The National Weather Service on Thursday lowered the chances that a La Nina will form this fall to 60%, down from 71% a month ago.

If a La Nina takes shape, it’s expected to be weak and could lack the snowpack-building, drought-busting punch of a stronger La Nina, according to the weather service’s Climate Prediction Center.

Below-average Pacific Ocean temperatures trigger a La Nina. In the past month, temperatures remained near normal, or “neutral.” Even if seas cool, they aren’t expected to cool as much as previously expected.

“I wouldn’t be surprised if it didn’t just end up being neutral,” Oregon State Climatologist Larry O’Neill said.

La Nina generally leads to wetter and cooler winters in the northern tier of the U.S. and has the opposite effect in the southern tier. An El Nino, linked to warm and dry winters in the Northwest, prevailed last winter.

Climatologists categorize La Ninas as weak, moderate or strong. A strong La Nina would be better for building snowpacks, but even a weak La Nina should help, O’Neill said.

There have been eight weak La Nina winters since 1981. In six of those years, the snowpack was above average in Oregon. “It’s encouraging news as far as the drought situation,” O’Neill said.

The U.S. Drought Monitor reported Thursday that 60% of Oregon is in a drought. Some 65% of Idaho is in a drought, while 42% of Washington is in a drought. Only 13% of California is in a drought, though 75% of the state is abnormally dry.

The Climate Prediction Center weighed 28 climate models in forecasting the odds a La Nina will form. Most models predict a weak La Nina, though one model produced by NASA predicted a strong La Nina.

“If a strong La Nina was coming, we’d be seeing the evidence of it by now,” O’Neill said.