmest Januaries after the 2nd coldest December. That December would have been considered cold back in the Little Ice Age. Time Series Summary for NY CITY CENTRAL PARK, NY - Month of Dec Click column heading to sort ascending, click again to sort descending. 1 1917 25.0 0 - 1876 25.0 0 2 1989 25.9 0 3 1880 26.4 0 4 1872 26.7 0 5 1926 28.9 0 Time Series Summary for NY CITY CENTRAL PARK, NY - Month of Jan Click column heading to sort ascending, click again to sort descending. 1 2004 24.7 0 2 1994 25.5 0 Time Series Summary for NY CITY CENTRAL PARK, NY - Month of Jan Click column heading to sort ascending, click again to sort descending. 1 2023 43.5 0 2 1932 43.2 0 3 1950 41.8 2 4 1990 41.4 0 5 2006 40.9 0

Yeah, the JFK ASOS is actually fairly close to the 5 Towns area in Nassau in a very marshy spot. Readings would be much warmer especially during the summer if the ASOS was closer the Belt. When I lived in LB JFK readings were several degrees warmer than what I got a few blocks from the beach. But I would get the sea breeze sooner in the warm season so my highs would be a little lower than JFK. Oceanside was fairly close to JFK with the sea breeze timing and temperatures. The Newark ASOS is fairly close to the Bay. So any SSE component will drop the temperatures relative to downtown Newark. Unfortunately, that whole corridor in NJ is the warmest spot in the area due to how urbanized NE NJ is plus the warm down sloping from the hills to the west. So my guess is that we are probably missing the highest temperatures in that region since there isn’t a good downtown Newark site. We probably owe it to the people that live there and don’t get the benefit of a sea breeze like EWR gets. Harrison may be the closest in number of 90° days that the downtown of Newark gets. Data for January 1, 2024 through December 18, 2024 Click column heading to sort ascending, click again to sort descending 90° days HIGHTSTOWN 2 W COOP 41 HARRISON COOP 41 CANOE BROOK COOP 37 SOMERSET AIRPORT WBAN 35 NEWARK LIBERTY INTL AP WBAN 33 CALDWELL ESSEX COUNTY AP WBAN 33

It’s a good question. I have noticed that the JFK departures can vary either up or down from the other sites from time to time. It could be the onshore influence.

Is anyone working on an AI bias correction to the EPS weeklies numerical forecasts? It seems like this is the way to go. Since the AI forecasts on their own I have seen haven’t been the greatest. But maybe if they join forces with NWP they could make some real progress in modeling beyond 10 days.