Winter '11 / '12 - October Snow Cover

Too bad this classic benchmark storm didn't show its hand early enough to kick-off the 13th Annual NEWxSFC.

UPDATE:  ABE - 6.8

Image courtesy NOHRSC

Winter '11 / '12 - Trending: The North Atlantic Oscillation

The North Atlantic Oscillation (NAO) often plays an important role in defining the character of sensible weather during east coast winters.  It and its godfather the Arctic Oscillation (AO) are also two of the harder features to forecast beyond a week or ten days which leaves seasonal forecasts vulnerable to considerable error.

The developing consensus for Winter '11 / '12 leans heavily on a strengthening la Nina fortified by the trending cool phase of the Pacific Decadal Oscillation (PDO).  These conditions in the eastern Pacific ocean favor a predominantly northern stream storm track passing west of the Appalachian Mountains into northern New England, the result of a blocking ridge axis over the SE CONUS...especially during a positive phase of the Northern Annular oscillations (NAO and AO).

Given the recent trend shown below...how probable is it the phase of NHEMI annular oscillations will be positive this winter?

The time-series above shows the total number of months the NAO was positive or negative during each year.  These data are quite noisy but do show most years during the '50s had greater than or equal number of negative months than positive months and the late '80s to the mid-'90s were dominated by years with more positive months than negative.

Summing the positive and negative months over five years produces a smoother plot and reveals clearly the negative dominance during most of the '50s...the mid-'60s to early '70s...and ever since 2000.  The 'even' line for the period is 30 months.

Positive months held sway between the mid-'80s and much of the '90s during the peak of the AGW war.

Summing the positive and negative months over a decade removes all the noise and shows the positive phase has been the dominant state of the NAO for thirty years (1970 - 2000).  The 'even' line for this period is 60 months.

Coupled with conditions in the Pacific -- evidenced by the initial years of the PDO's cool phase -- the NAO's trending decadal data could be signaling an impending era of colder than 'normal' winters.

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More later about the correlation between NAO and west Atlantic ocean SST anomalies along with how a la Nina winter can be affected by negative NH annular oscillations..

Winter '11 / '12 - 1st Contact

Up to 9" of snow was observed earlier this week INVOF this picture taken in Snowshoe...W. Va. (map).

Right next door at Hot Springs...VA (KHSP)...winter's preview was observed Monday evening...

020255Z AUTO 28016G22KT 1/4SM -SN OVC003 02/02 A2990 RMK AO2 =

020235Z AUTO 27016G22KT M1/4SM SN OVC001 02/02 A2990 RMK AO2 =
020215Z AUTO 28016G21KT M1/4SM -SN OVC001 02/02 A2990 RMK AO2 =
020158Z AUTO 28017G24KT 1/4SM -SN OVC001 02/02 A2991 RMK AO2 =
020136Z AUTO 27017G21KT M1/4SM -SN OVC001 02/02 A2990 RMK AO2 P0003 =
020115Z AUTO 27018G21KT M1/4SM RA OVC001 02/02 A2991 RMK AO2 P0002 =
020056Z AUTO 27017KT M1/4SM -RA OVC001 01/01 A2991 RMK AO2 P0001 =
020035Z AUTO 28016G20KT M1/4SM SN OVC001 01/01 A2991 RMK AO2 P0001 =
020016Z AUTO 28015G21KT M1/4SM SN OVC001 01/01 A2992 RMK AO2 =
012355Z AUTO 28018G21KT M1/4SM SN OVC001 01/01 A2992 RMK AO2 =
012335Z AUTO 28014KT M1/4SM SN OVC001 01/01 A2992 RMK AO2 =
012315Z AUTO 28015G20KT M1/4SM SN OVC001 01/01 A2992 RMK AO2 =
012255Z AUTO 29017G20KT 1/4SM SN OVC001 01/01 A2992 RMK AO2 =
012235Z AUTO 28016G21KT M1/4SM SN OVC001 01/01 A2992 RMK AO2 =

For more than three hours...HSP vsby met or exceeded blizzard criteria.  Too bad the pressure gradient force was not up to the task.

Winter '11 / '12 - Quasi-Biennial Oscillation : ENSO

- QBO...having begun its negative phase in August...stands at -2.30 in September.  QBO will remain negative and intensify throughout the upcoming winter.

- ENSO consensus forecast (see Table 1) for D-J-F from the latest numerical and statistical model runs expects a neutral ENSO to 'weak' la Nina.

Forecast SST Anomalies (deg C) in the Niño 3.4 Region

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Easterly QBO during la Nina favors 1) a cold central US and 2) negative NAO and hi-latitude blocking.
- D'Aleo

Note the negative correlation between the QBO state and geo-potential heights over the Pole and the SE CONUS where a negative / east (positive / west) QBO means heights are positive (negative).  The former implies hi-latitude blocking and the latter suggests la Nina-like ridging.

The polar vortex is weaker and more easily disturbed during easterly QBO and low solar activity.  The current solar cycle is comparatively weak.

"...QBO determines the character of the early winter, leading to a colder and more stable polar vortex in December and January during the west phase of the QBO and a more disturbed and warmer Arctic during the east phase of the QBO."
- SPARC

"Major winter stratospheric warmings preferentially occur during the easterly phase of the QBO..."
- Holton and Tan (1980)

Major warmings can produce deep-layer anti-cyclonic circulations that descend into the troposphere resulting in blocking flow regimes over hi-latitudes.  Blocking is implicated when moderate to strongly negative NAO and AO indexes are observed.

"Pronounced weakenings 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..."
Thompson, et. al. (.pdf)

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QBO analog year of 'least regret' is 93/94, the bride's maid is 76/77...then it's 83/84...88/89....and finally 64/65.  Some winters can be eliminated when the ENSO is considered.

ENSO state for QBO analog winters are...
93/94:  neutral (+0.2)
76/77:  weakly positive (+0.6)
83/84:  neutral (-0.4)
88/89:  strongly negative (-1.7)
64/65:  weakly negative (-0.8)

Given the currently modeled ENSO forecasts...this winter's best QBO : ENSO analogs appear to favor 83/84...possibly 64/65 if there's strengthening.

More about the analog years and the current state of other analogs NAO/AO/PNA/PDO later...