Seasonal Forecast Briefing

CDC Latest Guidance for Seasonal U.S. Temp. and Precip.

CPC Long Lead Briefing

Observations by TAO buoys




CDC Seasonal Forecast Home-Page

Seasonal Forecast Appendix: September, 2004

2005 winter scenarios

Seasonal Forecast: June, 2004

Forecast by June 2004


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Seasonal Forecast Appendix: March, 2004

Verifiction for the DJF prediction made by November 1, 2003


Seasonal Forecast Appendix: February, 2004

Verifiction for the NDJ prediction made by October 1, 2003


CDC Seasonal Forecast Home-Page

Seasonal Forecast Appendix: October, 2003

Three idealized anomalous SST patterns are shown in: Fig.1. Assuming the patterns may occur in NDJ, DJF, JFM, or FMA, correponding CCA resposes are:

NDJ
DJF
JFM
FMA

Or, according to locations of the idealized SST anomalies:

155E
175W
145W


Corresponding CCM3 (20-member ensemble average) responses are:

anomalous SST centered at 155E
anomalous SST centered at 175W
anomalous SST centered at 145W


Corresponding SFM (20-member ensemble average) responses are:

anomalous SST centered at 155E
anomalous SST centered at 175W
anomalous SST centered at 145W


Background climate conditions for this month's forecast:

TOGA TAO 2-year SST-zonal wind-z20
OLR Hovmoller for last 2 years
Climate Division Temperature
Climate Division Precip.
OLR Hovmoller for last 8 months
Pacific Geostationary Satellite Image: Infra-Red
Pacific Geostationary Satellite Image: Water Vapor
Pacific Geostationary Satellite Image: More



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Seasonal Forecast Appendix: July, 2003

Persist the latest May-June mean SST anomalies as shown in Fig.1, the atmospheric response as predicted by the CCA tool would be as following:

DJF:
Tropical Precip.
500 mb Height
N.A. Precip.
N.A. Surf. Temp.

JFM:
Tropical Precip.
500 mb Height
N.A. Precip.
N.A. Surf. Temp.



CDC Seasonal Forecast Home-Page

Seasonal Forecast Appendix: June, 2003

Persist the SST anomalies of the latest available 4-weeks: May 11 - June 7, 2003 as shown in Fig.1, the atmospheric response as predicted by the CCA tool would be as following:

JAS:
Tropical Precip.
500 mb Height
N.A. Precip.
N.A. Surf. Temp.

ASO:
Tropical Precip.
500 mb Height
N.A. Precip.
N.A. Surf. Temp.

SON:
Tropical Precip.
500 mb Height
N.A. Precip.
N.A. Surf. Temp.

OND:
Tropical Precip.
500 mb Height
N.A. Precip.
N.A. Surf. Temp.

NDJ:
Tropical Precip.
500 mb Height
N.A. Precip.
N.A. Surf. Temp.

DJF:
Tropical Precip.
500 mb Height
N.A. Precip.
N.A. Surf. Temp.



Background climate conditions for this month's forecast:

1.   MJO-last two years

2.   TOGA-TAO Hovs. last two years
 
3.   OLR modes - last six months

4.   500mb z animation - last 30 days

5.   500mb z 30N-60N Oct. 2001 - June 2003

5a.   500mb z 30N-60N Oct. 2002 - June 2003

6.   150mb vector wind anoms 6-12 June 2003

7.   OLR anoms 5-11 June 2003

8.  SV2 - 250 psi - initial to final


CDC Seasonal Forecast Home-Page

Seasonal Forecast Appendix: March, 2003

Observed DJF mean SST anomalies (NOAA OI SST Version-2).

CCA using multimodel average:
Tropical Precip.
500mb Height
Northern Hemisphere Precip.
North America Surf. Temp.

CCA using NSIPP model 23-run average:
Tropical Precip.
500mb Height
Northern Hemisphere Precip.
North America Surf. Temp.


CDC Seasonal Forecast Home-Page

Seasonal Forecast Appendix: February, 2003

This month, several SST forecasts expect a development of cold SST anomalies in the eastern tropical Pacific ocean. Our CCA model also predict cold SST anomalies in the coming summer, a sharp contrast to the forecast made last month. Some analyses are made to understand this big change in our CCA model forecasts. It seems that the change in our CCA SST forecasts may be attributed to two reasons: (1) Seasonality in our model's sensitivity to initial conditions (reflecting the seasonality in the dynamic nature of the system); and (2) Change in initial condition. It is also noticed that starting from Jan. 2003, the NCEP SST of OI-Version-2 is used to replace the SST of OI-Version-1 for initial condition for the SST forecast here. However, the revision of processing for the observed SST data set has little impact to our SST forecast. More details are shown below:

Fig.1 , Observed SST: The subtle difference between the SST of OI-version-1 (top) and -2 (middle) is negligible. Notice that from Dec. 2002 to Jan. 2003 the warm SST anomalies in the central Pacific is weakenned, and the cold anomalies in the eastern Pacific enhanced (bottom).

Comparison between Fig.2 and Fig.3 shows that the revision of SST processing methods makes little impact to the CCA SST forecast.

Fig.4 shows the impact of change in initial condition. Here, we use the SST of Jan. 2003 to replace the Dec. 2002 as an modification to the forecast made last month. We still get a forecast of warm SST for the central Pacific ocean .

Fig.5 shows the effect of the seasonality in sensitivity to initial condition. Here, we modified the forecast of this month by using the SST of Dec. 2002 to replace the SST of Jan. 2003 as initial condition. Comapring to Fig.3 , it is clear that using an identical initial condition may get us quite different prediction of SST evolution just by changing the time of prediction.

Fig.6 shows the impact of change in SST from Dec. 2002 SST to Jan. 2003 to the CCA SST forecast. Comparing to Fig.5 , we see that the change in SST further helps the prediction of cold SST anomalies in the eastern Pacific ocean. And, the seasonality of sensitivity to initial condition may also be seen by comapring Fig.6 and Fig.4. In Fig.4 , the warm anomalies in the central Pacific are only slightly weakened and the cold anomalies in the eastern Pacific does not grow as strongly as it is in Fig.6 (e.g., for the season of MJJ).

The main message from this analysis is that the principal reason for the weaker amplitude SST anomalies in the new forecasts is related to the seasonality of the SST base state, presummably reflecting the fact that events in the eastern Pacific typically decay, rather than grow, after DJF. The fact that the analyzed January 2003 tropical SSTs are themselves weaker than the analyzed december 2002 is of secondary importance to generating weaker amplitude predictions for the next 2 seasons.



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Seasonal Forecast Appendix: January, 2003

Our CCA model predicts a persist of warm SST anomalies till the middle of this summer (MJJ). However, TAO data show a cold temperature anomaly has appeared in the western tropical Pacific ocean. It is interesting to see how this cold water body will develop. Recall that by the end of last year, all linear models predicted cold SST anomalies for the eastern tropical ocean (see Seasonal Forecast Appendix: August, 2001), but TAO showed anomalous warm water body under the surface in central Pacific ocean. Later, when the warm water emerged to the surface an El Nino occurred.



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Seasonal Forecast Appendix: December, 2002

By comparing the August forecast of the SON precip. over North America with that latest observed SST (persistence of this month's forecast), it seems that whether or not the SST in the eastern tropical Pacific ocean be warm and its amplitude is a major factor that matters to the possibility of more precip. over NA.

In addition, there seems to be a seasonal dependence of the NA precip. response to the SST. For example, the August NCEP's SST forecast for OND, NDJ, and DJF are also modest warm. But the responding NA precip. are more wet for these seasons than for the SON. And, our linear model is trained using a 4-model average, differences between this models August forecast and those by other models (e.g. the NCEP GCM) may reflect model dependence of the sensitivity of NA forecast to the SST.



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Seasonal Forecast Appendix: October, 2002

Warm SST anomalies in the tropical eastern Pacific ocean is associated with wet/cold in the southern North America. In contrast, warm SST anomalies in the tropical Indian Ocean helps drought/warm in the southern North America. The 500 mb height response to the warm SST anomalies in tropical Indian ocean is weak and out of phase to that of the response to the eastern tropical Pacific ocean.

El Nino Comparison

Sea Surf. Temp. Anom.

Z500

U.S. Precip.

U.S. Surf. Temp.



CDC Seasonal Forecast Home-Page

Seasonal Forecast Appendix: July, 2002

Comparison of the NA precip. responses to the NCEP SST forecast versus NSIPP SST forecast indicates that the warm SST anomalies in the tropical Indian and western Pacific ocean helps drought in the southern NA, an opposite impact to the warm SST anomalies in the tropical central and eastern Pacific ocean.

Sea Surf. Temp. Anom.

Z500 (SSTA x 2)

U.S. Surf. Temp. (SSTA x 2)

U.S. Precip. (SSTA x 2)

Comparison of NCEP and NSIPP (SSTA x 2)



Seasonal Forecast Appendix: August, 2001