raindancewx

My winter forecast included the idea that the NAO would go negative in December and then revert positive for Jan-Feb based on 'NAO analogs' which match the 2020 NAO in predictive periods to similar behaving predictive periods. Will be curious to see how that goes. The NAO is a much more important as a national feature for Jan-Apr than at other times.

Date Tahiti (hPa) Darwin (hPa) Daily Contribution 30 day Av. SOI 90 day Av. SOI 20 Dec 2020 1011.45 1005.80 10.02 12.80 9.49 19 Dec 2020 1012.11 1002.50 30.57 13.03 9.54 18 Dec 2020 1012.34 1002.05 34.10 12.68 9.35 17 Dec 2020 1013.64 1003.35 34.10 12.22 9.08 16 Dec 2020 1013.54 1004.30 28.65 11.67 8.85 Keep your eyes on the end of the month. That's a pretty massive drop for one day. The SOI is still positive, so it's probably a northern stream system with some pop if something is going to come through. The SOI crashed pretty hard in a very positive month about this time (12/18-12/19) in 2018 ten days before the end of the month system. 2018 352 1014.64 1006.70 21.90 2018 353 1013.25 1008.05 7.68 This is late 2016 - 2016 355 1010.63 1002.35 23.66 2016 356 1010.94 1003.25 20.60 2016 357 1009.60 1005.95 -0.36 2016 358 1007.23 1006.85 -17.33 Pretty hard to find 20 point drops in a day at this time of year.

Date Tahiti (hPa) Darwin (hPa) Daily Contribution 30 day Av. SOI 90 day Av. SOI 20 Dec 2020 1011.45 1005.80 10.02 12.80 9.49 19 Dec 2020 1012.11 1002.50 30.57 13.03 9.54 18 Dec 2020 1012.34 1002.05 34.10 12.68 9.35 17 Dec 2020 1013.64 1003.35 34.10 12.22 9.08 Those 20 point crashes are rare...but fun usually. No idea if this will work, but if you run objective "closest high" matches for 22 US cities and then pull out the most common top-10 close matches as analogs, you get a pretty good map for December, followed by an extremely warm US winter. I would say, very generally, either 2011 or 2012 or both were common western matches, while 1999, 2011, 2017 were more likely in the East. Overall, 2001 was the year that most commonly appeared as a top 10 match, which surprised me a bit.

Nino 4 in the prior winter is fairly predictive of what the NAO does in February. Bodes better for February 2022 in the East with Nino 4 likely to finish in the low 27s. But Nino 4 was 29.19C last winter. Not a good sign for this year. Above 28.7C in Nino 4 the prior winter, only 1 in 20 winters is below -0.2 for the Feb NAO. February NAO averages +0.6 for years following Nino 4 over 28.7C in winter, but averages -0.1 in the remaining colder years. This is your +NAO La Nina composite - although I'd expect a somewhat different result.

I use this for snowfall data. Locally it is imperfect and has some small data issues, but it's 99% right. https://xmacis.rcc-acis.org/

Let's say the -NAO holds on for December. The transition from a +NAO November to a -NAO December is extremely rare: only seven years do it from 1950 to 2019. Those years are 1953, 1958, 1967, 1976, 1978, 1989, 2001. None of these years are La Ninas. But, 1967 is close, and 1978 and 1989 and 2001 are cold-Neutral. The closest match to US temperatures in Nov-Dec is actually 1953 though and it isn't close. But: 1989, 2001 are next, and then 1958. I would weight the years like this for January: 1954 (x3) - closest temperature match Nov-Dec, and low solar 1959 (x1) - follows an El Nino 1968 (x1) - closest to a La Nina 1979 (x1) - cold-Neutral following two El Ninos 1990 (x2) - OK temp match, neutral 2002 (x2) - OK temp match, neutral

The Weather Channel says winter is over. Don't really buy it personally. I wouldn't expect the South or Southwest to be cold overall, but I think January won't be super warm out here, and I doubt March will be real warm in the Southeast or Northeast. Southwest should roast in March, but I don't buy it getting into Wyoming or Nebraska either. It may be more of a +3 look than the +5 or +8 they seem to be implying.

Looks like 6.6" total for Philadelphia, 10.0" total for Central Park, and 12.9" for Boston (Logan). Those figures are all within range of my five winter analogs.

As of Midnight eastern: Central Park had 6.5" Philadelphia had 6.3". The difference is, Philadelphia has had rain/freezing rain in recent hours, while NYC (Central Park) is still reporting snow at this hour. From 1931-2019, Philadelphia has only had at least six inches of snow on a December calendar day 12 times - so this was pretty solid. The bigger snows that can happen are almost always later in the season. Philadelphia went over to plain cold rain for about an hour around Midnight, so I'd imagine some to most of the snow is gone already.

Snow totals for Philadelphia, New York City and Boston are not final yet, but for reference: In Boston, from 1931-32 to 2019-20, from October-May, 84/89 years see four or fewer days with at least six inches of snow. It's not official yet, but I'd expect Boston to top 6 inches on 12/17. The median from 12/18 to 5/31 is one day with six inches of snow. I would go above the median though for Boston, with 3-5 days over six inches, since my analogs had four for Boston. In New York City, from 1931-32 to 2019-20, from October-May, 82/89 years see two or fewer days with at least six inches of snow. It's not official yet, but I can't see NYC not topping 6 inches today. The median from 12/17 to 5/31 is one day with six inches of snow. So I would expect two days overall with 6"+ this winter, instead of the median of one. In Philadelphia, from 1931-32 to 2019-20, from October-May, 85/89 years see two or fewer days with at least six inches of snow. It's not official yet, but I think Philly will (just) top 6 inches today. The median from 12/17 to 5/31 is zero days with six inches of snow. So I would expect just this one day overall with 6"+ this winter, especially with the snowstorm today and in October following my winter outlook idea, with rapid deterioration in totals from Boston to NYC and NYC to Philly, i.e. more extreme cut off than the normal 41"/25"/22" seasonal totals.

Jamstec has an El Nino trying to develop in Nino 1.2 in Summer. Sort of like the 1996-97 to 1997-98 transition but weaker/slower.

Not bad for Western Colorado yesterday.

Where is it then? That snow in the north here has been there since September.

It looks like a lot of the Northeast has soil temperatures in the low 40s still. That's not super warm, but it doesn't help either. Usually shave off 20% from the model depictions if the ground is above 40 out here. I'd have to look but you guys were probably in the 60s in the 2009 storm before it happened, but this isn't as ideal as that setup either.

The weeklies imply December is around 25.45C in Nino 3.4 so far. It was 25.31C officially for November. The models show Nino 3.4 warming throughout the winter. So if December finishes around 25.5C, the winter should be above that. The last winter to finish below 25.5C in Nino 3.4 was 2010-11, so this is going to be one of the longest stretches in the data without a major La Nina. For my purposes, a La Nina warmer than 25.5C in Nino 3.4 in winter isn't moderate. On the CPC ONI standard, there will probably be three trimesters below -1.0C: SON, OND, NDJ. I don't think December to February will qualify. On the Jan Null standard, it will just barely qualify as a Moderate La Nina. Against 1951-2010 averages, it's pretty likely that only October & November are 1.0C below average or colder, with only OND likely to qualify as -1.0C or colder. I mention all this because with the current readings and forecast warming, this event may not end up materially stronger in winter than years like 1995-96, 2011-12, or 2017-18, which all had Nino 3.4 at about 25.75C in winter. The Fall peaked more impressively than those years though, which is interesting.

Actually think Uncle Sam has the right idea here in most spots. I'd go a bit lower for NYC/NJ/Philly/Western CT. The short range models are good at detecting sleet and small warm profiles above the ground from what I can remember in college when we evaluated model performance in Nor'easters.

Nino1+2 Nino3 Nino34 Nino4 Week SST SSTA SST SSTA SST SSTA SST SSTA 04NOV2020 20.3-1.0 23.6-1.3 25.1-1.5 27.8-0.8 11NOV2020 21.2-0.3 24.1-0.9 25.7-1.0 27.9-0.7 18NOV2020 21.0-0.7 23.6-1.4 25.2-1.5 27.9-0.7 25NOV2020 21.0-1.0 23.7-1.3 25.3-1.3 27.9-0.7 02DEC2020 21.8-0.5 24.4-0.7 25.5-1.1 27.6-1.0 09DEC2020 22.4-0.1 24.3-0.8 25.4-1.2 27.7-0.8 I don't know if people realize, this event has actually been weaker in Nino 1.2/3 compared to 2017-18 for a while now. I would say it's easier to get canonical La Nina conditions with Nino 3/1.2 both cold. This event is much colder in the West. 08NOV2017 20.2-1.2 23.8-1.2 25.6-1.1 28.3-0.3 15NOV2017 20.6-1.0 23.8-1.1 25.6-1.1 28.2-0.4 22NOV2017 20.6-1.2 23.9-1.1 25.9-0.8 28.5-0.1 29NOV2017 20.8-1.3 23.9-1.1 25.9-0.7 28.5-0.0 06DEC2017 20.8-1.6 24.1-1.0 25.7-0.8 28.2-0.3 13DEC2017 21.3-1.3 24.0-1.1 25.8-0.8 28.1-0.3 2010 is still much colder than this event at the moment. But the 2007-08 event is still close in Nino 3.4/4, and it warms rapidly in Nino 1.2 after mid-December. 03NOV2010 19.7-1.6 23.4-1.6 25.2-1.4 27.0-1.6 10NOV2010 19.5-1.9 23.5-1.5 25.2-1.4 27.2-1.5 17NOV2010 20.2-1.5 23.5-1.5 25.0-1.6 27.1-1.5 24NOV2010 20.6-1.3 23.3-1.7 24.9-1.7 26.9-1.7 01DEC2010 20.5-1.7 23.3-1.7 25.0-1.7 27.0-1.5 08DEC2010 20.9-1.5 23.4-1.7 25.0-1.6 26.9-1.6 07NOV2007 19.3-2.1 23.0-2.0 25.0-1.6 27.5-1.1 14NOV2007 19.2-2.3 23.2-1.7 25.2-1.5 27.3-1.3 21NOV2007 19.8-2.0 23.2-1.8 24.9-1.7 27.1-1.5 28NOV2007 19.8-2.2 23.3-1.8 25.1-1.6 27.4-1.1 05DEC2007 20.6-1.8 23.5-1.5 25.1-1.5 27.5-1.0 12DEC2007 20.3-2.4 23.3-1.8 24.9-1.7 27.5-1.0 December 2000, 2007, 2008, 2011 are all kind of close but not quite right for the current look. 08NOV2000 20.6-0.8 24.0-1.0 25.6-1.1 28.1-0.6 15NOV2000 20.3-1.3 24.2-0.7 25.9-0.7 28.2-0.4 22NOV2000 20.2-1.7 24.1-0.9 25.9-0.7 28.1-0.5 29NOV2000 21.4-0.7 24.4-0.6 25.9-0.7 27.8-0.7 06DEC2000 21.8-0.6 24.4-0.7 25.6-1.0 27.5-1.1 05NOV2008 21.3 0.0 24.6-0.3 26.3-0.3 28.2-0.4 12NOV2008 21.8 0.3 24.9-0.1 26.5-0.2 28.1-0.5 19NOV2008 21.5-0.2 24.9-0.1 26.3-0.3 28.0-0.6 26NOV2008 21.2-0.8 24.6-0.4 26.1-0.5 27.9-0.6 03DEC2008 21.4-0.9 24.8-0.3 26.0-0.6 27.9-0.6 10DEC2008 22.1-0.4 24.6-0.5 25.8-0.8 27.7-0.7 02NOV2011 20.5-0.8 23.9-1.1 25.6-1.0 27.9-0.8 09NOV2011 20.5-0.9 23.9-1.1 25.7-0.9 27.9-0.7 16NOV2011 20.5-1.1 23.8-1.1 25.6-1.0 27.9-0.7 23NOV2011 21.4-0.5 24.0-1.0 25.6-1.0 27.8-0.8 30NOV2011 21.0-1.2 23.8-1.3 25.4-1.2 27.7-0.9 07DEC2011 21.4-1.0 23.9-1.2 25.5-1.1 27.5-1.0 06DEC2000 21.8-0.6 24.4-0.7 25.6-1.0 27.5-1.1 12DEC2007 20.3-2.4 23.3-1.8 24.9-1.7 27.5-1.0 10DEC2008 22.1-0.4 24.6-0.5 25.8-0.8 27.7-0.7 07DEC2011 21.4-1.0 23.9-1.2 25.5-1.1 27.5-1.0 Blended: 21.4 24.1 25.5 27.6 09DEC2020 22.4-0.1 24.3-0.8 25.4-1.2 27.7-0.8 My guess is this La Nina becomes a Modoki / West-Central La Nina, with Nino 4 taking over as the coldest zone in January. For now, Nino 4 is ~5C warmer than Nino 1.2, compared to ~7C warmer than in 2017.

I'm generally happy with my national snow outlook. But I wish that area along the border of IL/MO would fill in.

Boston has had two calendar days in December with 12 inches of snow or more from 1891-2019. Would be a pretty impressive feat to pull that off again. Last time was December 1960, and before that December 1909. I'm sure there are several more storms that have topped 12" in 24 hours if you include storms that start late one day and continue the next day. Only three storms since 1891 have brought 3"+ snows for Boston on 12/16, and five have done it on 12/17. 1 2013-12-17 6.4 0 2 2016-12-17 4.3 0 3 1970-12-17 3.8 0 4 1976-12-17 3.3 0 5 1988-12-17 3.1 0 1 2007-12-16 7.6 0 2 1896-12-16 5.0 0 3 1980-12-16 3.2 0 Accuweather has a 65% chance of 6-10 inches of snow for Boston...but does not buy totals higher than that. NYC is at 3% for 10"+ too, with Philly at 3% for 8"+.

BAM WX had this on their Twitter a few hours ago.

Meanwhile...in the 'warm dry' Southwest...

Last two systems really helped take snowpack here from pretty awful, to near average north and lousy south.

Big time downward trend in La Nina strength on the UKMet.

1990 actually showed up in the CPC analogs today. Nice to see the East bathing in warmth on their outlook. I'd imagine the warmth is pretty muted though. Not really expecting a whole lot of snow south of NYC east of the fall line but it would keep the warmth in control for a bit in the East. It's like a ~12 days in 90 year frequency for Philadelphia to get even six inches of snow in December though.