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December 2024


TriPol
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A cooling trend is getting underway. That trend will culminate with a sharp shot of cold will during the weekend. The temperature will likely fall into the teens for the first time this season in New York City and Philadelphia. Many areas outside those cities will likely experience single-digit lows.

Before that, a system will bring some periods of rain tonight into tomorrow. Afterward, another system will likely bring some periods of light snow to the region late Friday into early Saturday morning. A minor accumulation is possible in the Philadelphia to New York City region. Boston will likely pick up 1"-3" of snow.

Beyond that, the cold will recede beginning around the middle of next week.  December will likely close with above normal temperatures. The opening days of January will likely also begin with above normal temperatures. Snowfall prospects will remain limited.

On account of a lack of snowfall, 2023-2024 will likely set a new records for the lowest snowfall over a two-year period for Boston and New York City.

Boston: 2023-2024 Total to Date: 21.5"; Record: 38.2", 1979-1980
New York City: 2023-2024 Total to Date: 9.8"; Record: 17.4:, 1997-1998

In past days, an occasional run of the operational GFS showed a significant snowstorm from Washington, DC to New York City. However, the pattern makes such an event very unlikely for this region. Since 1950, there were 5 December snowstorms that brought 6" or more snow to all three of these cities. Four (80%) occurred with a PNA+/NAO- pattern. The NAO is forecast to be positive. In addition, three (60%) occurred when the MJO was in Phase 8, which is not likely over the next 10 days. Only the December 23-25, 1966 event produced 6" or more snow in all three cities with a positive NAO, but the AO was strongly negative (< -2.000), which is not likely during the next 10 days. In sum, the interior sections will be far more favored for an appreciable or perhaps greater snowfall than the Washington-Baltimore-Philadelphia-New York City area over the next 10 days. A smaller snowfall remains plausible. One example will be the upcoming Friday-Saturday snowfall in parts of the region.

The NAO fell to a preliminary -2.751 on September 24th (all-time September record: -2.371, September 12, 1971). That was the 9th lowest value on record. La Niña winters following September cases where the NAO fell to -1.900 or below featured a predominantly positive NAO. The most recent such winters were 2016-2017 and 2022-2023. The mean temperatures for those winters in New York City were 39.3° and 41.0° respectively. The 1991-2020 normal value is 36.2°. A warmer to much warmer than normal outcome is favored by the November run of the ECMWF for Winter 2024-2025.

The ENSO Region 1+2 anomaly was -0.2°C and the Region 3.4 anomaly was -0.6°C for the week centered around December 11. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.17°C and the ENSO Region 3.4 anomaly has averaged -0.27°C. Neutral ENSO conditions may still evolve into a La Niña event during the winter. Uncertainty as to whether a La Niña will actually develop continues to increase. Currently, 47% of dynamical models and 22% of the statistical models forecast the development of a La Niña.

The SOI was +17.33 today.

The preliminary Arctic Oscillation (AO) was -0.109 today.

Based on sensitivity analysis applied to the latest guidance, there is an implied 79% probability that New York City will have a colder than normal December (1991-2020 normal). December will likely finish with a mean temperature near 37.3° (1.8° below normal).

 

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12 minutes ago, the_other_guy said:

Don’t be a dick guys! he saw it and you guys kept saying nothing was happening

 

If we get a flake of snow, he was more accurate than most of you on here… a week out

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. 

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The Friday-Saturday light snow event should give Central Park its first measurable snowfall of the season. In fact, the share of ECMWF ensemble members showing 1" or more has decreased since 12/18 12z. Overall, it continues to look like less than 1" of snow in and around NYC and also Philadelphia. Colder suburbs should see a bit more.

image.thumb.png.5711787d9bad7aeef08bbe2a706b23c6.png

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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
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Noon Christmas Eve (24th) - Noon Christmas Day I84 corridor: Looks to me like periods of snow and possibly sleet along and north of I80 in PA-NJ to at least I90 NYS-MA. Just too uncertain but several more inches of snow could accumulate by the time Santa has accomplished the mission Christmas morning. Even NYC might get a little snow. The does not take into account the 06z/19 EC OP which might say no way?

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6 minutes ago, wdrag said:

Noon Christmas Eve (24th) - Noon Christmas Day I84 corridor: Looks to me like periods of snow and possibly sleet along and north of I80 in PA-NJ to at least I90 NYS-MA. Just too uncertain but several more inches of snow could accumulate by the time Santa has accomplished the mission Christmas morning. Even NYC might get a little snow. The does not take into account the 06z/19 EC OP which might say no way?

6z euro

676409ec63091.png

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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
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1 hour ago, bluewave said:

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

Near impossible to sustain a long term drought here. 

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18 minutes ago, jm1220 said:

It’s still nothing like the droughts you see out West or even places like TX without so many ways to get rain. 

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°.

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6 hours ago, bluewave said:

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

Agreed, the very dry Sept and Oct appear to have just been a blip in the wet pattern. Nov was a little over 1" above average IMBY and Dec to date is .63" above average.

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