bluewave

The ridge today was a little weaker over Oregon with the fast Pacific flow lowering heights from yesterday for the storm on the 6th. So the storm ends up further south today under the block. We probably have to be patient with patterns like this since it can take time for the Pacific and Atlantic get in sync for a nice east coast storm. New run Old run

It may take some time for the fast Northern Stream to back off a bit. We saw it was a big player in December. The EPS is just a few degrees too far east with the systems. So it has an active storm track into British Columbia and just off the East Coast. Slow the Pacific flow just a bit and we will be in business here.

The breaks of sun allowed Central Park to jump up to 61°.

That’s why we get such big variance between the collection of OP Euro, GFS, and CMC runs beyond 120 hrs. The ensemble means try to smooth out the spacing and amplitudes of each individual shortwaves. So ensemble means probably are good starting point for us.

NAO and AO volatility continue to be the big story since the summer. Big swings both using 500mb anomalies and the raw teleconnection indices. Very challenging to do a long range forecast of these indices with such record swings. We have seen unprecedented volatility since 2009-2010. New EPS run first week of January Old run

This rapid increase in AO blocking over the last 10 days of runs may be getting and assist from the record warmth around Hudson Bay with the lowest ice there on record for this time of year. New EPS run first week of January Old run

Low 60s today from CNJ to Newark with 50s most other spots.

It’s patterns like this that make us want to see OP runs only be made available through 120-168 hrs. Everything beyond that point should just be ensemble means. People posting these individual long range OP snowfall charts on social media will actually cause issues for the NWS. We saw this several years ago when some long range OP snowfall charts were posted around Philly and the NWS had to issue a statement due to a poster on social media. I think it’s the responsibility of the modeling centers to do this since once a model forecast is in the public domain it’s going to be posted by somebody.

Yeah, it can snow pretty much anytime in January or February regardless of the monthly average temperatures with the right storm track. We got this with the snow near the 80° day in February 2018. Then again multiple times in winters like 16-17 with blizzards the day after 60s record warmth.

Storm track is more important than average temperatures for NYC snowfall in January. Since it can always snow even when it’s warm this time of year with the right storm track with the average temperatures most Januaries.The temperatures only matter on the day of the event along with the storm track. NYC January average temperatures and snowfall last 10 years 2024….37.0°….2.3” 2023….43.5°…T 2022….30.3°…15.3” 2021….34.8°…2.1” 2020….39.1°…2.3” 2019….32.5°…1.1” 2018….31.7°….11.2” 2017….38.0°…7.9” 2016….34.5°…27.9” 2015….29.9°…16.9”

The OP and ensemble mean are different sides of the same coin. One is overamped on the northern stream and the other is a weaker system moving through in the fast flow. Hopefully, we can slow the Northern Stream influence enough to allow us to maximize the window of opportunity we get this month.

From JFK to ISP and Shirley it’s in the low 50s.

The highs already beat guidance today as we are low 50s around NYC and Long Island instead of mid 40s.

Maybe if you lose the primary running through the lakes and turn it into more of a SWFE event. But that would risk a scenario like the CMC has a weaker wave north and the southern stream getting suppressed. Too dominant a northern stream and you get a 1-3 or 2-4 then with mixing issues after.

Just goes to show how important storm tracks are. The December before that one was the 2nd coldest on record at 25.9° in NYC. But the Northern Stream was so overpowering that NYC only finished with 1.4” of snow as the big snowfall event missed to our south. December 1990 was the 10th warmest on record at 42.6°. But NYC was able to finish the month with 7.2” due to a favorable storm track on one day even in a sea of warm.

The last back to back below average temperature winter months were December 2017 into January 2018. NYC Feb 24…+4.2 Jan 24..+3.3 Dec 23..+5.5 …………..+4.3 Feb 23…+5.2 Jan 23…+9.8 Dec 22…-0.6 …………..+4.8 Feb 22….+1.4 Jan 22….-3.2 Dec 21….+4.7 ……………..+1.0 Feb 21….-1.7 Jan 21….+1.1 Dec 20…+1.7 …………..+0.4 Feb 20…+4.8 Jan 20….+6.5 Dec 19….+0.8 …………….+4.0 Feb 19….+0.9 Jan 19….-0.1 Dec 18…+2.6 …………….+1.1 Feb 18…+6.7 Jan 18….-0.9 Dec 17…..-2.5 …………….+1.1 Feb 17…..+6.3 Jan 17….+5.4 Dec 16….+0.8 …………….+4.2 Feb 16….+2.4 Jan 16….+1.9 Dec 15….+13.3 …………….+5.9

This winter was the strongest lagged La Niña that we have ever seen. Notice how much warmer the global SST state is than all the other La Ninas over the last 30 years. It allowed the RONI to drop well below the actual Nino 3.4s.

Looks like the AAM is forecast to drop as per the CFS forecast as the La Niña moves into the moderate range.

The cold departures will be shrinking to close out the month with 3 days going +10 or higher.

The UHI in Manhattan has been in effect since the 1890s and Queens since the 1930s to 1950s. But it’s just more obvious when we have calm winds. Plenty of strong high pressure this month for radiational cooling.

A place like ISP made up enough rain to finish the year over +2.00” since they were so wet up until the end of August. But Philly is still down around -5.00 due to the drier year there before the fall and less rain since then . So some of the NJ reservoirs are still low. THE ISLIP NY CLIMATE SUMMARY FOR DECEMBER 25 2024... CLIMATE NORMAL PERIOD 1991 TO 2020 CLIMATE RECORD PERIOD 1963 TO 2024 WEATHER ITEM OBSERVED TIME RECORD YEAR NORMAL DEPARTURE LAST VALUE (LST) VALUE VALUE FROM YEAR NORMAL ................................................................... TEMPERATURE (F) YESTERDAY MAXIMUM 37 213 PM 65 2015 42 -5 53 MINIMUM 24 623 AM 3 1983 28 -4 37 AVERAGE 31 35 -4 45 PRECIPITATION (IN) YESTERDAY 0.00 1.29 2002 0.15 -0.15 0.00 MONTH TO DATE 4.62 3.87 0.75 5.47 SINCE DEC 1 4.62 3.87 0.75 5.47 SINCE JAN 1 47.19 45.15 2.04 47.10 PHILADELPHIA PA CLIMATE SUMMARY FOR DECEMBER 25 2024... CLIMATE NORMAL PERIOD: 1991 TO 2020 CLIMATE RECORD PERIOD: 1872 TO 2024 WEATHER ITEM OBSERVED TIME RECORD YEAR NORMAL DEPARTURE LAST VALUE (LST) VALUE VALUE FROM YEAR NORMAL ................................................................... TEMPERATURE (F) YESTERDAY MAXIMUM 40 3:16 PM 68 1964 44 -4 53 2015 MINIMUM 31 11:06 PM 1 1980 29 2 39 1983 AVERAGE 36 36 0 46 PRECIPITATION (IN) YESTERDAY 0.00 1.11 1945 0.12 -0.12 0.00 MONTH TO DATE 2.28 3.30 -1.02 6.23 SINCE DEC 1 2.28 3.30 -1.02 6.23 SINCE JAN 1 38.23 43.44 -5.21 40.50

Many spots will be approaching 10.00 or rain since November 20th which is a nice change from the drought last fall. Data for November 20, 2024 through December 26, 2024 Click column heading to sort ascending, click again to sort descending. CT PAWCATUCK 0.8 SE CoCoRaHS 9.39 CT COLCHESTER 0.6 ENE CoCoRaHS 9.16 NY MOUNT SINAI COOP 9.06 CT STONINGTON 1.4 NNW CoCoRaHS 9.02 NY NESCONSET 1.4 SSW CoCoRaHS 9.01 CT SALEM 3.6 SE CoCoRaHS 9.01 CT PAWCATUCK 1.8 SSE CoCoRaHS 8.94 CT OAKDALE 2.6 WNW CoCoRaHS 8.93 CT MYSTIC 1.6 W CoCoRaHS 8.76 NY ST. JAMES COOP 8.71 NY CENTER MORICHES 0.5 N CoCoRaHS 8.64 NY MANORVILLE 1.8 SSE CoCoRaHS 8.63 NY BAITING HOLLOW COOP 8.57 NY CENTERPORT 1.1 SE CoCoRaHS 8.54 CT EAST LYME 0.6 N CoCoRaHS 8.53 NY RIDGE 1.8 SE CoCoRaHS 8.51 CT NEW CANAAN 1.9 ENE CoCoRaHS 8.44 NY SELDEN 1.6 ESE CoCoRaHS 8.42 NY PORT JEFFERSON STATION 0.3 SSW CoCoRaHS 8.39 NY CENTERPORT COOP 8.37 CT CHESTER CENTER 2.7 WNW CoCoRaHS 8.37 CT NORWICH 5.4 SE CoCoRaHS 8.35 CT HIGGANUM 0.8 NE CoCoRaHS 8.31 CT HIGGANUM 0.7 N CoCoRaHS 8.29 CT STONINGTON 0.5 NNE CoCoRaHS 8.27 CT GUILFORD COOP 8.24 NY UPTON COOP - NWSFO NEW YORK COOP 8.23 NY FISHERS ISLAND 0.5 NE CoCoRaHS 8.23 NY CENTEREACH 1.3 NE CoCoRaHS 8.21 CT EAST LYME 0.5 SW CoCoRaHS 8.17 NY RIVERHEAD RESEARCH FARM COOP 8.13 NY ISLIP TERRACE 1.1 NNE CoCoRaHS 8.09 CT MOODUS 0.7 SSW CoCoRaHS 8.07 CT NORWICH 5.2 SE CoCoRaHS 8.03 CT NEW LONDON 1.0 NNW CoCoRaHS 8.01

The only thing that matters if you want to see a NYC 4”+ snow event is slowing the Pacific flow long enough for the ridge to stay anchored along the West Coast. That along with the increased AO blocking could allow for a coastal storm track with cold in place. But the period in question is still out closer to the 2nd week of January and requires it showing up in the shorter range in order to be believable.

Looks like the coming warm up will be a rainy one to close out the year.

We haven’t been getting the usual MJO composites this winter due to the competing influences like the +AAM. It’s possible the WPAC forcing has been driving the much faster Pacific Jet and the +AAM rise the +PNA. So we get the faster Pacific Jet pushing the +PNA ridge axis too far east. It’s not really a pattern combo we have seen before. Since other big +PNA Decembers featured a weakened Pacific Jet and ridge axis anchored along the West Coast allowing big 6”+ snowstorms near NYC. So it looks like more of the same into the first week of January. Beyond the first week we’ll have to monitor if the Jet can weaken enough to allow the ridge to hold near the West Coast. That would be the best chance to try and shift the storm track to more of a coastal track allowing 4” events in NYC. The question then becomes how long can we hold that pattern if we get it before the usual seasonal La Niña more -PNA pattern emerges during the mid to late winter. And if the recent +AAM can back against that La Niña seasonal tendency.