Three questions have been on San Diego County residents’ minds the last few days.
1) When is this heat wave gonna end?
2) Can we finally turn off the AC today?
3) Why did the forecasters keep telling us it’s going to cool down, when it hasn’t?
“We’re trying to figure it out, too,” National Weather Service forecaster Miguel Miller said apologetically.
Some of it has to do with short memories, both on the part of computer forecast models and the meteorologists.
Long hot spells in the middle of summer are nothing new, but the last two summers were virtually devoid of them. Miller said statistical models can start to build up a bias based on the recent past.
What the models have seen in the last couple of years is heat waves in other seasons, and those have lasted just a few days. So the models start to think this one will be like those and be over quickly.
But the forecasters, the humans who actually make the call, should have remembered what summers are usually like around here, Miller said. It gets hot, 10 or more miles inland, anyway, and it stays hot for long stretches. In the middle of August, rapid pattern changes don’t tend to happen frequently, he said.
Miller also said he and other forecasters were also fooled by what they saw happening around Thursday of last week. The marine layer looked like it was ready to flower off the coast. Miller expected the layer to cool the beaches starting over the weekend, then gradually spread inland and cool the valleys by Monday.
Instead, the marine layer went into retreat, and monsoonal moisture from the southeast was the dominant player.
“I got burnt by the last couple of summers when the marine layer was king,” Miller said.
Why did the marine layer wimp out this time? Miller said it may have lost its momentum because the ocean temperatures near the shore warmed up into the low 70s, and the high pressure over the region that the models kept insisting would weaken never retreated.
Miller said the forecasters are trying to use this heat wave that wouldn’t die as a teaching tool.
“We should not forecast a cool-down until we see the whites of its eyes,” he said.