Marylanders will likely go another round with fierce summer heat Tuesday as temperatures threaten to punch into the high 90s and humidity levels shove the misery index into triple-digits.
Forecast highs for BWI-Marshall Airport and downtown Baltimore are 98 degrees, which would topple the month's record daily high: 97 degrees on July 12, 1908.
Relief is due Tuesday night or Wednesday morning as a cold front sweeps through the region, with a slight chance of some thunderstorms to mark its passage.
Much drier air will arrive behind the front, forecasters said. Daytime high temperatures are expected to drop back to the upper 80s on Wednesday and to the mid-80s through Sunday. The average high for this time of year in Baltimore is 87 degrees.
"Even though we're seeing above-normal temperatures, they will be near normal once the front passes. That's not an uncommon summertime pattern," said Kevin Witt, a National Weather Service meteorologist at the regional forecast office in Sterling, Va.
Better still, Witt said, "It isn't going to feel as oppressive, as sticky." Dew points are forecast to drop to the low 60s by midweek.
The weather service has issued a heat advisory for Tuesday in Central and Southern Maryland and the Eastern Shore, with forecast temperatures in the upper 90s to 100 degrees.
Baltimore City summer school programs are canceled because of the high temperatures, the system announced Tuesday.
Heat index values, a measure of the combined effects of heat and humidity on the body's cooling mechanisms, could reach 102 to 106 degrees.
That kind of weather increases the risks of heat-related illness. Health authorities urged residents to avoid the outdoors if possible, and to avoid the sun and drink plenty of fluids when outside.
That's even more important amid high air pollution readings. Code Orange air pollution alerts were in place Tuesday for the Mid-Atlantic. That means the air quality is expected to be unhealthy for vulnerable groups, including young children, the elderly, and people with cardiac or respiratory illnesses.
Nine people were taken to Baltimore hospitals Tuesday for heat-related illness, city Health Department spokesman Brian M. Schleter said Wednesday.
Monday's high at Baltimore-Washington International Thurgood Marshall Airport reached 93 degrees at 3:38 p.m. It was 98 degrees at the Inner Harbor and 96 at The Baltimore Sun's weather station at Calvert and Centre streets.
Washington's Reagan National Airport reported a high Monday of 95 degrees, while Dulles International reported 94 degrees.
BGE officials reported no problems Monday meeting customers' demand for power to keep fans and air conditioners humming. Consumption peaked for the day at 6,600 megawatts, short of the season's high — 6,775 megawatts, which was reached on June 9, according to utility spokeswoman Linda Foy.
Hospital reports on heat-related illnesses Monday were not due until Tuesday morning, according to city health officials.
Baltimore's Health Department extended Monday's Code Red heat alert into Tuesday, opening cooling shelters across the city and sending outreach workers into the community to check on vulnerable residents.
This week's 90-plus weather is being driven by a combination of factors, Witt said.
With high pressure centered over Delmarva, Central Maryland is getting light south or southwesterly breezes, bringing warm, humid air in from the Deep South.
At the same time, generally dry weather in recent weeks has limited the amount of water vapor in the atmosphere; and water vapor tends to slow atmospheric heating. "So we really don't have a lot of moisture to slow down the warming process," he said.
Hot weather is the norm for Baltimore in July, of course. Statistically, the hottest days of the year fall between July 16 and July 25, when the long-term average for the daily highs reaches 88 degrees.
After that, dwindling hours of sunshine and lower sun angles begin to cool things down, at least on paper. Ninety-degree weather is common in August, too.
If spring and summer seem abnormally warm, that's because they have been.
Through Sunday, July was averaging 79.1 degrees, about 3.4 degrees above the long-term averages for the month.
June averaged 75.7 degrees, or 3.9 degrees above the long-term average. May was 4.3 degrees above average, and April ended 4.5 degrees above average for Baltimore.
This is Central Maryland's third bout of weather in the high 90s this summer. Airport highs reached 98 degrees on May 30 and June 1. The broiler went on again a week later, with highs reaching 99 on June 8 and 100 degrees on June 9.
Even so, the area is running well behind last year's pace for 90-degree weather. Through July 11 last year, BWI had clocked 28 days with highs of 90 degrees or more. This year, the total for the same period is 17 days.
The official, long-term outlook for the region shows no clear temperature trend for July, August and September, with equal chances of normal, hotter- or cooler-than-normal weather.
Precipitation chances look the same, except on the drought-stricken Lower Eastern Shore, where there are increased chances for above-normal precipitation.