Heat Warning issued for Ottawa and eastern Ontario

Ottawa is under its first heat warning of the year.

Environment Canada issued the heat warning on Monday afternoon, warning humidex values will reach 35 degrees for the next three days.

“High daytime temperatures In the low 30s are expected Tuesday afternoon and temperatures are forecast to be similar Wednesday and Thursday,” Environment Canada said in a statement.

“Humidex values in the mid to upper 30s are also expected.”

Showers and cooler temperatures are expected to arrive in the region late Thursday.

The heat warning covers Ottawa, Gatineau and eastern Ontario.

Environment Canada’s forecast calls for a mix of sun and cloud on Tuesday, with a chance of showers. A high of 33C.

Wednesday: A mix of sun and cloud with a chance of showers. High 33C.

Thursday: Cloudy with a chance of showers. High 27C.

Moist, tropical air bringing summerlike heat

Environment Canada Senior Climatologist David Phillips told CTV Morning Live Monday morning that the shift from cooler weather at the start of May to warm weather now is a result of where the air above Ottawa is coming from.

"A couple of weeks ago, you hard air from the north, cold, polar air," he said. "Now, it's air from the south, warm, tropical air from the Gulf of Mexico."

The fact that this is happening in May and not July, when one would expect heat and humidity like this, has both pros and cons, Phillips said.

"For this first kind of heat bout, from a health point of view, it's worse. We need to acclimatize to it," he said. "The warm, Gulf of Mexico air is bringing a lot of moisture but we're not adding our own moisture sources. Crops and gardens aren't growing like they would be in July. If they were, we might even see more humidity."

Phillips suggests Wednesday, May 27 could be a record-breaker. The forecast calls for a high of 33°C, while the Ottawa Airport record for that date is 31.9°C, set in 1978.

Temperatures are expected to return closer to normal by the end of the week and Phillips believes June could start off a bit cooler than average, though certainly not like the record cold we saw in early May.

"We see June beginning a bit on the cool side, about 10 degrees below where we are now," he said. "We might see a little bit more rain in June, which is good, we need the rain."

Rain showers at around 5 a.m. Monday were the first in Ottawa since May 15.

Environment Canada's long-term outlook for summer is expected to be released June 1.