My Winter Outlook 2017-18 - VERIFICATION

[raindancewx]

I know you don't like using SSTs, but if you think this is an East based La Nina, I'd say you are underselling Nino 1.2 a bit in your outlook with the years you picked. I'd also be worried that the placement of precip/temp anomalies will be off some since you have the Atlantic/Pacific so much colder than reality by both US coasts. The Indian Ocean is also much warmer than you have it, which probably has some MJO implications. Overall though, idea could be right.

The cold waters north of Nino 3/Nino 1.2 would worry me if you really expected a dry winter in the SW, when Nino 1.2/3 is cold and the waters north are warm, we often see the storm track dip pretty far south out here. If the track is dry, like 2012-13 it stays dry, but cold, but more often than not we get near average rain/snow even down towards Mexico when that feature appears. Look at the differences along the coast of North America:

 

[Isotherm]

15 hours ago, Stebo said:

Yeah I really love this outlook, great work and I hope it verifies, would be a nice roller coaster ride for this region.

 

 

Thanks Stebo, appreciate it! Should be interesting to see how the pattern unfolds.

[Stebo]

Just now, Isotherm said:

 

 

Thanks Stebo, appreciate it! Should be interesting to see how the pattern unfolds.

Likewise, will be interesting to see how this advances into Spring severe season too, you do have some years that popped early on your list.

[Isotherm]

14 hours ago, raindancewx said:

I know you don't like using SSTs, but if you think this is an East based La Nina, I'd say you are underselling Nino 1.2 a bit in your outlook with the years you picked. I'd also be worried that the placement of precip/temp anomalies will be off some since you have the Atlantic/Pacific so much colder than reality by both US coasts. The Indian Ocean is also much warmer than you have it, which probably has some MJO implications. Overall though, idea could be right.

The cold waters north of Nino 3/Nino 1.2 would worry me if you really expected a dry winter in the SW, when Nino 1.2/3 is cold and the waters north are warm, we often see the storm track dip pretty far south out here. If the track is dry, like 2012-13 it stays dry, but cold, but more often than not we get near average rain/snow even down towards Mexico when that feature appears. Look at the differences along the coast of North America:

 

 

Thanks for the post. Your point is definitely valid, and one of the issues I had was reconciling the not insignificant differences in background warmth both oceanically and atmospherically now versus analog years in the 1950s, 70s, and to a lesser extent 80s. I even mentioned in the outlook itself, that geopotential heights will appear artificially lower due to the warmer base state of recent decades (amplified further this year specifically). We're essentially in uncharted territory as far as seeing a La Nina of this magnitude occur coincidently with such warmth to the SW of Mexico. I do think it's plausible that could enhance the STJ at times this winter. Whether that's sufficient to engender above average pcpn for the SW US, we'll see.

[Paragon]

4 hours ago, Isotherm said:

 

Thanks for the post. Your point is definitely valid, and one of the issues I had was reconciling the not insignificant differences in background warmth both oceanically and atmospherically now versus analog years in the 1950s, 70s, and to a lesser extent 80s. I even mentioned in the outlook itself, that geopotential heights will appear artificially lower due to the warmer base state of recent decades (amplified further this year specifically). We're essentially in uncharted territory as far as seeing a La Nina of this magnitude occur coincidently with such warmth to the SW of Mexico. I do think it's plausible that could enhance the STJ at times this winter. Whether that's sufficient to engender above average pcpn for the SW US, we'll see.

I find the record warmth here in October highly concerning.  I find our best winters occur when October is cold, and November a little milder than normal (sounds counterintuitive but works out.)  I'm not sure December will be our best month, I think we might "snap back" after November's chill back to above normal.  If that's the case, this might be much more of a backloaded winter than a book ended one- I think both February and March will produce our best wintry weather.  It might be a situation where Dec and Jan are + temp and Feb and Mar are - temp.

 

[raindancewx]

Warmth West of Mexico, almost to Asia, north of a cold Nino 1.2/3 existed in 1943. I'm not a huge fan of the reconstructions pre-1930, but I find that the 1931-1950 era is pretty reasonable. The ONI anomalies for the 1950s are based on observational means for 1936-1965, so the 1930s/1940s tropical data is pretty reliable.

There is some research out there that suggests 1942-43 should have been a negative QBO winter, like 2016-17, but the triple El Nino of 1939-40, 1940-41, 1941-42, kind of broke the QBO process and it didn't go negative until 1943-44, so that's kind of similar too. The whole "La Nina" temperature anomaly thing with a super wet SW/interior SE showed up in 1931-32 and 1942-43, so that's why I've been looking hard at 1943-44 and 1932-33 for this year. The 40s have the added bonus of being near a long-term PDO flip in that era.

[Isotherm]

Verification:

 

http://www.lightinthestorm.com/archives/1108

 

VERIFICATION

 

Meteorological Winter Temperature Departures:

 

 

 

Meteorological Winter Precipitation Departures:

 

 

 

Local Statistics:

Dec-Jan-Feb Temperature Departure Outlook: +0.5 to +1.5; Warmer than normal

Actual DJF Departures:

NYC: +1.1

Newark, NJ: +1.4

LGA, NY: +1.2

Snowfall Forecast: New York City: 27-34”

Actual Snowfall for Winter 2017-18:

NYC: 35.2″

Newark, NJ: 33.9″

LGA, NY: 32.0″

*Note* – snowfall was significantly greater immediately south of NYC, and east of NYC over Long Island with totals of 40-50″+.

 

Commentary and Grading

This winter could not have gone much better as far as overall temperature departures – values fell directly within the ranges provided from the winter outlook, circa +1 for the DJF period. The way in which we arrived there was quite volatile, and expected to a significant extent. The cold/much colder than normal December verified, as did the very warm second half of the winter. The second half of January 2018 turned very warm, but the cold in the first half of the month led to a colder than normal January departure, an unexpected curve-ball. Nevertheless, the warmth was more than sufficient in the second half to countervail the negatives, and produce a solid positive/warm anomaly.

Nationwide, the idea that the South and the East would be warmer than normal w/ the core of the cold over the Rockies/N Plains verified well. One flaw was that the Southern Plains ended up cooler than forecasted.

Precipitation wise, the general idea of wetter than normal over the inter-mountain West, and the Appalachians/Northeast-Mid-Atlantic with drier conditions across the South verified fairly well.

Select snowfall for other cities:

Boston: 57.5″ / Forecast: 50-57”

NYC: 35.2″ / Forecast: 27-34”

LGA: 32″ / Forecast: 27-34”

JFK: 31.8″ / Forecast: 27-34”

Newark, NJ: 33.9″ /Forecast: 27-34”

Islip: 61.3″

Bridgeport: 39.9″

Philadelphia: 29.8″ / Forecast: 17-24”

New Brunswick, NJ: 40.6″ / Forecast: 27-34”

Wash DC: 7.8″ / Forecast: 9-16”

Baltimore: 15″ / Forecast: 12-19”

Dulles: 11.9″

Worcester, MA: 86.6″ (+/- 3″)

Hartford, CT: 48.3″ (+/- 3″)

Providence, RI: 45.9″

 

Overall, the snowfall forecast verified very well, with the forecast for less snow than normal south of the Mason-Dixon line, and snowier than normal in New England, working out correctly. NYC itself verified well. The one flaw/unexpected area was from portions of central NJ through Long Island, which had quite a bit more snowfall than I expected (40-50″+). Favorable storm tracks benefited these areas. Snowfall is always the most difficult part of a long range forecast due to the non-linear/stochastic nature of snow storms.

 

Final Grade – this, overall, will go into the “hit” column, bringing my long term accuracy rate since 2006-07 up to 82%.

Precipitation: A-

Temperatures: A

Snowfall: A-

Winter 2017-18 Final Grade: A-

 

[nzucker]

Great forecast. 

If you look at November-March, however, the winter takes a colder cast.

[Isotherm]

22 minutes ago, nzucker said:

Great forecast. 

If you look at November-March, however, the winter takes a colder cast.

 

Thank you @nzucker. Appreciate it. Yeah, I did mention in the outlook that the analogs suggested a return to snowfall/winter in March, although DJF was my forecast period temperature wise.

It was pretty clear, IMO, by early February - that we'd see a significant pattern change for March, given the historic downwelling SSW.

 

[nzucker]

7 hours ago, Isotherm said:

 

Thank you @nzucker. Appreciate it. Yeah, I did mention in the outlook that the analogs suggested a return to snowfall/winter in March, although DJF was my forecast period temperature wise.

It was pretty clear, IMO, by early February - that we'd see a significant pattern change for March, given the historic downwelling SSW.

 

Yes, you were always big on a snowy/cold March, which coincided with many of the La Nina analogs like March 1984, March 1967, and March 1956. All years that had a warmer mid-winter then a return to cold. The SSW along with the ENSO analogs painted a wintry picture for March, one that ultimately verified with 4 Nor'easters and the snowiest March on record at Islip. I had 16" here, a solidly above normal March snowfall though not quite historic.

[Isotherm]

17 hours ago, nzucker said:

Yes, you were always big on a snowy/cold March, which coincided with many of the La Nina analogs like March 1984, March 1967, and March 1956. All years that had a warmer mid-winter then a return to cold. The SSW along with the ENSO analogs painted a wintry picture for March, one that ultimately verified with 4 Nor'easters and the snowiest March on record at Islip. I had 16" here, a solidly above normal March snowfall though not quite historic.

 

Ended up with 23.1" here, my snowiest March on record per COOP data. 54.3" here on the season. 30-year normals are very, very impressive now.