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NYCweatherNOW

December 2019

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The long-modeled sharp increase in the Arctic Oscillation (AO) is now underway. Over the past 2 days, the AO has risen 2.5 sigma. Over the past 3 days, it has risen more than 2.8 sigma. Since 1950, there were seven prior years when the AO rose 2.5 sigma or more over a two-day period during December 20-31. During the 2010s, there has been a cluster of such events: 2014, 2015, 2016, and now 2019. Four of the prior cases saw monthly snowfall in excess of 10" in New York City during the following January: 1963-64, 1977-78, 2014-15, and 2015-16. Two had less than 4" snowfall in January: 1967-68 and 1972-73.

Widespread 0.50"-1.50" precipitation is likely in the region tonight into tomorrow. As a result, Allentown will very likely reach 60" precipitation for a record second consecutive year and Scranton could reach 50" for a record second consecutive year. 2019 will also rank among the 30 wettest years on record for New York City.

Through December 28, monthly anomalies for select cities were:

Baltimore: +2.0°, Boston: +1.6°, Islip: +0.6°, New York City: +0.2°, Newark: +0.3°, Philadelphia: +0.5°, and Washington, DC: +1.2°.

A week ago, those anomalies were:

Baltimore: +0.3°, Boston: -0.8°, Islip: -1.4°, New York City: -2.7°, Newark: -2.1°, Philadelphia: -1.3°, and Washington, DC: -0.4°.

A short-duration cold shot is possible late in the first week of January into the second week of January. Nevertheless, there is a growing risk that New York City and Newark could have an average temperature near or even above 40° for the first week of January. A tendency for ridging could develop during the latter part of the second week of the month. The predominant state of the EPO will likely be crucial to the persistence of any colder patterns.

Based on the forecast strongly positive AO to start January, the probability of a significant (6" or greater snowstorm) for the major cities of the Middle Atlantic region during the first week of January is low. Since 1950, the biggest snowfall for that region when the AO was +2.000 or above during the January 1-15 period occurred during January 14-15, 1954 when Philadelphia received 3.0" snow and New York City picked up 2.0". Boston has had numerous 6" or greater snowstorms during such cases, including one 10" or greater snowstorm. Therefore, the risk of significant snow would likely be greatest over New England assuming this relationship holds (no significant offsetting variables).

Some of the newer AO forecasts keep the AO at +2.000 or above through January 10. If so, that development could adversely impact Mid-Atlantic significant snowfall prospects beyond the first week of January.

Despite the development of a sustained colder than normal temperature regime, Utqiagvik (formerly Barrow) is nearing the end of its warmest year on record. 2019 will likely conclude with a mean temperature of 20.9°. The existing record is 18.9°, which was set in 2016. Currently, 2017 ranks as the second warmest year and 2018 ranks as the fourth warmest year.

The ENSO Region 1+2 anomaly was +0.4°C and the Region 3.4 anomaly was +0.6°C for the week centered around December 18. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.12°C and the ENSO Region 3.4 anomaly has averaged +0.56°C. The remainder of winter 2019-2020 will likely feature neutral-warm to weak El Niño conditions.

The SOI was -0.94 today.

Today, the preliminary Arctic Oscillation (AO) figure was +0.120.

No significant stratospheric warming event appears likely through January 7, but warming will likely develop in the upper stratosphere and approach or reach 5 mb toward the end of the first week of January. Wave 2 activity will remain relatively muted at 30 mb through most of the first week of January, but a moderate Wave 2 hit could occur at or above 10 mb leading to the upper stratospheric warming. Overall, most of the stratosphere is forecast to remain cold through the first week of January on the EPS. However, the upper stratospheric warming will need to be watched for downward propagation.

On December 28, the MJO was in Phase 7 at an amplitude of 1.233 (RMM). The December 27-adjusted amplitude was 1.511.

Since 1974, there were five cases when the MJO was in Phase 6 at an amplitude of 1.500 or above during the December 20-31 period, as has been the case this year. The temperature anomalies were closely tied to how much time the MJO spent in Phase 8 during that timeframe. The mean temperature for cases with more than 5 such days was 29.0° in New York City. The mean temperature for those with 5 or fewer such days was 36.1°. The overall 1981-2019 mean temperature for January 1-15 is 33.8°.

Based on sensitivity analysis applied to the latest guidance, there is an implied >99% probability that December will wind up warmer than normal in New York City with a monthly mean temperature near 38.5°.

At present, a warmer than normal January appears likely in the region.

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As of 7:25 pm, New York City had picked up 0.12" rain. That brought the precipitation total for 2019 to 52.14". As a result, 2019 has moved ahead of 1979 when 52.13" precipitation was recorded to become New York City's 31st wettest year on record. Records go back to 1869.

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44 minutes ago, donsutherland1 said:

As of 7:25 pm, New York City had picked up 0.12" rain. That brought the precipitation total for 2019 to 52.14". As a result, 2019 has moved ahead of 1979 when 52.13" precipitation was recorded to become New York City's 31st wettest year on record. Records go back to 1869.

Way above that yearly total here on SI.... Will finish the year with around 63" after this current event.

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38 minutes ago, doncat said:

Way above that yearly total here on SI.... Will finish the year with around 63" after this current event.

South and west of Manhattan picked up quite a bit more precipitation this year.

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The last two days of December are averaging 46degs., or about 13degs. AN.

Month to date is  +0.4[38.2].          December should  end near  +1.2[38.7].

The first 6 days of January are averaging 42degs.     The first halve of January looks like toast.       Just 7/16 days with a low of 32 or less----just 2 of them below the average of 27and 13/16 with a high of at least 40.

Second halve looks even worse, especially Week 3.      

Might as well keep in mind these numbers: JAN. NORMAL   32.6.    RECORD is 43.2.     Winning pace would be  +10.7.      A +5.8 would net us Top Ten status.

43* here at 6am, drizzle.        46* by Noon.       42* by 5pm.

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With two milder days to go, all our stations will finish another warmer than average December. Not much in the way of cold across the US as the Pacific continues to dominate.

Through 12-28

EWR....+0.6

NYC....+0.4

LGA....+0.2

JFK.....-0.1

BDR....+0.3

ISP.....+0.7

BD7B6DA0-632B-4A33-8161-902E22E23BB5.png.e990ba4c088eb9377ff38515e011b6ee.png

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16 hours ago, doncat said:

Mean monthly temp here  after today is 35.8°...Normal for Dec  is 36.2°, so will finish very close to normal.

 

5 hours ago, bluewave said:

With two milder days to go, all our stations will finish another warmer than average December. Not much in the way of cold across the US as the Pacific continues to dominate.

Through 12-28

EWR....+0.6

NYC....+0.4

LGA....+0.2

JFK.....-0.1

BDR....+0.3

ISP.....+0.7

BD7B6DA0-632B-4A33-8161-902E22E23BB5.png.e990ba4c088eb9377ff38515e011b6ee.png

 

 

Exactly +1.0 here through this morning. After today and tomorrow, likely near 50F, I expect that will be a bit higher. Departures about as I expected nationwide; slightly warmer than normal in the NYC-metro region; a little lower than I had for Dec, but good overall. Snowfall here was 3.7". How much do you both have to date?

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51 minutes ago, purduewx80 said:

Impressive storm out there w/ tops to 40,000'. Think some of these could affect the city ~3-5PM. 

From OKX AFD:

Fcst models show a developing axis of elevated instability with
MUCAPE up to 500 J/kg moving across the NYC metro area and
Long Island this afternoon, right on the back edge of the rain
shield, and have added isolated thunder to the forecast for
those areas.
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Impressive looking cell for late December. Continuation of the steep midlevel lapse rates that have become more common in recent years.

 

E3DC162B-AFEB-46E5-8C6F-60AB1565EAF4.thumb.png.6a017b027d7670e6caebb91df3ac33c7.png
58986A32-9A87-406E-8BFB-C7E068977F37.gif.2601a35e14d8e1ac2c47f824a07f26d1.gif

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18 minutes ago, weathermedic said:

Nice article that explains why thunder sounds louder and travels further/lasts longer in colder temperatures:

https://weather.com/science/weather-explainers/news/2019-02-21-cold-thunderstorms-winter-temperature-inversion-thunder

Yeah I first noticed that when I was a little kid. Pouring here now...no thunder.

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