La Niña conditions have returned

[CaptinCrunch]

EL NIÑO/SOUTHERN OSCILLATION (ENSO)
DIAGNOSTIC DISCUSSION
issued by
CLIMATE PREDICTION CENTER/NCEP


ENSO Alert System Status: La Niña Advisory

Synopsis: La Niña conditions have returned and are expected to gradually strengthen and continue into the Northern Hemisphere winter 2011-12.

La Niña conditions returned in August 2011 due to the strengthening of negative sea surface temperature (SST) anomalies across the eastern half of the equatorial Pacific Ocean (Fig. 1). With the exception of the far westernmost Niño-4 region, all of the latest weekly Niño index values were –0.5oC or less (Fig. 2). Also supporting the return of La Niña conditions was the strengthening of the below-average subsurface oceanic heat content anomaly (average temperature anomalies in the upper 300m of the ocean, Fig. 3), in response to increased upwelling and further shoaling of the thermocline across the eastern Pacific Ocean (Fig. 4). The atmospheric circulation over the tropical Pacific continued to exhibit La Niña characteristics, but remained weaker and less canonical than the wintertime atmospheric patterns. For example, convection continued to be suppressed near the Date Line, but remained south of the equator, while convection was only weakly enhanced near Papua New Guinea (Fig. 5). In addition, anomalous low-level easterly and upper-level westerly winds persisted over the central tropical Pacific. Collectively, these oceanic and atmospheric patterns reflect the return of La Niña conditions.

Over the last several months many models have predicted increasingly negative SST anomalies in the Nino-3.4 region during the upcoming Northern Hemisphere fall and winter. However, the majority of models continue to predict ENSO-neutral conditions for this period (Fig. 6). The NCEP Climate Forecast System (CFS) has performed quite well over the past several months (Fig. 7) capturing the recent decrease in SST anomalies. The better model performance, combined with the historical tendency for significant La Niña episodes (as in 2010-11) to be followed by relatively weaker La Niña episodes, leads to increased confidence that La Niña will persist into the winter. While it is not yet clear what the ultimate strength of this La Niña will be, La Niña conditions have returned and are expected to gradually strengthen and continue into the Northern Hemisphere winter 2011-12.

Across the contiguous United States, temperature and precipitation impacts associated with La Niña are expected to remain weak during the remainder of the Northern Hemisphere summer and early fall, and to generally strengthen during the late fall and winter. During September-November 2011, there is evidence that La Niña favors an increased chance of above-average temperatures across the mid-section of the country, and an increased chance of above-average precipitation across the Pacific Northwest (see 3-month seasonal outlook released on 18 August 2011).

This discussion is a consolidated effort of the National Oceanic and Atmospheric Administration (NOAA), NOAA's National Weather Service, and their funded institutions. Oceanic and atmospheric conditions are updated weekly on the Climate Prediction Center web site (El Niño/La Niña Current Conditions and Expert Discussions). Forecasts for the evolution of El Niño/La Niña are updated monthly in the Forecast Forum section of CPC's Climate Diagnostics Bulletin. The next ENSO Diagnostics Discussion is scheduled for 6 October 2011. To receive an e-mail notification when the monthly ENSO Diagnostic Discussions are released, please send an e-mail message to: ncep.list.enso-update@noaa.gov.

[CaptinCrunch]

EL NIÑO/SOUTHERN OSCILLATION (ENSO) DIAGNOSTIC DISCUSSION

issued by

CLIMATE PREDICTION CENTER/NCEP/NWS
10 November 2011

ENSO Alert System Status: La Niña Advisory

Synopsis: La Niña is expected to continue through the Northern Hemisphere winter 2011-12.

During October 2011, below-average sea surface temperatures (SST) associated with La Niña conditions strengthened across the east-central equatorial Pacific Ocean (Fig. 1). As a result, the recent weekly SST index values in the Niño-3.4 and Niño-3 regions dropped to near –1.0°C (Fig. 2). Also, the oceanic heat content (average temperature in the upper 300m of the ocean, Fig. 3) remained below-average, reflecting an extensive area of below-average temperatures at depth (Fig. 4). The atmospheric circulation over the global tropics featured strong week-to-week variability during October in response to the Madden Julian Oscillation (MJO). Averaged over the month, convection remained suppressed near the Date Line in association with La Niña, but was near-normal over Indonesia as the MJO acted to offset the increased convection typically associated with La Niña (Fig. 5). In addition, anomalous low-level easterly and upper-level westerly winds shifted into the western Pacific and over Papua New Guinea. Collectively, these oceanic and atmospheric patterns reflect the continuation of La Niña conditions, although modified slightly by the MJO.

A majority of the models now predict La Niña to continue through the Northern Hemisphere winter (Fig. 6) and then gradually weaken after peaking during the November – January period. The models are roughly split between those that predict La Niña to remain weak (3-month average in the Nino-3.4 region less than -0.9°C) and those that predict a stronger episode. Over the last half-century, La Niña events that were preceded by ENSO-neutral conditions during the Northern Hemisphere summer (May-August) were less likely to attain strong amplitude (less than –1.5°C) the following winter. This observation, in combination with the model forecasts, favors a weak-to-moderate strength La Niña during the Northern Hemisphere winter.

During November 2011-January 2012, there is an increased chance of above-average temperatures across the south-central U.S. with the odds favoring below-average temperatures over the north-central U.S. Also, above-average precipitation is favored across the northern tier of states, excluding New England, and drier-than-average conditions are more probable across the southern tier of the U.S. (see 3-month seasonal outlook released on 20 October 2011).

[bella_may]

Not good news for the snow lovers here down south

[Texas2Florida]

Well I was in TX during last year's La Nina and we had a record snowfall year in N. Texas so all hope is not lost.

I'm now in NE Pennsylvania where last year they also had a long and precipitous winter. Gosh what have I got myself into?

[yulou]

but this la nina is weaker.SOI index is around 10 now,just around critical point

[CaptinCrunch]

Well I was in TX during last year's La Nina and we had a record snowfall year in N. Texas so all hope is not lost.

I'm now in NE Pennsylvania where last year they also had a long and precipitous winter. Gosh what have I got myself into?

The record snowfall for DFW was in Jan 2010 and it was not during a La Nina winter, it was a El Nino winter which are usually colder/wetter. La Nina set in Spring of 2010 and was considered a strong eastern based La Nina for last winter. Which, even though brought ice and snow to DFW during the Super Bowl last winter, still averaged warmer and drier than normal. This winter is also a La Nina but in a much weaker state, however I think this winter for NTX will be more like a ENSO neutrel winter and will average out about normal.

[cycloneye]

but this la nina is weaker.SOI index is around 10 now,just around critical point

Is more than double from the +10 meaning that she is more stronger.