Friday marked 100 dry days in the Old Pueblo, with no significant rain since the end of February.
Cue the tumbleweeds.
But before moaning about this and above-average highs of the last week, remember, “it’s got to cook before it rains,” a former student once told Christopher Castro, an associate professor of hydrology and atmospheric sciences at the University of Arizona who studies the monsoon.
Luckily, the monsoon — the seasonal shift in winds bringing thunderstorms and rain to town — is on the horizon.
Monsoons here officially start June 15 and end Sept. 30. Any rain that falls between these dates will be added to official monsoon totals. Rain outside these dates is not tallied with monsoon totals.
However, pre-monsoon storms are notorious for perching at the city fringes, teasing us with what’s to come.
These storms bring dry lightning and shaggy clouds that contain virga, a rain that evaporates before it hits the ground and can cause dusty microbursts, said Michael Crimmins, a UA climatologist.
Some thunderstorms have already hit Cochise County southeast of Tucson, bringing a little rain, but also lightning that is being blamed for starting a wildfire near Bisbee on Thursday.
The rainy season
Actual characteristics of monsoon storms don’t emerge until Tucson has logged three days with dew points above 55 degrees, Crimmins said. This was how monsoon starts were defined before the weather service switched to a season with set dates.
Luckily, the National Weather Service in Tucson is predicting that storms could hit here before the official monsoon start date, which is Friday. The lack of rain has dried the soil which drives up temperatures. That heat can coax in storms by drawing in moisture from the cooler oceans to our south.
But Crimmins cautions that while the forecast over the next week or so leans toward slightly wetter-than-normal conditions, this time of year is usually so dry that “wet” could still mean very little rain.
He’s more optimistic for rain later in the season.
“The monsoon could be enhanced by tropical weather systems feeding off warmer September ocean temperatures,” according to NWS’ Tucson Monsoon 2018 Outlook.
“It’s just a heads-up there could be more activity than last year in August and September,” Crimmins said.
Comparatively, that shouldn’t be difficult. Rain in September 2017 fell 0.65-of-an-inch short of what was expected and August 2017 saw almost no rainfall.
Last year’s monsoon was mostly constrained to July, when 6.8 inches of rain fell — nearly three-quarters of an inch more than a typical season’s average total of 6.08 inches. The amount made the month the wettest July on record and the second-wettest month ever in Tucson.
Overall, this year’s forecasts lean toward a wetter-than-normal monsoon, the NWS predicts. Until then, Arizona will have to deal with bone dry deserts fueling for wildfires.
Fire season is expected to peak in late June, just before the regular monsoon rains arrive, according to National Interagency Fire Center reports.
“This part of the season is super dicey,” because of lightning and low moisture, Crimmins said.
Most public land in Southern Arizona, including national forests, parks and state land are on heightened fire restrictions — no open flames — because of the dry conditions.