An area of high pressure over Western Canada is to blame for the past two weeks of rainy weather in Baltimore -- and, more significantly, for an out-of-control wildfire spreading across Alberta.
A stubborn pattern is keeping what meteorologists call a trough of low pressure over the eastern United States. With that comes cloudy and cool conditions because low-pressure systems rotate counter-clockwise, generally bringing a flow of air from the north and the east.
Not only that, but when frontal boundaries have approached the region, they have been slow-moving or stalled, said Luis Rosa, a meteorologist with the National Weather Service's Baltimore/Washington forecast office.
Rain typically occurs along cold fronts because they lift warmer air upwards in the atmosphere, causing it to cool and condense and creating precipitation. If they pass through quickly, that can mean a short burst of rain or storms. But when they stall, the precipitation and unsettled conditions linger.
On the other hand, what is known as a ridge of high pressure has been stuck over the Rocky Mountains and western Canada, Rosa said. In the area of Fort McMurray, Alberta, temperatures were approaching 90 degrees as a wildfire sparked and rapidly spread over the past 10 days, he said.
A light rain and cooler temperatures that moved into that region Monday gave officials their first chance to survey much of the fire's damage.
Little change in the cool and wet pattern here is forecast over the next week, Rosa said. Showers are forecast through this week and into Saturday. While a brief spell of sunshine is forecast Sunday and Monday, more rain is possible next week, he said.
"If you don't like summer, you're fine," he said.
Wednesday extended Baltimore's rainfall streak to 15 days. First, storms passed through between midnight and 2 a.m., dropping more than half an inch of rain. Showers through the afternoon and evening added at least a quarter of an inch more.
The record streak of days with at least a trace of rainfall in Baltimore is 17, from March 31-April 16, 1935, according to the National Weather Service's Baltimore/Washington forecast office.
That record is within reach, based on forecasts through the weekend. On Thursday, morning drizzle is possible and then a 40 percent chance of evening showers is forecast. A 60 percent chance of showers is expected Friday, and passing storms are possible Saturday.