Winter '18 / '19 - Sudden Stratospheric Warming: Watch #1 - UPDATE 2

Brief ... less dramatic stratospheric warming at 30 mb on 20-DEC-18 has faded only to be replaced by a much larger  ... stronger ... and very well modeled event with its sprawling center over the northern Asia continent.

Figure 1.  10 hPa temperature change in a week in the Northern Hemisphere
Contour interval:  5 °C.
PINK and light BLUE shadings indicate warming and cooling, respectively.
RED shading denotes warming for values higher than 25 °C.

Image courtesy:  Tokyo Climate Center, Climate Prediction Division

Figure 2.  10 mb Zonal Mean Temperature for 2017 & 2018
Note the sharp on-going increase in temperature (far right) and the previous SSW events during FEB-18 (center) and FEB-17 and again in MAR-17 (far left).

Image courtesy:  CPC Stratosphere's Global Temperature Time Series 

Figure 3.  Latitude-height cross section of zonal mean temperature
Note the descending bulge of warm temperatures in bottom row as the current SSW event unfolds

Image courtesy:  Tokyo Climate Center, Climate Prediction Division
 

Figure 4.  Latitude-height cross section of zonal mean wind
Note the descending blue region in last panel as the easterly wind (negative values flow into the board) begins to disrupt the polar vortex.

Image courtesy:  Tokyo Climate Center, Climate Prediction Division
 

Figure 5.  240-hr 10 mb zonal wind forecast
Note the PV split (sister vortices) over NE Europe and NE North America

Once the circulations work their way to the surface ... they're expected to bleed a mother lode of numbing Arctic air into the Upper Midwest and ooze its way deep into the southern tier of states.  Arctic boundary likely to drape along the eastern seaboard providing favorable baroclinic conditions for coastal cyclogenesis.

Image courtesy:  Freie Universität Berlin Institute for Meteorology - Stratospheric Diagnostics

Winter '18 / '19 - VCP32: Merry Christmas

Winter '18 / '19 - Outlooks

Thread updated periodically as new outlooks and forecasts are issued from a variety of credible sources.

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Climate Prediction Center (CPC)

Cohen (AER)

Read more »

Winter '18 / '19 - Sudden Stratospheric Warming: Watch #1 - UPDATE

Game On!
Major sudden stratospheric warming (SSW) in the cards and being dealt.

Figure 1:  10 hPa temperature change in a week in the Northern Hemisphere

Contour interval:  5 °C.
PINK and light BLUE shadings indicate warming and cooling, respectively.
RED shading denotes warming for values higher than 25 °C.
Image courtesy:  Tokyo Climate Center, Climate Prediction Division
 
Action center over Hudson Bay and much of Canada.

"A major midwinter SSW event occurs when polar stratospheric temperatures increase by at least 25 K in one week, and the zonal-mean zonal wind at or near 10 hPa (~30km altitude) reverses direction and becomes easterly north of 60° N."
REF:  NASA Global Modeling and Assimilation Office

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NWP models continue projections for major SSW through month/s end.


Figure 2:  D+10 Latitude x height cross-section from EC prog

MAIN FEATURES:
- Stratospheric anticyclone progged to descend near the 20 mb level
Upper right corner - wind into the board ==> anticyclonic circulation

- Deep surface anticyclone at or above 500 mb
Lower right corner - wind into the board ==> anticyclonic circulation (Arctic surface HIGH)

Image courtesy  Wetterdaten des Meteorologischen Instituts, Standort Berlin-Dahlem

IMPACT:
"Pronounced weakening of the NH wintertime stratospheric polar vortex tend to be followed by episodes of anomalously low surface air temperatures and increased frequency of occurrence of extreme cold events throughout densely populated regions such as eastern North America, northern Europe, and eastern Asia that persist for ~2 months."
REF:  Thompson et al. (2002)

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Also note QBO-W depiction at 30 mb over the equator.
QBO flipped from East (negative) to West (positive) in NOV.
Not necessary a good thing.

QBO-W associated with ...

• pressure differences over the North Atlantic tend to be greater, which strengthens the jet stream which increases chances of mild and stormy winter weather.
• geopotential height at high latitudes is significantly lower
• In years with low solar activity the polar winter vortex tends to be ... deeper and undisturbed ==> +AO ==> inhibits spillage of Arctic air into mid-latitudes.
• -PNA
• warmer SE states
• +NAO

Some of the very same things found to be associated with DEC not having a contest-worthy snow storm.

Winter '18 / '19 - Dismal December

After a rousing early start to the season on 16-NOV ... winter left the building leaving the forecast area with little ... if anything ... to show for itself.

The lack of contest-worthy storms in DEC has happened several times in the past including NEWxSFC/s '99 / '00 inaugural season ... '06 / '07 ... '11 / '12 ... '14 / '15 ... and '15 / '16.

Worse yet ... - only '14 / '15 reached the Contest/s historical median of eight snow storms for the season and the NEWxSFC station/s aggregate observed season-total snowfall was above average (1,597" v. 1,096").

Winter/s not having a DEC snow storm have other dismal associations ...
- All years AO index > 0; 4 years > 0.74
- All years NAO index > 0; 4 years > 1.30
- Mixed bag for ENSO ... PDO .. and QBO (3/5 +ENSO; 3/5 +PDO; 3/5 QBO-W)

If the incipient sudden stratospheric warming event doesn't throw us a bone come JAN ... might could be time to stick a fork in Winter '18 / '19.

Winter '18 / '19 - Sudden Stratospheric Warming: Watch #1

Polar vortex (PV) displacement event appears to be in the cards come Christmas.

Full flow reversal + warming ==> major sudden stratosphere warming (SSW) event ...

BLUE:  into the board ==> east wind (-U)
ORANGE:  out of the board ==> west wind (U)

"A major SSW occurs when the 10 mb 60°N zonal mean zonal wind reverses from westerly to easterly and the 10 mb zonal mean temperature gradient increases poleward of 60°N." (.pdf)

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Last winter's SSW event crash-landed over the UK (weeks of late season snow + cold)

This year ... round and round she goes.
Where she stops ...
Nobody knows.

Winter '18 / '19 - VCP32: Winning the Lottery!

Winter '18 / '19 - November/s AO Predicts The State Of Winter/s AO

NOV/s Arctic Oscillation (AO) Index:  -1.116

Conventional meteorological wisdom holds the state of winter/s AO is next to impossible to forecast.

Some use analogs.  The analog forecasting methods seeks similarities between the AO state in the run-up to the coming winter with AO run-up states of winters past.  The NEWxSFC method ranks analog years by their sum of square errors (SSE) statistic.

Lower SSE errors ==> stronger analog

Constraining the number of analog winters for analysis to five is arbitrary.
See this year's analogs below.

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An alternative forecasting technique looks at the AO/s 'sign' (i.e., positive or negative) for any calendar-year's month preceding the pending winter as a potential leading indicator of the AO/s sign for upcoming D-J-F period.

Results from a chi-square 'test for independence' infers a statistically significant relationship ... at the 95% confidence level and a p-value < 0.05 ... between NOV/s AO sign and AO/s sign of the upcoming D-J-F period.

IOW ... if NOV/s AO is negative (positive) ... then the average AO state during the upcoming winter will also be negative (positive); although the classification model is stronger ... i.e., lower false alarm rate ... for the predictor's month with negative signs than positive.

True + ==> prediction is True
False + ==> prediction is False

Given NOV-18/s negative AO ... the 2x2 contingency table predicts a 73% likelihood (27/37) the three-month average AO (D-J-F) will also be negative this winter.  The results says nothing about the magnitude of the winter/s AO or which months will be negative ... only the sign of its average.

During a +ENSO ... this bodes well for a colder than average winter over southern portions and snowier than average winter over just about everywhere across the NEWxSFC forecast area.

Read more »

Winter '18 / '19 - 18th Annual 'Season-total' Snowfall Forecast Contest - The Forecasts!

20 forecasters + P-O-R-N + CONSENSUS

Two first-time forecasters
Welcome bdougherty and The Snowman

A lot of familiar faces ... too.  Many with 17 years experience.
Welcome back!

Forecaster table ranked by STP

BLUE - <= 25th percentile
RED - >= 75th percentile
ORANGE - Chief forecaster (1st Place - 17th Annual 'Season-total' Forecast Contest)
P-O-R-N - period of record normal
CONSENSUS - average station forecasts

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Station forecasts:  550 (including P-O-R-N & CONSENSUS)
Stations forecasts for ...
BELOW average snowfall - 84 (15%)
AVERAGE snowfall - 25 (5%)
ABOVE average snowfall - 441 (80%)

Confidence (at least 67% of forecasts) for stations with ...
BELOW average snowfall @ NONE
ABOVE average snowfall @ all stations except ACY
All forecasters expect above average season-total snowfall @ BGR & BDR

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All forecaster entries at the Contest/s web site here (direct link to forecasts).

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NEWxSFC/s regular season 'snow storm' forecasting contest began 16-NOV.
'Call for Forecasts' for subsequent snow storms are issued at NEWxSFC/s web site and blog (you are here) ... via e-mail ... and Facebook.

Web site:  http://www.newx-forecasts.com/index.htm
Facebook:  https://www.facebook.com/newxsfc/