NE.Wx Snowfall Forecast Contests

Wednesday, November 20, 2019

Winter '19 / '20 - Outlooks

Thread updated periodically as new outlooks and forecasts become available from a variety of credible sources.

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CPC ...

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From WCVB Boston...
"More cold outbreaks. More opportunities for snowstorms here along the East Coast. This could be a very active winter" said Dr. Judah Cohen (AER)

"Cohen thinks this winter may get off to a slow start but make up for lost time later in the winter. A disturbance of the polar vortex sometime in December could make for a very cold January and February.

"Boston could receive about 59 inches of snow ..." said Cohen.

Winter '19 / '20 - Severe Weather Europe: FINAL November Model Forecast for the Upcoming Winter

by TQ @ 1:59 PM

"Most forecasts are showing certain lower pressure in the North Atlantic, and higher pressure over Europe and USA, which means generally milder winter. The forecasts are on the same trend since September, which is very rare.

"Across the Atlantic, models generally agree on potential northerly flows over NW and NE USA and E Canada, while central USA currently has lower chances for winter weather overall.

"We still have the stratosphere as a major factor. Long-range forecasts are generally not as good at forecasting stratospheric dynamics in detail, which means they tend to underestimate any potential sudden stratospheric warming events (SSW’s) since the final forecast is made out of many individual calculations, which have different ideas about the stratospheric development.

"An SSW event can have a major impact on the circulation and can cause major pattern changes in the Northern Hemisphere. So a potential SSW event is an important factor that can change the course of winter in either way across the North Hemisphere."

More from Severe Weather Europe ...

Monday, November 18, 2019

Winter '19 / '20 - Pacific Decadal Oscillation (PDO): Leading Analogs' 500 mb Anomaly Height Composite ... as of OCT-19

by TQ @ 11:00 PM

Pacific Decadal Oscillation (PDO) composites of 500 mb (5H) geopotential height anomalies (GPHa) and 2-meter air temperature anomalies (2m Ta) for analog winters '66 / '67 ... '68 / '69 ... '90 / '91 ... '04 / '05 ... '17 / '18

5H GPHa composite
- Trof-W / Ridge-E
- High GPHa INVOF Aleutian Is. & low GPHa INVOF Hawaii ==> EPO < 0
- Azores HIGH ==> NAO > 0
- High GPHa dipole Azores & Aleutian Is. ==> AO > 0

5H GPHa weighted-composite

2m Ta weighted-composite

Winter '19 / '20 - Quasi-Biennial Oscillation (QBO): Leading Analogs' 500 mb Anomaly Height Composite ... as of OCT-19

by TQ @ 11:00 PM

Quasi-Biennial Oscillation (QBO) composites of 500 mb (5H) geopotential height anomalies (GPHa) and 2-meter air temperature anomalies (2m Ta) for analog winters '78 / '79 ... '85 / '86 ... '95 / '96 ... '99 / '00 ... '02 / '03.

5H GPHa composite
- Ridge-W / Trof-E
- Hi-latitude blocking over Greenland ==> NAO < 0

5H GPHa weighted-composite

2m Ta weighted-composite

Winter '19 / '20 - Arctic Oscillation (AO): Leading Analogs' 500 mb Anomaly Height Composite ... as of OCT-19

by TQ @ 8:33 PM

Arctic Oscillation (AO) composites of 500 mb (5H) geopotential height anomalies (GPHa) and 2-meter air temperature anomalies (2m Ta) for analog winters '53 / '54 ... '54 / '55 ... '59 / '60 ... '97 / '98 ... '14 / '15.

5H GPHa composite

- Overall North American pattern mimics Tropic/Northern Hemisphere's (TNH) negative phase often associated with +ENSO.

- Negative TNH ==> 1) stronger than normal Pacific jet farther south of its normal axis and 2) well above normal temperatures in eastern North America.

- Active sub-tropical jet

- Positive GPHa over eastern Canada would 1) advect cP flow from hi-latitude snow fields into the eastern U.S. and 2) effectively displace the Hudson LOW from its climatologically favored location.

5H GPHa weighted-composite

2m Ta weighted-composite

Winter '19 / '20 - 500 mb Geopotential Heights and 2m T Anomaly Composites: La Nada Years

by TQ @ 5:44 PM

La Nada or neutral ENSO comes in two flavors -
Cool (-0.5 < Region 3.4 SSTa < 0)
Warm (0 < Region 3.4 SSTa < 0.5)

Current consensus expects 'warm' La Nada for Winter '19 / '20.

Recent La Nada years by decade:
1967
1979
1981 ... 1982 ... 1986 ... 1990
1991 ... 1993 ... 1994 ... 1997
2002 ... 2004
2013 ... 2014 ... 2017

5H GPHa composite - all La Nada years (n = 15)

Prevailing feature common to cool and warm La Nadas ...
- Positive 5H GPHa INVOF Aleutian Is. & negative 5H GPHa INVOF Hawaii = EPO < 0 ==> Arctic outbreaks into central CONUS

Winter '19 / '20 - VCP 32: Appease the Mighty Snow Demons

by TQ @ 7:16 PM

Thursday, November 07, 2019

Winter '19 / '20 - Eurasia Snow Cover: OCT

by TQ @ 4:09 PM

Eurasia/s areal snow cover for OCT-19: ~ 12,800,000 SQ-KM
24% above 52-year P-O-R-N (~10,300,000 SQ-KM)
27% above 52-year median (~10,100,000 SQ-KM)

Rank: 7th
3rd highest past 10 years
4 of past 20 years below median ('05 ... '07 ... '08 ... '11)
OCT-18: ~10,400,000 SQ-KM
OCT-19: 23% greater than OCT-18

Ranked analog years 500 mb anomaly height composite for Winter '19 / '20
('15 / '16 ... '16 / '17 ... '09 / '10 ... '01 / '02 ... '14 / '15)

- High 500 mb geopotential heights at hi-latitude ==> NAO & AO < 0
- EPO > 0 ==> fast zonal flow over CONUS & mild PAC air masses
-weak evidence of trof over coastal M-A & NE CONUS

CORRECTION: '15 / '16 & '09 / '10 ENSO should be 'W+'

Key
ENSO: nada- (-0.5 < Region 3.4 SSTa < 0); C- (weak La Nina); W- (weak El Niño)
NAO: sign of D-J-F average
AO: sign of D-J-F average
PDO: sign of O-N-D-J-F-M average
QBO: + ==> west; - ==> east

Winter '19 / '20 - North Atlantic Oscillation (NAO): Leading Analogs' 500 mb Anomaly Height Composite ... as of OCT-19

by TQ @ 6:24 PM

Analog 5H composite ('80/'81 ... '08/'09 ... '12/'13 ... '14/15 ... '16/'17) ... as of OCT-19

- EPO-like ridge offset slightly to the west of preferred position for a 'Trof-East' regime
- Azores HIGH ==> NAO > 0
- Low geopotential heights over pole ==> AO > 0
- Negative height anomaly over southeast Canada favors primary storm track through the Upper Plains and across the Great Lakes in line with current soil moisture axis

Weighted analog 5H composite

Weighted analog 2m T composite

Winter '19 / '20 - Eurasia/s OCT Snow Advancement

by TQ @ 11:43 AM

UPDATE (31-OCT-19)
Dr. Cohen via Tweeter ..."... the snow cover advance index came in at +0.6.

"This does suggest a negative winter Arctic Oscillation and upcoming #PolarVortex disruption."

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UPDATE (29-OCT-19)
Dr. Cohen via Tweeter ... "October SCE will likely be more than one standard deviation above normal.

"My research shows this favors colder winter temperatures across the N Hemisphere mid-latitudes including East US (sic)"