bluewave

The WAA aloft and dryslot did their thing.

I only got 4” here before the sleet arrived. So the bar is set pretty low. I will go out on a limb say that there will be a better storm than that at some point this winter.

The Christmas storm looks to really create a major wave breaking event. So I am taking a wait and see approach as to how long after that we can expect a colder and snowier storm track. I am hoping that we can finally get a cold enough storm for the South Shore to finally get into the jackpot zone like we were in 15-16, 16-17, and 17-18.

We can get rapid snowmelt under a variety ENSO conditions. The last one that made local headlines was in March 2015. But I am glad that areas near the coast will have a chance to gradually reduce the snowpack going into the late week storm.

It’s interesting how persistent this solstice warm up has been especially since 2011. It has occurred under a wide variety of weather patterns. Some years like 2013 had a snowstorm just before the warm up like the forecast for this year. Others like 2017 went into the deep freeze right after Christmas. 2015 featured the historic +13.3 departure and the warmest day of the month was on the 24th. Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Ending Date Highest Max Temperature Dec 18 to Dec 25 Missing Count 2019-12-25 57 0 2018-12-25 61 0 2017-12-25 55 0 2016-12-25 58 0 2015-12-25 72 0 2014-12-25 62 0 2013-12-25 71 0 2012-12-25 56 0 2011-12-25 62 0

Areas to our north which were below 0° today may experience one of their biggest day 5-6 temperature rises for December. The records for December were set in 2013 and 2008.

Plenty of competing factors seem to be altering the typical La Niña forcing pattern for December. Notice how the VP anomalies are skewed further S and E than one would expect from a La Niña. The forcing near the DL is more of an El Niño look.

These are two great tweets on how the record warm SSTs to our east are providing extra moisture to snowstorms. But on the flip side, we also get bigger rain and wind storms when the intense lows track to our west. Especially with systems that can go negative tilt.

You can think of the warm storm track near Christmas as a sacrifice bunt. The ensembles are trying to use it as a means to shift the blocking from east of New England closer toward Greenland later in the month. We saw something like this with the warm storm track back around December 1st. So while the event around Christmas looks warm and wet, it could set the stage for a cold and snowy storm track as we approach and move into 2021.

There is plenty of missing climate data for some reason this month. But NYC is at +0.5 on the xmacis2 climate site. A very Niño-like temperature departure this month with warmth along the Northern Tier and cold South.

Thanks, Don. There is a long history of people making out of place responses to things that people didn’t actually say in their original post. BGM and ALY mention possible runoff issues in their AFD. People have to realize that we are having a long range model discussion. Obviously, the actual details that show up closer in will be the ones of most relevance. So to say that x model shows y solution a week out is not a 100% endorsement of what its showing. Just to begin to think about what types of impacts could arise if such solution was actually to verify. We have the existing significant snowpack to consider, and the implications for additional runoff. Milder temperatures and some rain will arrive for Thursday into early Friday. Deepending on how much rainfall and snowmelt occurs, there could be a response on area rivers and streams, although it is still too early to tell how much of an impact this will be.

Yeah, this was our first La Niña with a NYC 6”+ snowstorm in the week before Christmas since 1995. While patterns have changed greatly since then, maybe we could get another shot a major snow event like we did in early January 1996. It may come down to how strong the wave break is with the Christmas storm. The one on December 1st resulted in the record block east of Newfoundland. That blocking eventually shifted poleward and we got our significant snow event this week. Models are going for another big block east of Newfoundland after the Christmas storm. Beyond that time, models may not yet have a handle on how the blocking east of the Maritimes progresses. We can remember how models greatly underestimated the blocking over the North Pole this past week from the day 10-15 period. It suddenly popped up in the 7-9 day forecasts. So we need to watch for something like that near the end of December. That could potentially set the table for another significant snow event. The animation below is an excellent example of how blocking since early December shifted poleward over time. https://www.cpc.ncep.noaa.gov/products/intraseasonal/z500_nh_anim.shtml

I was posting cold model runs last week for this week when the models latched onto the big block over the North Pole. But the coastal sections had to deal with WAA around 850mb which I pointed out that lead to the sleet and the cement snowpack. You have to take the weather as it comes. What good would it be to only show the weather you like and ignore the kinds that you don’t. All different types of weather have an impact. There are many posters on this forum that are interested in a wide variety of weather. Imagine turning on you local weather forecast and they only showed a preferred type of weather and ignored all the rest.

Flood potential on the 12z Euro around Christmas. Especially for the interior areas with a 20-40” snowpack. Euro has heavy elevated convection and temperatures into the 50s in those areas. Maybe we can slowly melt our pack each day so there isn’t a more rapid melt like they could get north and west of the area if this solution verified.

If the guidance is anywhere close, this could be the 10th solstice warm up in a row with 55°+ temperatures. Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Ending Date Highest Max Temperature Dec 18 to Dec 25 Missing Count 2019-12-25 57 0 2018-12-25 61 0 2017-12-25 55 0 2016-12-25 58 0 2015-12-25 72 0 2014-12-25 62 0 2013-12-25 71 0 2012-12-25 56 0 2011-12-25 62 0

The storm around Christmas may turn into another wave breaker event like near the start of December. Notice the extreme block the models are moving to following the storm east of Newfoundland. That is very similar to what happened back in early December. This early December block east of the Maritimes came before the blocking built into the Arctic like we just saw. So maybe the Christmas storm will set the table for another -AO drop into January followed by the next major snowstorm potential.

Record warmth to some type of snowfall record is becoming more frequent in recent years. November 2020 was the warmest on record in NYC at 53.0°...5th earliest seasonal 10.0”+ snowfall of 10.5” in December January to March 2020 was the 2nd warmest on record in NYC at 42.4°...trace of snow on May 9th tied with 1977 for latest on record after 7th coldest winter at 28.3° February 2018 was the warmest on record around the area with a first 80° at Newark .....NYC warmest February at 42.0°....ISP snowiest March at 31.9” of snow December 2015 was warmest on record with a +13.3...50.3° in December....greatest snowstorm on record in NYC during January of 27.5” January 2006 was the 4th warmest in NYC at 40.9° followed by the 2nd biggest snowstorm in February of 26.9”

The big blocking high that quickly developed over the Arctic in the 6-10 day forecast period closed the deal. But the EPS did a good job forecasting the overall pattern. One of the better EPS performances from late November into December.

Updated for Dec 16-17,2020 https://nwschat.weather.gov/p.php?pid=202012171928-KOKX-NOUS41-PNSOKX 1 S EAST TREMONT 12.4 IN 0145 PM 12/17 TRAINED SPOTTER

While we have surpassed many previous snowfall records since 1994, that winter really stands as the last widespread severe ice storm. I had an ice storm in Long Beach on Valentine’s Day 2007 and Feb 2, 2011. But neither one of those were on par with Jan 1994. Jan 94 was my only ice storm in Long Beach lasting over 12 hours. It was remarkable how even Long Beach was able to stay in the 20s with freezing rain from the early morning into the night.

This looks like the 5th earliest 10” snowstorm for NYC. #1 Nov 26-27, 1898....10.0”. #2 Dec 5-7.......2003....14.0” #3 Dec11-12...1960.....15.2” #4 Dec 15th.....1916.....12.7” #5 Dec 16-17....2020.....10.0”

Once the models saw the SSW in February, they began to move toward the cold and snowy March.

That’s been my whole point since October. There have been too many competing influences since at least October to use ENSO as a sole indicator. Think of it more like a collection of overlapping influences adding their various inputs to what becomes the actual pattern. Front-loaded doesn’t mean that there can’t or won’t be other periods of active winter weather. On the whole though, La Ninas have been known for early wintery periods. The best winter DJF snowstorm of the 95-96 La Niña was on January 6th and the 00-01 La Niña December 30. The greatest winter snowstorm of the 17-18 La Niña was January 4th. But that doesn’t preclude a March 2018 or even 2001. The super El Niño in 15-16 had the historic event later in January. The 82-83 super El Niño had the best snowstorm of the season in February. Same for the snowiest month during the 09-10 El Niño in February which had a strong backloaded period late winter. So while there has been many overlapping influences, at least we got some element resembling a La Niña this month.

The last few months have been an extreme example of mixed influences. But at least we can say some element of La Niña has shown up. The La Niña front-loaded early winter snowfall period has worked out. Numerous La Ninas in NYC had a 6”+ storm and or monthly snowfall total for December.

Before I changed the title of the winter thread that I started back in October, it was about the MJO staying in 4-5 for October. I changed the title of the thread for a broader winter discussion. I actually deleted my first post which didn’t look like it may work out in November as not to get hopes up too high. It was about October La Niña forcing and seasonal snowfall. Cases focused near the Maritime Continent 4-5 usually had better snow outcomes than the IO phases back to 2000. I included the last 2 winters due to the strong Niña-like background state focusing the ridge north of Hawaii. But We have seen many Niño-like influences this month like the record NP warmth and the +AAM spike and strongest +PNA for a moderate La Niña in December. The MJO in October seemed to be hinting a better snowfall outcome this winter than the last two. Perhaps, the MJO in October can be a precursor to the amount of blocking in the winter during a La Niña even if many Niño-like features are present. There were so many conflicting features during October and November that it was really tough to know how everything would interact with each other until we got to December. This will be a first for such an extreme November to December AO reversal especially for a La Niña with record warmth in November. October 2020 forcing closer to snowier La Niña composite since 2000 Snowier outcomes Less snowy