CONTEST STATUS - Updated: TUE ... 15-JAN-19 @ 6:35 PM EST

Winter '18 / '19 - Snowfall Forecast Contests

20th Annual 'Regular Season' Snowfall Forecast Contest

What's A 'Contest-worthy' Storm?

Snow Storm #2
Possible 'Call for Forecasts' THU ... 17-JAN-19

Snow Storm #1
FINAL results here
18th Annual 'Season-total' Snowfall Forecast Contest

Deadline for entries has passed.
Forecasts here

Verification period: 01-DEC-18 thru 31-MAR-19

Winter '17 / '18 - Snowfall Forecast Contests
19th Annual 'Regular Season'

FINAL results here

17th Annual 'Season-total'
FINAL results here

Monday, January 14, 2019

Winter '18 / '19 - Snow Storm #2

Possible 'Call for Forecasts' slips to THU ... 17-JAN-19

Possible 'Call for Forecasts' TUE ... 15-JAN-19

Mid-latitude cyclone progged along leading edge of Arctic boundary (sub-zero post-frontal dew points).

Current guidance suggests mainly SNE forecasts stations in line for more than nuisance storm-total snowfall.

Overnight runs failed to deliver a contest-worthy snow storm over the forecast area.

NWS WFOs in VA and SE PA bumped their STP forecasts early this AM; however ... only a handful of stations came close to exceeding the 'nuisance' Contest criterion.

As of 8 PM post-time ... M-A/s weekend snow storm appears contest UNworthy (too few stations with more than nuisance snowfall)

Will re-evaluate the storm/s Contest potential FRI morning based on the overnight progs.

'Call for Forecasts' would come before noon ... if warranted.

Saturday, January 5, 2019

Winter '18 / '19 - Season-total Snowfall Forecast Contest: DEC totals

DEC-18 snowfall summary by Contest forecast station.
Rank ordered descending by percent of monthly period-of-record-normal (P-O-R-N).

Green ==> 75th - 100th percentile
White ==> less than 75th and greater than 25th percentile (inter-quartile range)
Red ==> 0 - 25th percentile

DEC Forecast Station Highlights
- DEC/s 8.9" was 1271% above its monthly P-O-R-N of 0.7"
- finished a full year's worth of work on the 9th and 10th by racking up 8.9"of storm-total snowfall  ... exceeding its annual P-O-R-N by 2.3".

- DEC/s 11.5" was 639% above its monthly P-O-R-N of 1.8" and contributed 91% toward its season-total P-O-R-N of 12.7".

- DEC/s 4.8" was 166% above its monthly P-O-R-N of 2.9" and 28% toward its season-total P-O-R-N of 17.3"

Biggest losers
DCA and BWI:  0"

Observed v P-O-R-N
BDL:  0.1" v 13.5"
ORH:  0.1" v 12.5"
ALB:  3.3" v 13.7"
CON:  3.4" v 13.7"
BGM:  7.9" v 18.2"
BTV:  8.6" v 18.8"

DEC normally contributes 210.5" (23%) toward the season-total snowfall (D-J-F-M) of 914".
DEC-18 observed snowfall:  85.3" (9% of season-total snowfall)

Teleconnection indexes and month-over tendency (updated as they become available)
AO:  +0.110
NAO:  +0.61
PDO:  pending
QBO: +8.05
SOI:  +9.3

Wednesday, January 2, 2019

Winter '18 / '19 - Sudden Stratospheric Warming: Watch #1 - UPDATE 3

 From Judah Cohen's (AER) blog ...

"I have been arguing for at least a decade now that the winter season is shifting ahead in time so that it starts later and ends later.  The fall months are warming across the NH (with one notable exception in Siberia) and that warming extends into December.  However surprisingly the next three months, January through March are cooling across the NH mid-latitudes.
"The frequency of severe winter weather is increased following an SSW across the NH mid-latitudes including more Arctic outbreaks and heavy snowfalls.  Therefore, temperatures are cooling for late winter starting in January and extending into March.
" ... if you are anticipating severe winter weather or a winter weather enthusiast the mild bland weather is necessary for a period of elevated risk of severe winter weather.  Sure, there has been nothing memorable (at least for me; not true if you live in the Carolinas or Virginia) about December but the non-first half of winter is not independent of what I anticipate is a more active second half of winter.
"So, if you are a winter weather enthusiast, at least in my opinion the lack of winter so far is a necessary condition for cold and snow to follow.  And if you like your winters mild then if the winter turns harsher in the near future it also was the cost for the benign winter so far.
" If the stratosphere and troposphere fail to couple, then I see no reason why the relatively benign winter weather can’t continue right up to spring.
"After the PV split the lowest heights and coldest temperatures are predicted to be in three regions in the stratosphere in Western Asia/Eastern Europe, the North Pacific and Southeastern Canada/Northeastern US.  The models all agree that in the troposphere the lowest geopotential height anomalies will also be in Western Asia/Eastern Europe and the North Pacific with the models only disagreeing in Southeastern Canada/Northeastern US.

"But for the biggest impact the Arctic in the troposphere needs to warm up in my opinion and that has not happened.  Also, the only region that is experiencing significant below normal sea ice extent is the Barents-Kara Seas.  If the positive temperature anomalies remain confined to this region this is supportive of cold in Asia but not eastern North America.[...] In fact, low sea ice in the Barents-Kara Seas favor warm temperatures in the Eastern US based on this plot alone."

Thursday, December 27, 2018

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

Sunday, December 23, 2018

Friday, December 21, 2018

Winter '18 / '19 - Outlooks

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

Climate Prediction Center (CPC)

Cohen (AER)

Thursday, December 20, 2018

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

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

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

- 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

"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)

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.

Saturday, December 15, 2018

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)

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.