February 20, 2021 Seasonal Forecasts: Part II, NOAA Comparison with JAMSTEC

Written by Sig Silber

We published the NOAA Long-Term Forecast Part I on February 18, 2021. Here we compare the NOAA forecast for Alaska and CONUS with the JAMSTEC forecast. It is easier to see the disagreements by comparing the maps which we show side by side in a table with a summary of the comparison. Obviously, the farther out you look, the less confidence you have in the forecasts and thus the differences in the forecasts. The major disagreements this time have to do with Summer and Fall precipitation. Also provided are the JAMSTEC World Forecasts.

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C. Comparison of the NOAA and JAMSTEC Forecasts

Below is the comparison of the NOAA and JAMSTEC temperature and precipitation forecast maps for three time-periods and from left to right the NOAA forecast for Alaska and CONUS (the contiguous mid-latitude U.S) and then JAMSTEC for North America (which includes Canada and part of Mexico). The NOAA forecast maps can be clicked on to enlarge. The JAMSTEC maps in the table are not set up to be clicked on to enlarge (because we have no larger version of them). We have concluded that these smaller images work fine for comparison purposes.  Later in the article, we show the World Forecasts.

JAMSTEC works with three-month seasons: Spring: MAM, Summer JJA, and Fall SON. Out of each three months, there is one where the months in the two forecasts align perfectly for the first time period. This is one of those months so for the first period we are comparing  MAM for both JAMSTEC and NOAA.

In addition to the value of comparing the JAMSTEC and NOAA forecasts, the JAMSTEC forecast by showing North America provides more context for the Alaska and CONUS Forecasts as the temperature and precipitation patterns cover North America, not just Alaska and CONUS.

Map Comparisons and our Comments

Temperature*

	NOAA Alaska Plus CONUS	JAMSTEC North America
SPRING MAM  2021
Summer JJA 2021
Fall SON 2021

Precipitation*

	NOAA Alaska Plus CONUS	JAMSTEC North America
SPRING MAM 2021
Summer JJA 2021
Fall SON 2021

* It is important to keep in mind that NOAA reports probabilities of being warmer or cooler than Climatology and JAMSTEC reports the degrees of temperature and millimeters of precipitation variation from Climatolory (Normal). So they are not exactly comparable. Also please keep in mind that we will shortly have a redefinition of Climatology which is the mean of the most recent three decades of weather. NOAA says that redefinition will take place with the May 20, 2021 release of the Seasonal Outlook Update and I suspect that JAMSTEC will do so at about the same time as they work closely with NOAA. Right now, Climatology is measured for the period 1981 – 2010, and when the adjustment is made it will be for the period 1991 – 2020. The impact on precipitation I believe will be relatively minor but for temperature, the ratio of red to white to blue on the NOAA maps will be reduced. So for CONUS, it will not be red almost everywhere. As the decade unfolds if the warming trend continues the predominance of red will return.

JAMSTEC World Forecasts

This month our comments for Spring and Summer are taken directly from the JAMSTEC discussion.

Spring which is MAM 2021

Temperature

Precipitation

Summer which is JJA 2021

Precipitation

“

And Fall 2021

Temperature

Precipitation

Here is the JAMSTEC Discussion

We provided the full JAMSTEC Discussion in Part I. We repeat it here.

Feb. 15, 2021 Prediction from 1st Feb., 2021

ENSO forecast:

Observation continues to show a La Niña Modoki-like state. The SINTEX-F continues to predict that this La Niña Modoki-like state will start to decay from early boreal spring. The tropical Pacific will return to a neutral-state from late spring.

Indian Ocean forecast:

Observation shows that the tropical Indian Ocean is a neutral state. The ensemble mean prediction suggests that the present condition will persist this year. Observation also shows the occurrence of Ningaloo Niño off the west coast of Australia, and the prediction suggests that it will persist in austral autumn (boreal spring).

Regional forecast:

On a seasonal scale, the SINTEX-F predicts that most part of the globe will experience a warmer-than-normal condition in boreal spring (austral autumn) except for Alaska, western Canada, northern part of the South American Continent, and Indochina Peninsula. In boreal summer (austral winter), the model predicts persistence of a similar condition except for Indochina Peninsula.

As regards to the seasonally averaged rainfall in boreal spring (austral autumn), a drier-than-normal condition is predicted for U.S.A., La Plata Basin, southeastern China, and Indonesia. In contrast, Canada, most part of Brazil, Philippines, Indochina Peninsula, India, Sri Lanka, and northern China will experience a wetter-than-normal condition. In boreal summer (austral winter), a wetter-than-normal condition is predicted for India, Philippines, and Indonesia. In contrast, eastern U.S.A, many parts of the South American Continent, central Africa, western Russia, and western China will experience a drier-than-normal condition.

The model predicts most part of Japan will experience a hotter-than-normal condition in spring and summer as a seasonal average. As regards to the seasonally averaged rainfall, Kyushu and Okinawa will experience a drier-than-normal condition in spring. In summer, Honshu (except for Hokkaido, Kyushu, Shikoku) will experience a drier-than-normal condition.

D. Conclusion

As usual, there is some disagreement between NOAA and JAMSTEC. The differences are mostly relative to precipitation in the Summer and next Fall.

It is difficult to relate the differences in the forecast to differences in assumptions on ENSO. But JAMSTEC tends to consider other factors that may not be considered by NOAA. On the other hand, the new versions of the JAMSTEC model are early in their usage and may not have been fully calibrated. I do not think I have gone into it in detail but when it comes to models we need to recognize that there are limitations and NOAA and JAMSTEC use very different approaches which I have summarized in the below table.

So it is kind of a pick your poison choice. But both agencies have great skill at employing approaches that have inherent limitations.

E. Additional Information

ENSO Phase

We showed some of this information in Part. I am repeating it with some additions here.

First, let us look at the NOAA ENSO Update

More information can be found here.

NOAA depends a lot on the IRI-CPC analysis.

It is useful to see how the view has changed if at all which is shown below

This compares the new forecast to the one made last month. The first forecast in each month is based on a survey of meteorologists and the second is based on climate models so they are not totally comparable.

The following was issued by IRI/CPC on February 19 and probably was not available to NOAA when they made their forecast but I can not be sure of that.

Here is another tool released on February 19, 2021 which we do not think that NOAA had in time to impact their Seasonal Outlook but we cannot be sure of that

NOAA has their own proprietary model which they rarely use. It is not exactly clear why they shun their own model.

In most cases, I freeze the models as of the date of publication but for this one, I am going to just let the above model run so if you refer to the article in the future, the values in the above may not relate well to the discussion. But I am doing that so if you refer to this article in say two weeks, you will see if there has been any change in the forecast from this model.

Comparison models would include JAMSTEC

And the JAMSTEC Modoki Index

And the Australian BOM

And here is one more graphic that I created from a different NOAA source. It is a cross-section of the Pacific Equator from the surface down to 450 meters. What is shown in this graphic is the temperature anomalies not the absolute temperature. ENSO is measured at the surface since only the surface interacts with the atmosphere. But the future of the surface often is impacted by the water below the surface. At some point, NOAA will update the normal values for this area as they do that every five years but they have not done so yet. See the note at the beginning of this article.

The current situation and three prior months are shown.

Last Month	Currently
Three Months Ago	Two Months Ago

Here is another way  of looking at it

The Southern Oscillation Index or SOI being above 7 confirms that the Atmosphere is in tune with the Sea Surface Temperatures in the Pacific along the Equator.

The Southern Oscillation Index, or SOI, gives an indication of the development and intensity of El Niño or La Niña events in the Pacific Ocean. The SOI is calculated using the pressure differences between Tahiti and Darwin.

Sustained negative values of the SOI below −7 often indicate El Niño episodes. These negative values are usually accompanied by sustained warming of the central and eastern tropical Pacific Ocean, a decrease in the strength of the Pacific Trade Winds, and a reduction in winter and spring rainfall over much of eastern Australia and the Top End. You can read more about historical El Niño events and their effect on Australia in the Detailed analysis of past El Niño events.

Sustained positive values of the SOI above +7 are typical of a La Niña episode. They are associated with stronger Pacific trade winds and warmer sea temperatures to the north of Australia. Waters in the central and eastern tropical Pacific Ocean become cooler during this time. Together these give an increased probability that eastern and northern Australia will be wetter than normal. You can read more about historical La Niña events and their effect on Australia in the Detailed analysis of past La Niña events.

The Southern Oscillation Index or SOI being above 7 confirms that the Atmosphere is in tune with the Sea Surface Temperatures in the Pacific along the Equator. I have not frozen the SOI graphic so we will be able to track the SOI in this article. It was until recently indicating a fairly strong La Nina but the trend is down so it may be an early indication of the decline in the La Nina.