LaNiña’s back。 Here’s how it will affect the weather

Just five months after the end of a LaNiñathat started in September 2020、the US National Oceanic and Atmospheric Administration announced a new cooling of the Pacific is underway。

LaNiña’s natural cooling of parts of the Pacific is the flip side of a warmer ElNiñopattern and sets in motion changes to the world’s weather for months and sometimes years。 But the changes vary from place to place and are not certainties、just tendencies。

LaNiñastend to cause more agricultural and drought damage to the United States than ElNiñosand neutral conditions、according to a 1999 study。 That study found that LaNiñasin general cause $ 2.2 billion to $ 6.5 billion in damage to US agriculture。

How strong will it be and how long will it last？

There’s a 57 per cent chance this will be a moderate LaNiñaand only 15 per cent that it will be strong、said Mike Halpert、deputy director of NOAA’s Climate Prediction Center。

He said it is unlikely to be as strong as last year’s because the second year of back-to-back LaNiñasusually does not quite measure up to the first。

This LaNiñais expected to stretch through spring、Halpert said。

WATCH | What a LaNiñayear could mean：

What does this mean for the weather？

In Canada、LaNiñatends to be linked to winter weather that includes above average precipitation in British Columbia、colder-than-normal temperatures in the Prairies and more rain and snow than average in Ontario and Quebec、 according to Environment Canada。

Much of both southeast Asia and northern Australia are wetter in LaNiña – and that’s already apparent in Indonesia、Halpert said。 Central Africa and southeast China tend to be drier。

For the entire southern third of the US and especially the Southwest、LaNiñaoften means drier and warmer weather。 The West has been experiencing a two decade-plus megadrought that’s worsened the last couple of years。

But for the Northwest – Washington、Oregon and possibly parts of Idaho and Montana – Halpert said LaNiñameans a good chance of rain and drought relief。

「Good for them、probably not so good for central、southern California」

The Ohio Valley and Northern Plains could be wetter and cooler。 LaNiñawinters also tend to shift snow storms more northerly in winter while places like the mid-Atlantic often do not get blockbuster snowstorms。

In general、expect it to be cooler in western Canada、southern Alaska、Japan、the Korean peninsula、western Africa and southeastern Brazil。

Much of both southeast Asia and northern Australia are wetter in LaNiña – and that’s already apparent in Indonesia、Halpert said。 Central Africa and southeast China tend to be drier。

WATCH | Hurricane Ida quiets New Orleans as recovery efforts start：

Hurricane Ida quiets New Orleans as recovery efforts start

Hurricane Ida has almost silenced New Orleans、most of which remains without power or water、as recovery efforts start in earnest and residents try to cope。 2:31

What about hurricane season？

During last year’s LaNiña、the Atlantic set a record with 30 named storms。 This year、without LaNiña、the season has still been busier than normal with 20 named storms and only one name left unused on the primary storm name list：Wanda。

The last couple weeks have been quiet、but Halpert said he expects things to pick up again。 「Just because it’s quiet now、it does not mean we will not still see more storms as we get later into October and even into November」

LaNiñastend to make Atlantic seasons more active because one key ingredient in formation of storms is winds near the top of them。 An ElNiñotriggers more crosswinds that decapitate storms、while a LaNiñahas fewer crosswinds、allowing storms to develop and grow。